march 2021 - der.wa.gov.au

Murrin Murrin Nickel Cobalt Project

17 Series Inpit Tailings Storage Facility Mining Proposal

and Works Approval Application

M39/342, M39/343, M39/421, M39/424 & M39/553

S0231679

Revision 1

March 2021

17 Series Inpit TSF Proposal | Murrin Murrin Nickel Cobalt Project March 2021

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CONTENTS

1 2020 Mining Proposal Checklist ....................................................................................................... i

2 Tenement holder authorisation ...................................................................................................... 1

3 Environmental Group Site Details ................................................................................................... 1

4 Proposal Description ....................................................................................................................... 2

4.1 Background ............................................................................................................................. 2

4.2 Location ................................................................................................................................... 3

4.3 Existing Facilities ..................................................................................................................... 5

4.4 Objective ................................................................................................................................. 6

4.5 Project Summary ..................................................................................................................... 7

5 Activity details ............................................................................................................................... 11

5.1 Proposed Mining Activities ................................................................................................... 11

5.2 Additional Detail for Key Mining Activities ........................................................................... 15

5.3 Disturbance Envelope ........................................................................................................... 23

5.4 Site Plan ................................................................................................................................. 23

6 Environmental legislative framework ........................................................................................... 25

7 Stakeholder engagement .............................................................................................................. 26

7.1 Principles of Stakeholder Engagement ................................................................................. 27

7.2 Targeted Community Engagement Strategy ......................................................................... 27

7.3 Stakeholder Engagement Register ........................................................................................ 29

8 BASELINE ENVIRONMENTAL DATA ............................................................................................... 31

8.1 Climate .................................................................................................................................. 31

8.2 Landscape ............................................................................................................................. 31

8.3 Geology at Murrin Murrin North .......................................................................................... 32

8.4 Material Characterisation ..................................................................................................... 36

8.5 Hydrology .............................................................................................................................. 40

8.6 Hydrogeology ........................................................................................................................ 41

8.7 Flora ...................................................................................................................................... 46

8.8 Fauna ..................................................................................................................................... 47

8.9 Social environment ............................................................................................................... 48

9 Environmental risk management .................................................................................................. 50

9.1 Risk assessment criteria ........................................................................................................ 50

9.2 Implications for Risk Assessment .......................................................................................... 52

9.3 Risk Analysis and Evaluation ................................................................................................. 53

9.4 TSF hazard rating classification ............................................................................................. 57


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9.5 Proposed Mitigation Measures ............................................................................................. 58

9.6 Emergency Action ................................................................................................................. 60

10 MONITORING ......................................................................................................................... 60

10.1 Groundwater Monitoring ...................................................................................................... 60

10.2 Pipeline Monitoring .............................................................................................................. 61

10.3 Freeboard Monitoring ........................................................................................................... 62

10.4 Decant system monitoring .................................................................................................... 62

10.5 Pit walls monitoring .............................................................................................................. 62

10.6 Monthly inspections.............................................................................................................. 62

10.7 Engineering inspections ........................................................................................................ 63

10.8 Process Plant ......................................................................................................................... 63

10.9 Achieved tailings density and strength ................................................................................. 64

10.10 Storage volume and deposition time remaining ........................................................... 64

10.11 Reporting on other environmental factors .................................................................... 64

10.12 Annual audit and management review ......................................................................... 64

11 Environmental Outcomes, Performance Criteria and Monitoring ........................................ 66

11.1 Summary of Environmental Impacts and Management Commitments ............................... 67

12 Environmental Management System .................................................................................... 69

13 Mine Closure .......................................................................................................................... 70

13.1 Post Mining Land Use and Closure Objectives ...................................................................... 70

13.2 Rehabilitation and Mine Closure .......................................................................................... 70

13.3 Completion Criteria ............................................................................................................... 73

13.4 Closure Monitoring ............................................................................................................... 75

13.5 Closure Maintenance ............................................................................................................ 77

14 References ............................................................................................................................. 78

FIGURES

Figure 4-1: Regional Location .................................................................................................................. 4

Figure 4-2: Project Location within Murrin Murrin Operations ............................................................ 10

Figure 5-1: Disturbance envelope ......................................................................................................... 24

Figure 8-1: Typical geological profile (Coffey 2020).............................................................................. 33

Figure 8-2: Annual Water Level Change Inpit TSF 8/5-9/4 ................................................................... 43


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TABLES

Table 3.1: Site Details .............................................................................................................................. 1

Table 4.1: Project Summary .................................................................................................................... 8

Table 5.1: Total footprint Inpit TSF expansion ...................................................................................... 11

Table 5.2: Proposed Activities for Murrin Murrin Project .................................................................... 11

Table 5.3: Additional Details for Key Mining Activities – Tailings Storage Facility ............................... 16

Table 5.4: Freeboard Requirements (Coffey 2020) .............................................................................. 20

Table 5.5: Scope of Works .................................................................................................................... 21

Table 6.1: Environmental Legislative Framework ................................................................................. 25

Table 7.1: Principles of Stakeholder Engagement ................................................................................ 27

Table 7.2: Stakeholder and Engagement Summary .............................................................................. 28

Table 7.3: Stakeholder engagement register ........................................................................................ 30

Table 8.1: Annual rainfall (mm) from 2010 to 2019 ............................................................................. 31

Table 8.2: Tailings analysis conducted in 2009 ..................................................................................... 36

Table 8.3: Tailings properties ................................................................................................................ 37

Table 8.4: Tailings consolidation characteristics .................................................................................. 39

Table 8.5: Expected settlement summary ........................................................................................... 39

Table 8.6: Hydraulic Conductivity ......................................................................................................... 42

Table 8.7: Baseline permeability testing ............................................................................................... 42

Table 9.1: Environmental Factors and Objectives (DMIRS 2020) ........................................................ 50

Table 9.2: Likelihood table .................................................................................................................... 51

Table 9.3: Consequence Table (Minara 2020) ...................................................................................... 51

Table 9.4: Risk Matrix (Minara 2020) .................................................................................................... 52

Table 9.5: 17 Series Inpit TSF inherent and residual risks ..................................................................... 53

Table 10.1: 17 Series Inpit TSF Monitoring Schedule ........................................................................... 60

Table 11.1: Environmental outcomes, performance criteria and monitoring ...................................... 66

Table 11.2: Impacts and management commitments .......................................................................... 67

Table 13.1: Chemical properties (2009 and 2019 samples) .................................................................. 72

Table 13.2: Physical properties (2009 and 2019 samples).................................................................... 72

Table 13.3: Construction completion criteria ...................................................................................... 73

Table 13.4: Proposed mine closure monitoring program. .................................................................... 75

Table 13.5: Conceptual post closure groundwater monitoring framework. ........................................ 76


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APPENDICES Appendix 1. DWER Part V Prescribed PremisesWorks Approval Application Form .......... 79

Appendix 2. Geotechnical Assessment of 17 Series In-pit TSF (Coffey 2020).................... 80

Appendix 3. Hydrogeological Assessment (Saprolite Environmental 2020) ...................... 81

Appendix 4. Potential Cover Layer configuration to manage capillary rise of salts (Landloch 2020) ....................................................................................................................... 82


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In 2003, ANL changed its name to Minara Resources Limited and Anaconda Operations Pty Ltd was renamed Murrin Murrin Operations Pty Ltd. In late 2011 Minara became a 100% subsidiary of Glencore and in early 2012 changed its name to Minara Resources Pty Ltd.

Murrin Murrin Operations is a world-class hydrometallurgical project, using sulfuric acid in high temperature, high pressure autoclave vessels to leach nickel and cobalt from lateritic (oxidised) ores.

4.2 Location

Murrin Murrin is located approximately 60 kilometres (km) east of Leonora, in the northeastern Goldfields region of Western Australia (Figure 4-1). The Murrin Murrin project is located within both the Shire of Leonora and Shire of Laverton.

The Murrin Murrin North (MMN) project area (this proposal) is located 60 km east of Leonora and incorporates the Murrin Murrin processing plant and associated infrastructure. The 17 Deposit Pits (part of MMN operations) will be utilised for the proposed 17 Series Inpit TSF which are located approximately 3km west of the plant site.

Mining of the 17 series pits commenced in 2007 with the first pit being 1701. Mining of the 17 series deposit is expected to be completed in June 2021.



4.3 Existing Facilities

Murrin Murrin was initially commissioned in 1999 and currently mines and processes approximately 4.5 million tonnes (t) of nickel laterite ore per year to produce 47,000 t/yr of nickel briquettes and 3,000 t/yr of cobalt briquettes. The operation uses open-pit mining techniques and processes the ore using High Pressure Acid Leach (HPAL) technology to recover the nickel and cobalt.

The current Murrin Murrin operations comprises the following:

• Open-cut nickel cobalt mining operations at Murrin Murrin North, Murrin Murrin South and Murrin Murrin East

• Dewatering operations

• Calcrete quarrying operations

• Processing plant with associated ancillary plants (e.g. power generation, sulphuric acid plant, hydrogen sulphide plant and water treatment facilities)

• TSFs, including inpit tailings disposal (Pit 2/3, Pit 8/5-9/4, Pit 8/4, Pit 2/2-2/4, Pit 9/2, Pit 18/3, Pit 18/6 and Pit 9/5)

• High Pressure Acid Leach (HPAL) facility

• Water supply borefields

• Landfill

• Wastewater treatment plant

• Supporting infrastructure such as the accommodation village, airstrip and roads.

MMO holds a Department of Water and Environmental Regulation (DWER) Part V Prescribed Premises Licence (L7276/1996/11) for the Murrin Murrin operations allowing for the following activities:

• 5 – Processing or beneficiation of metallic or non-metallic ore

• 6 – Mine dewatering

• 12 – Screening, etc. of material

• 31 – Chemical manufacturing

• 44 – Metal smelting or refining

• 52 – Electric power generation

• 54 – Sewage facility

• 64 – Class II or III putrescible landfill

Approximately 4.5 million tonnes (Mt) (dry solid) of tailings are produced each year from the processing operations associated with the Project. The life of the Project is expected to be until 2035 with a further 80–90 Mt of tailings space required for disposal. Tailings have been deposited on site



in both above ground and inpit tailings storage facilities (inpit TSFs). MMO currently operates eight approved inpit TSFs at MMN located at:

• 2/2-2/4 pit voids

• 2/3 pit void

• 8/4 pit void

• 8/5-9/4 pit voids

• 9/2 pit void

• 9/5 pit void

• 18/3 pit void

• 18/6 pit void

Given that the currently operational TSFs are reaching capacity, alternative tailing storage facilities are required to support operations. MMO has identified existing open pits 1701, 1702, 1706, 1707, 1708 and 1753 (the 17 series pit) as being suitable for this purpose. It is proposed to convert these open pit voids at the cessation of mining activity to an inpit TSF. This will enable rotation of tailings disposal, improving tailings consolidation, extend the life of existing inpit TSFs and minimize the risk of seepage to groundwater.

It is estimated that about 15 Mt of tailings will be stored in the proposed inpit TSF, based on a tailings dry density of approximately 0.8 t/m3. This corresponds to a monthly deposition rate of 375,000 tonnes (or 4.5 Mtpa) for approximately 40 months (Coffey 2020).

4.4 Objective

This Mining Proposal has been developed as a combined document to cover the following approvals:

• DMIRS Mining Proposal to seek approval under the Mining Act 1978

• DWER Works Approval Application to seek approval under Part V of the Environmental Protection Act 1986.

This Proposal includes two key components:

• 17 Series Inpit TSF, i.e. conversion of approved existing disturbed open pits 1701, 1702, 1706, 1707, 1708 and 1753 to inpit TSF

• Bunded tailings and decant water pipeline, i.e. construction of tailings and decant water pipeline corridor including associated infrastructure (bunding and a scour sump).

Developing the existing pit voids as TSF has benefits, which include (and are not limited to):

• The TSF is located within the existing ‘footprint’ of the operations. No significant additional disturbance or clearing of native vegetation is required (as would be the case for construction of additional above ground paddock-style storage facilities)



• Locating the TSF within the existing open pits removes the requirement for the construction of paddock-style TSF (with compacted fill embankments, inner and outer slopes) and the associated risks of land disturbance and TSF operation

• The volume of suitable fill material for use in construction (for example for pipeline bunding) is reduced

• Seepage migration from paddock-style facilities may occur near the ground surface, which has implications for vegetation health. Potential seepage from the inpit TSF void is more likely to occur at depth, beyond the root zone of vegetation recorded in the vicinity of the proposed inpit TSF. The provision of a suitable capping structure for the TSF on closure will further prevent impacts to vegetation

• Deposition of tailings effectively reduces the void area allowing for backfill and rehabilitation above the consolidated tailings surface. Without this process, it is unlikely that the 17 series pits would be backfilled and rehabilitated on closure of the mine

• Deposition of tailings will support exposed pit slopes and improve long term pit slope stability

• Inpit TSFs do not result in elevated landforms unlike rehabilitated paddock style facilities. Such landforms are highly visible with a high erosion potential

• Significantly lower capital requirement than for the establishment (construction) of above ground facilities

• Proximity to existing inpit TSF infrastructure with reduced infrastructure requirement (delivery and decant pipelines)

• Improved tailings consolidation across all TSFs through rotation of tailings deposition within the existing TSFs and the proposed 17 Series Inpit TSF.

4.5 Project Summary

To enable operation of the new inpit TSF, the following work is to be completed:

• Preparation of the 17 series open pits for use as an inpit TSF

• Extension of existing tailings delivery (4.47 km) and decant water return (3.2 km) pipelines within bunded pipeline corridors. The pipeline corridor will be approximately 6 m wide, bunded and will include an approximately 290 m3 scour sump.

Figure 4-2 and Figure 5-1 show the proposed TSF location with the MMN operations and disturbance area, including the location of the proposed pipeline corridor.

Reference should be made to Appendix D of Appendix 2 for a detailed description of the scope of works.

A total of 0.61 ha of native vegetation is proposed to be cleared to facilitate the development of the proposed inpit TSF and associated works/activities. Clearing will be undertaken under the exemption defined in clause 2(2) of Schedule 1 of Environmental Protection (Clearing of Native Vegetation) Regulations 2004, which allows clearing of up to 10 hectares per financial year per tenement under the Mining Act 1978. Therefore, a clearing permit will not be required to support this proposal.



Pipeline disturbance (ha)** 0.61

Construction specifics

Total Area of Disturbance (ha) 119.23

Construction Period Up to three months

Construction Commencement March 2020

Operations Workforce 80 personnel

* Previously disturbed area.

** New disturbance (11.51 ha total area to be utilised).

The site location within the MMN operations is presented in Figure 4-2, with existing disturbance detailed.



The solid is filtered resulting in a filter cake that is washed in situ. The filter cake is then re-pulped as feed for the refinery.

The first phase of the refinery leaches the mixed sulfides to produce a nickel and cobalt sulfate solution that is fed into an impurity removal circuit. This circuit is used to remove metal ions (such as iron, zinc, and copper) that can cause downstream problems with the process and impact final product quality.

This purified solution is then fed into the solvent extraction circuit where the cobalt is separated from the nickel using selective organic extraction. The cobalt is stripped from the organic mixture creating a pure cobalt sulfate solution suitable for hydrogen reduction to produce cobalt metal. The nickel remains in the raffinate from the solvent extraction process and it is subsequently reduced to nickel metal powder using hydrogen reduction.

The nickel and cobalt powders are washed, filtered and dried to form briquettes that are sintered to produce a high quality, refined product. Any residual nickel and cobalt in the solution after hydrogen reduction is precipitated with hydrogen sulfide, thickened and returned to the refinery. Ammonia, used for pH control during the refining process, is recovered as ammonium sulphate crystal, which is sold as a fertiliser product.

Design

The 17 Series Inpit TSF expansion has been designed in accordance with:

• DMIRS (2015), ‘Guide to the preparation of a design report for tailings storage facilities (TSFs)’

• DMIRS (2013), ‘Code of practice: tailings storage facilities in Western Australia’

• DMIRS (2020), ‘Statutory Guidelines for Mining Proposals’

Upon completion of construction of the TSF, an environmental compliance report will be prepared and submitted to DWER.

5.2.2.1 Tailings Deposition – Spigotting

Tailings deposition into the 17 Series Inpit TSF will be undertaken in stages in order to provide control over tailings beach development and to facilitate recovery of water from the facility. Tailings will be deposited from four sets of multiple spigots located at different positions along the eastern side of the pit.

The existing access ramps along the northern, western and southern sides of the TSF will be utilised as part of water recovery operations. Water recovery from the ramp will not be possible until the localised low points are filled up with tailings to a level (adequate height) such that the supernatant pond is formed around the ramp. Once the tailings level covers all the localised low points, discharge from multiple spigots will be relocated to the northern tip, while the southern access ramp will be used for water recovery operations.

Supernatant water at the northern end of the pit will be pumped using a decant pump deployed from the northern access ramp to recover water from the facility. The pumps will be moved up the ramps as the tailings and water levels rise within the pit. Deposition locations have been designed to optimise the storage capacity of the pit voids, whilst enabling the use of the existing access ramps for water recovery.

The storage life of the facility is estimated to be 3.35 years.



5.2.2.2 Topping up

Given the expected consolidation within each facility during and post operation, a topping up process will be required prior to decommissioning. The topping up process will enable the storage capacity of 17 Series TSF to be maximised by filling in any depressions on the tailing surface (due to consolidation) and by depositing tailings from around the perimeter of the pit where excess freeboard remains.

5.2.2.3 Supernatant water recovery

Supernatant water liberated from the tailings slurry will be recovered by decant pumps located at various points along access ramps at northern, western and southern sides of the pit. During the early stages of tailings deposition, decant pumps will be located on the lower sections of the access ramps. As deposition proceeds and the level of tailings within the TSF rises, the decant pumps would be moved up the access ramps.

The tailings deposition plan has been designed to position the supernatant water pond adjacent to the access ramp into the pit, from where the decant pump will be deployed. Some limitations to water recovery are expected in the initial phase of deposition, due to the requirement to infill low points in the pit prior to development of a tailings beach towards the proposed decant location. As the tailings and water level rise within the pit, the supernatant water pond will move up the access ramp, with the decant pump to be withdrawn up the ramp. The ramp will provide access to the decant pump for operation and maintenance purposes.

Once the localised low points are filled up, discharge will be from multiple spigots located at the northern tip with the decant location at the southern tip. Water recovered by the decant pump will be pumped to the evaporation ponds.

5.2.2.4 Underdrainage

No underdrainage system is proposed for the proposed 17 Series Inpit TSF. There is an increased potential for blockage of the underdrainage system as a result of the fine particle size distribution of the tailings (i.e. 71% passing 80-micron sieve based on 2016 laboratory test work). In addition, the distribution of low points throughout these pits and the associated difficulty in removing captured liquor from these dispersed collection points prohibits the use of underdrainage.

5.2.2.5 Freeboard requirements

The facilities have been designed such that a 1 in 100-year ARI, 72-hour duration storm event of 200 mm of rainfall can be temporarily stored, in addition to the normal operating decant pond.

The design assumes that correct operational controls are adhered to and, in particular, that water is continually removed from the facilities, such that maximum freeboard allowances are maintained.

Freeboard requirements have been assessed in accordance with DMIRS (2015) guidelines by Coffey (2020; Appendix 2). A minimum operational freeboard (vertical height between the tailings beach and embankment crest) of 300 mm is recommended along with the greater of a minimum beach freeboard (vertical height between the 100-year ARI water level and top of tailings beach) of 200 mm; or the runoff resulted from a 1:100 ARI, 72-hour duration rainfall event (200 mm).

MMO will construct a bund around the pit rim and the catchment area of the proposed TSF. This bund will enclose the 17 series pits and proposed pipeline corridors with a buffer of up to 50 m (as per the DE). It will not include any other areas surrounding the pit.



5.2.2.7 Liners

No artificial liners are proposed for the inpit TSF. It is not anticipated that liners should be required in construction of the proposed TSF.

The walls and floors of the exposed pits are characterised by extensive magnesite development. It is expected this material will have a neutralising effect when exposed to potentially acidic tailings as magnesium is an acid consuming element. The groundwater quality of the monitoring bores around the existing inpit TSFs showed compliance with the DWER licence L7276/1996/11 (pH levels for all monitoring bores were above 3.5).

Water Balance

A detailed water balance assessment has been conducted by Coffey (2020) and is presented in Appendix E of Appendix 2. The outcome of the study is summarised below.

Based on experience from other inpit tailings storage facilities in the Goldfields region, water returns of 50% to 60% of slurry water inflow can be expected from the TSF. Higher water returns are expected when compared with paddock facilities due to reduced evaporative losses. Water balance models were developed for the proposed 17 Series TSF based on mean water volumes (considering slurry with 27% solids and annual production of 4.5Mtpa) and accounting for:

• Rainfall

• Slurry water inflow

• Evaporation

• Seepage

• Retention.

Inflows comprise slurry water to the TSF and rainfall, while outflows comprise evaporation from the pond and beaches, seepage and decant water return.

The evaporation potential for the evaporation pond was estimated based on Luke et al. (1987), increased by a factor of 30% to account for discrepancies between evaporation at MMO (approximately 3,000 mm based on the average pan annual evaporation map produced by the Bureau of Meteorology) relative to the monitoring station data (Luke et al., 1987), a pan coefficient of 66% and an assumed pond plus running beach areas of approximately 55 ha. In the absence of seepage analyses, the total seepage out flow is estimated based on the assumed pit floor permeability of 1x10-

7 m/s.

MMO can expect an average annual water return of approximately 8.1 Mm3. The estimated annual average water return as a percentage of slurry water inflow was assessed as about 67%.

Operation

An Operating Manual has been prepared for the 17 Series Inpit TSF (Appendix F of Appendix 2) which provides an outline of:

• Procedures for the safe and efficient storage of tailings in accordance with specifications and principles documented in the design to minimise environmental impacts

• Processes complying with legislation and public expectations.



The Operating Manual has been prepared for use by process plant management personnel with responsibility for:

• Ensuring inpit facilities are operated and monitored to achieve the design objective

• Ensuring the facilities are operated in accordance with the parameters that have been used in their design. Where changes in these parameters are proposed, the process plant management must advise the designers in a timely manner so that the impact of the changes can be fully assessed.

The Operating Manual has been prepared for use by staff who are responsible for operation of the TSF and associated facilities/infrastructure. The Operations Manual provides a detailed description of the operating procedures, inspection criteria, monitoring requirements and log sheets for the TSF.

Support facilities

No additional support facilities are required as part of the proposal.

Workforce

No additional workforce is required as part of the proposal.

Transport corridors

No additional transport corridors are required as part of the proposal.

Resource requirements and regional infrastructure

No additional resources (i.e. water and power) are required as part of the proposal.

5.3 Disturbance Envelope

The Disturbance Envelope (DE) has been chosen to allow operational flexibility. The proposed DE occupies an area that has already been disturbed by mining activities.

Whilst the area of the 17 series pits and proposed inpit TSF is unlikely to change, a larger area has been selected for the DE to allow for:

• Alternative alignments for the tailings delivery and decant return pipeline corridors.

• Location of the proposed scour sump.

• Construction of the external bund that will enclose the inpit TSF and associated infrastructure.

A total area of 357 ha is required, as shown in Figure 5-1.

5.4 Site Plan

The Proposed Layout is shown in Figure 5-1, with existing disturbance and tenement boundaries shown in Figure 4-2.



8.3 Geology at Murrin Murrin North

The nickel cobalt ore deposits of the MMN project area are positioned over serpentinised peridotite komatiitic lava flows which occur low in the stratigraphy within a sequence of felsic volcaniclastics, clastic sediments, mafic volcanics and related intrusives in the upper parts of the stratigraphic sequence. The serpentinised peridotite protolith has been folded and faulted around the Kilkenny Syncline. The sequence forms a corridor constrained by major NNE trending, westerly dipping faults.

These faults splay off the major NW trending Keith-Kilkenny tectonic zone to the SW. Gradual oxidation and leaching of the ultramafic protolith has produced a regolith with sub-horizontal layers which hosts the ore deposits (Saprolite 2020).

The MMN Project is located within the Mt Morgan district of the Mt Margaret mineral field between Leonora and Laverton (Coffey 2020). The regolith profile can be broadly divided into five main geological units produced through lateritic weathering (Figure 8-1).

1. UM: the basal unit is slightly weathered locally silicified ultramafic that grades upward into saprolite

2. SA: saprolite zone, commonly magnesium and silica rich

3. SM: smectite is the main nickel bearing unit of the profile

4. FZ: ferruginous zone, dominantly comprised of kaolinite Fe oxides (typically hematite), commonly silica-rich and capped with colluvium

5. The uppermost unit consists of colluviums and mixed chlorite-kaolinite plastic clays, referred to as the mottled zone (Coffey 2016).

Ultramafic regolith profiles are commonly bound by weathered felsic and/or mafic volcanic and intrusive rock.

The original terrain around the 17 Series Inpit TSF grades to the south-west. The highest point is at the north-eastern tip (approximately +467m RL) from which ground levels gradually reduce to about +451m RL at the south-western tip (Coffey 2020).



Figure 8-1: Typical geological profile (Coffey 2020)

The report on the geology with respect to the potential of the 17 Series as in-pit TSF (Coffey 2020) is based on information sourced from:

• Recent geological mapping of mined pits (17.08, 17.02 and 17.07)

• Mapping and observations of older pit walls (17.56 and 17.01) which have experienced significant wall fretting with rill material covering most of the exposed pit wall due to drying of the clay walls

• For areas yet to be mined, computer modelling and interpretations of the geology.

The weathering profile of exposed 17 series pits generally conforms to the basic laterite sequence whereby it is bounded at the base predominantly by saprolite (SA) and minor exposures of ultramafic (UM).

The exposed SA and UM show varying degrees of jointing, shearing and silicification. The SA appears to be highly fractured with intersecting joint sets (joint systems). The walls and floors of the pits are approximately 30% SA by surface area exposure. The SA zones are generally high in magnesium and



are highly siliceous in areas. It is expected that the SA will have a neutralising effect when exposed to potentially acidic tailings as magnesium is an acid consuming element.

The SA is overlain by a clay rich ore zone characterised by a gradational contact between member horizons. These comprise soft, finer-grained clay and nickel rich saprolite, waxy textured smectite clays and ferruginous smectite material. The block model indicates that these materials cover approximately 55% of the pit walls and floors. The nickel rich saprolite unit that is part of this ore zone grades into the underlying saprolite and generally has a moderate to high magnesium content.

Above the ore zone is the ferruginous zone (FZ); a typically course grained, iron rich, red/brown highly oxidised clay horizon with dispersed hematite nodules. The block model indicates the thickness and depth of this unit to range from a few metres from the surface to more than 30 m in areas. The western side of the deposit, especially the western side of 17.08 is characterised by extensive magnesite development. Similarly, this material will react with and neutralise the potentially acidic tailings material.

Overlying the FZ are the plastic clays (PC), a low-Ni high-Al zone that is characterised geochemically by its reduced iron content and physically by its mottled nature. There is a felsic unit east of the deposit, but this is only exposed in the eastern ramp of the 17.08 pit.

A detailed description of regional geology is contained in Geotechnical Assessment of 17 Series In-Pit TSF (Coffey 2020), which is provided in Appendix 2.

Ore Sterilisation

The 17 series pits are located on the west of the MMN project area. Mining of the 17 series pits commenced in 2007 with the first pit being 17.01. Mining of the 17 series deposit is expected to be completed by June 2021.

All economically viable mineralisation will be extracted from the 17 series open pits prior to commissioning and discharge of tailings in the 17 Series Inpit TSF.

The DMIRS ‘Sterilisation report submission form for inpit waste/tailings disposal proposals’ is not required for shallow deposits such as nickel laterite.

Structural features

Economic mineralisation at the Murrin Murrin Ni-Co project is contained within the weathered profile of the ultramafic protolith. As a result, the mined pits rarely expose the fresh ultramafic rock to allow for detailed investigations of the structural features of the deposit. However, as these structural features have acted as conduits for fluid flow or as areas of increased permeability during the formation of the laterite profile, they tend to be revealed in the distribution of certain elements in the regolith profile (Coffey 2020).

The most effective elements for delineating structural features are silica (Si) below the FZ and chromium (Cr) above or within the FZ. As the 17 deposit has only been partially mined, analysis of the distributions of these elements must be relied on for interpretation of the deposit’s structural features (Coffey 2020).

The most significant structural feature observed in the 17 deposit is a major NW to SE striking fault zone that cuts across the southern end of the 17.02 pit. The zone has been exposed by mining and the fault structures are clearly visible in the walls.



This zone will likely act as a conduit for fluid flow (Coffey 2020) and monitoring has been placed in close proximity to this structural feature.

Soils and soil profiles

In general, the landscape at MMN is characterised by hardpan plains with red loamy earths and gently undulating sandy plains with red deeps sands, red shallow sandy duplexes and red sandy earths on the eastern side of the project area. The western side of MMN is characterised by gently undulating gravelly plains on laterite and hard pan as well as low ironstone hills and stony plains.

Broad scale sampling and analysis of topsoil across the MMN project area showed soils generally have:

• pH and electrical conductivity (EC) values in the range suitable for plant growth • High sodium base saturation percentage • High magnesium base saturation and low calcium base saturation • Very low available phosphorus • Very low sulfur • Low manganese • Low zinc in some areas.

Topsoil will be removed during construction and stockpiled for rehabilitation purposes.

Assessment of the pit wall and stability

A pit wall performance study for the 17 series pits was undertaken based on available geological data (Coffey, 2020). No site inspection was carried out in connection with this work (i.e.. this was a desktop assessment). The following conclusions were made (Coffey 2020):

• Mining activities in Pits 17.01 and 17.53 have been completed

• Mining in Pits 17.08, 17.07 and 17.02 is on-going

• There are no wall scale failures in the pit wall of recently mined Pit 17.08

• Presence of erosion gullies was observed in the older pits of 17.53

• Small volume of groundwater was observed at the bottom of the Pit 17.53.

Risk assessment implications

The geology of the proposed 17 series pits has the following implications in relation to their use as an inpit tailings facility:

• The weathered and locally unstable nature of the pit walls may lead to small scale slope failures prior to and during the early stages of tailings deposition

• Structural features (for example faults, shears and joints) that intersect the pit may act as preferential pathways for seepage away from the pit during tailings deposition (refer Section 8.3.4).



• May 2012 tailings sample was coarser, had a slightly higher density with more water than the 2008 sample

• The 2012 results, when compared to the testing done by Golder in 2004 on a tailings sample with 70 to 85% fines (passing the 75-micron sieve), returned a settled density of 0.64 t/m3 (dry), the 2012 results returned lower settled densities

• 2016 tailings sample was coarser than the 2012 samples.

A reconciliation of in situ tailings density within the inpit TSFs has been undertaken where Site surveyors calculated the remaining void volumes periodically within the pits and paddock TSF. The following reconciled densities were estimated:

• Pit 2/3 and the South Cell was estimated at 0.85 t/m³

• Pit 8/5-9/4 was estimated at 0.97 t/m³.

Based on these estimations, the reconciled density for tailings across the whole site was assessed to be around 0.92 t/m3 which is similar to values adopted in recent inpit design report submissions to DMIRS.

For the storage capacity estimation in the 17 series pits, a more conservative density of 0.8 t/m3 (dry) has been adopted.

The engineering properties of the tailings are summarised below:

• Slurry density ex-plant (average): 27% solids (Coffey Mining, 2016)

• Final tailings density (average): 0.8 t/m³ (dry density) (Coffey Mining, 2016 & (Coffey, 2020)

• Angle of internal friction (Φ) (deposited tailings): 25°

• Angle of internal friction (Φ) (compacted tailings): 35°

• Particle size distribution: 70-85% passing 75 microns

• Coefficient of consolidation: 4.2-4.75 m2/yr

• Tailings beach slope: 1:300 #

Notes: # Based on observation of the tailings beach slope on the existing and operating 2/3 TSF

8.4.1.4 Consolidation testing

Rowe cell testing was conducted in 2012 to confirm tailings consolidation characteristics. A slurry sample was received for analysis at approximately the ex-mill slurry density. Consolidation characteristics derived from the results are summarised in Table 8.4 and have been utilised in tailings settlement analyses.

Results indicate tailings have poor consolidation characteristics, with Cv values around an order of magnitude lower than estimated from CPT testing (Cv range 33.5 to 84); that is, consolidation would be likely to occur more slowly than that indicated by CPT testing (Coffey 2020).



Completed waste dump compositions demonstrate that 79% of the waste material at MMN is comprised of the three lithologies of FZ, SA and SM. Waste material characterisation studies have shown that the main waste types at MMN are all classified as non-acid forming (NAF) (Landloch 2015). Acid base accounting showed that the total S percent was very low in all samples from waste lithologies at MMN.

All waste types at MMN have a neutral to slightly alkaline pH and relatively low electrical conductivity (EC) levels.

8.4.2.1 Risk assessment implications

The main waste types at MMN are all classified as non-acid forming (NAF) (Landloch 2015). There are no implications for the risk assessment associated with mine waste materials.

8.5 Hydrology

Local topography is typically of low relief, which is a consequence of extensive alluvial and colluvial materials that have blanketed areas northwest, southwest and east-southeast of MMN (Saprolite 2016). These alluvial sediments form part of an extensive northwest orientated palaeo-drainage network (Saprolite 2016). Lake Carey and Lake Raeside are large playa lakes located approximately 25 km southeast and 40 km southwest of MMN respectively. These two lakes are the major receiving bodies for surface water in the area. MMN deposits straddle the drainage divide between the catchments of these two lakes (Saprolite 2016).

No naturally occurring permanent water occurs within the site. All waterways show signs of flooding, but do not retain water for any lengthy periods. Permanent water is only present in dams and other artificial structures associated with mining activities (Saprolite 2016).

The regional drainage system comprises of three salt-lake catchment areas:

1. Cement Creek Catchment: drains in an easterly direction via Cement Creek towards Lake Carey

2. Katata Creek Catchment: drains in a south-westerly direction via an extensive dendritic drainage pattern (including Katata Creek) towards Lake Raeside

3. Kilkenny Creek Catchment: drains in a south-westerly direction via Kilkenny Creek towards Lake Raeside.

Most of the tributaries within these catchments are ephemeral, only flowing after heavy rain, however, large semi-permanent waterholes are present near the confluence with Lake Carey (Environ 2010).

The MMN study area is dissected by a major drainage divide (ridge) between the Cement Creek and Katata Creek Catchments. The 17 series pits are located on the eastern margin of the Katata Creek Catchment. The Katata Creek Catchment drains in a south westerly direction via an extensive dendritic drainage pattern, towards the Raeside Lake system (Saprolite 2020).

Surface water flows through the MMN project area have been modified by extensive mine development.


Stormwater inflow to the proposed TSF will be prevented through the construction of external bunds and drainage control features. The operation manual for the proposed TSF includes



procedures that require regular inspection of these, and other infrastructure associated with the TSF.

There are no hydrological implications for the risk assessment.

8.6 Hydrogeology

Murrin Murrin North Hydrogeology

The findings of the hydrogeological investigations undertaken by Saprolite (2020) are attached in Appendix 3. Key points are:

• The laterite profile above the Archean greenstone belt in which the open pits are located is typically derived from preferential weathering with respect to the resistant nature of the parent host rock. Rocks that weather preferentially and faster (i.e. ultramafic rocks compared to mafics and felsics) are more susceptible to hosting groundwater, which then promotes weathering compared to rocks that are resistant and with shallower profiles. The deep weathering in the greenstones is further enhanced by near vertical bedding, intense shearing and variation in competence of contiguous rock units. Granitoids typically have greater mineralogical and structural homogeneity resulting in shallower depths of weathering (Saprolite 2020; Appendix 3).

• Chemical processes in the weathering profile have led to the removal of large quantities of soluble material and produced layers of widely differing permeability and storage within the weathering profile (Saprolite 2020).

• The ultramafic basal unit which underlie the open pits is interpreted to have relatively low hydraulic conductivity at depth, which increases markedly near the weathering front as fracturing increases towards the overlying saprolite unit.

• In the MMN project area the saprolite zone retains much of the structure of the underlying and unweathered ultramafic bedrock, including significant areas of shearing and jointing. These structural features are likely to act as permeability pathways, however, significant alteration during the formation of the saprolite zone has resulted in the abundance of magnesite and smectite clays, which, in combination with remobilised silica, are anticipated to suture these migratory zones to some degree (Saprolite 2020).

• The overlying smectite zone is comprised of dense clay in which most rock structures and textures have been obliterated. This zone is interpreted to have the lowest hydraulic conductivity of the five major units of the weathering profile (Saprolite 2020).

• The laterite profile is interpreted to be relatively transmissive compared to the underlying smectite and saprolite units (Saprolite 2020).

• In the MMN mining area ultramafic regolith profiles are commonly bound by weathered felsic and mafic volcanic intrusive rock. The contacts of these units can be heavily foliated and fractured, and potentially provide preferential pathways for seepage migration where contacts intersect pit surfaces.

The hydraulic properties of the various lithological units were approximated in 2004. Results were derived from constant head and falling head tests undertaken at monitoring bores near pit 2/3. The results are presented in Table 8.6 and show the laterite and fractured ultramafic units to be relatively conductive compared to the saprolite and smectite units (Saprolite 2020).



8.6.3.1 Inpit TSF 8/5-9/4

Pit 8/5-9/4 was commissioned as an inpit TSF in November 2010. In September 2009, prior to tailings deposition at the site, six monitoring bores were drilled around the perimeter of pits 8/5 and 9/4. Drilling observations indicated potentially low hydraulic conductivity.

Water levels have been monitored at quarterly intervals in 8/5-9/4 inpit monitoring bores since November 2009, one year prior to tailings deposition starting.

Figure 8-2: Annual Water Level Change Inpit TSF 8/5-9/4

The data illustrates similar water level rises at most monitoring sites between November 2010 and mid-2012 consistent with the initial stages of tailings deposition. IP904-3 is somewhat of an exception and shows a large spike in water level between February 2011 and March 2011 which is consistent with high February 2011 rainfall.

From mid-2012 water levels have been relatively stable at the majority of sites. Exceptions are IP904-3 where water levels have fluctuated and appear to be affected by rainfall and IP805-1, which had a longer rising trend and appears to have stabilised at 450 m AHD since mid-2016 (refer Appendix B1 of Appendix 3).

Sampling and water chemistry analysis were undertaken quarterly at inpit monitoring bores since commissioning. Laboratory TDS and pH results are presented in Appendix B1 of Appendix 3. The following results were observed:

• Highly variable TDS concentrations with an increasing trend at IP805-2 and IP805-3



• Stable rising trend of TDS prior to 2019 and constant trend of TDS in 2019 at IP805-1 and IP904-2

• Tailings deposition did not seem to have any impact on the TDS concentration at IP904-3 while an increase was noted at IP904-1.

IP904-3 and IP904-1 are situated north west and north east of 8/5-9/4, respectively. There has been a progressive divergence of pH at bores around 8/5-9/4 with initial pH values clustered around pH 8 and diverging to be between pH 6 and pH 8 as of November 2019. As with electrical conductivity (EC), IP805-3 shows the greatest variability in pH. Although showing the same trends as the other bores, IP904-3 has, as of November 2019, changed the least since the initial measurement.

8.6.3.2 Inpit TSF 8/4

Inpit TSF 8/4 is situated south and adjacent to Inpit TSF 8/5-9/4. Tailings deposition commenced at 8/4 in August 2014 and ceased in January 2018 and was the primary tailings storage during this time. The hydraulic conductivity at this site is inferred to be relatively high.

Water levels have been recorded at IP804-1/IP804-2 and IP804-3 on a quarterly basis since the bores were constructed in June 2010 and May 2014 respectively.

Water levels recorded at IP804-1 and IP804-2 rose during 2011 and early 2012, presumably as a response to tailings deposition upstream at Inpit TSF 8/5-9/4. Between mid-2012 and late 2014 water levels were relatively stable at these monitoring locations. Water levels rose at IP804-1 and IP804-3 in November 2014, which is in line with the commencement of tailings deposition at Inpit TSF 8/4. Water levels are presented in Appendix B2 of Appendix 3.

Sampling for laboratory analysis has been undertaken quarterly at inpit monitoring bores since they were constructed. Laboratory TDS and pH results are presented in Appendix B2 of Appendix 3. The chart illustrates a small initial increasing trend at IP804-1 followed by greater variability and a slightly steeper rise since 2014. IP804-2 had an increase in TDS concentration between February 2012 and November 2014 and a subsequent plateau and decline from mid-2016. IP804-3 has shown a generally increasing trend but with large rises and falls between measurements. Laboratory pH measurements show a slight decline in all three bores from 2015 in line with tailing deposition at 8/4. However, IP804-2 has shown an increase in stability of pH since 2017, distinct from its previous variability and the variability observed in the other two bores, Appendix B2 of Appendix 3.

8.6.3.3 Inpit TSF 18/6

Inpit TSF 18/6 is situated north and adjacent to Inpit TSF 8/5-9/4. Tailings deposition commenced at 18/6 in March 2018. Monitoring bores IP1806-1 and IP1806-2 were drilled in April 2017 to the east and west of 18/6 respectively while SP30, SP31 and SP32 were drilled on a land bridge between pits 9/5 and 18/6. Falling head permeability tests undertaken at IP1806-1 and IP1806-2 in 2017 indicated moderate conductivity between 3.33x10-2 m/d and 6.41x10-2 m/d. The transmissive zones were however interpreted to be relatively deep and somewhat confined by the overlaying clays (Saprolite, 2017).

Water levels have been recorded at IP1806-1, IP1806-2, SP30, SP31 and SP32 on a quarterly basis since the bores were constructed in April 2017. Water levels recorded at all five bores have risen since the beginning of tailings deposition, Appendix B3 of Appendix 3. Bores SP30, SP31 and SP32 are located on a narrow land bridge between Inpit TSFs 9/5 and 18/6 and would be expected to rise to match the level of tailings while the TSFs are active.



Sampling for laboratory analysis has been undertaken quarterly at inpit monitoring bores since they were constructed. Laboratory TDS and pH results are presented in Appendix B3 of Appendix 3. The chart illustrates stable TDS at IP1806-2 and variable TDS at IP1806-1. During initial construction IP1806-1 was noted to have a halocline at approximately 41 mbgl and this could account for some of the variability in measurements between quarters. Laboratory pH has remained relatively stable with a slight declining trend. As with TDS, IP1806-1 shows more variability than IP1806-3 and this could be a result of stratified groundwater with two different water types as presented in Appendix B2 of Appendix 3.

Hydrogeological implications for tailings deposition

As groundwater is expected to be encountered at the bottom of the pits, mining of the 17 series deposit is likely to require dewatering. This presents a risk of localised pit wall instability as a result of the increase of excess pore water pressures in the pit walls due to lowering of water levels. These failures may be circular slip-type failures or failures due to the presence of structural features (i.e. planar features) in the pit walls (Coffey 2020).

It should be noted that the pit wall stability will be improved as a result of tailings deposition, with the deposited tailings abutting the toe of the walls and increasing factors of safety for any existing potential failure zones (Coffey 2020).

The following aspects are relevant to management of an inpit TSF (Coffey 2020):

1. During dewatering of the pit, slumping of the pit walls may be apparent. Personnel considering entry to the pit should inspect the pit rim area and conduct HAZOPS before entering the pit. Construction activities at the base of the pit are not envisaged other than establishing decant pumps. After the tailings level exceeds the groundwater level, this will no longer be a concern

2. Initially, tailings are to be deposited from four sets of multiple spigots, located at different positions along the eastern side of the pit. The existing access ramps along the northern, western and southern sides of the 17 series pits will be utilised as part of water recovery operations. Once the tailings level covers all the localised low points, discharge from multiple spigots will be conducted only at the northern tip, while the southern access ramp will be used for water recovery operations

3. The ponds of supernatant water, liberated from the tailings slurry, will be located adjacent to the proposed decant access ramps to the pit. Pumps deployed from the access ramps will allow recovery of supernatant water. The pumps will be moved up the ramps as the tailings and water levels rise within the pit. Water should not be allowed to accumulate in the pit. Water recovery will increase factors of safety against wall instability and reduce seepage when the pit is nearly full.

Routine (daily) pit rim inspections during the operation of the proposed 17 Series Inpit TSF will be conducted.


The following risk assessment implications are associated with the development of the proposed 17 Series Inpit TSF:

• Risk of seepage along preferential drainage paths. Hydrogeological investigations for existing inpit TSFs have indicated relatively low hydraulic conductivity across the MMN project area, with potential for groundwater movement along discrete seepage pathways associated with



structural features (refer Section 8.6). This movement is anticipated to be restricted to discrete hydraulic pathways within the footprint of the mining area.

• Groundwater mounding and impacts to native vegetation. Groundwater levels are already somewhat depressed due to mining and water harvesting activities. Modelling of groundwater depths in the area of the proposed TSF indicates that groundwater may be encountered at the design pit depths. It is expected to take some time before water levels reach pre-mining levels and groundwater mounding commences. Groundwater mounding is unlikely to occur to an extent where it can negatively affect vegetation.

Whilst groundwater mounding is likely to occur and groundwater quality may deteriorate at discrete locations, risk to the surrounding environment from the proposed inpit TSF is expected to be low, when compared with paddock style facilities.

• Long term seepage post deposition. After deposition ceases it is expected that seepage from the proposed inpit TSFs will diminish over time as tailings consolidates, forming a hydraulic barrier. The risk of long-term seepage will be further reduced as the tailings are predicted to desiccate due to the extremely dry climate. It is anticipated the likelihood of seepage will be negligible even after prolonged periods of heavy rainfall.

8.7 Flora

Murrin Murrin is located in the Murchison Region of the Eremaean Botanical Province. The Murchison region is the ‘mulga region’ of Western Australia, this being the dominant vascular plant taxa and a significant component of the most extensive communities.

The vegetation communities associated with the Murrin Murrin project are generally well represented across the region (Mattiske 1996). Flora and vegetation habitats which exist within the project area are not pristine and have experienced a modification of structure and a loss of plant diversity as a result of long-term grazing by introduced stock.

The MMN project area was surveyed by Mattiske (1996a) and selected areas were surveyed again in 2011 and 2012 by G&G Environmental (2012) and 2018 and 2019 by Phoenix Environmental Sciences (2019). The vegetation communities that will be disturbed at MMN as a result of the limited clearing for this Proposal include:

• 1a – Open woodland of Acacia aneura and Acacia ayersiana over mixed shrubs and daisies in loam with scattered quartz pebbles on the surface

• 1b – Woodland of Acacia aneura, Acacia stowardii, Acacia ramulosa and Grevillea berryana over low sparse shrubs of Senna artemisioides subsp. filifolia , and Scaevola spinescens and herbs such as Ptilotus helipteroides and Velleia rosea on low stony rises.

• 2a – Very open shrubland of Acacia aneura and Acacia quadrimarginea on rocky outcrops and lower slopes of a banded ironstone and dolerite hill

Mattiske (1996a) and G&G Environmental (2012) considered vegetation community 2a to be unique to the local area but widespread outside the Murrin Murrin Project.

Flora and vegetation surveys by Mattiske (1996a), G&G Environmental (2012) and Phoenix Environmental Sciences (2019) did not identify any threatened flora or Threatened Ecological Communities (TECs) at MMN. The surveys did however identify populations of Priority Flora at MMN, including:



• Hybanthus floribundus subsp. chloroxanthus (Priority 3) • Hemigenia exilis (Priority 4) • Acacia websteri (Priority 1) • Hibiscus krichauffianus (Priority 3)

It is unlikely that development of the TSF (this Mining Proposal) would impact any priority species previously identified during vegetation surveys at MMN and impacts to native vegetation would be restricted because:

• The proposed TSF is being developed within an existing disturbed area of MMN. Clearing of undisturbed areas of native vegetation is to be restricted to 0.6 ha along proposed pipeline corridors.

• Field observations during vegetation clearing for mine development suggest that the Acacia woodlands are shallow rooted (<1 m) with an extensive lateral root system. Rooting depth is also constrained by the laterite / ferricrete layer near surface. Impacts from groundwater level rise on vegetation due to tailings deposition are unlikely due to the shallow rooted nature of surrounding Acacia woodland and contingency measures previously described (Saprolite 2020).

• Tailings deposition and groundwater levels will be managed such that standing water levels within the vicinity of the pit will not rise within 4 m of the natural ground level.

8.7.1.1 Risk assessment implications

The proposed TSF is located within an existing pit and hence an existing disturbed area. There is limited clearing of native vegetation required to allow completion of the construction works associated with the TSF development. The approximately 0.6 ha of vegetation that is to be cleared is well represented across the region.

The are no implications for the risk assessment associated with native vegetation and flora.

8.8 Fauna

A fauna survey of the MMN project area was undertaken in 2011-2012 by Ecosmart Ecology (2012) and 2018 by Phoenix Environmental Sciences (2019). The surveys found that habitats located at MMN project areas were uniform in structure and dominated by Mulga shrublands. Equivalent habitats to those found in the project areas were found to be extensive and contiguous throughout the Murchison bioregion. No fauna species of conservation significance were identified in the MMN project area.

No water birds have been observed on the existing inpit TSFs to date. Operational experience would suggest that there is a low risk of water birds becoming entrapped within the proposed inpit TSFs.


The proposed TSF is located within an existing pit and hence an existing disturbed area. There is limited clearing of native vegetation (approximately 0.6 ha) which may be habitat for native species of fauna to allow completion of the construction works associated with the TSF development. Habitats are well represented across the region.

The are no implications for the risk assessment associated with native fauna.



8.9 Social environment

Aboriginal heritage

A comprehensive program of Aboriginal studies and surveys have been completed across the areas of proposed development at MMN. The identification and management of Aboriginal Heritage sites was incorporated in the approval of the Murrin Murrin Expansion Project Public Environmental Review (PER) which was approved under Part IV of the Environmental Protection Act 1986 in 1999.

There are approximately 450 known Aboriginal heritage sites located within the area, the majority of which are archaeological sites that are located within or adjacent to the MMN, MMS and MME mining areas. All Aboriginal heritage sites are recorded in the ArcGIS database.

Section 18 approvals under the Aboriginal Heritage Act 1972 have been obtained for all sites which have been disturbed by mine development.

European heritage

The Murrin Murrin project area has been fully surveyed and no sites of European cultural value exist within the area.


There are no implications for the risk assessment in relation to impacts to the social environment from the proposed inpit TSF.

Land use and community

MMO have previously discussed the development of the Murrin Murrin project areas as part of ongoing consultation with local shires and the indigenous communities of the northern goldfields.

The areas of proposed development at MMN project area are located on the Glenorn pastoral lease, which is currently managed by Minara Pastoral Holdings Pty Ltd, a wholly owned subsidiary of Minara Resources Pty Ltd. Glenorn homestead is located approximately 35 km from the MMN project area.

The Pastoral Manager has been advised of the ongoing mining operations and has not raised any concerns regarding these activities.

The MMAELC meeting is conducted biannually and hosts members from the North East Indigenous Body (NEIB), Aboriginal groups from Leonora, Laverton, Mt Margaret and Mulga Queen, and Government representatives. The MMAELC meeting provides an opportunity for MMO to update the local community on the project, for the community to raise any questions or concerns. MMO will engage with the community regarding this proposal in the next meeting.

Mount Margaret Aboriginal Community is located approximately 30 km east of the Murrin Murrin plant site.

The Murrin Murrin accommodation village is located approximately 3.5 km north of MMN. Minara pastoral homestead is located 18 km south west of MMN.

Minara Community Foundation

In 2007 Minara set up a community foundation for the long-term benefit of people in the northern Goldfields region of Western Australia. Minara has donated $3.5 million to the Minara Community



Foundation (MCF) since 2008 and has awarded $2.5 million in grants to a wide range of community projects.

The endowment has been invested for growth to benefit communities and future generations beyond the life of the Murrin Murrin project. The donation contributions plus a portion of the return on the investment have been made available each year as charitable grants for use by the community.

The foundation supports projects that target:

• Educational benefits

• Economic, social, cultural and heritage benefits, including the protection of Indigenous culture

• Economic development and training opportunities, and

• Sustainable programs and initiatives for future generations.

The MCF and Equity Trustees work together for the benefit of the local community to oversee the governance and financial administration of the foundation and its grant-making program.

Groups wishing to access grant funds follow a formal application process that is managed in accordance with appropriate grant-making principles. A local advisory committee is in place and comprises northern Goldfields community members and Minara employees. The committee assists with evaluation of grant applications and proposed allocation of grant funds in order to ensure that reliable and sustainable projects receive support.



9.4 TSF hazard rating classification

A hazard rating system exists to classify the potential consequences of embankment or structural failure and controlled or uncontrolled release of tailings or seepage. It is derived from the life of the TSF and considers potential consequences on:

• The safety and health of people

• The environment

• Property

• Infrastructure.

Classification of the proposed 17 Series Inpit TSF, in accordance with Tables 1 and 2 of DMIRS (2013) Code of Practice (as far as it relates to inpit TSF) was undertaken by Coffey (2020). The outcome of the study resulted in a hazard rating of ‘Category 3 – Low’ given that:

• There is no potential for loss of life or injury

• Limited or no potential for human exposure

• Limited or no potential for destruction or loss of assets

• Insignificant loss of TSF storage capacity is possible

• Limited potential for adverse effects on flora and fauna

• Limited potential for damage of items of heritage or historical value

• Classification as a Category 3 storage as there will be no perimeter embankments. No dam break analysis is therefore required.



9.5 Proposed Mitigation Measures

TSF pit wall failure

If adequate pump operation, routine inspections and maintenance practices set out in the Operations Manual (Coffey 2020; Appendix F of Appendix 2) are adopted, the probability of pit wall failure during normal operations is low.

In the unlikely event of a major pit wall failure, the tailings within the facility will most likely remain within the facility or be confined within one of the adjacent pits.

No personnel shall enter the base of any operating pits (i.e. start-up). Access should be confined to ramps associated with decants.

Action to control a small-scale failure and limit environmental damage would include:

• Assess the requirement for direct deposition to alternative facilities or reduce process plant throughput

• Movement of tailings deposition to areas not affected by the small-scale pit slope failure

• Contact a suitably qualified geotechnical specialist for technical assistance

• Prior to the commencement of any repairs undertake a thorough inspection of the area

• Undertake remedial and repair work of the damaged embankment or affected area

• Clean up of tailings as soon as practical after repairs have been completed and the storage is assessed as safe for ongoing use/tailings deposition

• An incident report is to be completed.

Action to control a large-scale failure and limit environmental damage would include:

• Assess the requirement to shut down the process plant

• Direct tailings deposition to alternative facilities

• Contact a suitably qualified geotechnical organisation for technical assistance

• Advise relevant government departments particularly DMIRS and DWER

• Prior to the commencement of any repairs undertake a thorough inspection of the area with the assistance of a geotechnical specialist

• Repair the damaged pit slope in accordance with the specialist’s instructions

• Clean up of tailings as soon as practical after the repairs have been completed


The safe operation of the inpit facilities relies upon the implementation of operational procedures which comprise tailings deposition, decant operation; and routine inspections and maintenance, as set out in the Operations Manual to minimise the potential for a catastrophic event such as a failed embankment.

Pit wall erosion

Response to Hazard:



• If erosion has developed to a point where collapse may be imminent, proceed as per Section 9.5.1

• Otherwise install bunds or drains to divert water flow away from the area of erosion and install any necessary protective barriers to protect personnel or vehicles

• Report circumstances to Tailings and Water Coordinator

• The Tailings and Water Coordinator is to inspect the site and either; arrange appropriate rectification measures; or contact the Geotechnical Consultant for specific advice


Burst or leakage of tailings delivery or return water pipeline

The tailings lines from the process plant to the TSF and the return water lines from the decant pumps located on the access ramps to the evaporation ponds are to be located inside bunded open trenches/pipeline corridors to contain any spillage of materials resulting from lines which develop leaks or burst during operation. Scour sumps will also be constructed.

Response to Hazard:

• If a hazard alert arises from control room instrumentation (drop in pressure in delivery lines), immediate inspection of the line is required to locate and assess the leakage

• If automatic shutdown/diversion of tailings flow has not occurred, the Tailings and Water Coordinator shall arrange appropriate shut down or diversion

• If the hazard alert arises from inspection, the Tailings and Water Coordinator is to be advised immediately who shall arrange appropriate shut down or diversion of deposition

• At the location of the leakage, the Tailings and Water Coordinator is to inspect the site and arrange appropriate additional containment and/or clean up in association with the Environmental Advisor

• The Tailings and Water Coordinator is to ascertain the causes of the leakage/burst and institute procedures or measures to minimise risk of recurrence


Seepage

Response to Hazard

• If during any inspection of the TSF areas, identification of moisture, surface staining/discolouration, water ponding or surface water expression, which may be an indication of seepage from the TSF, are observed around and in the vicinity of the TSF, the Tailings and Water Coordinator is to be notified

• The Tailings and Water Coordinator is to inspect and photograph the site, ascertain details of location and extent of seepage and proceed as outlined in Section 9.5.12

• The Geotechnical Consultant is to be advised of the details as soon as possible.



10.2 Pipeline Monitoring

Tailings Pipeline

The tailings line is to be inspected at 12-hour intervals, and recorded in the Shift Foreman’s logbook.

All tailings lines will be bunded. The HDPE tailings lines on the crest of the facility are sensitive to temperature, and the expansion and contraction of this line can cause leaks. In extreme situations it may lead to failure of the pipeline. Pipelines shall be inspected for:

• External damage

• Potential fractures

• Stress due to temperature extremes

• Valves

• Welds

• Flange / joint leaks.

Any leaks or failures of the tailings pipeline will be immediately reported to the following personnel or project equivalents and an incident report completed.

• Shift Supervisor, or

• Ore Leach Superintendent or Processing Manager.

If necessary, emergency shutdown and containment procedures shall be initiated by either the Process Manager or Environmental Department.

Return water lines

The return water line comprises of a HDPE pipe which will be positioned in the same bunded corridor as the tailings delivery line from the process plant to the TSFs before splitting up into two separate corridors at the inpit TSF. The pipeline will have a series of valves allowing water to be diverted into the tailings line for flushing via junction points. Return water lines will be maintained and inspected, as decant water may contain traces of processing plant reagents which can have a detrimental environmental effect if released. The return water lines will be inspected for:

• External damage

• Potential fractures

• Stress due to temperature extremes

• Welds

• Joint leaks

• Valves.

Any leak or potential failure will be reported immediately to the following personnel after initiating emergency shutdown and containment procedures:

• Ore Leach Superintendent



• Process Manager and / or Environmental Department.

10.3 Freeboard Monitoring

Daily freeboard monitoring will be undertaken to ensure that limits are within those described in Table 5.4: Freeboard Requirements.

10.4 Decant system monitoring

The position and size of the pond and the position of the decant pump will be inspected at the same time as the tailings lines are inspected. Any abnormalities will be reported immediately to the following personnel or project equivalents:

• Tailings and Water Coordinator, or

• Production Manager.

The same personnel will also be advised if a large water volume is accumulating on the facility, so measures can be taken to reduce the pond size. The water discharged from the decant facility will also be inspected on a regular basis to ensure it is clear (i.e. not murky or turbid). The return water lines to the evaporation pond will also be inspected at the same time as the tailings line. Any leaks or failure of the water pipeline will be immediately reported to the following personnel or project equivalents:

• Tailings and Water Coordinator, or

• Production Manager.

10.5 Pit walls monitoring

Part of the general activities of the Shift Foreman, when visiting the storage facilities, will be to inspect the pit walls, including the crest. The inspection shall note any cracking or new features, such as seepage, pit wall failures or scour (caused by tailings deposition or rainfall runoff) or any other obvious changes or problems.

No personnel will enter the base of the TSF during operations (i.e. start-up). Access will be confined to ramps associated with decants. During high rainfall events, if personnel safety allows it, the inspection frequency shall be increased. The inspections will ensure that the freeboard of the supernatant pond is within DMIRS guidelines.

10.6 Monthly inspections

Inspections of the 17 Series Inpit TSF will be carried out on a monthly basis. The Monthly Inspection Log and Monitoring Sheet (Appendix A of Appendix F of Appendix 2) will be completed for each inspection.

Details of monthly monitoring is summarised below:

Pit walls

i. Is there cracking present along the pit crest, any intermediate berms/benches or walls?

ii. Is staining or discolouration of soil present outside the extent of the facility crest?

iii. Is there any water flow/seepage identified from the facility as indicated by the monitoring bores?



iv. Is the tailings freeboard adequate?

v. Is there water ponding against waste plugs, contrary to facility design?

Spigotting / placement

i. Is the distribution of the tailings into the storage as required by the design?

Supernatant water pond / decant pump

i. Is the distribution of the tailings into the storage as required by the design?

ii. Is the decant pump positioned appropriately within the supernatant water pond?

iii. Is the water pond surface (within the storage) as planned, or is there excess water on the storage?

iv. Can the decant pump efficiently handle and discharge any storm runoff in addition to the supernatant water?

Tailings and return water lines

i. Are the tailings and water return lines intact and free of cracks?

Groundwater / phreatic surface monitoring

i. Has all monitoring been performed and the results regularly reviewed?

ii. Has the monitoring been performed as specified in the DWER conditions of licence?

iii. Have any DWER exceedances been reported?

All the above points will be monitored closely to ensure stability is maintained. If problems are encountered, a geotechnical engineer will be consulted and an investigation will be undertaken

10.7 Engineering inspections

An inspection by a qualified geotechnical engineer with experience in the design, operation and auditing of tailings storages will be carried out annually.

10.8 Process Plant

In addition to the daily visual inspections of the water pond, spigots, water return pumps, and tailings and return water pipelines to the evaporation pond, the following information will be recorded on a monthly basis:

• Tailings production measured in dry tonnes

• Tailings slurry density measured in percentage solids or slurry water volume

• Water return from all sources from the tailing’s storage to the evaporation pond, measured in cubic metres or tonnes.

This information will be utilised to estimate a water balance as part of auditing of the tailings storage.



10.9 Achieved tailings density and strength

Sampling of deposited tailings, including recovery of disturbed bulk samples and undisturbed tube samples will be undertaken during TSF operations to assess performance of the facilities. Subsequent laboratory testing will include the following:

• Grading

• Atterberg limits

• Moisture content

• Density.

To further assess tailings strength, shear vane and / or cone penetration testing may be considered if required.

Currently, the average tailings slurry density is approximately 43.0% solids by weight. The average estimated in situ tailings density is approximately 1.48 t/m3 (dry).

10.10 Storage volume and deposition time remaining

Water pond level surveys are carried out on a monthly basis.

10.11 Reporting on other environmental factors

In addition to the above reporting, the following monitoring and reporting will be undertaken:

• Any fauna death on or near the TSFs (excluding roadkill)

• Any uncontrolled release of tailings slurry or return water and the cause (pipe break, overtopping, pump malfunction, automatic switch malfunction and operator error)

• Impacts due to seepage (vegetation distress, soil contamination, water quality changes)

• TSF defects, for example to the embankments or return water facilities

• Changes in water quality that exceed prescribed conditions of licence criteria

• Increases in production tonnages.

10.12 Annual audit and management review

In addition to daily and monthly inspections, an annual TSF audit and management review will be undertaken by a geotechnical engineer. The objective of the audit is to assess integrity of the facility against design and regulatory conditions. The audit will be undertaken via a site inspection and collection and review of relevant site data. The audit typically includes the following scope to satisfy DMIRS auditing requirements:

• Site visit to review and assess the TSFs

• Comment on condition of the facilities

• Review and comment on operational aspects (e.g. spigotting, water return)

• Review and comment on current licence conditions

• Review results of any relevant studies or investigations undertaken during the audit period



• Review monitoring bore water quality and water level information

• Review survey information

• Review information relating to environmental aspects.

• Compare any new information against the design. This typically includes an assessment of the filling rate; if the information varies from the design, a revised prediction of storage life for the facility can be made.

The following may also be undertaken, either independently of or in conjunction with the audit:

• Sampling of deposited tailings, including recovery of disturbed bulk samples and undisturbed tube samples. Testing that could be considered includes grading, Atterberg limits, moisture content and density. Sampling will only be undertaken if safe tailings beach access is possible

• Stability assessments using field and laboratory results and water level information to reassess factors of safety.

The requirement for sampling and testing in any subsequent audit will be based on the previous year’s results and any variations in the tailings feed, such that repetitive testing of similar materials is avoided.



12 ENVIRONMENTAL MANAGEMENT SYSTEM MMO operates in accordance with its operations-wide Work Health, Safety and Environmental Policy. MMO maintains an Environmental Management System (EMS) that is certified to the International Standard for Environmental Management Systems (ISO 14001:2015).

The Corporate EMS is the overarching structure for the management of environmental issues. Implementation of the project will be carried out in accordance with this EMS. The three primary drivers of the EMS are to:

• Protect the environment

• Operate within the law and meet CSR corporate objectives

• Ensure that our people know their environmental responsibilities and how those responsibilities are to be met.

MMO EMS is used for the following:

• Risk identification throughout the life of the project

• Implementing environmental management programs

• incorporating goals and targets, and legal obligations

• Implementing organisation structure and responsibility

• Ensure training and inductions for all employees are up to date and compliant

• Manage sitewide operational procedures

• Monitoring and management of performance

• Raising event reports for non-compliances and immediate corrective actions

• Internal and external reporting of performance

• Keeping all legal records

• Auditing of performance.



13 MINE CLOSURE MMO’s Mine Closure Plan (MCP) was recently updated and submitted to DMIRS for approval in 2020.

The existing disturbance types in this mining proposal such as the 17 series pits and part of the service corridor for the pipelines are covered under existing closure domains and updated disturbances will be included in the next review of the MCP.

13.1 Post Mining Land Use and Closure Objectives

Following closure of the Murrin Murrin mine site, the next land use is proposed to be returned to pastoral activities, further mineral exploration, mining or a combination of these. This will be determined closer to the planned closure date and in consultation with relevant stakeholders.

The objectives of closure of the Murrin Murrin project are:

• To create safe and stable landforms compatible with the surrounding landscape.

• To progressively rehabilitate the Project area to achieve a self-sustaining vegetation which is representative of local communities.

• To ensure surface water and groundwater is managed throughout the life of the mine, closure and post-closure, such that there is no long-term liability to MMO or the State.

• To involve the community and stakeholders in planning for closure to ensure that their interests are considered in closure of the project.

• To monitor environmental performance during progressive rehabilitation activities, closure and post-closure stages, and to take appropriate action until the specified completion criteria have been met.

As part of decommissioning:

• All the delivery and discharge pipes and valves should be removed from the closed TSFs;

• Power cable and pipe to the decant pump and the pump should be removed; and

• The standpipes of the piezometers and ground water monitoring boreholes should be replaced with ground level covers, so that they are less obtrusive, but still available for monitoring.

In view of the potentially soft tailings it is desirable to create a firm surface by inducing consolidation of the tailings and capping the tailings in accordance with Landloch (2020) (Appendix 4) recommendations.

13.2 Rehabilitation and Mine Closure

The following rehabilitation and mine closure activities are proposed to be undertaken for each of the disturbance types contained within this proposal:

Non-Potable Pipeline

The closure concept for the non-potable pipeline domain is to:

• Flush pipelines



• Dismantle and remove pipeline and sell/recycle/dispose of to a designated inpit disposal facility and cover with waste material

• Remove contaminated soil to an appropriate disposal facility

• Level the pipeline bund/v-drain to reinstate the natural topography

• Re-spread any available materials (tree mulch and topsoil)

• Determine a seeding mix based on species richness and density recorded in analogue communities, and

• In a one-pass operation rip, seed and fertilise the area on the contour.

Tailings Storage Facility

Prior to the commencement of the rehabilitation program, the facilities will undergo a topping up process. The topping up process maximises the storage capacity of the pits and reduces the impact of the final settlement of the tailings surface. Based on consolidation estimates, it is expected that rehabilitation work will not be able to commence for a period of up to six years post completion of filling due to the expected low strength of the deposited tailings (approximately 95% consolidation is expected to be achieved after six years).

Upon completion of tailings placement within each facility, the surface will undergo a rehabilitation program. The closure concept for the TSF domain is to:

1. Remove all infrastructure

2. Construct a stable, non-polluting landform

3. Establish a self-sustaining vegetation cover that reflects the natural vegetation communities of the area

4. Ensure no long-term groundwater liability for MMO or the State.

The rehabilitation program will include the identification of appropriate capping material and local flora species to revegetate the surface of the facility.

Analysis of the tailings material indicates a high level of salinity, which would not support vegetation growth. As a result of capillary action in the soil, salinization of the soil in the root growth zone of vegetation may occur.

13.2.2.1 Physical and chemical properties of tailings

The tailings are extremely saline, having a median EC1:5 of 18.7 dS/m and a median ECe value of 53.4 dS/m. Tables developed by the WA Department of Agriculture for salinity tolerances of common rangeland rehabilitation species (FAO 2002) suggest that ECe values greater than ~16 dS/m (equivalent to an EC1:5 of ~1-2 dSm)1 are likely to have adverse impacts on all but extremely salt tolerant species including and not limited to (Landloch 2020;Appendix 4) :

• Atriplex spp. (A. rhagodioides, A. vesicaria, A. paludosa, A. bunburyana, A. cinereal, A. lentiformis, A. nummularia, A. undulata)

• Acacia ampliceps

• Casuarina glauca



Trials

Capping trials will be conducted to ensure rehabilitation success. The following trial strategy is proposed:

• Individual trial plots of approximately 25 m x 25 m will be established. Trial areas will have zero gradient, will be accessible during wet weather and will be free from surface water inflows from adjacent areas

• The cover material will be placed over in situ tailings and the underlying tailings should be moist. The underlying tailing will be characterised for salt, moisture retention characteristics and moisture profiles prior to covering

• Placement of the cover material will include spreading and compacting. The cover materials will then be allowed to settle and consolidate either by rainfall or by spraying water on the top

• Loggable moisture measuring instrument to measure moisture over time will be installed. A logging weather station will also be installed. Small hole will be augered to collect soil samples for testing. The soil samples will be tested for pH and metals. The surface height change could also be assessed using LIDAR point clouds to assess rates of consolidation and potentially any sub-surface slumping that may be occurring

• The trial will be designed to collect rainfall, soil-water, salinity (and other contaminants as required), and seepage data that in turn is used to fine-tune the model input parameters to improve the accuracy of the model’s predictions. The short-term collection of the data will then be used to calibrate a soil-water model to inform on the long-term cover performance.

13.2.2.3 Surface water management

Surface water will be managed to control water runoff from rainfall and preventing water from pooling. Cell walls may be required across the surface area to prevent surface flow from travelling significant distances to accumulate in low-lying areas. Cell walls would be made up of constructed bunds 750 x 2000 mm, dividing the surface area into 4 ha cells.

The rehabilitated surface will be graded to a level surface prior to seeding, however, the surface may be subject to movement associated with the shrinking and swelling of subsurface clays.

13.2.2.4 Seeding

Scarification, seeding and application of ameliorants will occur as one rehabilitation event. Batter slopes will be worked on the contour to minimise the risks of erosion.

Local provenance seed will be utilised where possible. The proposed seed mix will be based on establishing a rehabilitation outcome which reflects the vegetation composition and density of the surrounding vegetation communities.

13.3 Completion Criteria

Completion criteria for rehabilitation and closure of the disturbance types associated with this Proposal have been developed and are outlined in Table 13.3. As the project progress to completion and more data becomes available, the completion criteria will be updated.

Table 13.3: Construction completion criteria



14 REFERENCES Beard JS (1976) ‘Vegetation Survey of Western Australia: Murchison’. University of Western Australia Press: Nedlands, WA.

Coffey Mining Pty Ltd (2016) ‘Geotechnical Assessment, In-pit Tailings Storage Facilities 9/5, 18/3, 18/6’, unpublished report for Murrin Murrin Operations Pty Ltd.

Coffey Services Australia Pty Ltd (2020), ‘Geotechnical Assessment of 17 Series In-Pit TSF’, unpublished report for Murrin Murrin Operations Pty Ltd.

Department of Mines and Petroleum (DMP) (2013) ‘Code of Practice, Tailings Storage Facilities in Western Australia’.

Environ Australia Pty Ltd (Environ) (2010) ‘Murrin Murrin North 8/5 and 9/4 Inpit Tailings Disposal: Mining Proposal and Works Approval Supporting Documentation’, unpublished report for Minara Resources Pty Ltd.

Hall NJ, McKenzie N and Keighery GJ (eds) (1994) ‘The Biological Survey of the Eastern Goldfields of Western Australia Part 10: Sandstone-Sir Samuel and Laverton-Leonora Study Areas’. Western Australian Museum Supplement No 47. Museum of Western Australia: Perth, WA.

Landloch Pty Ltd (2009) ‘Potential for capillary rise of salt from tailings’. unpublished report for Minara Resources Pty Ltd.

Phoenix Environmental Sciences (2019) ‘Flora, vegetation and terrestrial fauna surveys for the Murrin Murin Nickel Cobalt Project’. Unpublished report for Minara Resources.

Pringle HJR, Van Vreeswyk AME and Gilligan SA (1994) ‘An Inventory and Condition Survey of the North-Eastern Goldfields, Western Australia’. Technical Bulletin No. 87 Department of Agriculture Western Australia: South Perth, WA.

Saprolite Environmental (2016) ‘Murrin Murrin North Mining Area, In-Pit Tailings Disposal Into Pit Voids MM9/5, MM18/3 & MM18/6, Hydrogeological Assessment’, September 2016, unpublished report for Murrin Murrin Operations Pty Ltd.

Saprolite Environmental (2020) ‘Proposed In-pit Tailings Disposal into 17 Series Pit Voids, Hydrogeological Assessment’, unpublished report for Murrin Murrin Operations Pty Ltd.

Tongway DJ and Hindley NL (2004) ‘Landscape function analysis. Procedures for monitoring and assessing landscapes’. CSIRO Sustainable Ecosystems, Canberra, ACT.



APPENDIX 1. DWER PART V PRESCRIBED PREMISES WORKS APPROVAL APPLICATION FORM



APPENDIX 2. GEOTECHNICAL ASSESSMENT OF 17 SERIES IN-PIT TSF (COFFEY 2020)

Murrin Murrin Operations Pty Ltd Murrin Murrin Mine Geotechnical Assessment of 17 Series In-Pit TSF

14 July 2020

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Coffey Services Australia Pty Ltd ABN 55 139 460 521 ii

Table of contents

Executive Summary ............................................................................................................................ 1

1. Introduction .................................................................................................................................. 3

1.1. Scope of works .................................................................................................................. 3

2. Background ................................................................................................................................. 4

2.1. Location ............................................................................................................................. 4

2.2. Ownership ......................................................................................................................... 4

2.3. Existing facilities ................................................................................................................ 4

2.4. History ............................................................................................................................... 4

3. Information supplied .................................................................................................................... 5

4. General information ..................................................................................................................... 5

4.1. Process type...................................................................................................................... 5

4.2. Rated throughput .............................................................................................................. 5

4.3. Ore type ............................................................................................................................. 5

4.4. Environmental performance .............................................................................................. 5

5. Tailing properties ......................................................................................................................... 5

5.1. Geochemistry .................................................................................................................... 5

5.2. Tailings properties ............................................................................................................. 6

5.3. Consolidation testing ......................................................................................................... 7

5.4. Summary of engineering properties .................................................................................. 7

6. Site selection ............................................................................................................................... 7

6.1. Climate .............................................................................................................................. 7

6.2. Landform ........................................................................................................................... 8

6.3. Geology and soils .............................................................................................................. 8

6.3.1. Regional geology .................................................................................................. 8

6.3.2. Lithology ............................................................................................................... 8

6.4. Hydrogeology .................................................................................................................... 9

6.5. Flora and fauna ................................................................................................................. 9

7. Geotechnical assessment ........................................................................................................... 9

7.1. Assessment of the pit wall ................................................................................................. 9

7.2. Structural features of the exposed mined pits ................................................................. 10

7.3. Implications with respect to tailings deposition ............................................................... 10

7.4. Tailings settlement .......................................................................................................... 10

8. Tailings storage facility .............................................................................................................. 11

8.1. General ............................................................................................................................ 11

8.2. Hazard rating ................................................................................................................... 11

8.3. Drawings ......................................................................................................................... 11

8.4. Freeboard requirements .................................................................................................. 12

8.5. Tailings deposition .......................................................................................................... 12

Coffey Services Australia Pty Ltd ABN 55 139 460 521 iii

8.5.1. Topping up ......................................................................................................... 12

8.6. Water recovery ................................................................................................................ 12

8.7. Underdrainage................................................................................................................. 13

8.8. Construction .................................................................................................................... 13

8.9. Tailings storage capacity ................................................................................................. 13

8.10. Liners ............................................................................................................................... 14

9. Water balance ........................................................................................................................... 14

10. Operating procedures ................................................................................................................ 14

11. Monitoring .................................................................................................................................. 15

12. Emergency action plan .............................................................................................................. 15

13. Rehabilitation ............................................................................................................................. 15

14. References ................................................................................................................................ 17

Tables

Table 1 - MMO tailings properties

Table 2 - Tailings consolidation characteristics

Table 3 – Expected Settlement Summary

Table 4 – Summary of Freeboard Requirements

Table 5 - Estimated Storage Capacity

Figures

Figure 1 – General Arrangement of Murrin Murrin North Project Area

Figure 2 – Tenement Locations and Site Plan

Figure 3 – Location Plan of the Proposed 17 Series In-Pit TSF

Figure 4 – 17 Deposit Pits (Total volume = 19.6Mm3 when completely mined)

Figure 5 – Average Pan Evaporation - Annual

Figure 6 – Design Rainfall Intensity Curves for Leonora

Figure 7 – Regional Geology of Murrin Murrin Ni-Co Project

Figure 8 – Regional Geology and Structural Interpretation of Murrin Murrin Ni-Co Project

Figure 9 – Generic Weathering Profile of Murrin Murrin Nickel Laterite Deposits

Figure 10 – Photo Showing Regolith Profile of the 17 Series Pits

Figure 11 – Cross-Sections of 17 Series Pits

Figure 12 – Locations of Cross-Sections in Figure 11

Figure 13 – NW to SE Striking Fault Visible in the South Eastern Corner of Pit 17.02

Figure 14 – Sketches of Tailings Pipeworks & Spigot Off-Takes

Figure 15 – Existing Piping Layout

Figure 16 – Mine Closure Concept

Coffey Services Australia Pty Ltd ABN 55 139 460 521 iv

Appendices

Appendix A - Tailings SettlementAppendix B – Tailings Storage Data Sheet (TSDS)Appendix C – DrawingsAppendix D – Scope of WorksAppendix E – Water Balance AnalysisAppendix F – TSF Operation Manual

Murrin Murrin Mine

Coffey, A Tetra Tech Company Geotechnical Assessment of 17 Series In-Pit TSF 2

Drawings prepared for the project are attached as Appendix C. These drawings also form part of the Scope of Works (SoW) for pipeline corridor earthworks construction for the facility, attached as Appendix D. The estimated water volume decanted from the tailings storages to be discharged to the Evaporation Ponds is presented in Appendix E. An Operations Manual (OM) is attached as Appendix F, which has been prepared based on existing practices at MMO for use by process plant management and operations staff.

Upon completion of tailings placement within the facility, the surface will undergo a rehabilitation program that will include the identification of appropriate capping material and local flora species to revegetate the surface of the facility. It is expected that rehabilitation work will be delayed for a period of around 6 years following completion of filling due to ongoing consolidation of the deposited tailings and a need to develop a surface crust for safe access.

Murrin Murrin Mine


1. Introduction This document presents the details required by the Department of Mines, Industry Regulation and Safety (DMIRS), Western Australia, for preparation of a geotechnical assessment report for the proposed 17 Series In-Pit Tailings Storage Facility (17IPTSF), at the Murrin Murrin Nickel Cobalt Project, operated by Murrin Murrin Operations Pty Ltd (MMO). Murrin Murrin Mine is located approximately 60km east of Leonora, Western Australia.

MMO propose to utilise the 17 Series Pits for the storage of tailings in what will be known as the 17 Series In-pit Tailings Storage Facilities (17IPTSF). This 17 Series Pits are located in the Murrin Murrin North (MMN) project area. The development and use of the pits for tailings storage will utilise existing disturbed areas and allow the voids to be filled, which would otherwise remain open with the potential for some pit walls to collapse over time. Utilising the pits for the storage of tailings also reduces the requirement to disturb new land for a new above ground type storage facility. Figure 1 displays the general arrangement of the site.

It is estimated that about 15Mt of tailings will be stored in the proposed 17IPTSF, based on a tailings dry density of approximately 0.8 t/m3. This corresponds with a monthly deposition of 375,000 tonnes (4.5 Mtpa) for approximately 2 years.

Initially, tailings deposition into the 17IPTSF will be from four sets of multiple spigots, each set located at different locations along the eastern side of the pit. Water liberated from the tailings slurry will be recovered by centrifugal pumps to be located at various existing access ramps at northern, western and southern sides of the pit. Towards the end, discharge will be from multiple spigots located at the northern tip, while the southern access ramp will be used for water recovery operations. At the early stages of tailings deposition, water will be decanted at the relatively lower points of the access ramps, which will be followed by pumping from the higher points of the access ramps. As the tailings level increases, the water recovery point will move upward along the access ramps.

This report was compiled in accordance with the following guidelines:

DMIRS (2015)1, ‘Guide to the preparation of a design report for tailings storage facilities (TSFs)’

DMIRS (2013)2, ‘Code of practice: tailings storage facilities in Western Australia’

DMIRS (2006)3, ‘Guidelines for Mining Proposals in Western Australia’

In accordance with Table 1 and 2 of DMIRS (2013)2 (as far as it relates to in-pit facilities), the proposed 17IPTSF is classified with hazard rating of ‘Category 3 – Low’.

1.1. Scope of works The scope of work for the study, as identified in our proposal, P272398 dated 09 March 2020, included the following:

Review existing relevant documents.

Compile a TSF design report, including: Pit wall stability assessment, including consideration of wall performance post-mining. Review of groundwater monitoring information, with comment on groundwater management

and details of monitoring / recovery bores. TSF design concept. Input to a preliminary closure concept.

Assist MMO with their WAA and MP.

Murrin Murrin Mine


2. Background 2.1. Location The Murrin Murrin Nickel Cobalt Project prescribed premises consists of Mining Tenements M39/446, M39/820, L39/81, L39/62, L39/83, M39/299, M39/651, M39/300, M39/301, M39/435, M39/436, M39/421, M39/422, M39/423, M39/424, M39/342, M39/343, L39/136, L39/168, M39/314, M39/322, M39/562, M39/637, M39/686, M39/692, M39/714, M39/715, M39/716 & M39/737 (Figure 2). The MMN project area lies within the Mt Morgans district of the Mt. Margaret Mineral field, between the towns of Leonora and Laverton, Western Australia at latitude 28o50’S and longitude 121o54’E.

The 17 Deposit Pits to be utilised for the proposed 17IPTSF are located approximately 3km west of the plant site. A layout plan showing the location of the proposed 17IPTSF in relation to existing operations is presented as Figure 3.

2.2. Ownership The project is owned and operated by Murrin Murrin Operations Pty Ltd.

2.3. Existing facilities The facilities in MMO includes processing plant, four cells of evaporation ponds, a paddock TSF (North Cell and South Cell); and eight in-pit storages, namely, Pits 2/2-2/4, 2/3, 8/4, 8/5-9/4, 9/2, 9/5, 18/3 and 18/6. The primary active tailings storages were Pits 9/5, 18/3 and 18/6.

2.4. History Operations at MMO commenced in 1999 and are based on the mining and processing of laterite ore for the extraction of nickel and cobalt. Conventional open pit mining techniques are used, followed by ore processing comprising pressure acid leaching, mixed sulphide precipitation, cobalt refining and nickel refining. The production process also produces ammonium sulphate as a by-product, which is sold to the Western Australian fertiliser market. Based on previous report (Coffey Mining, 2016)4, the process plant was previously generating approximately 4.15Mt (dry) of tailings per annum (tpa). According to the most recent 2019 annual audit report (Coffey, 2020)5, reference to an MMO provided spreadsheet ‘Inception EOM Tails Data - Master (values, FY2017)’, indicated tailings production of 3.77Mtpa.

MMO currently has an above ground paddock type tailings storage facility (TSF1) comprising two cells with an area of approximately 500ha and eight in-pit facilities. At the time of the site visit for the 2019 annual audit, tailings deposition was taking place in the Pit 9/5, 18/3 and 18/6 TSF. Return water from the in-pit facilities is pumped directly to the evaporation ponds.

MMO propose to develop 17 series In-Pit TSF as future primary tailings storage areas. The north-eastern tip of the 17 series Pits is located to the west of Pit 9/5. The advantage of utilising these pits is that they are located near existing active in-pit TSFs (Pits 9/5, 18/3 and 18/6) and hence the cost of extending pipework and other infrastructure is reduced.

Based on the geological architecture report (Minara Resources, 2020)6, mining of the first pit started in 2007 with the 17.01 pit followed by the 17.53 pit in 2010. Mining in 17.08, 17.07 and 17.02 is on-going. The 17 series pits are expected to be completely mined out in January of 2021. The final volume from Pits 17.09 in the north to 17.08 in the south, is estimated to be about 19.6 million cubic meters (Figure 4). The currently active Pits 9/5, 18/3 and 18/6 are projected to be filled by the end of 2022.

Murrin Murrin Mine


3. Information supplied The following information was supplied by MMO:

Minara Resources report (2020)6 entitled, ‘Geological Architecture Report for the 17 Series of Pits – Murrin Murrin North, Potential Tailings Storage Facility’, dated February 2020.

Aerial photographs of the site showing pits and proposed in-pit tailings.

Tailings Particle Size Distribution results from May 2016.

AutoCAD dxf files of 17 Series Pits.

4. General information 4.1. Process type Ore is processed using pressure acid leaching, mixed sulphide precipitation, cobalt refining and nickel refining.

4.2. Rated throughput Based on previous report (Coffey Mining, 2016)4, the process plant was previously generating approximately 4.15Mtpa (dry) of tailings. The most recent 2019 annual audit report (Coffey, 2020)5, indicated tailings production of 3.77Mtpa. For this report, the tailings production rate is conservatively taken as 4.5Mtpa (dry).

4.3. Ore type The ore type comprises predominantly laterite ore for the extraction of nickel and cobalt.

4.4. Environmental performance Based on the 2019 audit and management review (Coffey 2020)5, it was concluded that the tailings storage facilities were generally being adequately managed. Water management on the evaporation ponds was also adequately managed.

The surface water levels (SWLs) of all the monitoring bores were below the 4m limit and 6m target, as per the DWER license conditions. A groundwater recovery plan was not necessary.

The groundwater quality showed compliance with the DWER license L7276/1996/11. The pH levels for all monitoring bores were above the stipulated pH levels of 3.5.

5. Tailing properties 5.1. Geochemistry The tailings are partially neutralised when they leave the plant and have a pH of approximately 2.3. Testing of the tailings liquor indicates that it is typically hyper-saline (TDS around 180,000mg/L) and enriched in Fe, Mg, Mn and Ni.

A review of the Graeme Campbell and Associates (18 May 2009)7 memorandum indicates that based on testing of site-waste-regolith materials, pit wall materials are likely to have minimal capacity to

Murrin Murrin Mine


6.2. Landform The original terrain around the 17IPTSF grades to the south-west, with the highest point at the north-eastern tip (approximately +467mRL) which dip gradually to about +451mRL at the south-western tip.

6.3. Geology and soils 6.3.1. Regional geology The recently mined pits (17.08, 17.02 and 17.07) have good exposures for geological mapping, while the older pits (17.56 and 17.01) have experienced significant wall fretting with rill material covering most of the exposed pit wall due to drying of the clay walls. For areas that are yet to be mined, interpretations of the geological architecture are based on computerised geological modelling. Therefore, the report on geological architecture of the potential 17 Series in-pit TSFs (Minara Resources, 20208), comprises a combination of field mapping and computer based geological mapping.

The regional geology of the MMN project area (Figure 7) lies within the Mt Morgans district of the Mt. Margaret Mineral field (Markwell T., 1999)9, between the towns of Leonora and Laverton, Western Australia; Laverton 1:250,000 map sheet (Wells MA., 2003)10.

The Ni-Co ore deposits of the MMN project area are positioned over serpentinised peridotite komatiitic lava flows (Hill et al., 1990)11 which occur low in the stratigraphy within a sequence of felsic volcaniclastics, clastic sediments, mafic volcanics and related intrusives in the upper parts of the stratigraphic sequence (Monti and Fazakerley, 1996)12. The serpentinised peridotite protolith has been folded and faulted around the Kilkenny Syncline (Markwell T., 1999)9 (Figure 8). The 17 Deposit Pits are located on the northern limb of the Kilkenny syncline. The sequence forms a corridor constrained by major NNE trending, westerly dipping faults. These faults are splays off the major NW trending Keith-Kilkenny tectonic zone to the SW (Monti and Fazakerley, 1996)12 (Figure 8). Gradual oxidation and leaching of the ultramafic protolith has produced a regolith with sub-horizontal layers which hosts the ore deposits (Camuti and Riel., 1996)13.

6.3.2. Lithology The regolith profile at MMN can be broadly divided into 5 main geological units produced through lateritic weathering (Figure 9):

1. The basal unit is slightly weathered locally silicified ultramafic (UM) (Elias M., 2006)14, that grades upward into,

2. Saprolite (SA) zone which is commonly magnesium and silica rich, 3. Smectite (SM) is the main nickel bearing unit of the profile (Elias M., 2006)14. This is overlain by, 4. Ferruginous zone (FZ) which is dominantly comprised of kaolinite Fe oxides (typically goethite

and hematite) (Wells M., 2003)10 and is commonly silica rich which is in turn capped with, 5. Colluviums and mixed chlorite-kaolinite plastic clays (PC) (Elias M., 2006)10, also referred to as

the mottled zone. The ultramafic regolith profiles are commonly bound by weathered felsic and/or mafic volcanic and intrusive rock.

The weathering profile of exposed 17 Pits generally conforms to the basic laterite sequence whereby it is bounded at the base predominantly by saprolite (SA) and minor exposures of ultramafic (UM). The exposed SA and UM show varying degrees of jointing, shearing and silicification. The SA appears to be highly fractured with intersecting joint sets (joint systems) which continue into the underlying semi-weathered UM protolith. The walls and floors of the pits are approximately 30% SA by surface area exposure. The SA zones are generally high in magnesium and are highly siliceous in areas. It is expected that the SA will have a neutralising effect when exposed to potentially acidic tailings as magnesium is an acid consuming element.

Murrin Murrin Mine


The SA is overlain by a clay rich ore zone which is characterised by a package of inter-fingered transitional units including soft, finer-grained clay and nickel rich saprolite, waxy textured smectitic clays and ferruginous smectite material. Interrogation of the block model indicates that this zone covers approximately 55% of the pit walls and floors. This ore zone is generally grouped as smectite (SM). The nickel rich saprolite unit that is part of this ore zone grades into the underlying saprolite and generally has a moderate to high magnesium content.

Above the ore zone is the ferruginous zone (FZ); a typically course grained, iron rich, red/brown highly oxidised clay horizon with dispersed hematite nodules. The FZ is well developed and exposed in the eastern half of the 17.53 pit (Figure 10a). The block model indicates the thickness and depth of this unit to range from a few metres from the surface to more than 30m in areas.

The western side of the deposit, especially the western side of 17.08 (Figure 10b) is characterised by extensive magnesite development. Similarly, this material will react with and neutralise the potentially acidic tailings material.

Overlying the FZ zone are the plastic clays (PC), a low-Ni high-Al zone that is characterised geochemically by its reduced iron content and physically by its mottled nature.

There is a felsic unit east of the deposit but this is only exposed in the eastern ramp of the 17.08 pit (Figure 10c).

6.4. Hydrogeology Based on Minara Resources (2016)8, the currently exposed 17 Series Pits are generally dry except for a small volume of groundwater in the bottom of the 17.53 mine void. However, modelling of groundwater depths in the area of the 17 Deposit indicate that most of the 17 series of pits will encounter groundwater at their design depths. This shall be confirmed when the 17 Deposits are completely mined out.

6.5. Flora and fauna The storage will be in a mined-out pit void. The pipeline corridor for the slurry and return water pipelines will be along existing tracks / accessways. Minor clearing will be required along the pipeline corridor to widen the existing track at some locations. This will result in limited clearing of scrub and low trees, mostly regrowth, along the track alignment. Large trees will be preserved.

7. Geotechnical assessment 7.1. Assessment of the pit wall The pit wall performance of the 17 Series Pits were assessed based on information provided in the geological architecture report (Minara Resources, 20208) and no site inspection was conducted.

Mining activities in Pits 17.01 and 17.53 had been completed. Mining in Pits 17.08, 17.07 and 17.02 is on-going. Cross-Sections traversing Pit 17.53 (Section A-B), Pit 17.01 (Section C-D) and Pit 17.08 (Section E-F) are presented in Figure 11. Locations of these cross-sections are shown in Figure 12. Photographs of the Pits 17.08 and 17.53 are in Figure 10.

Based on available photographs, there is no wall scale failures in the pit wall of recently mined Pit 17.08, while the presence of erosion gullies is evidence in the older pits of 17.53. Small volume of groundwater was also observed at the bottom of the Pit 17.53. The performance of the pit walls of existing and future pits of the 17 Deposit will need to be re-assessed when they are completely mined out by an experienced mining geotechnical engineer.

Murrin Murrin Mine


7.2. Structural features of the exposed mined pits Economic mineralisation at the Murrin Murrin Ni-Co project is contained within the weathered profile of the ultramafic protolith. As a result, the mined pits rarely expose the fresh ultramafic rock to allow for detailed investigations of the structural features of the deposit. However, as these structural features have acted as conduits for fluid flow or as areas of increased permeability during the formation of the laterite profile, they tend to be revealed in the distribution of certain elements in the regolith profile. The most effective elements for delineating structural features are Si below the FZ and Cr above or within the FZ. As the 17 Deposit has only been partially mined, analysis of the distributions of these elements must be relied on for interpretation of the deposit’s structural features.

The most significant structural feature observed in the 17 Deposit is a major NW to SE striking fault zone that cuts across the southern end of the 17.02 pit (Figure 13). The zone has been exposed by mining and the fault structures are clearly visible in the walls. This zone will likely act as a conduit for fluid flow and any monitoring should be placed in close proximity to this structural feature.

7.3. Implications with respect to tailings deposition When the 17 Deposit is completely mined out, groundwater is anticipated at the bottom of the pits. The main issue from a geotechnical perspective influencing pit wall stability is increase of excess pore water pressures in the pit walls due to lowering of water levels. Dewatering of the pit may initiate some pit wall slumping due to these excess pore pressures. These failures may be circular slip-type failures or failures due to the presence of structural features (i.e. planar features) in the pit walls.

It should be noted that the pit wall stability will be improved as a result of tailings deposition, with the deposited tailings abutting the toe of the walls and increasing factors of safety for any existing potential failure zones.

The following aspects are relevant to management of an in-pit TSF:

1. During dewatering of the pit, slumping of the pit walls may be apparent. Personnel considering entry to the pit should inspect the pit rim area and conduct HAZOPS before entering the pit. Construction activities at the base of the pit are not envisaged other than establishing decant pumps. After the tailings level exceeds the groundwater level, this will no longer be a concern.

2. Initially, tailings are to be deposited from four sets of multiple spigots, each set located at different locations along the eastern side of the pit. The existing access ramps along the northern, western and southern sides of the 17 Series Pits will be utilised as part of water recovery operations. Once the tailings level covers all the localised low points, discharge from multiple spigots can be conducted only at the northern tip, while the southern access ramp will be used for water recovery operations.

3. The ponds of supernatant water, liberated from the tailings slurry, will be located adjacent to the proposed decant access ramps to the pit. Pumps deployed from the access ramps will allow recovery of supernatant water. The pumps will be moved up the ramps as the tailings and water levels rise within the pit. Water should not be allowed to accumulate in the pit, i.e. as water recovery will increase factors of safety against wall instability and reduce seepage when the pit is nearly full.

Routine (daily) pit rim inspections during the operation of the proposed 17IPTSF are recommended.

7.4. Tailings settlement Table 3 presents a summary of the results of settlement modelling (based on traditional consolidation theory). The results of the settlement assessment are presented in Appendix A. Settlement within the facility is expected to occur both during and post deposition of tailings, as the tailings consolidate to form a stable mass. The actual settlement at any point within the pit will vary depending on the thickness of tailings, the rate of tailings placement within the pit, the rate of supernatant water removal during and after each deposition cycle and the efficiency of the topping up process.

Murrin Murrin Mine


8.10. Liners No artificial liners are proposed, nor should they be required in construction of the 17IPTSF. In addition, the walls and floors of the exposed pits are characterised by extensive magnesite development. It is expected that this material will have a neutralising effect when exposed to potentially acidic tailings as magnesium is an acid consuming element. The groundwater quality of the monitoring bores around the existing in-pit TSFs confirmed that and showed compliance with the DWER license L7276/1996/11 (pH levels for all monitoring bores were above 3.5).

9. Water balance Reference previously to an MMO provided spreadsheet ‘Inception EOM Tails Data - Master (values, FY2017)’, indicated tailings production of 3.77Mtpa. The spreadsheet ‘Exa 2017 Tailings’ showed that the estimated water volume decanted from the tailings storages was 6.32Mm3. This flow was delivered to the evaporation ponds. The average water return from the tailings storage based on the 2019 annual audit was assessed to be about 62% of slurry water inflow.

Based on experience from other in-pit tailings storage facilities in the Goldfields region, water returns of 50% to 60% of slurry water inflow can be expected from the TSF, with higher water returns than compared with paddock facilities expected due to reduced evaporative losses.

Water balance models were developed for 17IPTSF based on mean water volumes (considering slurry with 27% solids and annual production of 4.5Mtpa) and accounting for:

Rainfall;

Slurry water inflow;

Evaporation;

Seepage; and

Retention.

Inflows comprise slurry water to the TSF and rainfall, while outflows comprise evaporation from the pond and beaches, seepage, and water return. The water balance is provided on Appendix E.

The evaporation potential for the evaporation pond was estimated based on Luke et al. (1987)15, factored up by 30% to account for discrepancies between evaporation at MMO (about 3000mm based on the average pan annual evaporation map produced by BoM8, as presented in Figure 5) relative to the monitoring station data (Luke et al., 1987)15, a pan coefficient of 66% and an assumed pond + running beach areas of approximately 55ha. In the absence of seepage analyses, the total seepage out flow is estimated based on assumed pit floor permeability of 1x10-7 m/s.

MMO can expect an average annual water return of approximately 8.1Mm3. The estimated annual average water return as a percentage of slurry water inflow was assessed as about 67%.

10. Operating procedures The Operations Manual for the in-pit facilities is presented in Appendix F, which provides a detailed description of the operating procedures, inspection criteria, monitoring requirements and log sheets for the tailings storage.

Murrin Murrin Mine


11. Monitoring As part of construction, at least seven (7) monitoring bores should be installed in proximity to 17IPTSF. The final locations and construction details of the proposed monitoring bores shall be confirmed by the project hydrogeologist. Some of the monitoring bores should be placed in close proximity to known structural feature such as the fault zone that cuts across the southern end of 17.02 pit. The monitoring of the bores will need to be integrated into the monitoring programme for the other facilities.

It is also recommended that:

Groundwater level readings be taken quarterly and groundwater samples taken for laboratory analysis quarterly.

Information collected from the monitoring bores be reviewed regularly and reported in an annual audit.

12. Emergency action plan The Operations Manual for 17IPTSF provides a description of the operating procedures for the facilities and includes an Emergency Action Plan.

13. Rehabilitation Prior to the commencement of the rehabilitation program, the facilities will undergo a topping up process. The topping up process maximises the storage capacity of the pits and reduces the impact of the final settlement of the tailings surface. Based on consolidation estimates, it is expected that rehabilitation work will not be able to commence for a period of up to six years post completion of filling due to the expected low strength of the deposited tailings (approximately 95% consolidation is expected to be achieved after six years).

Upon completion of tailings placement within each facility, the surface will undergo a rehabilitation program. The closure concept for the TSF domain is to:

1. Remove all infrastructure. 2. Construct a stable, non-polluting landform (Figure 15). 3. Establish a self-sustaining vegetation cover that reflects the natural vegetation communities of the

area. 4. Ensure no long-term groundwater liability for MMO or the State.

The rehabilitation program will include the identification of appropriate capping material and local flora species to revegetate the surface of the facility.

Analysis of the tailings material indicates a high level of salinity, which would not support vegetation growth. As a result of capillary action in the soil, salinization of the soil in the root growth zone of vegetation may occur. Based on investigation by Landloch Pty Ltd on the potential for capillary rise of salts from the tailings material, a preliminary capping profile was determined (Figure 15). The total capping profile comprising:

0.1m thick vegetated topsoil.

2.5m waste layer.

0.3m laterite layer.

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A brief description of the environmental management and rehabilitation plans to be implemented at filling completion is as follows:

Monitoring of the tailings surface level within the facility after the last tailings deposition cycle.

Monitoring the formation of a crust in the facility following completion of the last tailings cycle, prior to the deposition of new tailings as part of the ‘topping up’ process. This monitoring may comprise moisture and density monitoring as well as shear strength testing, as appropriate.

Once topping up has been completed and little further settlement is expected (anticipated to be approximately three years after completion), the facility shall be covered and rehabilitated. The cover will comprise mine waste from adjacent waste dumps and topsoil (nominally 0.1 m thick) as a growth medium. In addition, any exposed pit walls will be battered down to 15o.

Murrin Murrin Mine


14. References The following standards and references were used in the preparation of this report.

1. Department of Mines, Industry Regulation and Safety (DMIRS) (formerly DMP) (2015), ‘Guide to the preparation of a design report for tailings storage facilities (TSFs)’.

2. Department of Mines, Industry Regulation and Safety (DMIRS) (formerly DMP) (2013), ‘Code of practice: tailings storage facilities in Western Australia’.

3. Department of Mines, Industry Regulation and Safety (DMIRS) Petroleum (2006), ‘Guidelines for Mining Proposals in Western Australia’.

4. Coffey Mining Pty Ltd (2016), ‘Geotechnical Assessment – In-Pit Tailings Storage Facilities 9/5, 18/3 and 18/6’, ref. GEOTPERT50032AA-AB Rev A.

5. Coffey Services Australia Pty Ltd (2020), ‘Annual Audit and Management Review – 2019’, ref. 754-PERGE271415 Rev A.

6. Minara Resources (2020), ‘Geological Architecture Report for the 17 Series of Pits – Murrin Murrin North’.

7. Graeme Campbell and Associates (2009), ‘Murrin Murrin Project: Geochemical Testing of Waste-Regolith Samples - Implications for In-Pit Containment of Process-Residue Streams (Memorandum)’.

8. Australian Government Bureau of Meteorology website, http://www.bom.gov.au/, accessed 15 April 2020.

9. Markwell T. (1999), ‘TR559 Murrin Murrin Project: Second Combined Annual Technical Report Number 308/1997”, 1st January 1998 – 31st December 1998, Vols 1 and 2.

10. Wells M.A. (2003), ‘Murrin Murrin Nickel Laterite Deposit, W.A. Cooperative Research Centre for Landscape Evolution and Mineral Exploration”.

11. Hill R.E.T., Barnes S.J., Gole M. J. and Dowling S.E., (1990), ‘Physical Volcanology of Komatiites – A Field Guide to the Komatiites of the Norseman – Wiluma Greenstone Belt, Eastern Goldfields Province, Yilgarn Block, Western Australia: Perth’, Geological Society of Australia, Western Australia.

12. Monti R. and Fazakerley V.W. (1996), ‘The Murrin Murrin Nickel Cobalt Project’, Nickel ’96 pp191-195, The Australian Institute of Mining and Metallurgy: Melbourne.

13. Camuti K.S. and Riel R.G. (1996), ‘Mineralogy of the Murrin Murrin Nickel Laterites’, Grimsey E.J. and Neuss I., Eds., Nickel ’96, Mineral to Market: Australian Institute of Mining and Metallurgy Special Publication 6/96 pp209-210.

14. Elias M. (2006), ‘Lateritic Nickel Mineralisation of the Yilgarn Craton’, Society of Economic Geologists, Special Publication 13, Chapter 7, pp195-210.

15. Luke G.J., Burke K.L. & O’Brien T.M. (1987), ‘Evaporation Data for Western Australia’,Department of Primary Industries and Regional Development.

Murrin Murrin Mine


Figures

Appendix A - Tailings Settlement

Appendix B – Tailings Storage Data Sheet (TSDS)

Appendix C – Drawings

Appendix D – Scope of Works

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Coffey Services Australia Pty Ltd ABN: 55 139 460 521 ii

Table of contents

1. Introduction .................................................................................................................................. 1

1.1. Contract drawings ............................................................................................................. 1

1.2. Code of practice ................................................................................................................ 1

1.3. Site inspection ................................................................................................................... 2

1.4. Safety ................................................................................................................................ 2

1.5. Site location and description ............................................................................................. 2

2. Description of work – specific ...................................................................................................... 2

2.1. General .............................................................................................................................. 2

2.2. Survey ............................................................................................................................... 3

2.3. Clearing and establishment works .................................................................................... 4

2.4. Earthworks ........................................................................................................................ 4

2.4.1. General ................................................................................................................. 4

2.5. Pipework ............................................................................................................................ 5

2.5.1. Pipeline corridors .................................................................................................. 5

2.6. Completion ........................................................................................................................ 5

2.7. Construction sequence ..................................................................................................... 5

2.8. Limits of the contract ......................................................................................................... 5

3. Exclusions ................................................................................................................................... 5

4. Principal-supplied items .............................................................................................................. 6

4.1. Survey ............................................................................................................................... 6

4.2. Materials ............................................................................................................................ 6

4.3. Water ................................................................................................................................. 6

5. Inspection .................................................................................................................................... 6

6. Permits, licences and approvals .................................................................................................. 6

7. Substitutions ................................................................................................................................ 7

8. Temporary services and facilities ................................................................................................ 7

8.1. Furnished by Principal ....................................................................................................... 7

8.1.1. Materials ............................................................................................................... 7

9. Data requirements ....................................................................................................................... 8

9.1. As-built drawings ............................................................................................................... 8

10. Construction programme ............................................................................................................. 8

Coffey Services Australia Pty Ltd ABN: 55 139 460 521 iii

Appendices

Appendix A - DrawingsAppendix B - Estimate of Quantities

17 Series In-Pit TSF Scope of Works

Coffey 754-PERGE272398 14 July 2020

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1. Introduction This Scope of Work covers the construction of the tailings delivery and return water pipeline corridors, scour sumps and the associated infrastructure for the 17 Series In-Pit Tailings Storage Facilities (17IPTSF) and is to be read in conjunction with the Drawings. Construction mainly entails the cut to fill excavation to form the pipeline corridor and the parallel corridor containment bunds. The scour sumps will also be formed by cut to fill methods.

The Scope of Work shall comprise the provision of all material, construction plant, equipment, labour, supervision, tools, services, warehousing if required, testing equipment, and each and every item of expense necessary for the construction, and preparing of ‘as built’ drawings and documents for work shown in the Drawings, Schedules and Specifications forming part of the Contract for the construction of the 17IPTSF at Murrin Murrin Operations (MMO), located approximately 60km east of Leonora, Western Australia.

All works shall be constructed complete and operational except as specifically excluded and shall include all necessary auxiliary works, accessories and the incorporation of all miscellaneous material, minor parts and other such items, whether or not the items are specified, where it is clearly the intent of the Contract that they should be supplied or where they are obviously required and necessary to complete and commission the work.

1.1. Contract drawings The following drawings complete this Scope of Work:

Title Drawing No.

In-Pit TSF Plan 754-PERGE272398-01

Pipeline Corridor Bunding – Sections and Details 754-PERGE272398-02

Arrangement of Spigotting 754-PERGE272398-03

Tailings and Decant Water Pipeline Routes 754-PERGE272398-04

1.2. Code of practice Unless otherwise specified, or shown on the Drawings, the Contractor is to provide all materials and carry out all the work in accordance with the latest revisions of the relevant Australian Standards.

All work under this Contract shall be performed strictly in accordance with the following Specifications, Drawings and other documents, which by this reference forms part of this Contract, unless expressly noted otherwise.

AS 1289 Methods of testing soils for engineering purposes

AS1181-1982 Method of measurement of civil engineering works and associated building works

Western Australian Mines Safety Act and Regulations

The Works shall be carried out to comply with the latest revision of the Drawings, Codes and Standards specified, or where no standards are specified, to Australian Standards, or to the appropriate British or other recognised Standards.



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Before making any change in any work under the Contract to comply with any revisions to the relevant codes and standards, the Contractor shall give to the Principal written notice specifying the reason therefore and requesting their direction thereon. The Principal shall decide whether a change is necessary and issue an order accordingly under the provisions of the General Conditions of Contract.

1.3. Site inspection The Contractor shall inspect the site and must allow for the following factors in their price:

The nature and requirements of the work to be done.

All conditions on and adjacent to the site.

Access to the site.

The types of soil and vegetation present on the site.

The expected or known water table.

The nearest sources of suitable fill material which complies with this Specification.

The source of water for construction purposes.

Location of any heritage sites in or near the work area.

1.4. Safety The Contractor shall:

Carry out the works in a safe manner.

Conform to all relevant Acts or Statutes of Parliament, Regulations, By-Laws or Orders relating to the safety of persons and property on or about the site.

1.5. Site location and description MMO is located approximately 60km east of Leonora, Western Australia. The landform at MMO is slightly undulating. Numerous open pits are located throughout the site, many of which are non-operational. Stockpiles of topsoil, waste oxide material and ore are located at various locations across the site.

2. Description of work – specific The Scope of Work shall include, but is not necessarily limited to the following:

2.1. General The Contractor shall:

Attend a Site Induction before the commencement of works.

Carry out all works indicated or implied in the Drawings or in the Specification.

Supply all labour, plant and materials (except those indicated as being supplied by the Principal) necessary for completion of the works.



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Maintain all works as required by the Contract documents and for the period stated therein.

All construction shall be to the minimum lines and grades shown on the Drawings or as required by the Owner’s Representative as work progresses.

During the progress of the works, the Owner’s Representative may find it necessary to revise the lines, levels and grades of any part of the works because of the conditions revealed by the works.

The Contractor shall accept reasonable delays due to inspection and checking of any part of the works to determine grades and levels.

2.2. Survey The Contractor shall:

Perform all ground surveys using conventional and agreed surveying techniques.

Survey and set out the works based on the datum points provided by the Owner’s Representative.

Be responsible for the protection of all permanent and temporary beacons or bench marks.

Be wholly responsible for the setting out of the works in accordance with the terms of the specification. Although the Owner’s Representative will cause such setting out to be checked from time to time, such checking will not relieve the Contractor of full responsibility for the accuracy of such setting out.

Carry out surveys prior to the commencement of the item of work and at the completion of the item of work.

Carry out a post construction survey of the works by a competent surveyor to verify that the works were constructed within the specified tolerances and submit to the Owner’s Representative.

Submit their survey data and calculations to the Owner’s Representative.

Ensure initial and/or final surveys are undertaken and approved by the Owner’s Representative prior to the removal or placement of any material, especially where such action will destroy or cover the surface just surveyed. All survey checks or quantity measurements must be supplied to the Owner’s Representative. Suitable time must be given to the Owner’s Representative to allow such calculations to be checked and approved prior to the works being covered or removed.

The Owner’s Representative may undertake their own survey of any item, either in conjunction with the Contractor, or separately. The Contractor and Owner’s Representative shall agree on the results of measurement surveys that are carried out prior to any works being covered up or within seven (7) days of a survey being undertaken. Should agreement not be reached, the difference shall be documented such that the matter can be later decided without disruption to the Contractor's programme.

The maximum permissible horizontal deviation from the finished lines or zone boundaries shall be -0 m to +0.5 m.

Vertical deviation shall be -0 m to +0.2 m, provided no abrupt changes in slope or level are present on any finished surface.



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Measurement for payment of all embankment fill material shall be made for the compacted material, measured in place and only to the lines and grades required.

2.3. Clearing and establishment works The Contractor shall, as appropriate:

Remove all vegetable matter and scrub from the area of the proposed tailings pipeline corridor and scour sumps. The area to be cleared shall extend approximately 1.0m past the footprint of the pipeline corridor where necessary. All stripped vegetation should be pushed into heaps in locations as indicated by the Owner’s Representative.

Remove all solid obstructions, tree stumps, roots and logs from beneath the footprint of the pipeline corridor and proposed scour sump locations.

Remove all topsoil from the area of the proposed tailings pipeline corridor and scour sumps. The area to be cleared shall extend approximately 1.0m past the footprint of the pipeline corridor where necessary. All stripped topsoil should be pushed into heaps in locations as indicated by the Owner’s Representative.

If required, clear the agreed routes of access roads of all vegetation standing and fallen. Push vegetation into heaps as approved by the Owner’s Representative.

Keep all roads sprayed and wetted to prevent the generation of airborne dust during the course of construction and road usage.

2.4. Earthworks 2.4.1. General The pipe corridor and scour sump will be formed by cut to fill operations. The access track shall be formed by cut and fill operations where required. As an alternative, bunding may be formed by importing mine waste from the waste dump or pit areas.

The Contractor shall, as appropriate:

Ensure borrow materials are stockpiled, transported and placed in such a manner as to minimise segregation.

Allow for maintaining the borrow areas free of large accumulations of water.

The containment bunds shall be watered, and traffic compacted.

If there is a shortfall in cut materials the Owner’s Representative will advise the location of a suitable waste dump or borrow area.



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2.5. Pipework 2.5.1. Pipeline corridors The Contractor shall construct the tailings delivery and return water pipeline corridors in the location and to the details shown on the Drawings. The alignment of the corridors may vary on site, as directed by the Owner’s Representative, to limit clearing of trees. All surplus excavated material shall be stockpiled adjacent to the pipeline corridor for future rehabilitation purposes.

The Contractor shall:

Excavate and form the new pipeline corridors from the plant to 17IPTSF, including the scour sump, and place spoil material to form the parallel containment bunds.

Grade the surface of the pipeline corridor smooth and free of projections that could damage the pipework.

2.6. Completion The Contractor shall:

Clean up all rubbish, remove all plant and supply materials, trim all banks neatly, spread all excavated material not specified to be removed from the site and leave the site in a clean and tidy condition.

2.7. Construction sequence The Contractor shall liaise with the Owner’s Representative to agree a sequence for the works. The Contractor shall endeavour to complete the works in the sequence agreed.

2.8. Limits of the contract The limits of the Contract are as shown on the Drawings.

3. Exclusions The following works shall be performed by the Principal simultaneously to the Works in this Contract:

Supply and installation of tailings delivery pipework.

Decant pipework and pump installation, and any associated electrical works.

Installation of control and telemetry systems.

The Contractor shall fully cooperate with the Principal and work in with their activities at all times.



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4. Principal-supplied items 4.1. Survey The Principal will provide coordinates and levels of survey marks within the vicinity of the Works. The Contractor shall set out all lines and levels using the survey marks provided.

4.2. Materials If required, the Principal will supply appropriate open pit or waste dump locations for bund fill material.

The Principal will supply crushed aggregate for the access track sheeting.

4.3. Water Water will be made available to the Contractor at no charge. Supply will be from a standpipe located near the plant site. Access to the standpipe will not be exclusive to the Contractor. The Contractor shall determine the type and suitability of the water supplies for use in this Contract.

The Contractor shall make their own arrangements for loading and hauling water.

NOTE: Potable water supplies are limited and the Principal may, from time to time, direct the Contractor to use alternative sources.

5. Inspection The Owner’s Representative will at all times be entitled to inspect, examine and test the materials and workmanship be provided under the Contract. Such inspection, examination or testing, if made, shall not release the Contractor from any obligation under the Contract.

The Contractor shall cooperate with and provide full opportunity to the Owner’s Representative to monitor regularly the progress of the Works of the Contractor and their subcontractors to the detailed extent necessary to satisfy progress relative to the Construction Program.

All pertinent information to enable the Owner’s Representative to determine the adequacy of advanced planning for material procurement, machine and manpower resources to meet the Construction Program shall be made freely available to the Owner’s Representative.

These requirements shall be incorporated in orders placed with Subcontractors.

6. Permits, licences and approvals Further to the General Conditions of Contract, the Principal will obtain approval from the Department of Mines, Industry Regulation and Safety (DMIRS) and Department of Water and Environmental Regulation (DWER) to conduct the Works.

All other necessary permits, licenses and approvals shall be obtained by the Contractor in liaison with the Principal / Company Representative.



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7. Substitutions The Contractor shall:

Not substitute any alternative to the equipment and materials included in the Works without the prior written consent of the Principal.

Make diligent efforts to utilise the specified materials to be incorporated into the Works but where the Contractor considers there are commercial or other advantages to be derived by the Principal, the Contractor may submit a proposal for a substitute material for approval by the Principal prior to commencement of the work. Such proposal for substitution shall be in writing and state reasons for and (if applicable) advantages of the substitute material. The Principal shall determine whether the substitute material will be permitted and such determination shall be binding and conclusive upon the Contractor. Approval of a substitution will be given as a variation under of the General Conditions of Contract incorporating any adjustment to the Contract Sum.

8. Temporary services and facilities 8.1. Furnished by Principal This section provides a list of Principal-furnished services other than those items listed in Sections 1.2 and 4.0.

Any services or materials not specifically identified as being provided by the Principal shall be provided by the Contractor.

8.1.1. Materials Where the Principal agrees to supply Materials to the Contractor in the performance of the Contract then the following conditions will apply:

The items shall be included in the Contractor's materials procurement schedules. The Contractor shall, upon arrival at Site to commence work, check and ensure that Principal-Supplied Materials are available and will not cause any delay to the Contractor's work progress.

Items stored by the Principal shall be removed from the Principal’s store or storage area by the Contractor when required by him or when directed by the Superintendent (whichever is sooner). However, no items shall be removed from the Principal’s store or storage area by the Contractor without first obtaining authority from the Owner’s Representative and the Contractor shall sign receipts or other documentation required acknowledging receipt of the Free Issue Materials.

From the time the Principal-Supplied Materials are removed from the Principal’s store or storage area or are delivered to the site the Contractor shall be responsible for and shall keep safely and in good order all those Principal Supplied Materials including any returnable packing or containers.

The Contractor shall account for all Principal-Supplied Materials used and shall return to the Principal in good order and condition any Principal-Supplied Materials remaining unused on completion of the work. Subject to any insurance cover the Contractor shall be responsible for the cost of replacement or repair of any Principal-Supplied Materials lost or damaged while he is responsible therefore.

The Contractor shall immediately notify the Owner’s Representative of any damage to or loss of any of those Principal-Supplied Materials at any time and shall as soon as possible specify the extent and circumstances of the damage or loss.



8

Principal-Supplied Materials used by the Contractor are used at the sole risk of the Contractor. Any failure to perform the Contract by the Contractor shall not be excused by any matter or thing arising from or incidental to the use of Principal-Supplied Materials.

9. Data requirements The Contractor shall submit the following data in addition to the data requirements detailed elsewhere in this Specification to the Principal as part of the Work.

The Contractor shall show the reference Contract Number and identifying item numbers, if applicable, on all data submitted.

9.1. As-built drawings Further to the General Conditions of Contract, the Contractor shall supply as-built drawings within 14 days of the issue of a Certificate of Practical Completion and a detailed list of quantities.

10. Construction programme The Contractor shall provide a construction programme and indicate the following milestone dates.

Contract Award

Notice to Proceed with the Fieldwork

Principle Completion Date

Final Completion Date

Appendix A - Drawings

Appendix B - Estimate of Quantities

FPTSF

PROJECT Murrin Murrin Mine Site Date 19-06-20Job No 754-PERGE272398

CLIENT Murrin Murrin Operations Pty Ltd FileSubject Quantities

LOCATION near Leonora, WA Revision 0Page 1 of 1

SUBJECT MMO 17 IN-PIT TSF EARTHWORKS QUANTITIES

Item Description Unit Quantity Rate Amount

17IPTSF TAILINGS AND RETURN WATER PIPELINE CONSTRUCTION

1.0 Preliminaries & Site Preparation1.1 Site establishment, including all preliminaries, insurances etc, mobilisation, demobilisation,

borrow management, maintenance of existing tracks Item -$

1.2 Site clearing including grubbing and stockpiling of vegetation from the pipeline corridor, scour sump and access road (900m x 6m approx for cooridor and 400m2 x 1 sump) ha 4.6

-$

2.0 Earthworks2.1 Strip topsoil (0.1m depth) from the pipeline corridors and scour sump areas and stockpile

seperately from vegetation m3 844 -$

2.2 Excavate scour sump 12m x 12m x 1.5 deep m3 2,851 -$

2.3 Borrow, transport and traffic compact 600mm high earth bund to both sides of pipeline corridor (2no. Bunds) m3 6,075 -$

2.4 Grade and make smooth 5m wide access track to the pipeline corridors m 0 -$

2.5 Sheet Access Roads width 10mm aggregate sheeting material m 0 -$

3.0 Tailings Pipework3.1 Supply and install requisite tailings pipework m 4,470 -$

4.0 Decant Pipework4.1 Supply and install pontoon mounted pump to enable water recovery No. 4 -$

4.2 Supply and install requisite decant return pipework m 3,200 -$

SUBTOTAL -$

5.0 Ancilliary Items5.1 Airfares for Contractors / Superintendant personnel No. -$

5.2 Accomodation and meals for Contractors Person days -$

5.3 Fuel supplied by Principal L -$

5.4 Construction monitoring costs (Superintendant and vehicle incl misc) Item -$

5.5 QA/QC Geotechnical Testing Days -$

SUBTOTAL -$ Contingency 10% -$

TOTAL BUDGET CONSTRUCTION COST -$ Notes:1. The above quantities have not been calculated by a Quantity Surveyor.

F:\PROJECTS OCT 2016 ONWARDS\Murrin Murrin Operations Pty Ltd\754-PERGE272398 - Murrin Murrin In-Pit TSF Design\8. Drawing\754-PERGE272398 Schedule of Quantities Rev0.xlsx

Appendix E – Water Balance Analysis

PROJECT : MMO 17 SERIES IN-PIT TAILINGS STORAGE FACILITY Date 14-Jul-20Job No 754-PERGE272398

CLIENT : MURRIN MURRIN OPERATIONS PTY LTD FileSubject Water Balance

LOCATION : MURRIN MURRIN MINE Revision 1

SUBJECT : WATER BALANCE - CLIMATE AVERAGES

INFLOWS JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC TOTAL

RAINFALLRainfall (mm) 22.00 30.00 25.00 18.00 27.00 28.00 20.00 17.00 12.00 9.00 10.00 16.00 234.00Average Daily Rainfall (mm) 0.71 1.06 0.81 0.60 0.87 0.93 0.65 0.55 0.40 0.29 0.33 0.52Tailings Dam Storage Area (m2) 912,159.00 912,159.00 912,159.00 912,159.00 912,159.00 912,159.00 912,159.00 912,159.00 912,159.00 912,159.00 912,159.00 912,159.00Runoff Coefficient Tailings 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50Catchment Area above Storage (m2) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Runoff Coefficient Catchment 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40Pool Area (m2) 250,000.00 250,000.00 250,000.00 250,000.00 250,000.00 250,000.00 250,000.00 250,000.00 250,000.00 250,000.00 250,000.00 250,000.00Running Beaches (m2) 300,000.00 300,000.00 300,000.00 300,000.00 300,000.00 300,000.00 300,000.00 300,000.00 300,000.00 300,000.00 300,000.00 300,000.00Rainfall Inflow Total Volume (m3/day) 518.83 776.37 589.58 438.65 636.75 682.34 471.66 400.91 292.43 212.25 243.69 377.33

SLURRY WATERTotal tonnes per month 375,000.00 375,000.00 375,000.00 375,000.00 375,000.00 375,000.00 375,000.00 375,000.00 375,000.00 375,000.00 375,000.00 375,000.00 4,500,000.00% Solids = 27 27.00 27.00 27.00 27.00 27.00 27.00 27.00 27.00 27.00 27.00 27.00 27.00Tailings Output Solids (tpd) 12,096.77 13,274.34 12,096.77 12,500.00 12,096.77 12,500.00 12,096.77 12,096.77 12,500.00 12,096.77 12,500.00 12,096.77Volume of Water (m3/day) 32706.09 35889.87 32706.09 33796.30 32706.09 33796.30 32706.09 32706.09 33796.30 32706.09 33796.30 32706.09 12,166,666.67

OTHER WATER INFLOWSPit Dewatering (m3/day) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Other 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Other Water Inflow Total (m3/day) (seepage from underdrainage) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

TOTAL INFLOW (m3/day) 33224.92 36666.24 33295.67 34234.94 33342.84 34478.64 33177.76 33107.01 34088.73 32918.34 34039.99 33083.42

OUTFLOW-LOSSES FROM TAILINGS DAM JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC TOTAL

EVAPORATION (from pond and beaches)Evaporation Rate (mm) 1.3 679.90 527.80 479.70 317.20 211.90 140.40 150.80 204.10 287.30 421.20 491.40 603.20 4,514.90Pan Factor 0.66 0.66 0.66 0.66 0.66 0.66 0.66 0.66 0.66 0.66 0.66 0.66Monthly Dam Evaporation Rate (mm) 448.73 348.35 316.60 209.35 139.85 92.66 99.53 134.71 189.62 277.99 324.32 398.11 2,979.83Average Daily Evaporation Rate (mm) 14.48 12.33 10.21 6.98 4.51 3.09 3.21 4.35 6.32 8.97 10.81 12.84Pool Area & Running Beaches (m2) 550,000.00 550,000.00 550,000.00 550,000.00 550,000.00 550,000.00 550,000.00 550,000.00 550,000.00 550,000.00 550,000.00 550,000.00Daily Evaporation Loss (m3/day) 7,961.41 6,782.00 5,617.13 3,838.12 2,481.28 1,698.84 1,765.82 2,389.95 3,476.33 4,932.12 5,945.94 7,063.28Total Evaporation Outflow (m3/day) 7,961.41 6,782.00 5,617.13 3,838.12 2,481.28 1,698.84 1,765.82 2,389.95 3,476.33 4,932.12 5,945.94 7,063.28 4,496.02

EVAPO-TRANSPIRATION (from drying tailings)Evaporation Rate (mm) 679.90 527.80 479.70 317.20 211.90 140.40 150.80 204.10 287.30 421.20 491.40 603.20Evapo-transpiration Rate (Pan/3) 226.63 175.93 159.90 105.73 70.63 46.80 50.27 68.03 95.77 140.40 163.80 201.07Average Daily Evapo-transpiration Rate (mm) 7.31 6.23 5.16 3.52 2.28 1.56 1.62 2.19 3.19 4.53 5.46 6.49Area Transpiring (m2) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Daily transpiration Loss (m3/day) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

SEEPAGEDownstream Embankment (m3/day) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Upstream Embankment (m3/day) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Pit Floor (m3/day). 2,160.00 2,160.00 2,160.00 2,160.00 2,160.00 2,160.00 2,160.00 2,160.00 2,160.00 2,160.00 2,160.00 2,160.00Total Seepage Outflow (m3/day) 2,160.00 2,160.00 2,160.00 2,160.00 2,160.00 2,160.00 2,160.00 2,160.00 2,160.00 2,160.00 2,160.00 2,160.00

RETENTIONTailings Output (tpd) 12,096.77 13,274.34 12,096.77 12,500.00 12,096.77 12,500.00 12,096.77 12,096.77 12,500.00 12,096.77 12,500.00 12,096.77Assumed Moisture Content of Tailings (average) 40.0%Volume Retained in Tailings (m3/day) 4,838.71 5,309.73 4,838.71 5,000.00 4,838.71 5,000.00 4,838.71 4,838.71 5,000.00 4,838.71 5,000.00 4,838.71

TOTAL OUTFLOW-LOSSES FROM TAILINGS DAM 14,960.12 14,251.73 12,615.84 10,998.12 9,479.99 8,858.84 8,764.53 9,388.65 10,636.33 11,930.83 13,105.94 14,061.99

BALANCE INFLOW-OUTFLOW/LOSSES (m3/day) 18,264.80 22,414.51 20,679.83 23,236.82 23,862.85 25,619.80 24,413.23 23,718.35 23,452.40 20,987.52 20,934.05 19,021.44

BALANCE INFLOW-OUTFLOW/LOSSES (m3/month) 566,208.94 633,209.87 641,074.78 697,104.72 739,748.34 768,593.91 756,810.08 735,268.94 703,571.94 650,613.00 628,021.48 589,664.56

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DECSummary of Water BalanceTotal water Available (m3/day) 18,264.80 22,414.51 20,679.83 23,236.82 23,862.85 25,619.80 24,413.23 23,718.35 23,452.40 20,987.52 20,934.05 19,021.44 266,605.60

56% 62% 63% 69% 73% 76% 75% 73% 69% 64% 62% 58%Total Water Available (m3/month) 566,208.94 633,209.87 641,074.78 697,104.72 739,748.34 768,593.91 756,810.08 735,268.94 703,571.94 650,613.00 628,021.48 589,664.56 8,109,890.57

Annual Average Water Available (m3) 8,109,890.57

Annual Average Water Available (%) 66.66%

Appendix F – TSF Operation Manual

Coffey Services Australia Pty Ltd ABN: 55 139 460 521 ii

Table of contents

1. Introduction .................................................................................................................................. 1

1.1. Department of Mines, Industry Regulation and Safety Guidelines ................................... 1

1.2. Management Plan & Operating Procedures ..................................................................... 1

2. Background ................................................................................................................................. 2

2.1. Paddock TSF..................................................................................................................... 3

2.2. 2/2-2/4 IPTSF .................................................................................................................... 3

2.3. 8/4 IPTSF .......................................................................................................................... 3

2.4. 9/2 IPTSF .......................................................................................................................... 3

2.5. 18/3 IPTSF, 18/6 IPTSF and 9/5 IPTSF ........................................................................... 3

2.6. 17 Series IPTSF ................................................................................................................ 4

2.6.1. Design Parameters ............................................................................................... 4

2.6.2. Storage Volume .................................................................................................... 4

2.6.3. Tailings Storage Facility Freeboard ..................................................................... 5

3. Hazard Rating .............................................................................................................................. 5

3.1. Paddock TSF..................................................................................................................... 5

3.2. In-Pit Storages................................................................................................................... 7

4. Operating procedures .................................................................................................................. 8

4.1. General .............................................................................................................................. 8

4.2. Tailings deposition ............................................................................................................ 8

4.2.1. Deposition principles ............................................................................................ 8

4.2.2. Tailings line flushing ............................................................................................. 9

4.3. Tailings pipework and spigotting ....................................................................................... 9

4.3.1. South Cell TSF ..................................................................................................... 9

4.3.2. 9/2 IPTSF ........................................................................................................... 10

4.3.3. 2/2-2/4 IPTSF ..................................................................................................... 10

4.3.4. 9/5 IPTSF ........................................................................................................... 10

4.3.5. 18/3 IPTSF ......................................................................................................... 10

4.3.6. 18/6 IPTSF ......................................................................................................... 10

4.3.7. 17IPTSF ............................................................................................................. 11

4.4. Return water operation .................................................................................................... 11

5. Inspections and maintenance .................................................................................................... 11

5.1. Daily routine inspections ................................................................................................. 12

5.2. Monthly inspections ......................................................................................................... 13

Coffey Services Australia Pty Ltd ABN: 55 139 460 521 iii

5.3. Details of the routine inspection ...................................................................................... 13

5.3.1. Tailings lines ....................................................................................................... 13

5.3.2. Return water lines .............................................................................................. 14

5.3.3. Decant system .................................................................................................... 14

5.3.4. Pit walls / mine waste embankments ................................................................. 14

5.3.5. Embankment (South Cell) .................................................................................. 15

5.4. Details of monthly inspections ......................................................................................... 15

5.4.1. Pit walls / mine waste embankments ................................................................. 15

5.4.2. Spigotting / placement ........................................................................................ 15

5.4.3. Supernatant water pond / decant pump ............................................................. 15

5.4.4. Tailings and return water lines ........................................................................... 16

5.4.5. Groundwater / phreatic surface monitoring ........................................................ 16

5.5. Engineering inspections .................................................................................................. 16

6. Monitoring .................................................................................................................................. 16

6.1. Environmental and structural monitoring ........................................................................ 17

6.1.1. Climatic data ....................................................................................................... 17

6.1.2. Water quality ...................................................................................................... 17

6.2. Pit walls / mine waste embankment monitoring .............................................................. 17

6.3. Process plant................................................................................................................... 18

6.4. Achieved tailings density and strength ............................................................................ 18

6.5. Storage volume and deposition time remaining .............................................................. 18

6.6. Performance during significant seasonal events ............................................................ 18

6.7. Instrumentation and groundwater bores ......................................................................... 19

6.8. Annual audit and management review ............................................................................ 19

7. Emergency action plan .............................................................................................................. 20

7.1. Response actions ............................................................................................................ 20

7.1.1. Tailings lines and return water line ..................................................................... 20

7.1.2. Decant pump ...................................................................................................... 20

7.1.3. Tailings storage facility ....................................................................................... 21

7.2. Incident reporting ............................................................................................................ 21

7.3. Roles and responsibilities ............................................................................................... 22

7.4. Operational stage hazard register ................................................................................... 23

7.4.1. Mitigation measures ........................................................................................... 24

7.4.2. TSF embankment failure/pit wall failure ............................................................. 26

7.4.3. Embankment/pit wall erosion ............................................................................. 26

7.4.4. Embankment settlement or lateral movement.................................................... 27

7.4.5. Burst or leakage of tailings delivery pipeline ...................................................... 27

7.4.6. Burst or leakage of return water pipeline ........................................................... 28

Coffey Services Australia Pty Ltd ABN: 55 139 460 521 iv

7.4.7. Seepage ............................................................................................................. 28

7.4.8. Decant Pump ...................................................................................................... 28

8. Closure and rehabilitation plan .................................................................................................. 28

8.1. Topsoiling ........................................................................................................................ 29

8.2. Rehabilitation trials .......................................................................................................... 29

Tables

Table 1 - TSF Monitoring Bore Frequency ........................................................................................ 19

Table 2 - Organisational Structure and Responsibilities ................................................................... 22

Figures

Figure 1 – General Arrangement of Murrin Murrin Mine Site Figure 2 – Location Plan of the Proposed 17 Series In-Pit TSF Figure 3 – 17IPTSF Plan Figure 4 – Storage Capacity Curve of 17IPTSF Figure 5 – Freeboard Nomenclature from DMIRS Figure 6 – Sketches of Tailings Pipeworks & Spigot Off-Takes

Appendices Appendix A - Tailings Storage Forms

Murrin Murrin Operations 17 Series In-Pit Tailings Storage Facilities - Operating Manual

Coffey 754-PERGE272398_MMO IPTSF Ops Manual 14 July 2020

1

1. Introduction This Operating Manual has been prepared as a guide for process plant staff in the operation and management of the active Tailins Storage Facilities/In-Pit Tailings Storage Facilities (TSFs/PTSFs) at Murrin Murrin Operations Pty Ltd (MMO) Mine site, located approximately 60km east of Leonora, Western Australia. The mine processes laterite ore for the extraction of nickel and cobalt. The process plant is currently generating approximately 4,110,000 (dry) tonnes of tailings per annum (tpa).

The tailings storages at MMO comprise:

Two cells of a paddock TSF - North Cell and South Cell;

Eight In-pit storages – Pit 2/2-2/4, Pit 2/3, Pit 8/4, Pit 9/2; Pit 8/5-9/4; Pit 18/3, Pit 18/6 and Pit 9/5;

One future in-pit storages – 17 Series Pits.

These facilities are located within 5km of the process plant/refinery area as shown in Figure 1 (Locality Plan). The evaporation ponds exist to the east of the South Cell. (Storing decant and seepage water from the above-ground TSFs and Pit 2/3).

The provisions of the operating manual must be strictly adhered to by the owner and the storage must be operated strictly in accordance with its provisions. Coffey Services Australia Pty Ltd (Coffey) shall not be liable in any respect whatsoever for any damage to or failure in the operation of the TSFs resulting from failure of the Owner, its servants or agents to comply with the provisions of this operating manual.

Reference should be made to the relevant design reports, regulatory approvals for the TSFs and associated drawings to ensure that the design concepts and management requirements are fully understood in order to achieve the operational objectives, which are to:

1. Allow the TSFs to function with minimal daily input;

2. Maximise water return from the facility;

3. Maximise storage capacity of the facility;

4. Ensuring an adequate monitoring programme is in place; and

5. Reducing the environmental impact of the project.

1.1. Department of Mines, Industry Regulation and Safety Guidelines

This operating manual is based on requirements of the Department of Mines, Industry Regulation and Safety (DMIRS) (formerly DMP) (2013) ‘Code of practice: tailings storage facilities in Western Australia’ and intended for use by process staff who operate, undertake regular inspections of and maintain the TSFs.

1.2. Management Plan & Operating Procedures The main body of this document includes tailings management and operating procedures.



2

Tailings Management

The management plan is for the use of the process plant management who have the responsibility for:

1. Ensuring the in-pit facilities are operated and monitored to achieve the design objectives.

2. Ensuring the facilities are operated in accordance with the parameters that have been provided by the client for use in their design. Where changes in the parameters are proposed, the process plant management must advise the designers in order that the impact of the changes can be fully assessed.

The tailings management plan sets out, in broad terms, the technical details associated with the design of the storages and the technical requirements for operating the storage facilities including:

1. Tailings Storage Management:

Water recovery;

Tailings placement/deposition; and

Staging of operations.

2. Objectives and requirements of the monitoring programme.

Operations Manual

The Operations Manual is for the use of staff who have the responsibility for the general day to day activities associated with the operation of the tailings storage facility, such as inspecting the tailings lines, changing the spigots and inspecting the water return system.

The Operations Manual sets out details of the components of the storage facilities, which are influenced by the general day to day activities. Each of these components comprise part of the overall operation of the storage facility and attention must be paid to each component to ensure the storage facility is operated to achieve the design objectives. The purpose of this manual and the attached proformas is to allow both shift and daily inspection records to be taken and recorded and, if required, reported to senior staff.

The components which are influenced by the general day to day activities include:

1. Tailings deposition and placement.

2. Decant operation.

3. Return water system operation.

4. Routine inspections and maintenance.

2. Background Operations at MMO commenced in 1999 and are based on the mining and processing of laterite ore for the extraction of nickel and cobalt. Conventional open pit mining techniques are used, followed by ore processing comprising pressure acid leaching, mixed sulphide precipitation, cobalt refining and nickel refining. The production process also produces ammonium sulphate as a by-product, which is sold to the Western Australian fertiliser market. Based on previous annual audit reports, the process plant was generating approximately 3.8Mt to 4.5Mt (dry) of tailings per annum (tpa).



3

MMO currently has an above ground paddock type tailings storage facility (TSF1) comprising two cells with an area of approximately 500ha and eight in-pit facilities. Currently, tailings deposition is taking place in the Pit 9/5, 18/3 and 18/6 TSF as other facilities have reached capacity. Considerations for decommissioning, closure and rehabilitation of these TSFs/PTSFs are presented in this manual. Tailings deposition can also be conducted in the southern cell for emergency use only. Return water from the in-pit facilities is pumped to the evaporation ponds.

2.1. Paddock TSF The paddock TSF comprises two cells (North Cell and South Cell) with a combined tailings storage area of approximately 460ha (2 x 230ha cells) and perimeter embankment length of 9km. The TSF is east of the process plant (Figure 1). The North Cell is full and has remained inactive for over nine years, while the South Cell is active and intermittently receives small amounts of tailings.

2.2. 2/2-2/4 IPTSF Pits 2/2 and 2/4 located 2km north of the process plant are two adjacent pits joined by a bridge constructed from mine waste backfill. The total pit length is approximately 1.2km and it is orientated north–south. The depth of Pit 2/4 is a maximum of approximately 50m, with the deepest point occurring centrally within the pit. The depth of Pit 2/2 is a maximum of approximately 40m, with low points distributed throughout the pit.

Pits 2/2 and 2/4 is used for tailings deposition. Tailings is deposited from a single point at the north end of 2/4 and a single point into the 2/2 pit (either or cannot be together). The decant water pools at the southern ramp of 2/2 and is pumped to the 2/3 pit for evaporation.

The 2/2 2/4 pit takes 5% of the plant tailings production.

2.3. 8/4 IPTSF Pit 8/4 is located 4km south-west of the process plant. Pit 8/4 is separated from the in-pit facility by a mine waste ‘plug’ several hundred metres wide. Pit 8/4 is square with approximate dimensions of 500m x 500m. The pit depth varies from approximately 30m at an internal ridge separating northern and southern sections of the pit, to approximately 50m north and 60m south of the ridge.

The 8/4 IPTSF is currently not utilised and is in the process of being decommissioned.

2.4. 9/2 IPTSF Pit 9/2 is located approximately 1.5km west of the process plant. The pit is approximately 1.2km in length, 500m wide and orientated north-south. The pit depth varies from approximately 30m at the southern end to 40m at the northern end.

The 9/2 IPTSF is still an active tailings pit with about 20,000m3 of tailings pumped into the pit every three months. No decant water is recovered from this pit as it is allowed to evaporate.

2.5. 18/3 IPTSF, 18/6 IPTSF and 9/5 IPTSF These pits are located approximately 4km east of the process plant. The maximum tailings depths for Pits 18/3, 18/6 and 9/5 will be 42m and 64m and 48m respectively. The pit floor of Pit 9/5 is relatively uneven compared to Pits 8/3 and 8/6.

A pump will be deployed from the ramp on the north section of Pit 18/3 (deepest section) where ponding of water is expected to occur. Access to the pit is via a haul road north-east of the pit.



4

A pump will be position on the north section of Pit 18/6 (deepest section) where ponding water is expected to occur. Access to the pit is via a haul road north of the pit.

A pump will be deployed from the ramp on the west section of Pit 9/5 (deepest section) where ponding water is expected to occur. Access to the pit is via haul roads east and west of the pit.

2.6. 17 Series IPTSF The 17 series In-Pit TSF (Figure 2) is for future primary tailings storage areas. Mining of the first pit started in 2007 with the 17.01 pit followed by the 17.53 pit in 2010. Mining in 17.08, 17.07 and 17.02 is on-going. The 17 series pits are expected to be completely mined out in January of 2021. The currently active Pits 9/5, 18/3 and 18/6 are projected to be filled by the end of 2022.

The following documents are relevant to the design of the 17IPTSF:

Coffey Services Australia Pty Ltd documentation titled ‘Geotechnical Assessment of 17 Series In-pit Tailings Storage Facilities, Murrin Murrin Operations Pty Ltd’, dated 24 April 2020, document reference: 754-PERGE272398 -Murrin Murrin In-Pit TSF Design Rev A.

Coffey Services Australia Pty Ltd documentation titled ‘Scope of Works, 17 Series In-Pit Pty Ltd, Murrin Murrin Operations Pty Ltd’, dated 24 April 2020, document reference: 754-PERGE272398-SOW Rev A.

2.6.1. Design Parameters Design parameters provided by the client, at the time of the most recent works approval application, are as follows:

Tailings Production Rate of 4,500,000tpa (dry)

Average Slurry Density ex plant 27% solids

Final tailings dry density (average) 0.8t/m³

2.6.2. Storage Volume Figure 3 presents the deposition plans of the 17IPTSF. Depth vs. capacity curves for the facilities are attached as Figure 4.

Table 1 presents the parameters for the 17IPTSF.

Pit Min. Crest Level (mRL)

Max. Tailings Depth (m)

Tailings Storage Volume (Mm3)

Storage Life* (years) Pit Wall Angles

17IPTSF 457.6 36 18.87 3.35 40o – 70o

: * Storage life calculated at a tailings production rate of 4,500,000tpa and an expected dry density of 0.8 t/m3

The estimated storage life of the facilities should be verified and corrected as filling proceeds, by carrying out regular surveys of the facilities and reconciling the volume deposited against the tonnages milled. It is recommended that these surveys be conducted at least on an annual basis.

When appropriate, in-situ testing of the tailings should be undertaken to assist in determining settled tailings densities.



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2.6.3. Tailings Storage Facility Freeboard The DMIRS (2015) ‘Guide to the preparation of a design report for tailings storage facilities (TSFs)’ sets out freeboard requirements. The DMIRS define terminology relating to tailings storage freeboard and provide minimum criteria.

For the purposes of TSF operation, the following is emphasised with respect to freeboard. Freeboard comprises three distinct elements, namely: operational, beach and total freeboard. These elements are illustrated graphically on Figure 5. Each element is defined as follows:

Operational freeboard is the difference in height between the embankment crest and the adjacent tailings beach. The minimum required operational freeboard according to the DMIRS is 300mm.

Beach freeboard is formed by sloping tailings beaches. The average beach freeboard relates to the average depth of the inverted cone, measured from the tailings beach around the perimeter of the storage, to the normal operational water level surrounding the central decant facility. The beach freeboard is the requirement to account for the runoff resulted from a 1:100 year ARI, 72-hour duration rainfall. The minimum beach freeboard specified by the DMIRS is 200mm. It is understood that MMO will construct a bund around the pit rim and the catchment area of the 17IPTSF will only involve the size of the pit, without the surrounding area above the pit. At MMO, the 1 in 100 year, 72-hour rainfall event is equivalent to approximately 200mm.

Total freeboard as defined by the DMIRS is the sum of the above two components, operational and beach freeboard, with a minimum value of 500mm. Considering the 1 in 100 year, 72-hour rainfall event, the minimum freeboard required between the crest and any water pond at the decant facility for the site is 500mm.

3. Hazard Rating Based on the DMP Code of Practice (2013)2, the hazard rating is derived considering the potential adverse impacts or damage from:

Embankment or structural failure, and

Controlled or uncontrolled release of tailings/water, or seepage.

3.1. Paddock TSF The hazard rating for the Paddock TSF is considered by Coffey to be ‘Category 1 - Medium’ based on the hazard rating (DMP 2013)2 shown in the Tables 1 and 2.



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4. Operating procedures 4.1. General Successful management of the TSFs to achieve the operational objectives requires a thorough understanding of the major operating components of the facilities. These are:

Tailings deposition.

Surface water control within the facility.

Routine inspections and maintenance.

An operating manual is required to assist the operators in safe and preferred management of the TSFs and to enable staff to be familiar with correct operating procedures. This section outlines the operating and monitoring criteria that will be adopted during the operational life of the facility.

The focus of the operating procedures is on deposition of tailings at a low velocity from a ring main using multiple spigots (Paddock TSF) or discrete discharge locations (IPTSFs), such that sloped tailings beaches are developed. The sloped beaches allow liberated surface water to be concentrated around the decant facility and subsequently returned to the process plant. This is achieved by the regular cycling of the active deposition points in a methodical manner around the facility. The management and operation of the decant pump will address the requirement of keeping the pond as small as practical by maximising water recovery. Under no circumstances should water be allowed to pond against the perimeter embankments/walls.

The following considerations relate to the operation of the In-pit TSFs:

i) Frequent inspections should be made of the tailings line, water return line, discharge point, water recovery system and the position of the supernatant pond in relation to the water recovery system. The facility should be inspected 4 hourly, in accordance with the MMO Operating License.

Only by regular inspection and appropriate remedial action can the performance of the water return system be optimised and operational problems be avoided.

ii) Operation, safety and environmental aspects should be periodically reviewed during an inspection by a suitably experienced and qualified engineer. This inspection should be done at least every year.

4.2. Tailings deposition 4.2.1. Deposition principles The method of deposition of tailings into the storage is one of the major controlling factors in achieving:

i) Higher in-situ densities in the tailings storage;

ii) Higher water returns, and

iii) Maintaining pit wall and mine waste embankment (plug) stability.

In order to understand the tailings deposition requirements a detailed knowledge of the components of the tailings system is required. These components include and will be discussed in more detail below:



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i) Tailings Pipework;

ii) Spigotting Process; and

iii) Ring Main Flushing.

The following details are provided to enable an efficient tailings disposal system to be operated:

The discharge points (Paddock TSF) shall be regularly moved to allow beaching of tailings placed in layers (increments) of approximately 300mm thickness and to allow sufficient drying time to maximise the in situ dry density of the deposited tailings. Figure 6 shows the distribution pipe with spigot offtakes, each of which will be used in a sequential manner.

Tailings will be deposited sub-aerially (exposed to air) in thin layers at a low velocity from numerous spigot discharge points (Paddock TSF), to form a beach that slopes towards the central decant. Deposition will occur for a period of several days from each group of spigots. Information regarding tailings spigotting will be recorded on log sheets.

The deposited tailings should be allowed to dry for as long as possible before being covered by the next layer of tailings.

Low velocity discharge is preferred, as this allows the coarser slurry fraction to drop out of suspension at the point of discharge, due to sudden change or drop in velocity, with the finer material progressively deposited towards the centre of the facility.

High discharge velocities result in erosion of previously deposited tailings and formation of channels towards the centre of pit, causing uneven deposition of tailings, uneven beach development and turbid water, and as such should be avoided.

4.2.2. Tailings line flushing At the completion of sequential deposition of tailings, each line to the distribution point will be flushed with water until it is clean. Flushing proceeds in the same sequential manner as tailings spigotting. Flushing shall be undertaken so any discharge is directed away from the embankment and monitored to ensure water does not flow back towards the embankment and cause any scour or erosion. If flushing is undertaken on night shift, adequate temporary lighting shall be installed to allow visual monitoring of water flow. The flushing operation will be supervised by the Tailings and Water Coordinator.

4.3. Tailings pipework and spigotting Tailings is transported from the process plant to the active tailings storage via a large diameter 560mm OD PE100 PN12.5 pipe. At the spigot/discharge points the tailings delivery pipe extends a minimum distance of 5.0m over the crest, from where the tailings is deposited into the facility.

The inspection and maintenance of the pipework and spigots shall also form part of the regular operational activities associated with inspections of the facility.

4.3.1. South Cell TSF Tailings deposition into the TSF is undertaken sub-aerially utilising multiple spigots located on the perimeter embankments. Spigots were located at approximately 20m intervals. The tailings beach slope based on the previously provided survey data was generally in the order of 1:300 (V:H).



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4.3.2. 9/2 IPTSF Tailings in the form of slurry will be discharged sub-aerially from multiple spigots, located initially in the southern end of the 9/2 IPTSF. Depositing the tailings in this manner will enable the water pond to remain adjacent to the access ramp in the north-west end of the facility. As the tailings surface approaches the crest in the northern end, gradually moving the spigot towards the east along the southern crest will help to optimise the storage capacity of the 9/2 IPTSF.

The spigots are spaced at 75m intervals. The tailings will cascade over the benches within the pit to the pit floor and gradually flow towards the far end of the pit, forming a beach slope angle of up to 5% near the spigot location and a slope angle of up to 1% at a distance from the spigot. It is expected that the facility will be predominantly filled from one spigot location.

4.3.3. 2/2-2/4 IPTSF Tailings in the form of slurry will be discharged sub-aerially from two spigots, one located in the northern end of 2/2 IPTSF and the other in the north western side of 2/2 IPTSF. Tailings will be discharged intermittently between the two spigots.

Tailings discharge or spigotting is to be carried out such that the supernatant water pond is maintained adjacent to the access ramp in the southern end of the facility. The supernatant pond is to be maintained as small as practical.

4.3.4. 9/5 IPTSF Tailings deposition into 9/5 IPTSF will be undertaken using multiple spigots located along the eastern pit rim at approximately 100m intervals. Tailings deposition will be cycled between all the spigots, resulting in the development of a tailings beach with a slope towards the western side of the pit, where a decant pump deployed from the existing access ramp will be able to recover water from the facility. The decant pond will initially form in the lowest part of the facility in the centre, before expanding further west to a point accessible by the decant pump.

The storage capacity of the 9/5 IPTSF is limited by the lowest point of the pit rim, located along the south-western side of the facility.

4.3.5. 18/3 IPTSF Tailings deposition into 18/3 IPTSF will be undertaken using multiple spigots located along the southern pit rim at approximately 100m intervals. Tailings deposition will be cycled between all the spigots, resulting in the development of a tailings beach with a slope towards the northern extent of the pit, where a decant pump deployed from the existing access ramp will be able to recover water from the facility.

The storage capacity of the 18/3 IPTSF is limited by the lowest point of the pit rim, located along the southern side of the facility.

4.3.6. 18/6 IPTSF Tailings deposition into 18/6 IPTSF will be undertaken from a single spigot located on the southern pit rim. Tailings deposition will be undertaken to achieve a tailings beach with a slope towards the northern end of the pit, where a decant pump deployed from an existing access ramp will be used for water recovery. The decant pond will initially form in the lowest part of the facility in the centre, before expanding further north to a point accessible by the decant pump.



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4.3.7. 17IPTSF Tailings deposition into 17IPTSF will be undertaken in stages in order to provide control over tailings beach development and to facilitate recovery of water from the facility. Initially, tailings are to be deposited from four sets of multiple spigots, each set located at different locations along the eastern side of the pit. The existing access ramps along the northern, western and southern sides of the 17IPTSF will be utilised as part of water recovery operations. Water recovery from the ramp will not be possible until the localised low points are filled up with tailings level of adequate height such that the supernatant pond is formed around the ramp.

Once the tailings level covers all the localised low points, discharge from multiple spigots can be relocated to the northern tip, while the southern access ramp will be used for water recovery operations. Supernatant pond at the northern end of the pit, will be pump using a decant pump deployed from the northern access ramp to recover water from the facility. The pumps will be moved up the ramps as the tailings and water levels rise within the pit.

The storage life of the facility is estimated to be 28 months.

4.4. Return water operation During tailings deposition, the facilities will house a manually operated decant pump which removes supernatant water by a dedicated pumping system that delivers the water to the evaporation pond. The location of the supernatant water pond will be controlled by the tailings discharge sequence employed. The pond should be maintained at the smallest practical operational size to maximise water return to the evaporation ponds. The size of the pond will be governed by the efficiency of the pontoon mounted pump in removing water from the tailings storage.

Other controlling factors will be:

evaporation from the surface of the pond;

variations to the in-put of tailings water (percent solids);

rainfall events;

difference in permeability between the tailings and the underlying rock units; and

the ratio of horizontal to vertical permeability of the tailings.

5. Inspections and maintenance The following section details the frequency of the inspection activities that should be undertaken to ensure each storage facility is operated and maintained in a satisfactory manner.

Inspection log sheets for recording the results of the daily and monthly inspections should be implemented. The suggested formats for proforma sheets are provided in Appendix A. These log sheets have been developed based on a combination of procedures developed by Coffey and details as indicated by DMIRS requirements. All information should be completed in full. A detailed written report is required for the Engineering Inspections.

Hard copies of all inspection records should be filed and retained on site for auditing purposes. DMIRS have a requirement that they can and will inspect any prepared operating manual and reporting criteria for compliance to the prepared manual. All records, including daily recording sheets,



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the operations manual completion form and operation manual update form should be held on site for the life of the mine.

5.1. Daily routine inspections The following routine inspection and maintenance procedures are to be carried out by Process Plant Staff, who have the responsibility for the general day to day activities associated with the operation of the facility such as inspecting the tailings lines, changing the spigots and inspecting the water return system. Reporting sheets are attached covering the following inspections:

Personnel Contact Details (1 page)

Staff Confirmation Log (1 page)

Daily / Shift Inspection Log Sheet (1 page)

Routine inspections, as detailed below, are to be undertaken by an operator or shift supervisor 4 hourly, in accordance with the MMO Operating License. The date and time of each inspection is to be entered into the Shift Foreman’s log book and is to be signed by the person allocated to undertake the inspection on that shift to ensure the requirements have been undertaken. The shift Inspection Log Sheet is to be filled out on a daily basis. The frequency of the routine inspection is to be increased to twice daily in the event that the frequency of the mine waste embankment movement accelerates at any time.

The inspections should cover:

The pipelines (tailings delivery line and water return line) to and from the tailings storage facility.

Leak detection.

Pumps.

Spigots and valves.

Spigotting and deposition.

Location and size of the water pond.

The decant pump.

The evaporation ponds.

Seepage from the facility as indicated by the monitoring bores.

The general integrity of the crest and pit walls i.e. any new cracking, any new seepage from waste plugs (daily).

The general integrity of the mine waste embankments (plug), i.e. any new evidence of movement/settlement or seepage.

Any changes to existing cracking or seepage.

Access roads.

The process plant management has the responsibility for verifying that the inspections for Process Plant Staff have been carried out.



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5.2. Monthly inspections Monthly inspections of the tailings storages should to be carried out by process plant management. The Monthly Inspection Log and Monitoring Sheet (Appendix A) should be completed for each inspection.

The inspections should assess the following items and note any changes which have occurred since the previous inspection. Questions which are of particular interest are listed under the relevant items.

The applicable sheets attached to this document are:

Monthly Inspection Log & Monitoring Sheet (1 page)

DMIRS Incident Report Sheet (3 pages)

Outline of Yearly Audit Criteria (8 pages)

Any points of concern or unusual occurrences observed during any inspection should be reported to Process Plant Management for their review and considerations and if required Coffey (or others) should be contacted for assistance or advice with a record kept of any actions that are planned or are taken.

5.3. Details of the routine inspection 5.3.1. Tailings lines The tailings line is to be inspected 4 hourly, in accordance with the MMO Operating License. The date and time of each inspection is to be entered into the Shift Foreman’s log book.

All tailings lines should be bunded. The HDPE tailings lines on the crest of the facility are sensitive to temperature, and the expansion and contraction of this line can cause leaks, and in extreme situations, failure of the pipeline. Pipelines shall be checked for:

External damage

Potential fractures

Stress due to temperature extremes

Valves

Welds

Flange / joint leaks

Any leaks or failures of the tailings pipeline should be immediately reported to the following personnel or project equivalents and an incident report completed.

Shift Supervisor or

Ore Leach Superintendent or Processing Manager.

If necessary, emergency shutdown and containment procedures shall be initiated by either the Mill Supervisor, Process Manager or Environmental Department.



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5.3.2. Return water lines The return water line comprises an HDPE pipe positioned in the same bunded corridor as the tailings delivery line from the process plant to the TSFs. The pipeline will have a series of valves allowing water to be diverted into the tailings line for flushing via junction points. Return water lines shall be maintained and inspected, as decant water may contain traces of processing plant reagents which can have a detrimental environmental effect if released. The return water lines shall be checked for:

External Damage

Potential Fractures

Stress due to Temperature Extremes

Welds

Joint Leaks

Valves

Any leak or potential failure should be reported immediately to the following personnel after initiating emergency shutdown and containment procedures:

Mill Supervisor.

Process Manager and / or Environmental Department.

5.3.3. Decant system The position and size of the pond and the position of the decant pump should be inspected at the same time as the tailings lines are inspected. Any abnormalities should be reported immediately to the following personnel or project equivalents:

Shift Foreman or

Mill Superintendent (Processing Manager).

The same personnel shall also be advised if a large water volume is accumulating on the facility, so measures can be taken to reduce the pond size. The water discharged from the decant facility should also be inspected on a regular basis to ensure it is clear (i.e. not murky or turbid).

The return water lines to the evaporation pond should also be inspected at the same time as the tailings line. Any leaks or failure of the water pipeline should be immediately reported to the following personnel or project equivalents:

Shift Foreman or

Mill Superintendent (Processing Manager).

5.3.4. Pit walls / mine waste embankments Part of the general activities of the Shift Foreman, when visiting the storage facilities, shall be to inspect the pit walls, including the crest. The inspection shall note any cracking or new features, such as seepage, pit wall failures or scour (caused by tailings deposition or rainfall runoff) or any other obvious changes or problems.



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The crest area, upstream slope and downstream slope of the mine waste embankments within the facilities are to be inspected a minimum of twice per day. The inspection shall note any evidence of movement or settlement of the embankments, or any signs of new seepage through the embankments. If settlement rate/ crack width increases, a geotechnical engineering specialist should be contacted. No personnel shall enter the base of the IPTSF during operations (i.e.. start-up). Access should be confined to ramps associated with decants.

During high rainfall events, if personnel safety allows it, the inspection frequency shall be increased. The inspections should ensure that the freeboard of the supernatant pond is within DMIRS guidelines.

5.3.5. Embankment (South Cell) The perimeter embankments of the South Cell and batter slopes need to be inspected for cracking, seepage, scouring (caused by tailings deposition or rainfall runoff) and external embankment erosion.

The review shall also monitor vegetation growth such that no trees are allowed to become established while the facility is active and before any vegetation reaches the sapling stage. Any such vegetation shall be removed. Reviews shall also check for any evidence of burrowing by animals and its prevention should be ensured as appropriate.

If there is an increase of seepage water at the toe of the embankments, containment trenches (or any other measures) should be put in place to collect water. Any water collected in containment trenches at the toe of the embankments should be monitored regularly to note any changes (especially increases). An increase may indicate a deteriorating condition of the embankment.

No decant water should be allowed to rest against perimeter walls. Any problems or concerns must be noted on the inspection log sheet and reported to the following Processing Manager.

5.4. Details of monthly inspections 5.4.1. Pit walls / mine waste embankments (i) Is there cracking present along the pit crest/mine waste embankment, any intermediate

berms/benches or walls?

(ii) Is staining or discolouration of soil present outside the extent of the facility crest or on the downstream slope of the mine waste embankment?

(iii) Is there any water flow/seepage identified from the facility as indicated by the monitoring bores?

(iv) Is the tailings freeboard adequate?

(v) Is there water ponding against waste plugs, contrary to facility design?

5.4.2. Spigotting / placement (i) Is the distribution of the tailings into the storage as required by the design?

5.4.3. Supernatant water pond / decant pump (i) Is the supernatant water pond positioned against the applicable access ramp?

(ii) Is the decant pump positioned appropriately within the supernatant water pond?



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(iii) Is the water pond surface (within the storage) as planned, or is there excess water on the storage?

(iv) Can the decant pump efficiently handle and discharge any storm runoff in addition to the supernatant water?

5.4.4. Tailings and return water lines (i) Are the tailings and water return lines intact and free of cracks?

5.4.5. Groundwater / phreatic surface monitoring (i) Has all monitoring been performed and the results regularly reviewed?

(ii) Has the monitoring been performed as specified in the DWER conditions of licence?

(iii) Have any DWER exceedances been reported?

All of the above points must be monitored closely to ensure stability is maintained. If problems are encountered, Coffey (others) should be contacted, as an investigation may need to be instigated.

5.5. Engineering inspections An inspection by a qualified geotechnical engineer with experience in the design, operation and auditing of tailings storages should be carried out at least once every year.

Typical aspects that need to be addressed are outlined in the Yearly Audit Criteria forms (attached) and below.

6. Monitoring Regular inspections and monitoring are aimed at identifying and acting on any problems before they have a major impact on the TSF operations or integrity. The inspections may result in the identification of an event that requires reporting to senior staff and in some cases to relevant government departments, namely the DMIRS and / or Department of Water and Environmental Regulation (DWER).

The DMIRS and DWER also have reporting criteria for specific events or occurrences specified in mining lease clauses or under environmental licence conditions. Typical reporting events include:

Any fauna death on or near the TSFs (not roadkill).

Any uncontrolled release of tailings slurry or return water and the cause (pipe break, overtopping, pump malfunction, automatic switch malfunction and operator error).

Impacts due to seepage (vegetation distress, soil contamination, water quality changes).

TSF defects, e.g. to the embankments or return water facilities.

Changes in water quality that exceed prescribed conditions of licence criteria.

Increases in production tonnages. Water quality and water level information results should be recorded on spreadsheets and plotted and graphed as soon as possible. The information should be reviewed after being entered and graphed to allow any changes to be identified and acted upon.



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The plotting of recorded information allows trends to be determined. Where newly recorded information deviates (generally significantly) from a previously established trend, the reading should be checked, the general area inspected, and the information reported to plant management for consideration and action.

6.1. Environmental and structural monitoring Details of the routine inspections are provided in Section 5.1.

6.1.1. Climatic data If climatic information is collected on site, the following climatic data is to be collected daily or at the end of each month:

(i) Rainfall for the month.

(ii) Evaporation for the month.

This information can be utilised in order to assist with determining a water balance for the annual audit of the facilities.

6.1.2. Water quality Water quality monitoring (sampling and testing) is required from the following areas or sources:

(i) Monitoring bores located around the facility.

(ii) Slurry water discharged into the storage, water stored on the storage and water returned to the evaporation pond.

The frequency of the water quality monitoring is usually determined by the regulatory authorities with the details of the water quality requirements stipulated either on a licence or other approval documents issued by the regulatory authorities. The licence stipulates water quality sampling and testing at a frequency of every 3 months (quarterly).

Copies of the current leased licence conditions (DMIRS and DWER) relevant to the tailings storage should be attached to this document to allow for easy reference. Each time the DMIRS mining lease conditions or DWER conditions or licence are renewed or updated all conditions should be checked for any changes, with appropriate confirmation they have been read and records have been updated and will be acted upon as considered appropriate.

In particular when the DWER licence is issued it should be reviewed to ensure any changes to the testing regime (frequency, elements) and water quality criteria are noted and acted upon.

6.2. Pit walls / mine waste embankment monitoring The stability of the pit wall / mine waste embankment (plug) is crucial in the safe operation of the facility. A management system should be implemented to enable the identification of potential instability of the mine waste embankment.

The following is recommended:

Continue daily crack monitoring and consult a geotechnical specialist if the rate of crack development changes.



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Make general observations regarding crack development in order to assess if a circular failure is developing.

Check for signs of piping of the embankment (i.e. internal erosion), downstream of the embankment.

If seepage becomes apparent at the Pit or waste plug (assessed as unlikely), tailings spigotting should be swapped to another locations.

Report of the visual inspection should be entered into an inspection log which details the date the inspection was carried out, comments from the inspection, remedial works required, if any, and the date the remedial works are completed.

6.3. Process plant In addition to the daily visual inspections of the water pond, spigots, water return pumps, and tailings and return water pipelines to the evaporation pond, the following information should be recorded at a minimum on a monthly basis or more frequently if possible:

(iii) Tailings production, measured in dry tonnes.

(iv) Tailings slurry density, measured in percentage solids or slurry water volume.

(v) Water return from all sources from the tailings storage to the evaporation pond, measured in cubic metres or tonnes.

This information will be utilised to estimate a water balance as part of auditing of the tailings storage.

6.4. Achieved tailings density and strength Sampling of deposited tailings, including recovery of disturbed bulk samples and undisturbed tube samples should be undertaken during TSF operations to assess performance of the facilities. Subsequent laboratory testing may include: grading, Atterberg limits, moisture content and density. To further assess tailings strength, shear vane and / or cone penetration testing may be considered.

Currently, the average tailings slurry density is approximately 43.0% solids by weight. The average estimated in situ tailings density is approximately 1.48t/m3 (dry).

6.5. Storage volume and deposition time remaining Detailed mud-line and water pond level surveys are to be carried out at least on an annual basis. A comparison should be made of any new information against design information. This would typically include an assessment of filling using survey combined with tailings production data to assess tailings density, and may include field and laboratory sampling and testwork results. Based on the results, ongoing predictions of the storage life of the facility can be made.

As-built survey plans should be updated if any associated construction work is undertaken.

6.6. Performance during significant seasonal events During high rainfall events, if personnel safety allows, the inspection frequency shall be increased. The inspections should ensure that the TSF freeboard is within DMIRS guideline limits. The condition of the external embankments and presence of any erosion channels or scouring due to rainfall runoff and wind should be observed and remediated as appropriate, when possible.



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Compare any new information against the design. This typically includes an assessment of the filling rate; if the information varies from the design, a revised prediction of storage life for the facility can be made.

The following may also be undertaken, either independently of or in conjunction with the audit:

Sampling of deposited tailings, including recovery of disturbed bulk samples and undisturbed tube samples. Testing that could be considered includes: grading, Atterberg limits, moisture content and density. Sampling will only be undertaken if safe tailings beach access is possible.

Stability assessments using field and laboratory results and water level information to reassess factors of safety.

The requirement for sampling and testing in any subsequent audit will be based on the previous year’s results and any variations in the tailings feed, such that repetitive testing of similar materials is avoided.

7. Emergency action plan 7.1. Response actions To enable the emergency action plan to be implemented and to allow a safe and timely response to be instigated, the attached documents (Personnel Contact Details, Assembly Points and Staff Confirmation Log) outline current information pertaining to assembly points and contact names. The sheets shall be reviewed at least six monthly or updated as required when new staff become responsible for activities in and around the facilities.

Contractors shall also be made familiar with the location of the assembly point and be made aware of their reporting responsibilities and to whom they shall report to.

The attached sheets should provide a list of relevant contact details of staff associated with the tailings storage, senior site responsible staff, safety officers and emergency services.

All personnel who are associated with the facilities are also required to sign a form as evidence that they have been inducted and are aware of assembly points and reporting procedures.

7.1.1. Tailings lines and return water line The tailings lines from the process plant to the tailings storages and the return water lines from the pontoon mounted pumps to the evaporation ponds/ paddock facilities are to be located inside bunded open trenches to contain any spillage of materials resulting from lines which develop leaks or burst during operation.

In the event of pipeline failure the plant is to be notified and the affected pipeline is to be shut down until repaired and the spilled materials collected and/or pumped, as appropriate, and deposited in the tailings storages.

7.1.2. Decant pump The decant pump is operated manually and run at all times. The pumps are only switched off during:

Shutdowns;

When dirty water is pumped into the evaporation pond; and



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When it is necessary during periods of rainfall to ensure minimal water on the storage.

7.1.3. Tailings storage facility Under normal operating conditions the walls of the IPTSFs and the mine waste embankments (plugs) are not expected to become unstable. Normal operating conditions refer to a water pond located adjacent to the access ramp of the facility.

Given the adoption of the tailings deposition philosophy, adequate pontoon mounted pump operation, routine inspections and maintenance practices set out in the Operations Manual the probability of pit wall/mine waste embankment (plug) failure during normal operations is low.

In the unlikely event of a major pit wall/mine waste embankment failure, the tailings within the facility will most likely remain within the facility or confined within one of the adjacent pits.

No personnel shall enter the base of the 17IPTSF during operations (i.e.. start-up). Access should be confined to ramps associated with decants.

Action to control a pit wall/mine waste embankment failure affecting decant or tailings deposition (i.e.. tailings is not likely to go beyond the confines of the pits) would include:

Assess the requirement to shut down of the process plant or reduce throughput.

Contact a suitably qualified geotechnical organisation for technical assistance.

Advise relevant government departments particularly DMIRS and DWER.

Prior to the commencement of any repairs undertake (as appropriate) a thorough inspection of the area with the assistance of a geotechnical specialist.

Repair the damaged area, if appropriate.

Prepare an incident report, detailing all factors prior to the incident and the situation after cleanup. The report should identify causes of the problem and what actions will be taken to prevent a similar occurrence. This report should detail the ongoing monitoring programme to fully assess the impact of the incident.

Advise all appropriate government departments as necessary of the incident, review DMIRS conditions of licence in respect to the timing of advising the DMIRS and reporting criteria.

It must be stressed however, that the safe operation of the in-pit facilities relies upon the implementation of operational procedures which comprise tailings deposition, decant operation; and routine inspections and maintenance, as set out in the Operations Manual to minimise the potential for a catastrophic event such as a failed embankment.

7.2. Incident reporting The undertaking of regular inspections and monitoring is aimed at identifying any problems prior to them causing a major impact on the operation or integrity of the structure. The inspections may result in the identification of an event that may require reporting to senior staff and in some cases to relevant government departments (DMIRS and/or DWER), i.e. new seepage.

In addition to incidents that require reporting under section 78 and 79 of the Mine Safety and Inspection Act of 1994, the following events or occurrences also need to be reported to DMIRS within 7 days or sooner of identifying a incident/problem or likely incident/problem. DWER conditions of licence should also be reviewed in respect to the timing and detail required for incident reports.



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Routine inspections as per Section 5.1.

Acceptable outer slope geometry validated by construction compliance reports.

Stability to be validated during annual audits against an adequate factor of safety determined from assessments in the design report.

Adequate construction compaction.

Pit Walls

The pit voids from the mining process constitute the pit walls. Although considered stable (experience from stable adjacent pit voids and tailing pits) routine inspections should still be undertaken during the operation of the facility as per Section 5.1.

Pond Control

In order to reduce the risk of embankment failure due to high phreatic surface the following measures should be taken into consideration:

Routine inspections and groundwater monitoring as per Sections 5.1.

Maintain relatively small water pond with no free water ponding against the perimeter embankments.

A resultant low phreatic surface within the embankment.

Adequate decant operation.

Pipelines

Appropriate management of delivery, distribution and return water pipelines will reduce the risks of downtime and/or environmental damage associated with pipe blockages, leaks and bursts. The pipelines should be managed as discussed in Section 4.5 as well as considering the following measures:

Routine inspections as per Section 5.1.

Periodic rotation of pipelines (flanges to be date stamped for reference).

Pipe wall thickness checking.

Preventive maintenance through a periodic replacement policy.

Automatic shut-off valves linked to pressure transducers located on the pipelines.

Periodic clearing of vegetation under and around the pipelines to prevent damage from bush fires.

Seepage

To ensure drainage flow through the tailings contained in a storage facility does not compromise the stability of the embankment the following measure should be considered:

Routine inspections and groundwater monitoring as per Sections 5.1.

Following operational aspects in this manual to achieve a desirable beach slope to keep pond away from perimeter embankment.

Maintain drainage recovery bore operation.



26

7.4.2. TSF embankment failure/pit wall failure Under normal operating conditions the walls of the IPTSFs are not expected to become unstable.

Given the adoption of the tailings deposition philosophy, adequate pontoon mounted pump operation, routine inspections and maintenance practices set out in the Operations Manual the probability of pit wall failure during normal operations is low.

In the unlikely event of a major pit wall failure or embankment failure, the tailings within the facility will most likely remain within the facility or be confined within one of the adjacent pits.

No personnel shall enter the base of any operating pits (i.e. start-up). Access should be confined to ramps associated with decants.

Action to control a small-scale failure and limit environmental damage would include:

Assess the requirement to direct deposition to alternative facilities, or reduce process plant throughput.

Movement of tailings deposition to areas not affected by the small scale embankment failure.

Contact a suitably qualified geotechnical specialist for technical assistance.

Prior to the commencement of any repairs undertake a thorough inspection of the area.

Undertake remedial and repair work of the damaged embankment or affected area.

Clean up of tailings as soon as practical after repairs have been completed and the storage is considered in a safe condition.

An incident report is to be completed, as discussed in Section 7.2.

Action to control a large-scale failure and limit environmental damage would include:

Assess the requirement to shut down of the process plant.

Direct deposition to alternative facilities.

Contact a suitably qualified geotechnical organisation for technical assistance.

Advise relevant government departments particularly DMIRS and DWER.

Prior to the commencement of any repairs undertake a thorough inspection of the area with the assistance of a geotechnical specialist.

Repair the damaged embankment in accordance with the specialist’s instructions.

Clean up of tailings as soon as practical after the repairs have been completed.


It must be stressed, however, that the safe operation of the in-pit facilities relies upon the implementation of operational procedures which comprise tailings deposition, decant operation; and routine inspections and maintenance, as set out in the Operations Manual to minimise the potential for a catastrophic event such as a failed embankment.

7.4.3. Embankment/pit wall erosion Response to Hazard

If erosion has developed to a point where collapse may be imminent, proceed as per Section 7.4.2.



27

Otherwise install bunds or drains to divert water flow away from the area of erosion and install any necessary protective barriers to protect personnel or vehicles.

Report circumstances to Tailings and Water Management Supervisor/Coordinator/Superintendent.

The Tailings and Water Management Supervisor/Coordinator/Superintendent is to inspect the site and either; arrange appropriate rectification measures; or contact the Geotechnical Consultant for specific advice.


7.4.4. Embankment settlement or lateral movement Response to Hazard

If movement has developed to a point where collapse may be imminent, proceed as per Section 7.4.2.

Otherwise install bunding or drains to limit flow of water into depression cracks and install any necessary protective barriers to prevent personnel and vehicles entering the area and to limit additional loading of the surface at the area of movement.

Placement of rockfill (consider use of filters as appropriate) against the toe of the embankment if there is evidence of lateral movement outwards.

Report circumstances to the Tailings and Water Management Supervisor/Coordinator/Superintendent.

The Tailings and Water Management Supervisor/Coordinator/Superintendent is to inspect the site and arrange any additional emergency measures and contact the Geotechnical Consultant for specific advice.


7.4.5. Burst or leakage of tailings delivery pipeline The tailings lines from the process plant to the tailings storages and the return water lines from the pontoon mounted pumps to the evaporation ponds/ paddock facilities are to be located inside bunded open trenches to contain any spillage of materials resulting from lines which develop leaks or burst during operation.

Response to Hazard

If alert to hazard arises from control room instrumentation (drop in pressure in delivery lines), immediate inspection of the line is required to locate and assess the leakage.

If automatic shutdown/diversion of tailings flow has not occurred, Tailings and Water Management Supervisor/Coordinator/Superintendent shall arrange appropriate shut down or diversion.

If alert to the hazard alert arises from inspection, the Tailings and Water Management Supervisor/Coordinator/Superintendent is to be advised immediately who shall arrange appropriate shut down or diversion.

At the location of the leakage, the Tailings and Water Management Supervisor/Coordinator/Superintendent is to inspect the site and arrange appropriate additional containment and/or clean up in association with the Environmental Advisor.

The Tailings and Water Management Supervisor/Coordinator/Superintendent is to ascertain the causes of the leakage/burst and institute procedures or measures to minimise risk of recurrence.




28

7.4.6. Burst or leakage of return water pipeline Response to Hazard

If alert to hazard arises from control room instrumentation (drop in pressure in delivery lines), inspection of the line is required to locate and assess the leakage.

If automatic shutdown of the return water pump has not occurred, pump is to be shut down immediately.

If the hazard alert arises from inspection, the Tailings and Water Management Supervisor/Coordinator/Superintendent is to be advised immediately who shall arrange appropriate shut down.

At the location of the leakage, the Tailings and Water Management Supervisor/Coordinator/Superintendent is to inspect the site and arrange appropriate additional containment and/or clean up in association with the Environmental Advisor.

The Tailings and Water Management Supervisor/Coordinator/Superintendent is to ascertain the causes of the leakage/burst and institute procedures or measures to minimise risk of recurrence.


7.4.7. Seepage Response to Hazard

If during any inspection of the TSF, wet surface areas or areas in the vicinity of the TSF, the Tailings and Water Management Supervisor/Coordinator/Superintendent is to be notified.

The Tailings and Water Management Supervisor/Coordinator/Superintendent is to inspect and photograph the site, ascertain details of location and extent of seepage and proceed as outlined in Section 7.4.3.

The Geotechnical Consultant is to be advised of details as soon as possible.

7.4.8. Decant Pump The decant pump is operated manually and run at all times. The pumps are only switched off during:

Shutdowns;

When dirty water is pumped into the evaporation pond; and

When it is necessary during periods of rainfall to ensure minimal water on the storage.

8. Closure and rehabilitation plan The preliminary rehabilitation and closure design for the TSFs should be based on the following guiding principles, which in order of priority are:

Protect public health, safety and property;

Ensure long-term physical and chemical stability of disturbed area;

Design for a sustainable ecosystem and land use;

Employ rehabilitation methods that are technically effective and cost efficient; and



29

Standard and proven engineering practices to minimise ongoing maintenance.

As part of decommissioning:

All the delivery and discharge pipes and valves should be removed from the closed TSFs;

Power cable and pipe to the decant pump and the pump should be removed; and

The stand pipes of the piezometers and ground water monitoring boreholes should be replaced with ground level covers, so that they are less obtrusive, but still available for monitoring.

In view of the potentially soft tailings it is desirable to create a firm surface by inducing consolidation of the tailings and capping the tailings with waste rock.

8.1. Topsoiling Rehabilitation of the TSF areas would be designed to re-create, as far as possible, the vegetation cover that originally existed.

For this purpose the topsoil removed from the TSF (or other facilities) prior to construction will be redeployed on the final downstream slopes of the final batters of the TSF to assist with rehabilitation. The downstream slopes will be covered with topsoil, contour ripped, seeded with native species and fertilised as appropriate. Any remaining topsoil will be stockpiled in an adjacent location for use in later rehabilitation.

8.2. Rehabilitation trials Recommendations for rehabilitation of TSFs should be researched and reviewed during the life of the project under the direction of personnel from the MMO environmental team. A detailed closure/ decommissioning plan should be prepared prior to decommissioning to confirm the feasibility of the preliminary rehabilitation and closure plan, including:

Confirming water balance and final closure design;

Review cover quantities, sources and cost of soil and rock materials available;

Contact seed suppliers and identify any issues;

Review re-vegetation opportunities;

Carry out nutrient tests of local stockpiles soils; and

Reassess closure plan, incorporating changes based on annual reviews.

Figures

Appendix A - Tailings Storage Forms

PROJECT TAILINGS STORAGE FACILITY Date April 2020Job No 754-PERGE272398

CLIENT MURRIN MURRIN OPERATIONS PTY LTD File Op M Forms Apr20Subject Inspections

LOCATION MURRIN MURRIN OPERATIONS Revision 0

SUBJECT DAILY INSPECTION LOG SHEET TSF Form 3 sheet 1 of 1

Date Time Shift Day/Night

Shift Supervisor Inspection by Verified by

Item CriteriaN/S D/S

TSF Access Roads

Good condition? Maintenance required:

Pit crest area Any distress or any cracking present since previous inspection?

Any staining (darker coloured patches) of soil?

Are the recovery bores running?

Any tailings spillages?

Any new seepage. If so, where?

Existing seepage : any change in flow?

Is the number of spigots operating and the location of the spigots as planned?

Is the tailings deposition on the beaches in 300 mm layers?

Is the tailings level closer than 300 mm from the crest of the pit wall?

Pipelines Leaks?

Return water Decant pump operating? If pump is working is discharge clear?

Maintenance Outline any maintenance requirements and nominate responsible person.

Integrity. Any cracks in the decant access embankments?

Is the water in the decant pond clear?

Is the water pond positioned around the decant and approximately 300m away from the perimeter of the wall?

Is the water pond against or near the pit wall? If so arrange for it repositioning

Fauna Any deaths

Flora Any new distress Any vegetation requiring removal due to potential growth size

NOTES Please provide any comments or notes relating to the tailings storage facility

Tailings discharge

Decant Facility

YES/NO Comments

Within embankments/

pit walls

Seepage

Number open

PROJECT : TAILINGS STORAGE FACILITY Date April 2020Job No 754-PERGE272398

CLIENT : MURRIN MURRIN OPERATIONS PTY LTD File Op M Forms Apr20Subject Inspections

LOCATION : MURRIN MURRIN OPERATIONS Revision 0

SUBJECT : MONTHLY INSPECTION AND MONITORING LOG SHEET- BY MANAGEMENT TSF form 4 sheet 1 of 1

Date: Time: Shift Number:Shift Supervisor: Inspection by: Verified by:

Start Finish

1.0 Embankment Crest/Pit Crest / Walls Is cracking present on the crest/walls of the facility? If yes, is it new cracking or existing cracking. Photograph No.If existing has the cracking got larger?

Is staining or discolouration present outside the extent of the facility? Photograph No.Is there water flow from any part of the facility? Photograph No.Is the freeboard adjacent to the pit wall above the designated level? (Based on DMP criteria it is 300 mm)Have the water levels in the monitoring bores been measured and the data entered and graphed to the appropriate sheet?Is there supernatant water against the pit walls? If so arrange for its repositioning

2.0 SpigottingIs the distribution of the tailings on the beaches as required by the operations manual?Do any of the spigots leak or need repair?Is the spigotting effective in keeping the water around the water recovery point?

3.0 Water Recovery System (Decant)Is the supernatant water positioned around the decant facility? Photograph No.Is the supernatant water as planned, or is there excess water on the storage? Diameter of supernatant water against wall: m Can the decant system handle storm runoff in addition to the supernatant water efficiently?

4.0 Process Plant InformationOre processed for the month (tonnes)Average tailings slurry density, measured in percentage solidsWater return from the tailings storage to the process plant (in tonnes and m³)

5.0 Water BalanceRecord volume of water discharged into TSF for this monthRecord volume of water recovered from the TSFRecord any other inflowsRecord any other outflowsCalculate the % water return

6.0 MonitoringHas the water depth from the monitoring bores been measured, checked and the data entered and graphed into the appropriate spreadsheet?Has the water quality data from the monitoring bores been checked and data entered into the appropriate spreadsheet?

7.0 Climatic DataAny significant rainfall events? Record as required

8.0 MaintenanceCheck on the status of any nominated maintenance or repair issues. Escalate repairs if required

9.0 Other AsepectsComments

Remedial Works Description of Inspection ActivityCommentsItem

Tailings storage facility audit Page 4 of 8

4.9 The actual operating characteristics of the TSF have been assessed against the original design assumptions.

Yes Refer to design reports.

4.10 Periodic geotechnical and engineering reports are submitted as outlined in the DMIRS publication Guide to Departmental requirements for the management and closure of TSFs.

Yes This audit.

4.11 The recommendations included in the annual geotechnical and engineering reports have been acted upon.

Partially Refer to recommendations section.

4.12 The TSF site is secured against access by unauthorised personnel.

Yes Remote site with controlled system in place.

4.13 Roads on and around the TSF are designed for the equipment using them.

Yes

4.14 The TSF roads are demarcated by windrows, railings or other such indicators of safe travel limits.

Yes Speed signage in place, windows in place, TSF traffic management plan in place.

4.15 The TSF roads are controlled by suitable signage indicating speed limits, direction etc.

Yes TSF traffic management plan in place

4.16 Traffic control measures on the TSF are effective at night.

Yes Reflected delineators in place.

4.17 Where there is deep water in a TSF, rescue equipment is provided.

N/A TSFs are dry with no water. The in-pit tailings have pumps away from the water with controlled access.

Tailings storage facility audit Page 8 of 8

8.4 A risk assessment has been conducted for the long term stability of the TSF structure post closure.

Partially High level at this stage.

8.5 The Closure Plan includes decommissioning and rehabilitation aspects for the decommissioned TSF structure.

Yes Conceptual design

8.6 Where operational changes have occurred the Closure Plan has been revised to take the changes into account.

Yes Busy with an update, due June 2020.



APPENDIX 3. HYDROGEOLOGICAL ASSESSMENT (SAPROLITE ENVIRONMENTAL 2020)

FINAL REPORT TRN 0978

MURRIN MURRIN NORTH MINING AREA

PROPOSED IN-PIT TAILINGS DISPOSAL INTO

17 SERIES PIT VOIDS

HYDROGEOLOGICAL ASSESSMENT


REPORT NUMBER: L0113-11-01 – ver C

Prepared For

Murrin Murrin Operations Pty Ltd


May 2020

SAPROLITE PTY LTD (ACN 135 590 724) PO Box 2234 Ellenbrook WA 6069 52B Mornington Parkway Ellenbrook WA 6069 Ph: +61 8 6296 7760 www.saprolite.com.au Fax: +61 8 6296 7762 [email protected]

Copies of Final Reports to: MMO Environment (e-copy)

11 May 2020 Hydrogeological Assessment – In-pit Tailings Disposal into 17 Series Pits


SAPROLITE ENVIRONMENTAL

TABLE OF CONTENTS

1. INTRODUCTION 1

2. OBJECTIVES AND SCOPE OF WORK 3

3. CLIMATE 4

4. GEOLOGY AND HYDROGEOLOGY 5

4.1 Regional Geology 5 4.2 Murrin Murrin North Geology 5 4.3 Murrin Murrin North Hydrology 6 4.4 Murrin Murrin North Hydrogeology 6 4.5 17 Series Pits 7

4.5.1 Lithological Overview 7

4.5.2 Structural Features 8 4.5.3 Hydrogeology 8

5. GROUNDWATER MONITORING 10

5.1 In-pit TSF MM8/5-9/4 10 5.2 In-pit TSF MM8/4 11 5.3 In-pit TSF MM18/6 11 5.4 Summary 12

6. SEEPAGE ANALYSIS 13

7. DISCUSSION 16

7.1 Groundwater Impacts 17

8. RECOMMENDATIONS 18

8.1 Pre-Construction of the In-pit TSFs 18 8.2 Operation of the In-pit TSFs 19

9. REFERENCES 20

LIST OF TABLES, CHARTS, FIGURES, PLATES AND APPENDICES

TABLES

Table 1.1 MMO – Distribution of Tailings Discharge - 2019 ..................................................................... 1 Table 3.1 Annual Rainfall (mm) 2010-2019 ............................................................................................... 4 Table 4.1 Estimated Hydraulic Properties of the Weathering Profile ....................................................... 7

CHARTS

Chart 1 Annual Water Level Change In-pit TSF MM8/5-9/4 .............................................................. 13 Chart 2 Annual Water Level Change In-pit TSF MM2/3 ..................................................................... 15




PLATES

Plate 1 NW-SE striking fault MM17/2..................................................................................................... 8

FIGURES

Figure 1 Regional Location Plan .............................................................................................. L0100-776 Figure 2 Murrin Murrin Project Area ......................................................................................... L0100-994 Figure 3 Proposed In-Pit Tailings Disposal 17 Series Pits...................................................... L0100-992

APPENDICES

Appendix A Glossary Appendix B Bore Hydrographs

DOCUMENT REVISION HISTORY

Revision Number

Status Revision Date

Revision Comments Primary Author

Reviewer Approved

A Draft 08/04/2020 Issued for internal review R.Hollis G. Richards - A Draft 14/04/2020 Draft issued for client review R.Hollis T.B/L.V. G. Richards B Draft 29/04/2020 Addressed client comments G. Richards T.B/L.V. G. Richards C Draft 05/05/2020 Amendment to Table 1.1 G. Richards T.B/L.V. G. Richards C Final 11/05/2020 Report Issued as Final G. Richards - G. Richards

STATEMENT OF LIMITATIONS

Aquifer materials and groundwater flow systems are a product of continuing natural and man- made processes and thus exh bit a variety of characteristics and properties that vary from place to place and can change with time. Geology/hydrogeology involves gathering and assimilating limited facts about these characteristics and properties in order to understand and predict the behaviour of the ground on a particular site under certain conditions. This report may contain such facts obtained by inspection, drilling, excavation, probing, sampling, testing or other means of investigation, particularly pumping and drawdown data. If so, they are directly relevant only to the groundwater system at the place where, and the time when the investigation was carried out. Any groundwater modelling predictions presented should not be regarded as matters of fact.

This report and other reports referred to contain comments on works being carried out by others. Saprolite Environmental cannot and will not take respons bility for works carried out by others on site to date. We do not guarantee the performance of the project in any respect, only that our work and judgement meet the standard of care of our profession at this time.

Any interpretation or recommendation given in this report shall be understood to be based on judgement and experience, not on greater knowledge of facts other than those reported. The interpretation and recommendations are therefore opinions provided for the Client's sole use in accordance with a specific brief. As such they do not necessarily address all aspects of the groundwater system on the subject site.

© Saprolite Pty Ltd, 2020.

This document may not be reproduced in part or whole by electronic, mechanical or chemical means, including photocopying, recording or any information storage system, without the express approval of Saprolite Pty Ltd and/or Murrin Murrin Operations Pty Ltd. Neither this document nor its contents may be referred to or quoted in any manner, report or other document without the express approval of Saprolite Pty Ltd and/or Murrin Murrin Operations Pty Ltd.

Additional copies and or enquiries about this document should be addressed to The Principal, Saprolite Environmental, PO Box 2234 Ellenbrook, WA, 6069 or by email to [email protected]



SAPROLITE ENVIRONMENTAL 1

1. INTRODUCTION

The Murrin Murrin Nickel Cobalt Project (Murrin Murrin) is located approximately 60km east of Leonora, 220km north of Kalgoorlie, and 680km north east of Perth, Western Australia, Figures 1 and 2. Murrin Murrin is operated by Murrin Murrin Operations Pty Ltd (MMO); a wholly owned subsidiary of Minara Resources Pty Ltd. Minara Resources Pty Ltd is a 100% subsidiary of Glencore plc.

MMO are proposing to utilise additional mined-out pits (pit voids) in the Murrin Murrin North (MMN) mining area to supplement the existing tailings storage capacity. Saprolite Environmental (Saprolite) was engaged by MMO to undertake a desktop hydrogeological assessment for proposed in-pit Tailings Storage Facilities (TSFs) utilising 17 series pit voids. This hydrogeological assessment is written based on existing information; notably historical monitoring data from active and adjacent in-pit TSFs, and detailed geological architecture reports.

The 17 series pits are a chain of open pits west of existing in-pit TSF facilities and comprises pits MM17/1, MM17/2, MM17/53, MM17/6, MM17/7, MM17/8 and MM17/9. All pits will form a continuous pit void on the completion of mining.

Tailings storage at MMO currently comprises two paddock style TSFs (TSF1 and TSF2) and eight in-pit TSFs (MM2/2-2/4, MM2/3, MM8/4, MM9/2, MM8/5-9/4, MM9/5, MM18/3 and MM18/6):

TSF1 is full and has been inactive for over 10 years, whilst TSF2 has limited remaining capacity and is used for water transfer from in-pit TSFs to evaporation ponds.

MM2/3 is effectively full and tailings have not been deposited to the facility since June 2014.

MM8/4 and MM8/5-9/4 effectively full. MM2/2-2/4 and MM9/2 are only used for emergencies. MM9/5, MM18/3 and MM18/6 are all active

In 2019 MMO produced approximately 4.15Mt of tailings discharge, which was distributed as per Table 1.1.

Table 1.1 MMO – Distribution of Tailings Discharge - 2019

Facility Evap Ponds MM2/2-2/4 MM9/2 MM18/6 MM18/3 MM9/5 Total

Discharge (Mt) 0.04 0.09 0.00 0.77 1.28 1.96 4.15

% of total discharge 1% 2% 0% 19% 31% 47% 100%

The remaining storage capacities of existing tailing storage facilities at MMO are estimated in the 2018 Tailings Storage Audit and Management Review (Coffey, 2019). The total remaining storage capacity of existing facilities is approximately 12.90Mt. Given an estimated 4.27Mt and 4.15Mt of neutralised dry tailings was produced in 2018 (Coffey, 2019), and in 2019 respectively, current facilities have a storage life of approximately 1 year.




The Office of the Environmental Protection Authority (EPA) has assessed existing and future completed pits for tailings deposition within the mining area and recommended as “Not Assessed – Managed under Part V (Works Approval)”. The EPA, the Department of Mines, Industry Regulation and Safety (DMIRS) and the Department of Water and Environmental Regulation (DWER) are favourable to the in-pit TSF approach. The numerous environmental benefits of using existing pit voids for tailings storage are described as follows:

Utilising the existing ‘footprint’ of the operations, rather than extending laterally through establishment of additional above ground paddock-style storage facilities.

There is no requirement for additional land clearing, and little requirement for earthwork preparation in comparison to paddock-style facilities.

Seepage migration from paddock-style facilities may occur near the ground surface, which has implications for vegetation health. Potential seepage migration from pit voids is more likely to occur at depth, beyond the root zone.

The deposition of tailings effectively reduces the void area allowing for backfill and rehabilitation above the consolidated tailings surface. Without this process pits are unlikely to be backfilled and rehabilitated.

Rehabilitated paddock style facilities create an elevated landform, making them highly visible and providing the potential for erosion.

There are also several economic benefits of using existing pits voids for tailings disposal, including a significantly lower capital requirement than what is required for the establishment of above ground facilities, and proximity to existing in-pit TSF infrastructure. A glossary of terms and units is presented as Appendix A.




2. OBJECTIVES AND SCOPE OF WORK

The primary objective of this hydrogeological assessment is to evaluate the potential impacts on the groundwater environment from tailings disposal into completed 17 series pits.

The scope of work includes the following:

Assessment and discussion of the groundwater environment at the 17 series pits (based on available information).

Analytical &/or simple numerical model to examine the potential mounding/seepage from proposed pits.

Comparison with findings from previous hydrogeological investigations and performance of existing in-pit facilities.

Discussion of potential implications of tailings disposal into the 17 series pits.

Nominal locations and specifications for monitor bore drilling (specific details provided separately to this document).




3. CLIMATE

The climate of the Laverton-Leonora area is warm and semi-arid, with irregular rainfall. Weather stations are located at Laverton, Leinster Aerodrome and Murrin Murrin with varying degrees of continuity as listed.

The Weather Station at Laverton was opened in 1899, and other than sporadic readings from 1969 to 1978, has been in continuous operation.

The Leinster Aerodrome Weather Station was opened in December 1994, and with the exception of a period between February and July 2015, has been in continuous operation.

Rainfall data has been collected at Murrin Murrin since mid-1999. With the exception of a period between July 2009 and December 2011, the station has been in continuous operation.

Annual rainfall totals for the past ten years are presented in Table 3.1. Annual mean and median statistics for historical rainfall data are also presented. Annual rainfall totals are comparable across the three stations, and show significant variation year to year which is attributable to the variable nature of short duration high intensity rainfall events that result from cyclonic depressions. Rainfall occurs predominantly in the early parts of the year (January to May) as a result of the incursion of tropical maritime air masses from the north or due to the influence of cyclonic depressions that move inland off the coast. Rainfall during the winter months is usually the result of low pressure systems.

Total rainfall recorded during the 2019 calendar year was significantly lower than the mean and median annual rainfall for respective stations.

Table 3.1 Annual Rainfall (mm) 2010 to 2019

Location 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 Annual Mean

Annual Median

Murrin Murrin NA* NA* 286 235 345 251 317 342 233 78 259 251

Laverton (012045) 221 512 273 245 319 253 352 492 336 67 236 219

Leinster Aerodrome

(012314) 258 282 239 207 284 63# 283 390 228 140 259 243

Data for Laverton and Leinster Aerodrome courtesy of Bureau of meteorology. #Rainfall data not available for March to June 2015 *Not available from July 2009 to December 2011 due to unreliability Note: Mean and median statistics presented for periods 2000-2019 for Murrin Murrin, 1899-2019 for Laverton Station and

1898-2019 for Leonora station and exclude periods where data is not available.




4. GEOLOGY AND HYDROGEOLOGY

The following sections present a summary of the geological and hydrogeological setting of the Murrin Murrin North mining area. Information has been sourced from published papers and from the Geological Architecture Report for MMN 17 Series Pits (Addison and Temu, 2020).

4.1 Regional Geology

The Ni-Co ore deposits of the MMN project area are positioned over serpentinised peridotite komatiitic lava flows (Hill et al, 1990) which occur low in the stratigraphy within a sequence of felsic volcaniclastics, clastic sediments, mafic volcanics and related intrusives in the upper parts of the stratigraphic sequence (Monti and Fazakerley, 1996). The serpentinised peridotite protolith has been folded and faulted around the Kilkenny Syncline (Markwell, 1999). The sequence forms a corridor constrained by major NNE trending, westerly dipping faults. These faults are splays off the major NW trending Keith-Kilkenny tectonic zone to the SW (Monti and Fazakerley, 1996). Gradual oxidation and leaching of the ultramafic protolith has produced a regolith with sub-horizontal layers which hosts the ore deposits (Camuti and Riel, 1996).

4.2 Murrin Murrin North Geology

The generalised geological and lateritic weathering profile at Murrin Murrin can be broadly divided into five major units. The lithology was described in the 2009 Geological Architecture Report for Murrin Murrin North (Douglas, 2009) and is reproduced below:

1. The ultramafic basal unit is a slightly weathered locally silicified unit (Fazakerley and Monti, 1998). It is a serpentinised medium to coarse grained olivine cumulate which originated as extruded komatiite flows (Markwell, 1999).

2. The saprolitic zone has retained the primary rock texture of the ultramafic bedrock beneath. Its composition is largely serpentine with accessory chlorite, magnesite, silica and smectite (Wells, 2003; Fazakerley and Monti, 1998).

3. The Smectite Zone (SZ) is the dominate nickel bearing zone (Gaudin et al, 2005). It varies in colour and texture from waxy apple green to black/dark brown to a granular yellow brown composition depending on the content of Fe and Mn oxides. There is a gradational boundary between the SZ and Ferruginous zones (FZ), known as the Ferruginous Smectite Zone.

4. Ferruginous Zone (FZ) is fine to coarse grained and iron rich. Typically red/brown in colour with hard brown/black nodules within. The majority of nodules are goethite with hematite and maghemite increasing in proportion towards the surface (Anand, 1998).

5. The upper most units of colluvium/plastic clays are distinctive by its mottled white/pink/red texture. It is often up to 20m thick and commonly shares a sharp lithological boundary with the FZ underneath.




4.3 Murrin Murrin North Hydrology

The Murrin Murrin operations area is situated in a region of low relief, a consequence of extensive alluvial and colluvial materials which have blanketed areas to the northwest, southwest and east-southeast of the Murrin Murrin Ni laterite deposits (Wells, 2003). These alluvial sediments form part of an extensive NW orientated paleodrainage, bounded by the Carey Lake system and the Raeside Lake system to the NE and SW respectively (Golder Associates, 2004). The Murrin Murrin deposits straddle the drainage divide between these lake systems, Figure 2.

The MMN study area is dissected by a major drainage divide (ridge) between the Cement Creek and Katata Creek Catchments. The 17 series pits are located on the eastern margin of the Katata Creek Catchment. The Katata Creek Catchment drains in a south westerly direction via an extensive dendritic drainage pattern, towards the Raeside Lake system.

4.4 Murrin Murrin North Hydrogeology

The laterite profile above the Archean greenstone belt is typically the derivation of preferential weathering with respect to the resistant nature of their parent host rock. Rocks that weather preferentially (i.e. ultramafic rocks compared to mafics and felsics) and faster are more susceptible to hosting groundwater, which then promotes weathering compared to rocks that are resistant and with shallower profiles. The deep weathering in the greenstones is further enhanced by near vertical bedding, intense shearing and variation in competence of contiguous rock units (Johnson et al, 1999). Granitoids typically have greater mineralogical and structural homogeneity resulting in shallower depths of weathering (Johnson et al, 1999). Mining across the study area is primarily contained within the weathered profile of the ultramafic protolith; it is expected that the weathering front exists slightly beyond the mined depth.

In the weathering profile, complex chemical processes have led to the removal of large quantities of soluble material, some of which, such as silica, iron, calcium carbonate and calcium sulphate have been re-deposited elsewhere. These processes have produced layers of widely differing permeability and storage within the weathering profile, so that the groundwater to some degree has shaped the nature and thickness of the ‘aquifer’ in which it occurs (Johnson et al, 1999).

The ultramafic basal unit is interpreted to have relatively low hydraulic conductivity at depth, which increases markedly near the weathering front as fracturing increases towards the overlying saprolite unit. This more fractured ultramafic rock is anticipated to be hydraulically conductive; however, it typically exists below the base of respective pits, which are typically constrained within the weathering profile of the ultramafic protolith.

In the MMN project area the saprolite zone retains much of the structure of the underlying and unweathered ultramafic bedrock, including significant areas of shearing and jointing. Structural features are likely to act as permeability pathways; however, significant alteration during the formation of the saprolite zone has resulted in the abundance of magnesite and smectite clays, which, in combination with remobilised silica, are anticipated to suture these migratory zones to some degree.

The overlying smectite zone is comprised of dense clay in which most rock structures and textures have been obliterated. This zone is interpreted to have the lowest hydraulic conductivity of the five major units of the weathering profile.




The lateritic profiles of ultramafic rocks tend to be very ferruginous towards the surface (Brand et al, 1998), which is a product of laterisation under high water tables (during a more humid period in the Miocene-Pliocene) and leaching under progressively lower water tables (during a post-Miocene change to an increasingly arid climate). The lateritic zone is coarse grained with clay horizons and dispersed hematite nodules and has developed deep in the profile in some areas due to fluid migration along shear zones during the formation of the profile. The laterite profile is interpreted to be relatively transmissive compared to the underlying smectite and saprolite units.

The hydraulic properties of the various lithological units were approximated in 2004 (Golder Associates, 2004). Results were derived from constant head and falling head tests undertaken at monitoring bores near pit MM2/3. The results are replicated in Table 4.1 and show the laterite and fractured ultramafic units to be relatively conductive compared to the saprolite and smectite units.

Table 4.1

Estimated Hydraulic Properties of the Weathering Profile

Geological Horizon Horizontal Hydraulic Conductivity (m/s)

Horizontal Hydraulic Conductivity (m/d) Porosity (%)

Ferruginous 1 x 10-6 8.64 x 10-2 5 Smectite 1 x 10-8 8.64 x 10-4 40 Saprolite 2 x 10-8 1.73 x 10-3 20

Fractured Ultramafic 1 x 10-6 8.64 x 10-2 5 Bedrock 1 x 10-9 8.64 x 10-5 1

In the MMN mining area ultramafic regolith profiles are commonly bound by weathered felsic and mafic volcanic intrusive rock. The contacts of these units are structural control zones of increased fluid flow, and can result in the formation of deeper weathering profiles. Furthermore, the contacts of these units can be heavily foliated and fractured, and potentially provide preferential pathways for seepage migration where contacts intersect pit surfaces.

4.5 17 Series Pits

The 17 series pits are located on the west of the MMN project area, with mining commencing in MM17/1 in 2007. The mining of the 17 series of pits is expected to be completed in January 2021. Interpretations presented in the Geological Architecture Report (Addison and Temu, 2020) were based on geological and structural mapping within the mined out sections, and computerised geological modelling for areas yet to be mined.

4.5.1 Lithological Overview

The 17 series pits are situated on the northern limb of the Kilkenny Syncline. The weathering profile generally conforms to the basic laterite sequence for the MMN mining area (detailed in Section 4.3).

The bases of the pits are predominantly bound by saprolite. The saprolite unit is high in magnesium (12 to 13%) and silica (20%) and makes up 30% of the pit walls and floor by surface area exposure.




The saprolite is overlain by a clay rich ore zone which is characterised by a package of inter fingered transitional units including soft, finer-grained clay and nickel rich saprolite, waxy textured smectitic clays and ferruginous smectite material. This zone encompasses approximately 55% of the pit walls and floor, with average magnesium and silica grades of 6% and 22% respectively.

Above the ore zone is the Ferruginous Zone; a typically coarse grained, iron rich, red/brown highly oxidised clay horizon with dispersed hematite nodules. The thickness of the Ferruginous Zone is interpreted to range from a few metres to over 30m in areas. The ferruginous zone exposed in the eastern half of MM17/53 is well developed.

Plastic clays overly the Ferruginous Zone and comprise the uppermost unit in the weathering profile. They have low nickel, high aluminium and are characterised by reduced iron content and a mottled texture.

4.5.2 Structural Features

The most significant structural feature observed in the 17 deposit is a major NW to SE striking fault zone that cuts across the southern end of the 17/2 pit. The zone has been exposed by mining and the fault structures are clearly visible in the walls

Plate 1 NW-SE striking fault MM17/2

Reproduced from Geological Architecture Report (Addison and Temu, 2020)

4.5.3 Hydrogeology

The geology and weathering profile encountered at the 17 series pits generally conforms to the basic laterite sequence for the MMN mining area (detailed in Section 4.3). As such hydrogeological interpretations, presented in Section 4.4, for the greater MMN project area are largely valid.

Mining at the 17 series pits is planned to be largely confined within the weathering profile. As such mining is not expected to extend below the saprolite unit into fractured ultramafic rock, which may be more hydraulically conductive. Although the saprolite unit retains much of the structure of the underlying fractured ultramafic bedrock, the unit is highly siliceous (averaging 22% silica) and remobilised silica is anticipated to suture potential migratory zones to some degree. The estimated hydraulic conductivity of the saprolite unit is 2x10-8m/s, Table 4.1.




The Smectite Zone is the dominant lithological unit at the 17 series pits and is estimated to cover approximately 55% of the pit walls and floor (Addison and Temu, 2020). This zone is interpreted to have low hydraulic conductivity (approximately 1x10-8m/s, Table 4.1) and should impede seepage movement from the facility.

The only major structural feature is at the south end of MM17/2, a north-west to south-east striking fault zone. The fault zone is the most likely pathway for potential seepage migration and should be monitored during tailings deposition.

A small volume of water is present at the bottom of MM17/53 which is planned to be the deepest part of the 17 series pits at 410mAHD. The maximum planned depth at the other 17 series pits is 416mAHD which is approximately 10m to 20m below the interpreted groundwater level. The interpreted groundwater level is however based on monitoring bores located next to current in-pit tailings facilities as there are no monitoring bores in the immediate vicinity of the 17 series pits. Ongoing tailings deposition will result in groundwater mounding, which may result in preferential tailings migration through shallower ferruginous units. Monitoring bores should provide an adequate means of identifying any groundwater changes.




5. GROUNDWATER MONITORING

Considerable monitoring data has been collected from monitoring bores adjacent to existing in-pit TSFs, including: water chemistry laboratory analysis and water level measurements. The performance of existing facilities is considered to be fundamental to this hydrogeological assessment, especially considering proximity to proposed sites and similarities in lithology and geological structure. The proposed 17 series in-pit TSFs are situated directly west of existing in-pit TSFs MM8/5-9/4, MM8/4 and MM18/6, Figure 2.

The following sections provide a summary of historical monitoring data collected at the nearest in-pit TSFs, MM8/5-9/4, MM8/4 and MM18/6. Monitoring data is charted on bore hydrographs, Appendix B1-B3.

5.1 In-pit TSF MM8/5-9/4

MM8/5-9/4 was commissioned as an in-pit TSF in November 2010 and was established to allow deposition cycling with other storages, notably MM2/3 which was rapidly being filled (AWA, 2011). In September 2009, prior to tailings deposition at the site, six monitoring bores were drilled around the perimeter of pits MM8/5 and MM9/4. Drilling observations indicated potentially low hydraulic conductivity, with no groundwater discharge observed during drilling and only minor moisture (groundwater seepage) in samples at some sites. Subsequent falling head permeability testing confirmed low hydraulic conductivity at the majority of sites, with results typical of semi-impervious rock types or weathered bedrock (Saprolite, 2009). Higher relative hydraulic conductivity was however recorded at monitoring bore IP805-2 (Saprolite, 2009).

Water levels have been recorded quarterly at MM8/5-9/4 in-pit monitoring bores since they were constructed and are charted as Appendix B1. The chart illustrates consistent water level rises at most sites between November 2010 and mid-2012 consistent with the initial stages of tailings deposition. IP904-3 is somewhat of an exception and shows a large spike in water level between February 2011 and March 2011 which is consistent with high February 2011 rainfall. Beyond mid-2012 water levels have been relatively stable at the majority of sites, except for IP904-3, where water levels have fluctuated and appear to be affected by rainfall and IP805-1, which had a longer rising trend that appears to have stabilised at 450mAHD since mid-2016, Appendix B1.

Sampling and water chemistry analysis has been undertaken quarterly at in-pit monitoring bores since they were constructed. Laboratory TDS and pH results are presented on Appendix B1. The chart illustrates highly variable TDS concentrations at IP805-2 and IP805-3 with a general increasing trend, while IP805-1 and IP904-2 have more stable rising trends that plateaued in 2019. TDS concentration in IP904-3 does not appear to have been influenced by tailings deposition, while TDS at IP904-1 has only just begun to rise. IP904-3 and IP904-1 are situated NW and NE of MM8/5-9/4, respectively. There appears to have been a progressive divergence of pH at bores around MM8/5-9/4 with initial pH values clustered around pH 8 and diverging to be between pH 6 and pH 8 as of November 2019. As with EC, IP805-3 shows the greatest variability in pH. Although showing the same trends as the other bores, IP904-3 has, as of November 2019, changed the least from the initial measurement.




5.2 In-pit TSF MM8/4

In-pit TSF MM8/4 is situated south and adjacent to in-pit TSF MM8/5-9/4. Tailings deposition commenced at MM8/4 in August 2014 and ceased in January 2018.. Monitoring bores IP804-1 and IP804-2 were drilled in June 2010 as downstream seepage indication bores for in-pit TSF MM8/5-9/4. One additional bore was drilled in May 2014 (IP804-3) prior to tailings deposition at in-pit TSF MM8/4, and was positioned to the south of the pit. A falling head permeability test was undertaken at IP804-3, although the results could not be accurately analysed, the hydraulic conductivity at this site is inferred to be relatively high (Saprolite, 2013).

Water levels have been recorded at IP804-1 and IP804-2 on a quarterly basis since the bores were constructed in June 2010. Similarly, water levels have been recorded at IP804-3 on a quarterly basis since the bore was constructed in May 2014. Water levels recorded at IP804-1 and IP804-2 rose during 2011 and early 2012, presumably as a response to tailings deposition upstream at in-pit TSF MM8/5-9/4, Appendix B2. Between mid-2012 and late 2014 water levels were relatively stable at these monitoring locations. Water levels rose at IP804-1 and IP804-3 in November 2014, which is in line with the commencement of tailings deposition at in-pit TSF MM8/4 however water levels have remained relatively stable since, Appendix B2.

Sampling for laboratory analysis has been undertaken quarterly at in-pit monitoring bores since they were constructed. Laboratory TDS and pH results are presented on Appendix B2. The chart illustrates a small initial increasing trend at IP804-1 followed by greater variability and a slightly steeper rise since 2014. IP804-2 had an increase in TDS concentration between February 2012 and November 2014 and a subsequent plateau and decline from mid-2016. IP804-3 has shown a generally increasing trend but with large rises and falls between measurements. Laboratory pH measurements show a slight decline in all three bores from 2015 in line with tailing deposition at MM8/4. However, IP804-2 has shown an increase in stability of pH since 2017, distinct from its previous variability and the variability observed in the other two bores, Appendix B2.

5.3 In-pit TSF MM18/6

In-pit TSF MM18/6 is situated north and adjacent to in-pit TSF MM8/5-9/4. Tailings deposition commenced at MM18/6 in March 2018. Monitoring bores IP1806-1 and IP1806-2 were drilled in April 2017 to the east and west of MM18/6 respectively while SP30, SP31 and SP32 were drilled on a land bridge between pits MM9/5 and MM18/6. Falling head permeability tests undertaken at IP1806-1 and IP1806-2 in 2017, indicated moderate conductivity between 3.33x10-2m/d and 6.41x10-2m/d. The transmissive zones were however interpreted to be relatively deep and somewhat confined by the overlaying clays (Saprolite, 2017).

Water levels have been recorded at IP1806-1, IP1806-2, SP30, SP31 and SP32 on a quarterly basis since the bores were constructed in April 2017. Water levels recorded at all five bores have risen since the beginning of tailings deposition, Appendix B3. Bores SP30, SP31 and SP32 are located on a narrow land bridge between In-pit TSFs MM9/5 and MM18/6 and would be expected to rise to match the level of tailings while the TSFs are active.




Sampling for laboratory analysis has been undertaken quarterly at in-pit monitoring bores since they were constructed. Laboratory TDS and pH results are presented on Appendix B3. The chart illustrates stable TDS at IP1806-2 and variable TDS at IP1806-1. During initial construction IP1806-1 was noted to have a halocline at approximately 41mbgl and this could account for some of the variability in measurements between quarters. Laboratory pH has remained relatively stable with a slight declining trend. As with TDS, IP1806-1 shows more variability than IP1806-3 and this could be a result of stratified groundwater with two different water types, Appendix B2.

5.4 Summary

Hydrogeological investigations have indicated low to moderate hydraulic conductivities at the majority of in-pit monitoring sites (surrounding in-pit TSFs MM8/5-9/4 MM8/4 and MM18/6). This is typical of lithologies which are dominated by thick units of highly weathered saprolite and clays. However, comparatively high hydraulic conductivity at discrete sites (e.g. IP805-2 and IP804-3) indicates the prevalence of anisotropic groundwater movement through the heterogeneous weathering profile. Increases in salinity are inferred to be a result of seepage migration through discrete pathways of higher hydraulic conductivity.

Groundwater with pH between 6 and 8.5 has been sampled at most monitoring sites (with the exception of IP904-3). Water chemistry laboratory analysis has indicated high concentrations of dissolved magnesium at a number of sites within the MM8/5-9/4 and MM8/4 project areas. It is expected that the prevalence of magnesium carbonate within the weathering profile is providing buffering capacity for acidity, mitigating significant falls in pH.

More acidic pH has been recorded at IP805-3, IP804-2 and IP804-3 on the eastern side of the existing line of in-pit TSFs. The 17 Series Pits lie to the west where pH is generally neutral to slightly alkaline.




Chart 1 shows a large positive change in water levels occurred between November 2010 and November 2011 coincident with the beginning of tailings deposition in MM8/5-9/4. The positive changes continue in a diminishing fashion until the period between November 2015 and November 2016 where a negative water level change is recorded. This coincides with a pause in tailings deposition in 2016.

After the first year of tailings deposition (2011) the groundwater level at monitoring points around MM8/5-9/4 had risen approximately 6m not including IP904-3 which has shown much more water level variability between readings than the other bores, Appendix B1. As of November 2019, water levels in the monitoring bores are more than 10m below ground level (ground level is approximately 467mAHD) this includes peaks of the highly variable IP904-3. The shallowest water level is at IP805-1 which has been stable since 2016.

The variability in water levels at IP904-3 is possibly linked to rainfall as there has been no substantial change in pH or TDS that would indicate direct seepage from MM8/5-9/4, Appendix B1.

Comparing pH, TDS and water levels on Appendix B1 the bores that appear to experience the slowest rate of influence from MM8/5-9/4 are IP904-1, IP904-3 and IP805-1 which are to the north and west of the proposed 17 series in-pit TSF.

Analytical modelling conducted in 2009 estimated mounding of 19.65m at 200m from the centreline of the pit after 4 years of deposition (Saprolite, 2009). Current monitoring results put IP805-2, IP805-3, IP904-2 and IP904-3 at similar or lower levels than predicted. IP805-1 had a water level similar to the original analytical model’s 4-year prediction in 2013. The water level at IP805-1 is a further 10m above this level as of December 2019 however there has only been a 0.86m change in the last 5 years.

In-Pit TSF MM2/3 Groundwater monitoring data has been collected at monitoring bores around in-pit TSF MM2/3 since November 2004, four years before the commencement of tailings deposition in December 2008 (Saprolite, 2009a). Changes in water level heights (at one year intervals) from 2004 are presented on Chart 2.




7. DISCUSSION

Review of available information was undertaken for proposed tailings disposal into 17 series pit voids. With the combination of: experience with the hydrogeology of weathering profiles within the NE Goldfields, case-study evidence and other supportive work undertaken at existing in-pit TSFs; there is sufficient information to suggest the following:

The weathering profile comprises layers of widely differing permeability and storage. Complex chemical processes have led to the removal of large quantities of soluble material, some of which, such as silica, iron, magnesium carbonate and calcium carbonate have been re-deposited elsewhere.

Structural features (e.g. faults, shears, contact zones, joints) that intersect the pits may act as preferential pathways for seepage migration.

Ferruginous units have developed to greater depths along structural control zones and may act as preferential pathways for tailings water seepage. The geological architecture report identified one fault that could provide a conduit for fluid migration enhancing chemical mobilisation and leaching processes within the wall of the 17 series pits.

Infill by impermeable and resistant silica is likely to suture migratory/leaching zones to some degree. Structural features, such as faults, shear zones, contacts and joints are likely to have been preferentially filled by silica deposition.

Water levels may be rapidly affected at proposed in-pit TSF monitoring sites, particularly during early stages of deposition. Groundwater monitoring data at existing in-pit TSFs has indicated steadily rising water levels at the majority of in-pit monitoring bores, in line with tailings deposition at respective in-pit TSFs.

Increases in salinity are possible at discrete sites due to seepage migration through pathways of higher hydraulic conductivity. Groundwater monitoring data at existing in-pit TSFs has indicated increases in concentrations at several sites, notably those with proportionately higher hydraulic conductivity.

The prevalence of magnesium carbonate within the weathering profile is likely to provide some degree of mitigation for falls in pH, in the event that acidic groundwater migrates from proposed facilities.

There is potential for groundwater flow paths to be established should water levels return to or rise above their pre-mining elevation as a result of natural groundwater inflow or from tailings deposition within the pits. Should groundwater mounding occur the effect on local vegetation can be mitigated by adopting a suitable freeboard at or below the bottom of the root zone.




7.1 Groundwater Impacts

Whilst groundwater mounding is likely to occur and groundwater quality may deteriorate at discrete sites, the risks of the proposed in-pit TSF to the environment are considered to be low, especially compared with paddock style facilities. The risk of impacts of the proposed 17 series in-pit TSF are expected to be low given the following:

New facilities allow for continued rotational deposition as older facilities fill up. Rotational deposition permits periods of rest, where deposition into a particular TSF is paused, allowing for tailings to desiccate and seepage to be reduced.

Hydrogeological investigations for existing in-pit TSFs have indicated relatively low hydraulic conductivity across the MMN project area, with potential for groundwater movement along discrete seepage pathways associated with structural features. This movement is anticipated to be restricted to discrete hydraulic pathways within the footprint of the mining area.

Groundwater levels are already somewhat depressed due to mining and water harvesting activities. Groundwater mounding is unlikely to occur to an extent where it can negatively affect vegetation provided an adequate freeboard is maintained.

After deposition ceases it is expected that seepage from the proposed in-pit TSF would diminish over time as tailings consolidates, forming a hydraulic barrier.

The climate is extremely dry, therefore once completed the tailings are predicted to desiccate, reducing the likelihood of seepage after closure, even after prolonged heavy rainfall (Department of Industry, Tourism and Resources, 2007).




8. RECOMMENDATIONS

8.1 Pre-Construction of the In-pit TSFs

The following nominal works program is recommended at the proposed 17 Series in-pit TSF site:

Monitoring Bores

Seepage monitoring bores should be installed around the perimeter of proposed in-pit TSF. The monitoring bores should be of a diameter such that they can be equipped as recovery bores if required, and should be drilled to fully penetrate to the same depth as the 17 Series Pits, nominally 60m. Bores should be sited in locations where potential structural/chemical pathways may prevail such as the NW-SE striking fault that cuts across the southern end of MM17/2.

Baseline Testing

Baseline testing should be conducted at monitoring bores prior to deposition of tailings into the proposed 17 Series in-pit TSF. Baseline testing should include:

Field measurements of groundwater pH and EC during drilling and upon completion of bore construction.

EC profiling pre and post airlifting of constructed monitoring bores.

Groundwater sampling for laboratory chemical analysis upon completion.

Falling head and/or constant head permeability tests.

It is recommended that at least two quarterly monitoring events are completed prior to the commencement of tailings deposition to allow for sufficient time series baseline data to be collected. Monitoring events should include field measurements of pH and EC, water level measurements and laboratory analysis for select analytes.




8.2 Operation of the In-pit TSFs

Much of the recommended operation of the proposed in-pit TSF is expected to be prepared by others; however, we submit the following for consideration:

Routine groundwater monitoring should include water levels, water sampling and laboratory analyses. Groundwater monitoring of new in-pit TSF bores should be incorporated into MMO’s existing water monitoring schedule. The groundwater sampling should be conducted quarterly and in accordance with AS/NZS5667, with groundwater samples sent to a NATA accredited laboratory for analysis.

The bores should be included in MMO’s Sampling Measurement and Analyses Plans (SMAPs) for the MMO Waste Facilities that includes TSF/EP and Landfill. The SMAPs detail the site specific monitoring requirements, and are prepared in accordance with AS/NZS 5667.

Groundwater from the proposed in-pit TSF should be abstracted such that the pits are almost entirely dewatered prior to tailings deposition.

Tailings Deposition – tailings should be deposited via appropriately placed spigot(s) to ensure a suitable beaching angle. Management of the deposition will enable better control of the decant pond formation, with suitable freeboard of 500mm between the pond level and the lowest elevation of the edge of the decant pond.

Supernatant Pond is to be managed through decant recovery to prevent the areal extent from becoming too great and to reduce the amount of seepage water available for release into the groundwater.

Should excessive groundwater mounding occur tailings deposition and water recovery should be managed to prevent the groundwater from rising high enough to affect vegetation.

Undertake a hydrogeological review and assessment of the monitoring data collected at 1 and 2 years after commencement of tailings disposal and then on completion. The reviews would examine the monitoring data and actual operation of the in-pit TSFs.




9. REFERENCES

Addison, D and Temu, D., 2020, Geological Architecture Report for the 17 Series of Pits– Murrin Murrin North, Potential Tailings Storage Facility, February 2020, unpublished internal report by Minara Resources Ltd.

Anand, R.R., 1998. Development of Lateritic Profiles: Cooperative Research Centre for Landscape Evolution and Mineral Exploration Report 74.

AWA, 2011, Annual Dam Safety Review and Operational Audit, December 2011, unpublished report for Minara Resources Ltd.

Brand, N.W., Butt, C.R.M., and M. Elias. 1998. Nickel Laterites: Classification and Features, AGSO Journal of Australian Geology and Geophysics 17(4), pp. 81-88.

Camuti, K.S., and Riel, R.G., 1996. Mineralogy of the Murrin Murrin nickel laterites, in Grimsey E.J., and Neuss I., eds., Nickel ’96, mineral to market: Australian institute of Mining and Metallurgy Special Publication 6/96 pp. 209-210.

Coffey Mining Pty Ltd, 2016, Geotechnical Assessment, In-pit Tailings Storage Facilities 9/5, 18/3, 18/6, July 2016, unpublished report for the Murrin Murrin Operations Pty Ltd.

Coffey Services Australia Pty Ltd, 2019, Murrin Murrin Operations Tailings Storage Audit and Management Review 2018, June 2019, unpublished report for the Murrin Murrin Operations Pty Ltd.

Department of Industry Tourism and Resources, 2007. Tailings Management – Leading Practice Sustainable Development Program for the Mining Industry

Douglas, R., 2009. Potential Tailings Storage Facility (TSF), Geological Architecture Report for Murrin Murrin North, July 2009, unpublished internal report by Minara Resources Ltd.

Elias M., 2006. Lateritic Nickel Mineralization of the Yilgarn Craton, Society of Economic Geologists, Special Publication 13, Chapter 7, pp. 195-210.

Fazakerley, V.W., and Monti, R., 1998. Murrin Murrin nickel-cobalt deposits, in Geology of Australian and Papua New Guinean Mineral Deposits. (The Australasian Institute of Mining and Metallurgy: Melbourne).

Gaudin, A., Decarreau, A., Noack, Y., and Grauby, O., 2005. Clay Mineralogy of the Nickel Laterite Ore Developed from Serpentinised Peridotites at Murrin Murrin, Western Australia: Australian Journal of Earth Sciences, 52:2, pp. 231-241.

Golder Associates Pty Ltd, 2004. Technical Support Documentation Notice of Intent Tailings Deposition into Pit 2/3, Murrin Murrin Nickel Cobalt Project, August 2004. Report No: 04641141-R01.

Hill, R.E.T., Barnes, S.J., Gole, M.J., and Dowling, S.E., 1990, Physical volcanology of komatiites – a field guide to the komatiites of the Norseman-Wiluna Greenstone Belt, Eastern Goldfields Province, Yilgarn Block, Western Australia: Perth, Geological Society of Australia.

Johnson, S.L., Commander, D.P., and O’boy, C.A. 1999. Groundwater Resources of the Northern Goldfields, Western Australia Water and Rivers Commission, Hydrogeological Record Series, Report HG2.

Markwell, T., 1999. TR 559 Murrin Murrin Project: Second Combined Annual Technical Report Number 308/1997 1st January 1998 - 31st December 1998 - Volumes 1 and 2.

Monti, R. and Fazakerley, V.W. 1996. The Murrin Murrin Nickel Cobalt Project. In: E.J .Grimsey and I. Neuss (Editors), Proceedings Nickel ‘96’, the Australian Institute of Mining and Metallurgy, Melbourne. Pp. 191-196.

Saprolite Environmental, 2009. Murrin Murrin North Mining Area Proposed In-Pit Tailings Disposal into Pit Void MM8/5 and MM9/4 Hydrogeological Study, November 2009, unpublished report for Murrin Murrin Operations Pty Ltd.

Saprolite Environmental, 2009a. Murrin Murrin North Mining Area, Strategic In-pit Tailings Disposal – Current and Future Pit Voids Hydrogeological Study, May 2009, unpublished report for Murrin Murrin Operations Pty Ltd.

Saprolite Environmental, 2013, Murrin Murrin North Mining Area, Proposed In-Pit Tailings Disposal into Pit Voids MM2/2_2/4, MM8/4 and MM9/2, Hydrogeological Assessment, December 2013, unpublished report for the Murrin Murrin Operations Pty Ltd.

Saprolite Environmental, 2016, Murrin Murrin North Mining Area, In-Pit Tailings Disposal Into Pit Voids MM9/5, MM18/3 & MM18/6, Hydrogeological Assessment, September 2016, unpublished report for the Murrin Murrin Operations Pty Ltd.

Saprolite Environmental, 2017, Murrin Murrin North Mining Area, In-Pit Tailings Disposal Into Pit Voids MM9/5, MM18/3 & MM18/6, Monitoring Bore Completion Report, July 2017, unpublished report for the Murrin Murrin Operations Pty Ltd.




Temu, D., 2016a, Geological Architecture Report for Pit 0905 – Murrin Murrin North, June 2016, unpublished internal report by Minara Resources Ltd.

Temu, D., 2016b, Geological Architecture Report for Pit 1803 – Murrin Murrin North, July 2016, unpublished internal report by Minara Resources Ltd.

Temu, D., 2016c, Geological Architecture Report for Pit 1806 – Murrin Murrin North, July 2016, unpublished internal report by Minara Resources Ltd.

Wells, M.A., 2003. Murrin Murrin Nickel Laterite Deposit, WA. Cooperative Research Centre for Landscape Evolution and Mineral Exploration.

Hydrogeological Assessment – In-pit Tailings Disposal into 17 Series Pits



FIGURES




APPENDIX A

GLOSSARY - Units & Terms




GLOSSARY

Units

Km Kilometre

Ha Hectare = 10,000m2

kL Kilolitre = 1m3

ML Megalitre = 1,000m3

GL Gigalitre = 1,000,000m3

MTPA Million Tonnes Per Annum

mg/L Milligrams per litre

Terms

Abstraction Pumping groundwater from an aquifer

Alluvium (alluvial) Detrital material transported by streams and rivers

Aquifer A geological formation or group of formations able to receive, store and transmit significant quantities of water

Basin A discrete Phanerozoic age (less than 545Ma) geological structure containing sedimentary and sometimes volcanic rocks and groundwater resources with porous, permeable formations

Bedrock General term for solid rock underlying unconsolidated materials

Bore Drilled small diameter well, usually lined with steel or plastic casing for the purpose of obtaining or monitoring groundwater

Brackish Water containing between 1,500 and 3,000 mg/L total dissolved solids (TDS), tasting slightly salty

Cavitation A phenomena of cavity formation, or formation and collapse, especially in regard to pumps, when the absolute pressure within the water reaches the vapour pressure causing the formation of vapour pockets

Colluvium (colluvial) Detrital material transported by gravity down slopes

Confined aquifer An aquifer located between upper and lower layers of low permeability

Dewatering Removal of free-draining water resulting in lowering the watertable and reduction of groundwater in storage

Drawdown The distance between the static water level and the surface of the cone of depression

Formation A lithological distinctive stratum or sequence of rocks deposited during a finite period and constituting a mappable unit

Fractured rock aquifer Crystalline rocks that yield economic supplies of groundwater from fractures or weathering profiles

Fresh Water containing less than 500mg/L TDS, and generally suitable for drinking

Groundwater Water occurring below the land surface in the saturated zone in pores and fissures, generally in motion and part of the hydrologic cycle

Hydraulic conductivity A measure of the rate at which water moves through a porous medium

Hydrogeology Science concerned with the study of groundwater occurrence and movement and its relation to the geological environment




Inferred A geological boundary or resource estimate that is based on experience, comparisons to geological relationships, and has not necessarily been ground truthed or verified from field investigations or drilling.

Karst A type of topography produced by solution and collapse of limestone formations

Leakage Vertical (and or horizontal) flow of groundwater from one aquifer to another, generally through a less permeable layer

Marginal quality Water containing between 500 and 1,500mg/L TDS, in the upper range of acceptability for drinking

Outcrop Portion of land surface occupied by a particular geological formation

Permeability A measure of the rate at which fluid or gas can move through a porous medium

Potentiometric surface The level to which water from a confined aquifer will rise

Recharge The water that infiltrates the watertable originating from rainfall and streamflow

Renewable resources The amount of groundwater that accrues each year from recharge

Saline Water containing more than 3,000mg/L TDS

Salinity A measure of the concentration of total dissolved solids (TDS)

Specific capacity The rate of discharge of a water well per unit of drawdown, commonly expressed in m3/day/m. It varies with duration of discharge

Specific yield The volume of water that an unconfined aquifer releases from storage per unit surface area of the aquifer per unit decline in the watertable

Storage coefficient The volume of water that a confined aquifer releases from storage per unit surface area of aquifer per unit decline in the potentiometric surface

Sustainable yield The amount of groundwater that may be abstracted from an aquifer in perpetuity without adverse impact

Transmissivity The rate at which water is transmitted through a unit width of an aquifer under a unit hydraulic gradient; in the International System, transmissivity is given in m3/day through a vertical section of an aquifer one meter wide and extending the full saturated height of an aquifer under a hydraulic gradient of 1.

Throughflow The process or amount of groundwater flowing through an aquifer

Unconfined aquifer An aquifer overlying a relatively impermeable layer which is saturated from the watertable (at atmospheric pressure) downwards and generally with free vertical infiltration of recharge from the surface

Weathering Process whereby surface rock materials are broken down and chemically altered by exposure and biological agents

Well A hole or dug excavation designed to facilitate the abstraction of groundwater (term also applied to drilled bores)

Wellfield (borefield) A group of wells or bores used together to provide a groundwater supply

Yield The amount of water that can practically be pumped from a well/bore or aquifer




APPENDIX B

BORE HYDROGRAPHS



APPENDIX 4. POTENTIAL COVER LAYER CONFIGURATION TO MANAGE CAPILLARY RISE OF SALTS (LANDLOCH 2020)

march 2021 - der.wa.gov.au

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