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Surface Mining

University of Saskatchewan

As part of course: Introduction to Mining/Metallurgy

Presented by

Louis-Pierre Gagnon, M.A.Sc, P. Eng.

Mine Engineering Superintendent, The Mosaic Company

October 7, 2010

Table of Contents● Mineral Resources in Saskatchewan

● Infrastructure Required

● Examples of Surface Mines and Open Pits

– Coal

– Oil Sands

● Pit Wall Terminology

● Potential Impact of Slope Steepening

● Slope Design Process

– Lerchs-Grossman and Floating Cone Methods

– Stripping Ratio, Cut Off Grade and Impact on Production

– Optimum Production Scheduling

– Important Design Considerations

– Open Pit Blasting

Table of Contents● Mobile Equipment

– Chart

– Cycle Time and Fleet Size

● Ore – Crusher and Stockpiling

● Waste Dumps

● Secondary Ore Recovery

● Rehabilitation

● Other Operational Challenges

● Open Pit Versus Underground Methods

● Accidents and Incidents

Mineral Resources in Saskatchewan

● Uranium and Base Metals -in the North

● Potash, Magnesium - in the centre

● Oil, Gas, Coal, Peat with some diamond potential - in the South

● Gold – spotty all over

● Building materials and Silica Sands

Infrastructure Required Surface Mines - Open Pits

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Coal Mining – History and Stats

- The oldest continuously worked deep-mine in the United Kingdom is Tower Clliery in

South Wales (1805 to now).

- Coal was mined in America in the early 1700s, and commercial mining occurred around

1730 in Midlothian, Virginia.

- Most open cast mines in the United States extract bituminous coal. In Australia and South

Africa open cast mining is used for both thermal and metallurgical coals. In South Wales

open casting for steam coal and anthracite is practiced.

- Surface mining accounts for around 80% of production in Australia, while in the USA it is

used for about 67% of production. Globally, about 40% of coal production involves surface

mining.

Coal Mining

● Sensitivity to price

● Concept of “Stripping Ratio”

● Large deposits

● Large volume of material displaced

● Large equipment

Coal Mining – Methods of Extraction

- Coal-cutting machines were invented in the 1880s. Before: underground with a pick and

shovel. By 1912, surface mining was conducted with steam shovels designed for coal

mining.

- Many coals extracted from both surface and underground mines require “washing” in a

coal preparation plant.

- Surface mining and deep underground mining are the two basic methods of mining. The

choice of mining method depends primarily on depth of burial and thickness of the coal

seam. Seams relatively close to the surface, at depths less than approximately 180 feet

(55 m), are usually surface mined. Coals that occur at depths of 180 to 300 feet (91 m) are

usually deep mined

.

Coal Mining – Strip or Open Cast

Strip mining exposes the coal by removing the overburden in long cuts

- The spoil from the first strip is deposited in an area outside the

planned mining area. Spoil from subsequent cuts is deposited as fill in

the previous cut after coal has been removed.

- Usually, the process is to drill the strip of overburden next to the

previously mined strip. The drill holes are filled with explosives and

blasted. The overburden is then removed using large earthmoving

equipment such as draglines, shovel and trucks, excavator and trucks,

or bucket-wheels and conveyors.

Coal Mining – Strip or Open Cast

-The exposed block of coal may be drilled and blasted (if hard) or

otherwise loaded onto trucks or conveyors for transport to the coal

preparation (or wash) plant. Once this strip is empty of coal, the

process is repeated with a new strip being created next to it.

- This method is most suitable for areas with flat terrain.

- The life of some area mines may be more than 50 years.

SHOW DRAGLINE VIDEO

Coal Mining - Contour

The contour mining method consists of removing overburden from the seam in a pattern

following the contours along a ridge or around a hillside. This method is most commonly

used in areas with rolling to steep terrain. It was once common to deposit the spoil on the

downslope side of the bench thus created, but this method of spoil disposal consumed

much additional land and created severe landslide and erosion problems.

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Coal Mining - Contour

The limitations on contour strip mining are both economic and technical. When the

operation reaches a predetermined stripping ratio (tons of overburden/tons of coal), it is not

profitable to continue. Depending on the equipment available, it may not be technically

feasible to exceed a certain height of highwall. At this point, it is possible to produce more

coal with the augering method in which spiral drills bore tunnels into a highwall laterally

from the bench to extract coal without removing the overburden.

Coal Mining – Technical & Economic Feasibility

Based on:

- Regional geologic conditions;

- Overburden characteristics;

- Coal seam continuity, thickness, structure, quality, and depth;

- Strength of materials above and below the seam for roof and

floor conditions;

- Topography (especially altitude and slope);

- Climate;

- Land ownership as it affects the availability of land for mining

and access;

Coal Mining – Technical & Economic Feasibility

Based on (continued):

- Surface drainage patterns;

- Ground water conditions;

- Availability of labor and materials;

- Coal purchaser requirements in terms of tonnage, quality, and

destination;

- Capital investment requirements.

** The same considerations are to be taken for other types of

minerals to be mined!

Oil Sands

Oil Sands – History and Stats

-The written history of the oil sands dates back over 200 years ago when the first Europeans

spotted bitumen along the riverbanks of the Athabasca River. The local Aboriginal people had

already long been tapping the resource to waterproof their canoes.

- Many interested by oil sands in the first half of the 1900’s: nothing sustainable.

- In 1962, the Government of Alberta announced an oil sands policy to provide for the orderly

development of oil sands in such a manner that it would supplement, but not displace,

conventional crude oil policy.

- The first project off the mark was the Great Canadian Oil Sands (GCOS) Project. GCOS went

through a number of ownership changes after its incorporation but, by 1963, prior to the

construction decision, ownership rested with the Sun Oil Company (later Suncor Energy). The

Suncor project came on stream in 1967 and became the world's first oil sands operation.

Oil Sands – History and Stats

- In the meantime, the Syncrude consortium was formed in 1964. Syncrude's initial objective

was research on the economic and technical feasibility of mining oil from the Athabasca oil

sands. Syncrude's proposal for a production facility was finally approved in 1969. In 1973,

construction began on the Syncrude site and, after five years of construction, the first barrel

was shipped on July 30, 1978. The official opening of the Syncrude Project was on

September 15, 1978. Production steadily increased in the ensuing years and, on April 16,

1998, the billionth barrel was sent down the pipeline, five years ahead of schedule.

SHOW OIL SANDS MINING AND RECLAMATION VIDEO

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Pit Wall Terminology Potential Impact of Slope Steepening

Slope Design Process Example of Block Model and Pit Design performed on Whittle

Natalka Gold Project, Russia

Lerchs-Grossman MethodThe two-dimensional Lerchs-Grossman method will design on avertical section the pit outline giving the maximum net profit.The method is appealing because it eliminates the trial-and-error process of manually designing the pit on each section.The method is also convenient for computer processing.

The results must still be transferred to a pit plan map andmanually smoothed and checked. The example in the nextfigure represents a vertical section through a block model of adeposit.

Lerchs-Grossman Method with Whittle for 45-degrees slopeVertical section showing the net value of each block

VALUES MATRIX

1 2 3 4 5 6 7 8 9 10 11 12 13

1 -1.00 -2.00 -1.00 -2.00 -2.00 -1.00 -1.00 -1.00 -1.00 -1.00 -2.00 -1.00 -2.00

2 -2.00 -1.00 -1.00 -1.00 1.00 -1.00 2.00 1.00 2.00 1.00 0.00 0.00 -1.00

3 -1.00 0.00 1.00 1.00 1.00 1.00 3.00 2.00 0.00 0.00 1.00 -1.00 -1.00

4 -1.00 0.00 1.00 2.00 2.00 2.00 2.00 2.00 1.00 2.00 1.00 -1.00 0.00

5 0.00 -1.00 0.00 0.00 2.00 2.00 3.00 1.00 1.00 1.00 0.00 -2.00 -1.00

6 -2.00 -1.00 0.00 -1.00 -1.00 2.00 2.00 1.00 0.00 -1.00 -1.00 -1.00 -2.00

M MATRIX Cumulative

1 -1.00 -2.00 -1.00 -2.00 -2.00 -1.00 -1.00 -1.00 -1.00 -1.00 -2.00 -1.00 -2.00

2 -3.00 -3.00 -2.00 -3.00 -1.00 -2.00 1.00 0.00 1.00 0.00 -2.00 -1.00 -3.00

3 -4.00 -3.00 -1.00 -2.00 0.00 -1.00 4.00 2.00 1.00 0.00 -1.00 -2.00 -4.00

4 -5.00 -3.00 0.00 0.00 2.00 1.00 6.00 4.00 2.00 2.00 0.00 -3.00 -4.00

5 -5.00 -4.00 0.00 0.00 4.00 3.00 9.00 5.00 3.00 3.00 0.00 -5.00 -5.00

6 -7.00 -5.00 0.00 -1.00 3.00 5.00 11.00 6.00 3.00 2.00 -1.00 -6.00 -7.00

Summation of blocks within a column

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Lerchs-Grossman Method

P MATRIX M+maxP(left)

1 -1.00 -2.00 -1.00 -2.00 -2.00 -1.00 -2.00 -1.00 3.00 10.00 16.00 19.00 22.00

2 -3.00 -4.00 -4.00 -4.00 -3.00 -4.00 0.00 4.00 11.00 18.00 20.00 24.00 22.00

3 -4.00 -6.00 -5.00 -6.00 -4.00 -4.00 4.00 10.00 18.00 22.00 25.00 25.00 21.00

4 -5.00 -7.00 -6.00 -5.00 -3.00 0.00 8.00 17.00 22.00 26.00 27.00 24.00 21.00

5 -5.00 -9.00 -7.00 -6.00 -1.00 2.00 13.00 20.00 24.00 27.00 27.00 22.00 19.00

6 -7.00 -10.00 -9.00 -8.00 -3.00 4.00 15.00 21.00 24.00 26.00 26.00 21.00 15.00

Final Design

1 -1.00 -2.00 -1.00 -2.00 -2.00 -1.00 -2.00 -1.00 3.00 10.00 16.00 19.00 22.00

2 -3.00 -4.00 -4.00 -4.00 -3.00 -4.00 0.00 4.00 11.00 18.00 20.00 24.00 22.00

3 -4.00 -6.00 -5.00 -6.00 -4.00 -4.00 4.00 10.00 18.00 22.00 25.00 25.00 21.00

4 -5.00 -7.00 -6.00 -5.00 -3.00 0.00 8.00 17.00 22.00 26.00 27.00 24.00 21.00

5 -5.00 -9.00 -7.00 -6.00 -1.00 2.00 13.00 20.00 24.00 27.00 27.00 22.00 19.00

6 -7.00 -10.00 -9.00 -8.00 -3.00 4.00 15.00 21.00 24.00 26.00 26.00 21.00 15.00

Final pit outline

Summation of blocks within a column

Lerchs-Grossman Method

There are the three steps in the Lerchs-Grossman method:

Step 1: Add the values down each column of blocks and enter these numbers into the corresponding blocks (M-matrix).

Step 2: Start with the top block in the left column and work down each column (P-matrix).

Step 3. Scan the top row for the maximum total value. For example the optimal pit would have a value of $22. This is the total net return of the optimal pit. The last figure shows the pit outlined on the section.

Floating Cone Method

If the grade of the base is above the mining cutoff grade, the expansion is projected upward to the top level of the model. The resulting cone is formed using the appropriate pit slope angles. If the total revenues are greater than the total costs for the blocks in the cone, the cone has a positive net value and is economic to mine.

A second block is then examined. Each block in the deposit is examined in turn as a base block of a cone.

Floating Cone Method

Cone centered on a

base block

Cone formed by a second

base block

Cutoff0.6% Cu

Tons Avg.%Cu

0.5% Cu

Tons Avg.%Cu

0.4% Cu

Tons Avg.%Cu

Ore 100,000,000 0.90100,000,000 0.9040,000,000 0.55

140,000,000 0.8055,000,000 0.45

Total OreTons Waste

Stripping Ratio

1,000,000 0.90250,000,000

2.5:1

140,000,000 0.80210,000,000

1.5:1

195,000,000 0.70155,000,000

0.8:1

Annual Production:Ore

Copper (0.8889 Rec)

5,000,000 tons80,000,000 lb

5,000,000 tons70,500,000 lb

5,000,000 tons61,000,000 lb

Tons per day:Ore

WasteTotal

16,00040,000

56,000

16,00024,000

40,000

16,00013,000

29,000

Source: Arial bold, size 10

Stripping Ratio, Cut Off Grade & Impact on Production● For a copper mine

Cutoff0.6% Cu

Tons Avg.%Cu

0.5% Cu

Tons Avg.%Cu

0.4% Cu

Tons Avg.%Cu

Plant:Mine

Mill

$28,000,000$24,000,000$52,000,000

$20,000,000$24,000,000$44,000,000

$15,000,000$24,000,000$39,000,000

Life 20 years 28 years 39 years

Costs:Mining

StrippingMilling & general

Treatment, etc.

Total direct cost

Per ton$0.45

$1.00$1.25$2.70

Per lb Cu

$0.169$0.059

$0.228

Per ton$0.45

$0.64$1.25$2.34

Per lb Cu

$0.169$0.060

$0.226

Per ton$0.45

$0.36$1.25$2.06

Per lb Cu

$0.169$0.062

$0.231

Stripping Ratio, Cut Off Grade & Impact on Production (continued)● For a copper mine

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Cutoff0.6% Cu

Tons Avg.%Cu

0.5% Cu

Tons Avg.%Cu

0.4% Cu

Tons Avg.%Cu

Profit @ $0.30 Cu:Per lb

Annual IncomeAmortization

Depletion

Taxable IncomeTax @ 52%Annual cash flow

Total cash flowPayout

$0.072

$5,760,000$2,600,000$3,160,000$1,580,000

$1,580,000$822,000

$4,938,000

$98,760,00010.5 years

$0.074

$5,217,000$1,571,000$3,646,000$1,823,000

$1,823,000$948,000

$4,269,000

$119,532,00010.3 years

$0.069

$4,209,000$1,000,000$3,209,000$1,604,000

$1,605,000$835,000

$3,374,000

$131,586,00011.6 years

Discounted cash flow return

7.1% 8.8% %8.2

Stripping Ratio, Cut Off Grade & Impact on Production (continued)● For a copper mine

Optimum Production Scheduling

The objective of production scheduling is to maximize the net present value and return on investment that can be derived from the extraction, concentration, and sale of some commodity from an ore deposit.

The method and sequence of extraction and the cutoff grade and production strategy will be affected

by the following primary factors.

Optimum Production Scheduling

(1)Location and distribution of the ore in respect to topography and elevation;(2) Mineral types, physical characteristics, and grade/tonnage distribution;(3) Direct operating expenses associated with mining, processing and converting the commodity into a salable form;(4) Initial and replacement capital costs needed to commence and maintain the operation;(5) Indirect costs such as taxes and royalties;(6) Commodity recovery factors and value;(7) Market and capital constraints;(8) Political and environmental considerations.** It is an iterative process

Important Design Considerations

(1) Grade - exploration and block model;(2) Geotech and hydro-/hydrogeological – pit slopes, bench characteristics.

Hazardous Bench Mapping Condition

Open Pit Model Showing Major Structures

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Water Control in a Mine Water Control Challenges

Bench Erosion Surface Water Control

Typical Wedge Failure Effect of Noses on Pit Geometry

Note:

Change in

geology

Loss of

confinement

Better to

maintain slope

& add support

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Example of Ground Support Open Pit Blasting

When you cannot “free dig”, you must drill and blast.

Conventional Open Pit – Drilling & Blasting

Blasting Design

No Visible Blast Damage

Note:

Half-barrels

Little loose

Conventional Open Pit – Drilling & Blasting

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Explosives and Blasting

One man’s observations of Explosives and Blasting in

Eastern Kentucky:

- In the 1950’s-Dynamite in the smokehouse

- In the 1960’s-ANFO makes an entrance

- In the 1970’s-Blasting starts to get serious

- In the 1980’s-Cast blasting comes of age

- In the 1990’s-Blasting moves near homes

- In the 2000’s-Flyrock strains the friendship

Concerns with open pit blasting

- Flyrock

- Vibration

- Airblasts

Open Pit – Mobile Equipment

Show PT Inco Chapter 2 Video

Open PitEquipment

Cycle Time and Fleet Size

Note: Graph provided as an example & does not match cycle time calculations

Ore – Crusher and Stockpiling

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Waste Dumps

In most surface mining operations, the waste materialremoved from the pit is deposited on an adjacent area. Thearea required for waste disposal is usually equal to or greaterthan the pit area because the disturbed waste mater has agreater volume than in-situ, a lower slope angle than the pitwalls, and rarely can the material be stacked as high as the pitis deep.

In designing waste dumps, particular consideration has to be given to reclamation needs if the cost is to be minimized.

Waste Dumps

Secondary ore recoveries

Sometimes, secondary ore recovery in waste dumps iseconomically feasible. Usually, low grade ore placed on a linerleaches out (naturally or not) in a solution which is collectedand treated. Production rates are usually low.

Telfer Gold Mine in AustraliaThe purpose of reclamation is to upgrade the physicalcharacter of all or part of a mining area after the mineralvalues have been removed and, thereafter, to protect thesurrounding environment from contamination.

In surface mining operations, the three largest areas that are reclaimed are the mine extraction, the mine waste dump and the mill tailings areas.

Rehabilitation

If the commodity extracted is a bedded deposit of largeextent and of relatively shallow depth such as in coalmines, the backfilling of worked-out areas is a commonmethod of waste disposal and reclamation. Waste materialremoved from the initial box cut or pit either be stockpiledand later transported to fill the final excavation or thestockpile could be reclaimed and not moved and the lastpit left with little reclamation effort applied.

In most surface operations for commodities other than coal, the amount of backfilling is restricted to totally impractical. Therefore, most of the reclamation effort is directed toward the waste disposal area.

Rehabilitation Other Operational Challenges

-People

- Language

- Different cultures

- Different ethnicities

- Skills and experience

- Different values

All – to work together!!

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Training

Critical for safety of operations and proper

production ramp-up, especially for large

operations with low skilled workforce

Show

Immersive

Technology

Video

Environmental Controls

-Minimizing the footprint of the mine

-Equipment washing station: oil, grease, parasites

-Water trucks: dust control

-Sedimentation ponds: construction and maintenance

Open Pit versus Underground Methods

Break even stripping ratio =

Underground mining cost / ton ore – Open pit mining cost / ton ore

Open pit stripping cost / ton waste

For example:

BESR = $2.00 - $0.30 = 4.86 waste : 1 ore

$0.35

For <4.86, consider open pit

For >4.86, consider underground method

Accidents and IncidentsThe “$” Equation

- Quarry’s Crash

Video

- Accident Mining

Video

Thank you!