LOCATION SELECTION OF A TAILINGS DAM FOR KOLWEZI

COPPER MINE (DEMOCRATIC REPUBLIC OF THE CONGO)

BY

ANDRe OOSTHUIZEN

Short Dissertation

Submitted in partial fulfilment of the

requirements for the degree

MAGISTER ARTIUM

in

GEOGRAPHY AND ENVIRONMENTAL MANAGEMENT

in the

Faculty of Arts

at the

RAND AFRIKAANS UNIVERSITY

SUPERVISOR: DR L G C SCHEEPERS

DECEMBER 1999

ABSTRACT

Environmentally, the past 10 - 15 years have experienced a very positive approach to improving

the quality of affluent discharged from the mining processes and ultimately the quality of seepage

from the tailings dam area to the receiving environment. With the concern and pressure by the

public and the regulatory agencies, and the cooperative efforts between industry, regulatory

agencies and research laboratories, much has transpired. These developments include improved

site selection and design methods.

Kolwezi Copper mine is in need of a new tailings dam. This study focuses on the elimination of

unsuitable areas and the identification of candidate tailings dam sites using criteria prescribed by

process specialists and engineers. These criteria were mapped and overlaid using a Geographical

Information System (GIS). The sites with inherent flaws were thus eliminated and the most

suitable locations identified for final selection taking in consideration operational requirements.

OPSOM1VHNG

Die afgelope 10 —15 jaar was daar 'n groot positiewe omgewingsbenadering tot die verbetering

van myn-afvalprodukte wat ontstaan as gevolg van mynbouprosesse. Gevolglik verbeter dit ook

die kwaliteit van uitvloeisel wat deursyfer tot in die ontvangsomgewing. Baie is vermag as gevolg

van druk van die publiek en owerhede en die samewerking van die bedryf, regulerende

agentskappe en navorsings laboratoriums. Hierdie ontwikkelings sluit in verbeterde terrein

seleksie en ontwerpmetodes.

Kolwezi Kopermyn benodig 'n nuwe slikdam. Hierdie studie fokus op die eliminering van

ongeskikte gebiede en die identifikasie van moontlike geskikte grond, sons voorgeskryf deur

proses-spesialiste en ingenieurs. Die kriteria was op kaarte neergele en oorle met die gebruik van

`n Geografiese Inligtings Stelsel (G.I.S). Gebiede mett tekortkominge is uitgeskakel en die mees

geskiktes is geidentifiseer vir verdere oorweging aan die hand van operasionele vereistes.

ACKNOWLEDGMENTS

My grateful thanks are due first and foremost to Dr. L. G. C. Scheepers who supervised the study

and provided tremendous insight and guidance, without which, this study could not have been

completed. I would also like to express my profound gratitude to all the staff of the Department

of Geography and Environmental Management which, in their different ways been of invaluable

help to me. My appreciation goes to all of them.

Special thanks are due to my colleagues, G. Stansfield and P. Morisson, whose selfless, technical

contribution enabled this study to be completed. I thank the Draughting Office staff for their

support and help with the drawings.

Special thanks are due to my family and friends for their encouragement and support. Finally, my

deep gratitude goes to Pieter and Ann Oosthuizen for their undying love, loyalty and support.

May God be honoured through this study, as everything comes from him, and he blessed us with

the intellect and ability to expand out knowledge.

ii

TABLE OF CONTENTS

ABSTRACT i

ACKNOWLEDGEMENTS ii

TABLE OF CONTENTS iii

LIST OF FIGURES v

LIST OF TABLES v

CHAPTER 1 1

INTRODUCTION AND LITERATURE REVIEW 1

1.1 INTRODUCTION 1

1.2 LITERATURE REVIEW ON TAILINGS IMPOUNDMENT SITE SELECTION 1

1.2.1 GENERAL PERSPECTIVE 1

1.2.2 TAILINGS IMPOUNDMENTS 2

1.2.3 TAILINGS DAM SITES 3

CHAPTER 2 6

PURPOSE OF THIS RESEARCH PROJECT 6

2.1 THE PURPOSE 6

2.2 SELECTED PARAMETERS 7

2.2.1 INFRASTRUCTURE 8

2.2.2 GEOLOGY 9

2.2.3 HYDROLOGY 10

2.3 STUDY AREA 11

CHAPTER 3 13

DATA ON SELECTED PARAMETERS 13

3.1 DATA IN THE GIS 13

3.2 DATA ON SELECTED PARAMETERS 15

i i i

3.2.1 INFRASTRUCTURE 17

3.2.2 GEOLOGY 24

3.2.3 HYDROLOGY 27

3.3 RESULTS 30

CHAPTER 4 33

EVALUATION AND CONCLUSION 33

4.1 THE PROBLEM 33

4.2 DATA 33

4.3 DATA ANALYSIS 34

4.4 RESULTS OF THE STUDY 34

4.5 CONCLUSION 35

LIST OF REFERENCES 36

ADDENDUM A 41

ADDENDUM B 42

iv

LIST OF FIGURES

1 Locality map of Kolwezi 12

2 Kolwezi Mine layout 16

3 Infrastructure Kolwezi area 18

4 Suitable/unsuitable infrastructure 19

5 Transportation Kolwezi area 21

6 Suitable/unsuitable infrastructure & transportation 22

7 Geological map of the Kolwezi region 25

8 Suitable/unsuitable infrastructure, transportation & geology 26

9 Drainage Kolwezi area 28

10 Suitable/unsuitable infrastructure, transportation, geology & drainage 29

11 Three suitable sites 31

LIST OF TABLES

1 River sampling 4

CHAPTER 1

INTRODUCTION AND LITERATURE REVIEW

1.1 INTRODUCTION

The mining industry in many countries often accounts for a major percentage of their

gross national products. However, with the nations also discovering environmental

pollution as a present and potential hazard, the minerals industry has been the subject of

concern to the public and government agencies. In order to recover the mineral wealth the

environment must be disturbed. This means that huge quantities of rock are moved,

crushed, pulverised and processed in order to extract the valuable metals, whilst the bulk

ofthe fine material is returned to the mining disposal area. These tailings constitute a large

proportion of the original ore that was crushed and therefore, when they are disposed,

they are easily visible and poses as a potential environmental problem.

1.2 LITERATURE REVIEW ON TAILINGS IMPOUNDMENT SITE SELECTION

1.2.1 GENERAL PERSPECTIVE

The mining operations is the largest single generator and accumulator of solid wastes in

South Africa. Mine tailings and coal discard accounted for 74 percent of the total waste

stream in 1990 (Fuggle & Rabie, 1992). The total area of land covered by mine residue

was 10 700 ha in 1981, most of which was in the Gauteng, Mumpumalanga, North West

and Free State provinces (Fuggle & Rabie, 1992).

Historically, the planning of tailings impoundment sites was based on minimum cost, the

availability of land and the safety of underground workings. Little or no regard was given

to the environment. Today the situation has changed dramatically. No fewer than six Acts

and their attendant regulations govern the location of tailings impoundments in South

Africa. (Fuggle and Rabie, 1992).

1

1.2.2 TAILINGS DAMS

Tailings dams are constructed to store the waste products from the ore milling process.

They are permanent hydraulic structures used to contain a large volume of semi-fluid

tailings and supernatant water (Robertson, 1984) . Tailings dams are traditionally made

of loose sand, silt and clay particles that may be susceptible to liquefaction and flow

failure due to high excess pore pressure that can be generated by rapid rates of increase

in ground motions caused by earthquakes (Douglas, 1995).

Since the tailings are deposited as a slurry, which are initially saturated with water and

often maintain a highly saturated phreatic surface, the slimes dam can be large in surface

area. The tailings chain comprises of many components including: tailings treatment in

mill; slurry thickening; slurry transport; tailings deposition; water recycling and

evaporation and restoration of the site. This discharge of tailings from a mining or mill

operations produces a potential source of contamination to the environment (Bruynesteyn

& Hackle, 1982).

Mine water discharged into the tailings dam may contain, in addition to trace metals, high

acid values, due to auto-oxidation or bacterial oxidation of sulphide in the ore. Such acid,

unless neutralized before disposal will react with the tailings to dissolve more metals and

therefore produce more possible contaminants (Ritcey, 1989). Many processes are

presently incorporating mine water back in the process circuits and so minimising the

tailings problem. Acid mine water drainage probably presents the single most important

factor in dealing with tailings and waste rock dumps and which can have serious impacts

on the environment (Robertson, 1984). Waste rock removed from underground or surface

mining operations, is often disposed randomly in unconfined areas. In many cases this

waste rock contains sulphide which on subsequent weathering oxidizes, which result in

acid mine drainage.

In the case of Kolwezi, the tailings dam water arriving on the tailings dam will be from

several sources. Barren tailings carrier water which has a relatively high proportion of

2

total dissolved solids, estimated at 6 g/l maximum (primarily magnesium sulphate) during

the dry season (pH 8.5 - 9.0). Secondly, from rain water falling on the dam (pH 3.5 -

nitric acid); rain water from the plant cut-off dam (pH --8) and lastly the Musonoi river

water from hydro sluicing operations of reject valley tailings (pH 5.0 - 6.0 sulphuric acid).

The blend pH will be in excess of 8.5 thereby confirming a minimum of heavy metal and

aluminium solubilisation.

The most common way of dealing with tailings is to construct a tailings dam. Some

potential environmental implications from a tailings site include (Robertson, 1984):

contamination of streams by seepage of acidic waters containing a high content

of metals and other substances;

contamination of streams due to surface runoff from the slimes dam site;

air and water contamination due to wind erosion of dried-out tailings;

possible risk of catastrophic dam failure and release of slimes and other substances

(due to high rainfall and inadequate construction methods);

physical and aesthetic modification to the environment;

difficulty of establishing vegetative cover to permanently stabilize the tailings, due

to the generally unfavourable soil conditions in the presence of pyritic tailings.

Table 1 presents an example of the possible contaminants that can pollute a given area if

the tailings dam is not located at the correct site.

1.2.3 TAILINGS DAM SITES

Site selection is probably the most important aspect affecting tailings impoundment

design. Each site will have advantages and disadvantages and the selection must be

considered in concert with the mining and milling operation. The type of mining/milling

process can have a significant effect on the type of tailings impoundment area and

therefore will affect the site selection. The impoundment systems are usually engineered

such that they meet the requirements for long term containment without the need for

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TABLE 1. River sampling (Roberston, 1984).

Sample Source Slurry Interstitial Fluid Solid Component

pH Co mg/1 Cd

mg/1

Zn mg/1 Cu

mg/1

Cd

mg/1

Zn mg/1

Upriver of Zinc plant 8.0 18 <0.3 <0.4 0.74 <6 50

Seepage from Zinc

plant residue pits

4.5 6.6 17 1614 5.9 52 2959

Tailings in contact

with acid spill

5.5 539 39 2946 13 46 3496

Tailings contaminated

with a Zn/H2SO4

outflow

5.7 35 3.3 578 2.9 22 2687

Tailings in river 50m

down stream of acid

spill

5.6 9.3 14 2640 58 249 26700

surveillance and maintenance. The objective of the design is for the isolation of the

tailings, using the best available technology to minimize future release rates. Any release

from the tailings that occurs can be an environmental problem, some more than others

depending on their particular mineralogy (O'Riordan, 1995). Sulphide or base metals may

be a problem for, say fifty years, but in uranium tailings, the radio nuclides could present

a problem of seepage to the environment for hundreds of years. Site selection is dependent

upon a number of factors, including required storage capacity, site availability, hydrology,

initial cost, ease of operations, geotechnical and geological conditions.

For the purpose ofthis study, which is the identification of a potential acid disposal site(s),

the selection criteria are as follows (Ritcey, 1989):

location of the tailings area such that the size of the catchment area is minimized

so that the water flow over the tailings after abandonment is reduced. A fully

dyked impoundment can be the most advantageous;

location of the tailings impoundment over a low permeability foundation in order

to reduce seepage from the tailings into the ground water. The flow of ground

water should be in an underlying aquifer (under clay or other liner) so that dilution

can occur;

4

the presence of calcitic minerals in and around the impoundment area, as well as

a high carbonate content in the ground water are desirable, in order that heavy

metals may be precipitated from the tailings pore water;

placement of tailings solids containing pyrite should be avoided, if possible, in

order to prevent acid generation and subsequent treatment problems;

careful design and construction of filter materials are required in order to reduce

the clogging resulting from precipitation or hydrolysis of the contaminated

solutions;

low permeability zones within the tailings area should be tested in the presence of

the leachate, as pore water chemistry may affect the permeability, strength and

compressibility of some clays;

permeability should be reduced to decrease the seepage oftoxic effluents from the

impoundment area. In the common spigotting method of tailings discharge, the

coarse fractions usually settles close to the discharge while fine slimes are

deposited some distance away. If the discharge is moved periodically along the

periphery of the impoundment area, the accumulation of previous tailings will be

minimized.

This study focuses on the elimination and identification of areas that have the potential for

a tailings dam site for Kolwezi. Goodchild (1993a) noted the site selection is largely

governed by the physical environment. Factors such as topographic features, climate,

hydrological conditions, geological structures and possible zones of mineralisation form

the basis for the elimination of unsuitable sites. Other environmental factors such as areas

that are part of nature reserves or of ecological, cultural or historical interest, as well as

the proximity of populated places have to be considered when deciding on the location

of the most suitable site. The selected criteria will be mapped and overlaid using a

Geographic Information System (GIS) so that the most suitable location for a new tailings

dam site for Kolwezi mine can be identified. Douglas (1995) observed the advantages of

GIS for the evaluation of multi criteria such as physical, economical and environmental

data. The next section will discuss the above mentioned parameters in detail and illustrate

the influence it will have on the site selection.

5

CHAPTER 2

PURPOSE OF THIS RESEARCH PROJECT

2.1 THE PURPOSE

The purpose of determining the location of a new tailings impoundment for the copper

mine at Kolwezi is:

To ensure that the site to be developed is environmentally acceptable and that it

provides for simple, cost effective design, which in turn provides for good

operation.

To ensure that this goal is achievable, a systematic and rational framework should be

followed. According to Robertson (1984), the site analysis is based on a detailed

investigation and evaluation of the area and consists of four steps.

Step 1. Regional screening.

The site must be considered with respect to:

anticipated production rate of tailings (solid and liquid)

expected life of the mine

the geology, hydrology, geochemistry, ecology and land use, topography, possible

mineralization in the site area and climate (precipitation, wind direction,

evaporation, temperatures, frequency of floods).

The criteria that will be used for excluding a particular site in locating the tailings

impoundment will take into consideration the above mentioned screening information and

are shown in Addendum A.

Step 2. Fatal flaw analysis in site selection

Having identified possible impoundment sites, the areas are then evaluated according to

a series of criteria to determine their suitability. Any one or more of the evaluating

characteristics may be sufficient to eliminate a site from further considerations. The fatal

flaw screening criteria are summarised in Addendum B.

6

Step 3. Investigation of remaining sites

After the gradual elimination of possible sites, the dimensions summarised below can aid

in a comparison of the remaining sites and with site visits, the ultimate selection can be

achieved.

area of impoundment area eventually required

height finally required for embankment

volume of selected site

area of upstream catchment

distance from mine

extra access road distance required

elevation change with respect to the mining complex

geology of rock and soil in area

distance to nearest river or stream

distance to nearest habitation

Step 4. Qualitative evaluation and ranking

Next the various factors are evaluated and each site is ranked according to the criteria

given (Bruyensteyn & Hackle, 1982; Burrough, 1986; Douglas, 1995; Robertson, 1984).

This study only involves the elimination of unsuitable areas and the identification of

candidate areas that have the potential to house a tailings impoundment (Step 1).

Elimination is primarily based on the physical and environmental parameters as outlined

in the next section.

2.2 SELECTED PARAMETERS

The identification of candidate impoundment sites will be done by evaluation of the study

area on the basis of certain parameters. Physical and environmental parameters have been

identified in reference to Robertson (1984) and Ritcey (1989). These parameters have

been identified as geology, hydrology and infrastructure. It is important to note that

factors such as soil characteristics; relief; wind direction; ground water; physical and

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7

chemical characteristics ofthe tailings should also be taken into account. Due to the scope

of this study, not all factors will be addressed (Burrough, 1986; Hawley, 1972). It is the

opinion of the writer, that by looking at geology, hydrology and infrastructure a reliable

site can be selected. The other factors mentioned will only enhance the analysis and verify

the answer (Chrisman, 1987).

2.2.1 INFRASTRUCTURE

Roads

Access roads are required to inspect the impoundment structure. It should be

noted that the impoundment area cannot be located too close to national roads or

public roads. If the structure should fail it should not flood any public roads

(Eagan & Ventura, 1993; Goodchild, 1993a; Ripple, 1991; Robertson, 1984).

Railways

Railways form an important transportation medium for mines Therefore the

tailings area cannot be located too close to a railway line in case of failure of the

impoundment structure (Eagan & Ventura, 1993; Goodchild, 1993a; Ripple,

1991; Robertson, 1984).

Populated places

Tailings dams can cause air pollution, especially in the case of dry disposal, where

the tailings are exposed to wind erosion. This means that the disposal area cannot

be to close to human habitation. Secondly, the disposal sight might also be a

source of Radon pollution (Eagan & Ventura, 1993; Goodchild, 1993a;

O'Riordan, 1995; Ripple, 1991; Robertson, 1984).

8

d) New plant

It is important that the tailings impoundment be as close to the processing plant

as possible, because if the tailings require pumping over a long distance there may

be several technical problems which have to be considered (Hawley, 1972; Ritcey,

1989; Robertson, 1984):

the slurry density should be as high as possible, preferably in the range of

40-65%, which requires a smaller pipe diameter and pump size. If water

is to be recycled from the tailings to the mill for reuse, a higher slurry

density means less volume to pump;

the velocity of the discharge is critical, for at low velocity the solids will

tend to sand-out and would therefore require larger diameter pipelines. On

the other hand, if the velocity is too high, there will be friction losses, wear

on the pipe and increased power consumption.

2.2.2. GEOLOGY

Highly permeable bottom rock with high water tables are unfit of forming the basis of a

tailings impoundment as leaching and spilling of slurry can lead to pollution of underlying

water sources. Geological characteristics of the area such as location, type and thickness

of strata should be described in the screening process. Resistance of the geology to

weathering and chemical attack are two important factors that should be looked at, as it

can alter the structure and stability of the underlying rocks. The presence of dips and

strikes are just as important as it affects ground water flow. Fracturing of bedrock and

existing or probability of subsidence or sinkhole development due to mining will affect the

stability of the tailings impoundment. It is advisable that the proposed site should first be

described in terms of the regional geology. This will indicate where it fits into the regional

stratigraphy. Thereafter the stratigraphic and lithological features adjacent to and

immediately beneath the site must be examined and described (Davis, 1982; Keller, 1992;

Ritcey, 1989; Star & Estes, 1990).

9

2.2.3 HYDROLOGY

The hydrology of an area is one of the most important factors to take into consideration

in deciding where to locate a tailings impoundment. Bruynesteyn & Hackle (1982)

affirmed that the pollution risk of ground and surface water is the greatest hazard that a

tailings impoundment has.

Local surface runoff can cause serious pollution to nearby rivers as well as to ground

water. In order to minimise the risk of water pollution, surface water should be diverted

away from the waste disposal area. This can be achieved by using stream diversion,

peripheral ditches and draining pipes (Bruynesteyn & Hackle, 1982).

The infiltration of rainfall into the disposal area can affect the stability of the tailings dam.

Impervious cover material can be used to prevent infiltration which will ensure rapid

runoff The provision of impervious and erosion-resistant intermediate ditches to direct

water away from the waste area can be beneficial. The determination of the depth of the

ground water phreatic surface and its seasonal fluctuations, particularly the position of the

wet season high elevation and the presence of any perched water surfaces, is advisable

(Douglas, 1995; Ripple, 1991).

Another minimum requirement is that the gradient and general flow direction of the

ground water and other relevant data must be determined and possibly illustrated by

appropriate maps and cross-sections. In addition, all significant geological features and

inferred structures must be explored to determine the possible presence and importance

of preferred ground water flow paths (Ritcey, 1989).

With regard to water quality it is advisable that the background quality of the ground

water, both up-gradient and down-gradient ofthe proposed site, must be determined prior

to any slurry disposal. A comparison of pre-disposal and post-disposal groundwater

quality then provide an indication ofthe impact of the tailings impoundment on the ground

water quality (Ripple, 1991; Ritcey, 1989; Robertson, 1984).

10

2.3 STUDY AREA

Kolwezi is situated in the Copperbelt region of the Democratic Republic of the Congo,

northwest of Lubumbashi (Figure 1). For the purpose of this study, the area of interest is

illustrated in Figure 2. The study area comprises the several open pit mines, the

Dima/Kamoto and Luilu plants, and numerous township areas. The two important villages

in the area are Musonoi and Kolwezi area.

The next section will concentrate on the importance of quality data and especially data

acquisition for the described study area.

11

L'ako: • Mseru kEPusuc OF

E: r: 2 E • 2

Scale 1: 5 000 000

Figure 1. Locality of Kolwezi (Democratic Republic of the Congo)

CHAPTER 3

DATA ON SELECTED PARAMETERS

3.1 DATA IN THE GIS

The increasing power of GIS and the availability of digital data have enabled users and

decision-makers to perform complex spatial analyses for a great variety of environmental

applications (Aronoff, 1992). The rapid expansion of the GIS has resulted in a parallel

growing concern about the quality of data (Campbell & Mortenson, 1989). The intended

use of data affects the type of data and the quality of data needed. The nature of the

decision-making may also help decision-makers determine the data quality they need

(Berry, 1994). A political, high-risk decision requires higher quality data than a

nonpolitical, low-risk decision because more public attention focuses on the former

decision (Ripple, 1991; Somers, 1994; Thapa & Bossler, 1992).

In order to optimise the data in the GIS the decision-maker has a variety of possible

courses of action, ranging from steps that attempt to minimize error and the effect it has

on decisions, to other less useful options. Possible actions can include the following (Dunn

et al, 1990):

First, the decision-maker could abandon any attempt to use a GIS because of the

errors associated with its use. At times, this may be the appropriate strategy, but

this approach ignores the potential benefits associated with GIS use (Tosta, 1993;

Walsh, 1989).

Second, the decision-maker could ignore the error associated with GIS use and

continue to use the GIS for decision-making. This type of "head in the sand"

approach is not advisable because of the potential liability associated with making

decisions based on inaccurate data (Brown & Gersmehl, 1987).

Third, the decision-maker could engage in an expensive and time-consuming effort

to collect highly accurate data in the hope of that error becomes a non-issue.

Depending on the intended use of the data, the cost of collecting more accurate

data may exceed the benefit (Kennedy, 1989).

13

Fourth, the decision-maker could assess whether the information available is

accurate enough for the intended purpose. If data quality is too low, the

decision-maker may opt to collect new data at the desired level of accuracy. If

collecting additional data is not possible, the decision-maker can explore what

types of decisions are possible given the attainable data quality (Openshaw, 1989).

For instance, Hunter and Goodchild (1993) found that the data they were using

were suitable only for initial screening rather than for regulatory and

land-purchasing decisions.

Fifth, procedures to ensure high quality data could be developed and used in the

data collection, input, and manipulation stages of building a GIS database

(Felleman & Griffin, 1990).

Sixth, the decision-maker could require a quantitative or at least a qualitative

report on the sources, magnitude, and effects of errors. The absence of an error

report does not mean the map is error-free (Heuvelink & Burrough, 1989).

Dutton (1991) predicts that in the near future users of geographic data will

demand error reports, confidence limits, and sensitivity analyses with

GIS-generated output.

Seventh, the decision-maker could ask for GIS-generated maps that adequately

portray the error in the final map. For example, areas where the uncertainty is high

could appear in red on maps. Another option is to place a buffer around lines to

indicate the relative positional accuracy of a line or to show transition zones

(Chrisman, 1991; Connin, 1994).

Finally, an analyst can present the output in ways other than a dichotomous yes

or no; instead, the analyst may use yes, maybe, or no depictions or even more

gradations. Finally, Beard (1989) introduced the concept of directing efforts

toward educating users about use error. She defines errors of usage as the

misinterpretation of maps or misapplication of maps to tasks for which they are

not appropriate. "We can't assume that GIS will automatically be less susceptible

to misuse than traditional maps, and it may, in fact, exacerbate the problem by

expanding access to mapped information" (p 34).

14

The ideal approach should be the fifth option where management procedures are in place

to ensure that high quality data is generated. Unfortunately this is not always the case. For

this study, data quality will not affect the analysis in such a way that the study becomes

obsolete, therefor the fourth approach will be followed.

3.2 DATA ON SELECTED PARAMETERS

Data relating to the study area (Figure 2) was primarily obtained from topographical and

geological maps published in the Democratic Republic of the Congo. Information on

aspects of the hydrology, geology and infrastructure were derived from these maps using

GenaMap - a geographic information software package.

After the data is captured in the GIS a certain workflow methodology will be followed.

The first step will be to examine and describe each data set (map) in isolation from one

another. For example, the geological map will be described according to the different

geological entities. After the geology had been mapped, the suitability of each geological

entity will then be scrutinised in the second step. The third step will be to classify the data

into two classes, namely suitable and unsuitable for the defined application. Fourthly,

according to the map derived form step three, the suitable area(s) will then be selected

(McGwire, 1992; Worral, 1996).

The above mentioned procedure will be applied to all data sets. After this has been

completed the classified data sets will, with the aid of the GIS software, be overlaid and

a final site selection can then be made. Map overlay is considered the most important

analytical function in a GIS package (Bonham-Carter, 1994:227). Map overlay allows

GIS users to superimpose two or more registered map layers and combine both spatial

and attribute data of the map layers to examine the spatial patterns caused by the

interactions of one map layer with another. In a vector-based system, the analysis is based

on a polygon interaction algorithm in which new polygons are created as needed, and

redundant boundaries are eliminated (Starr & Estes, 1990:148).

15

For the purpose of this study, the "join" overlay method will be used where certain

attributes in the second map takes precedence over attributes in the first map. For

example, the unsuitable areas of MapB will take priority over the suitable areas of MapA

and this "joined" map will then be MapC, and in turn the unsuitable areas of MapD will

take precedence of the suitable areas in MapC and forth-with.

3.2.1 Infrastructure

New plant

The location of the tailings dam relative to the new plant is one of the

most significant factors impacting on the cost ofthe tailings impoundment.

This study therefore focusses on the area immediately surrounding the

new plant in the north western portion of the mining area. The tailings

dam should be as close to the plant as possible to make it cost effective in

terms ofthe construction and length ofthe tailings and water pipelines and

capital and operating costs of the pumps (Figure 3).

The plant site is on the east bank of the Musonoi River overlooking the

Zinc Refinery (Figure 3). The plant layout of this site takes into

consideration natural gradients, preferred sites for locating water

reservoirs and a high tension electrical substation.

The plant area, as showed on Figure 3, contains the sulphuric acid plant

and limestone plants (located back to back for safety reasons); the leach

plant for treating tailings; purification and solvent extraction plants;

neutralisation plant; electrowinning plant and warehouses and rail siding

facilities. A natural progression of work in progress will be from west to

east. Adequate provision has been made for expansion of the plant.

Figure 4 shows the areas that are not suitable for the location of the

tailings dam. The plant, conveyer belt path and the open pit mine all form

unsuitable areas for the location of the dam.

17

POIN

T O

F R

EFE

RE

NC

E

UN

SUIT

AB

LE

Li, _1

1-- 5 co

co w cc I- tu 2

Roads

The roads in the area are 8 metres wide with a graded gravel surface.

Roads within the plant perimeter fencing, see Figure 5, are generally 8

metres wide with a sealed surface and kerbstone edging. Cognisance has

been taken of the heavy duty requirement of these roads which will

experience traffic ranging from motor cars to heavy duty forklifts, long

hauls and cranes requiring outriggers.

Access roads to the proposed sites are necessary for the construction

stages and for maintenance and inspection. As an all weather road,

allowing for two traffic lanes and shoulders for safety, leads to the new

plant, extending it to the dam will be easy. A buffer zone on either side of

the road has been created to restrict building the tailings dam to close to

the access road. It has been decided that a buffer zone of 10 metres will

be adequate as the tailings dam is located in a valley. These buffer zones

form the areas that are unsuitable for constructing the dam and are shown

overlayed on the already existing unsuitable areas of Figures 4 and 6.

Railways

The railway line (Figure 5) from Kolwezi to Likasi runs through the study

area. This railway line forms the main artery for exporting the minerals and

importing any raw material needed in the production process. It is

important to keep this line open as the mine depends on it. Thus, for safety

reasons a buffer zone of 100 metres on both sides of the railway line was

provided as a prohibited area and unsuitable for locating the tailings dam,

as shown in Figure 6 (which now combines all the previous unsuitable

areas). In this figure, only areas which are suitable regarding all the

previous land uses are shown as suitable. If one of the previous land uses

are regarded as unsuitable, that particular area will be shown as unsuitable

in the overlay map.

20

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The closest township, Musonoi (Figure 2) is 12 kilometres south east of

the proposed site. A study should be done on wind directions and drainage

patterns as air and water contamination can take place due to wind erosion

and washout of dried-out tailings. The topology will also influence the site

of the dam relative to the town to minimize possible risk of catastrophic

dam failure and release of slimes and other substances. Physical and

aesthetic modification to the environment and difficulty of establishing

vegetative cover to stabilize the tailings permanently, due to the generally

unfavourable soil conditions and the presence of pyritic tailing. It should

be noted that factors, such as topology and vegetation cover are not being

addressed in this study, and should be therefore form part in a more

comprehensive study.

Power transmission lines

The electrical supply authority to the province is SNEL. There are four

hydro electrical power stations in the area. These are located at Nseke,

Nzilo, Koni and Mwandingusha within a radius of approximately 70

kilometres of Kolwezi. These stations transmit power by means of a high

voltage network to the SNEL high voltage outdoor switchyard located

adjacent to the Zinc Plant (SNEL West Substation) at Kolwezi,

approximately 3 kilometres from the proposed plant site. The transmission

voltage is 120 KV 3 Phase 50HZ. In addition there are two DC lines

which originates from Inga. The capacity of these lines is 350 MVA each

and the transmission voltages are +500 KV and -500 KV. The DC is

inverted to 3 phase AC at 220 KV by two large invertor units, and then

transformed to 120 KV to link with the 120 KV bus in the SNEL West

Substation. The distribution around the Kolwezi area is generally at 120

KV.

23

As these are over head transmission lines, the tailings area should not be

near the transmission lines as pylons can not be anchored in the slurry. A

buffer zone of 10 metres have been selected along each side of the line as

a slurry wave may damage some of the pylons in case of a flood (see

Figure 2) and secondly, construction vehicles may damage the pylons

during the construction phase. The buffer zones were classified as

unsuitable areas and were superimposed onto the previously determined

suitable/unsuitable areas (Figure 6).

3.2.2 Geology

Based on the suggestions by Robertson (1984) the geological characteristics are

important factors which need to be assessed when doing site analysis. The

geological structures were captured from the 1:100 000 Kolwezi-Kalukundi

geological map, obtained from the New Democratic Republic of the Congo

government printer. The derived vector map (Figure 7 ) was then classified into

areas suitable or unsuitable for the location of a tailings dam and superimposed

onto the previously determined suitable/unsuitable areas (Figure 8 ).

The Roan Super-group (Schisto -Calcaire system), has a tertiary composition: the

lower or Kwilu stage (R.A.T. Group) is composed of dolomite, argillaceous

dolomite, and calcareous sandstone, succeeded by the Lukunga stage (Mines

Group) composed of limestone, argillaceous dolomite with chert partings and

calcareous shales, and overlain by the Bangu stage (Mwashya Group) consisting

of limestone and dolomite with carbonaceous material, black dolomite, cherts,

shale and calcareous shales. These dolomitic and sandstone structures are porous

and thus not suitable for any feature associated with seepage and spillage. Highly

permeable rock is unfit of forming the basis of a tailings impoundment as leaching

and spilling of slurry can lead to pollution of underlying water sources. Shale has

a low resistance to weathering and chemical attack and this can alter the structure

and stability of the underlaying rocks. No major faults exist in the area.

24

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The geology of the area underlaying the new plant forms part of the Grand

Conglomerat (a large pebble conglomerate) formation. At the base of this

formation is a very distinctive geological unit that at times attains a thickness of

several hundred metres and is composed of ill-sorted boulders in a clayey matrix

and is considered a finite. This is ideal for the location of a tailings impoundment

as it provides an area with a low permeability foundation that will reduce seepage

from the tailings into the ground water.

3.2.3 Hydrology

The Musonoi, a perennial river borders the mining area on the west and the data

was captured and generated into a hydrological map. Water management is

important to the mining complex for the successful implementation, operation, and

ultimately decommissioning of the site. Since overtopping has been one of the

most frequent causes of tailings dam failure, the selection of appropriate flood

management measures directly affects the safety of the environment.

For the purpose of being used as a suitable parameter, the perennial river was

given a buffer zone of 120 metres (Figure 9). Robertson (1984) stipulates that

perennial rivers be given a buffer zone of 100 metres. This barrier will form a

prohibited area and serves as a damage control area in the event of an accident.

Areas that fall outside this buffer zone were categorised as suitable for the

construction of the tailings dam. The buffer zone was classified as unsuitable and

superimposed on the previously determined suitable/unsuitable areas (Figure 10).

The primary dam will be constructed as rock-filled dike with cutoff walls to

prevent seepage into the river. It is important to note that aquifers will influence

the site location, but no data was available on the locations of such features.

27

3.3 RESULTS

As the focus was only on the area surrounding the new plant, three possible locations

were identified in close proximity to the new plant (Figure 11).

Figure 11 shows the three alternative locations that have been identified as candidate site

locations. All three sites have not only passed the suitability criteria, but also have

relatively large surface areas.

In terms of sheer size, area one and three are most suitable. Though area two has a large

surface area, it may not be convenient for it to be used for a tailings dam site as plants on

both sides of this area will limit expansion if necessary. Area three, south west of the new

plant, is not easily accessible from the existing roads, thus adding cost to the construction

costs.

Two of the candidate areas (sire 2 and 3) are close to populated places and should

therefore not be favourably considered for development into a waste site.

The final choice for the tailings dam depends on the economic and physical environmental

characteristics. One of the economic criteria, which can be calculated is the distance from

the plant to the tailings dam. Tailings dams are usually constructed as close to the plant

as possible (Ritcey, 1989: 61). In this regard, area number one is the closest to the plant.

One of important advantages of these three areas is that they are located off the

mineralised zones. The tailings dam will therefore have no impact on the effort to optimise

the pit and the structural geology indicates long-term stability to the dam.

After all these factors are carefully considered, area number one appears to have the

overall advantage and should thus be considered strongly as the potential site for the

tailings dam.

30

It should be noted however that the final choice for the location of the new tailings dam

requires integrated planning which should take into account all the important factors

mentioned earlier.

This study illustrated the importance of the identification of suitable locations for tailings

dams. Equally important is the design, monitoring and auditing of the tailings dam site.

These indeed are essential components of a more environmentally friendly operation.

32

CHAPTER 4

EVALUATION AND CONCLUSION

Even though time restraints and pressure of work would not allow the researcher to undertake

a more detailed research project, the researcher nonetheless has gained very useful insight, skills

and valuable experience in the conduct ofthis study. Without hesitation, the short-comings ofthis

study is acknowledged. These flaws relate to the analysis of the data and consequently the results

of the study.

4.1 THE PROBLEM

The problem the research set out to solve is that of finding a suitable location for the

tailings impoundment area for the copper mine at Kolwezi, based on requirements as

prescribed by the mining engineer which heads the project. These requirements were

based on the physical restrictions of the area as well as financial restraints. It should be

noted that not all the variables were addressed, but that the focus was on the functionality

of GIS in environmental analysis and management.

4.2 DATA

Though digital data is available from data suppliers, such as the 1:1 000 000 scale Digital

Chart of the World, this scale is too small for the kind of research undertaken. The

available digital topographical data on a scale of 1:50 000 was not of adequate quality to

be used for this study. If the data was of a better quality it would have greatly enhanced

the research in more ways than one. Apart from saving time, such information would

probably be derived from recent remotely sensed data. Features such as roads, railways,

rivers, town boundaries could have been captured from satellite images. Such data would,

therefore, have been more accurate and reflect a more exact picture of the current

situation on the ground. Data obtained from remote sensing would have been costly

though.

33

Data related to the geology, infrastructure and drainage was obtained from maps compiled

in 1982, 1991 and 1990 respectively. These maps are relatively outdated. It would

therefore be necessary to visit the so-called candidate site and verify the current state in

terms of land use and development. Furthermore, it is necessary to liaise with other

departments such as the mining engineers to ensure that areas currently undeveloped have

not been deliberately set aside for some other function.

4.3 DATA ANALYSIS

Data analysis was carried out primarily through a GIS. Data relating to the prescribed

criteria was digitized and classified. The data was only classified into two classes. A better

approach would have been to classify the data into four or even five classes: unsuitable,

less suitable, more suitable and most suitable. The unsuitable areas were then eliminated

by overlaying the data sets to create a new data layer. This layer is represented by Figure

1 1.

This procedure, though quite objective, failed to take into account some crucial factors.

Factors such as wind direction and magnitude, financial issues, topography (slope) and

soil characteristics were not considered. These could aggravate the negative impact ofthe

tailings dam.

This does not mean that this study have no purpose. GIS allows the user to view the data

sets in relationship with each other. Even though not all parameters were taken into

account, the GIS enabled the user to optimise limited data sources and still make an

objective decision.

4.4 RESULTS OF THE STUDY

The short-comings mentioned above render the results of the research imperfect. The

study, however, succeeded in identifying candidate sites which have the potential of being

developed into a tailings dam site (Figure 11). The next step however, is to verify the site

by visual inspection. This study provides the mining engineers with the basis on which

34

they can build by looking at parameters not included in this study.

4.5 CONCLUSION

GIS is an established and accepted technology, especially in applications related to natural

resource and environmental management. Despite the widespread proliferation ofGIS into

these areas, the available data are not always appropriate for the intended application.

Increased awareness of the sources and magnitude of error can help decision-makers

determine if the data is appropriate for their use. Decision-makers cannot leave the data

quality concerns to GIS analysts because efforts to improve data quality are not without

cost, and the decision-makers typically control funding. Decision-makers must not get

caught up in the glamour of the spatial analyses and outputs that a GIS can produce.

These attributes may lead decision-makers to ignore issues associated with uncertainty,

error, accuracy, and precision. Inexpensive digital data can make analysts and

decision-makers ignore data quality. If sub-sequent management decisions are made based

on poor quality data, the resultant decisions may be incorrect. This would give

decision-makers a jaded view of the usefulness of GIS.

Ultimately, the responsibility for proper use of GIS technology lies in the hands of

practitioners. Technical staff performing GIS analysis must be knowledgeable about

sources of error and uncertainty and ensure that users of their work are aware of their

influence on GIS output.

This study identified three areas as possible locations for a tailings dam as depicted in

Figure 11. More information about the environmental conditions of each ofthe three areas

must be gained and carefully weighed. Nevertheless, the use of GIS to determine

candidate sites which comply with the requirements has certain advantages. GIS enables

the user to make is quick and effective decisions and is especially suitable for the

evaluation of multi criteria such as physical, social, economic, environmental and policy

data. The ultimate purpose of GIS is to provide support to the environmental manager for

making decisions based on spatial data, as illustrated by this study.

35

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40

ADDENDUM A. Table 2 Criteria for excluding areas for tailings site (Robertson, 1984)

1. Topographic Features

Areas which are generally too steep, e.g. side slopes of mountains in excess of 15% slope

Areas where access is difficult

2. Climatic Factors

Areas which are completely exposed to prevailing winds and no shelter can be provided

Areas where severe weather conditions can influence disposal operations

3. Land Use and Ecological Features

Important recreational areas

Sensitive breeding areas or exceptional animal habitat

Areas with sensitive ecosystems or endangered species

Other mining operations in the area

Areas of archaeological importance

Areas of intensive use such as oil fields

4. Hydrological Conditions

Exclude sections of streams where catchment area is larger than 13 km 2 except if stream diversions can be done so that it will be effective in the long term

Ground water discharge areas

5. Geological Features

Delineate major faults

Areas of large alluvial and eolian deposits, i.e., areas which are easily erodible and highly permeable

Areas where special foundations problems may be experienced e.g. dolomite deposits

6. Possible zones of Mineralization

a)Delineate areas of known mineralization

41

ADDENDUM B. Table 3 Fatal Flaw-screening criteria (Roberston, 1984).

Visual

1.1 Unacceptable visual impact

Land Use/Ecological

2.1 Endangered species

2.2 Critical wildlife or fish habitat

2.3 Sensitive or unique ecosystem

2.4 Important recreation areas

2.5 Historic or archaeological sites

2.6 Mineralization (economic)

2.7 Man-made features (oil wells and pipelines)

Airborne release

3.1 Dust/erosion - high wind exposure

3.2 Radon - proximity to human habitation

Seepage release

4.1 Foundation (unsuitable for placed line or as a natural liner)

4.2 Ground water discharge area

4.3 Flood plain

Stability release

5.1 Topography (too steep)

5.2 Faults (active)

5.3 Upstream drainage area (too large)

5.4 Foundation conditions (poor)

Operational

6.1 Capacity (too small)

6.2 Access (too difficult)

6.3 Technical feasibility (not implement able)

Cost

7.1 Development cost (uneconomic project)

42