mining methods in australia

8/7/2019 Mining Methods in Australia

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Presentation titlePage 1

Open-Cut Mining

Used when: Ore body is less than 200 metres below the surface i.e. ore

is nearer to the surface and overburden layer is thin.

Ore and surrounding waste rock are mined at the same time & separated

later

Mining method:

Explosives

Front end loaders / Electric Shovels

Loading into Dumpers

Crushed using Primary Crusher

Mining is not feasible when:

Extraction becomes costlier due to increasing ratio of overburden to ore

Greater difficulty in mining the ore

Concepts:

Walls of the pit are generally dug on an angle less than vertical, to prevent

and minimize damage and danger from rock falls.

The walls are stepped. The inclined section of the wall is known as the

batter, and the flat part of the step is known as the bench or perm.

Waste rock is piled up at the surface, near the edge of the open pit. This is

known as the waste dump. The waste dump is also tiered and stepped, to

minimize degradation.

Ore which has been processed is known as tailings, and is generally aslurry. This is pumped to a tai lings dam or settling pond, where the water

evaporates.

Commonly mistaken with: Strip Mining, Borrows,

Placers, Quarries. Mines producing building

material and dimension stone referred to as

Quarries

Mineral extracted using this method: Coal andextensively in "hard rock" mining for ores such as

metal ores, copper, gold, iron, aluminum.

Adopted by: Australia, Bulgaria, Chile, Columbia,

Indonesia, Peru, Portugal, Russia, South Africa,

UK, US, Zambia.

India Status: Used by?


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Strip Mining / Surface Mining

Strip mining is a type of surface mining that involves excavating earth, rock,

and other material to uncover a tabular, lens-shaped, or layered mineralreserve.

Used when: Ore bodies are located close to the Earths surface.

Mining Method: Seam of mineral is mined by removing the overburden

Machines like bucket wheel excavators, draglines, stripping shovels are used alongwith explosives to move the overburden.

The extraction of the overburden is done in rectangular blocks called pits or strips.

The pits are parallel and adjacent to each other with each strip of overburden andthe mineral beneath extracted sequentially.

The mining process involves moving the overburden laterally to the adjacent emptypit where the mineral has been extracted

This movement is called casting oropen casting

Has two forms: Area Stripping : Used on relatively flat terrain to extract deposits.

Contour Stripping: Here the overburden is removed above the mineral seam nearthe outcrop in hilly terrain, where the mineral outcrop usually follows the contour ofthe land.

Strip mining is used to extract materials of sedimentary origin like coal andtar sand.

An advantage of this method is that the adjacent pits are filled with theoverburden which ensures reclamation of mined land.

A pictorial representation of a

typical strip mine


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Strip Mining / Surface Mining

.

Mineral extracted using this method: Coal and

tar sand

Adopted by: Australia

India Status: Used by?


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Underground Mining

Used When:

The ore body is deep beneath the earths surface and surface mining isunattractive.

Objective: To extract the ore below the surface of the earth safely , economically and with

as little waste as possible

Types:Borehole Mining

Drift miningHard rock mining

Soft rock mining

Shaft mining

Slope mining

Machinery used in underground mining:Dump Trucks

Shuttle Car

Continuous Miner

Longwall mining equipmentGetmanunderground mining equipment

Minerals, rocks and gemstones mined

this way:

Biotite. Calcite, Copper, Diamond,

Emerald. Gold, Graphite, Turquoise,

Silver, Ruby , Zinc, Nickel & Gypsum


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Ventilation is an extremely important aspect of underground mining. Mine

ventilation provides fresh air underground and at the same time removes noxiousgases as well as dangerous dusts that might cause lung disease like silicosis

The ratio of air circulated through the mine and coal produced from a mine is 6:1,which just emphasizes the importance of ventilation in underground mining.

Fresh air and return air are conducted through entry and exit points created inthe mine, termed as intakes and returns.

Underground Mining can be used both when the rock is hard as well as when it issoft.

Underground Hard Rock Mining:Used in excavation of hard minerals, mainly those containing metals such as ore

containing gold, copper, zinc, nickel and lead and also gems l ike diamonds.

Mining Method:

Access to the ore can be achieved via a decline (ramp), inclined vertical shaftor adits.

Concepts:

A Decline can be a spiral tunnel which circles either the flank of the

deposit or circles around the depositA shaft is a vertical excavation sunk adjacent to an ore body. Shafts are

used when haulage to surface via truck is not economical.

An Adit is a horizontal excavation into the side of a hill or mountain.Used for horizontal or near horizontal ore bodies where there is no needfor a ramp or shaft.

An underground mine with

shaft access

Underground Mining


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Underground Soft Rock Mining:Refers to a group of underground mining techniques used to

extract minerals or geological materials from sedimentary / softrocks.

Mining Method: Soft rock mining uses the following techniques formining of minerals:

LongwallMining

Room and Pillar Mining / Continuous Mining

Blast Mining

Shortwall Mining Not commonly used

Borehole Mining:A remotely operated method of extracting mineral resources

through boreholes by means of high pressure water jets.

Can be carried out from land surface, open pit floor, undergroundmine or floating platform or vessel through pre-drilled boreholes.

Mining Method:

A bore hole of a desired depth is drilled from land surface upto the place where actual mining will take place.

A large diameter pipe (casing column) is inserted down thehole and the desired mining tool is inserted down the columninto the hole.

Its advantages lie in its low capital cost, mobility, selectivity, abilityto work in hazardous and dangerous conditions and lowenvironmental impact .

A Borehole Mining site

Underground Mining


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Equipment used:

Dump trucksContinous Miner

Shuttle Car

Longwall mining equipment

Underground Mining

An abandoned shaft mine site

at Germany


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In Situ Leaching

Used When:Deposits are too deep or

Beds are not thick enough for conventional underground mining

Its a process involving recovery of minerals through drilling of

boreholes into the deposit

Extraction is carried out by pumping a leaching solution (also

called leachate solution) into the ore deposit. The solution

dissolves with the ore and is then pumped to the surface via a

second borehole and processed further

Solvents used include water, sulphuric acid, sodium bicarbonate

and many more depending on the properties of the ore

Its advantages are:

Miners are not exposed to the ore body.

There is reduced radiation because the ore is in solution form.

Less expensive because large masses of rock need not be broken up

this saves time too and therefore production runs of the end product areshorter.

Can also be used to mine smaller, narrower and lower grade ore bodies.

Diagrammatic representation of In Situ

LeachingMinerals extracted using this method: Uranium

and Copper


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Heap Leaching

An industrial mining process to extract precious metals andcopper compounds from ore.

Mining Method:

The soil on a sl ightly sloping ground is first compacted and then

covered with an impermeable pad like an asphalt layer or a flexible

plastic sheet.

The extracted ore is broken into small chunks and heaped on this

impermeable pad.

Here it is sprayed with the leaching reagent

Sprinklers or drip irrigation are used for this in order to minimize

evaporation.

The leachate (metal containing solution) drained from the heap is

collected in a pond and the solution is subsequently sent for metal

recovery. The solution containing the metal is also known as

pregnant solution

Precious metals are extracted using dilute cyanide solution and

sulphuric acid is used to extract copper and nickel.

Heap leaching takes months to process as compared to dump

leaching which takes years.

Diagrammatic representation of Heap

LeachingMinerals extracted using this method: Precious

metals, copper and nickel

In some cases Gold too.


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Heap Leaching

Factors to be considered for successful heap leaching are:Good permeability should be maintained

A good water balance should be maintained.

pH control

A steady supply of leaching reagents

Permeability is critical for the recovery rates from a heap. If the

heap is very compact, the leaching operation will take more

time as the reagent will percolate slowly through the heap. If

the heap is uneven, some part of the heap may remain

untreated.

To address such problems fine particles are agglomerated (or

clustered together) to ensure good permeability.

A heap leach plant at Al-Haja in Saudi

Arabia


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Land Rehabilitation / Reclamation

Land Rehabilitation is the process of returning land in a given area to some degree of its former state, aftersome process has resulted in its damage, like Mining, farming , forestry etc.

A re-engineering process that attempts to restore an area of land back to its natural state after it has been

damaged as a result of some sort of disruption. The process involves such things as removing all man-made

structures, toxins and other dangerous substances, improving the soil conditions and adding new flora.

Modern mine rehabilitation aims to minimize and mitigate the environmental effects of modern mining,

Reclamation after Open pit mining would involve moving a significant volume of rock.

A rehabilitation method followed after mining is done would involve among other things:

Flattening of waste dumps through contouring to prevent erosionOres containing sulphides are covered with a layer of clay to prevent access of rain and oxygen from the

air which could oxidize the sulphides to produce sulphuric acid

Landfills are covered with topsoil and vegetation is planted to help consolidate the material

Fencing is done to protect dumps from becoming devoid of vegetation, due to grazing by livestock

The open pit is surrounded with a fence to prevent access and it generally fills up with groundwater

Tailing Dams are left to evaporate, then they are covered with waste rock or clay if required and soil is

planted for stabilization purposes.

Rehabilitation is not a significant problem for underground mines, this is due the higher grade of the ore and

lower volumes of waste rock and tailings.

The plant and infrastructure are not always removed as many plants have cultural heritage and value.


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Glossary of terms

Overburden: It refers to the material that lies above the soil and ecosystem and that needs to be removedbefore the mineral can be removed by using strip mining.

Outcrop: An exposure of rock or mineral deposit that can be seen on surface, that is, not covered by soil or

water.

Placer / Placer Deposit: A placer deposit or placer is an accumulation of valuable minerals formed by

deposition of dense mineral phases in a trap site.

Longwall Mining: A form of underground coal mining where a long wall (typically about 250-400 m long) of coal

is mined in a single slice

Shortwall Mining: An underground mining method in which small areas are worked (15 to 150 feet) by acontinuous miner in conjunction with the use of hydraulic roof

Dredge: A power shovel to remove material from a channel or riverbed. It is a device for scraping or sucking the

seabed, used for dredging

Dredger: A dredger is a ship or boat equipped with a dredge

In Situ: In situ is a Latin phrase meaning in the place. It is used in many different contexts.

Leaching: The downward transport of dissolved or suspended minerals, fertilizers and other substances by

water passing through a soil or other permeable material.

Leachate: The liquid produced when water percolates through any permeable materialAquifer: An underground layer of water-bearing permeable rock or unconsolidated materials from which

groundwater can be usefully extracted.


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Glossary of terms

Asphalt: Asphalt is a sticky, black and highly viscous liquid or semi-solid that is present in most crudepetroleum and in some natural deposits.

pH: pH is the measure of the acidity or basicity of the solution

Permeability: It is a measure of the ability of a material (typically, a rock or unconsolidated material) to transmit

fluids.

Landfill: A low area that has been filled in.

Contouring: The process of removing material completely outside of a l ine or region.

Tailings - The material that remains after all economically and technically recoverable precious metals have

been removed from the ore during processing

mining methods in australia

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