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| Mining operations in underground Agnew gold mine |
The Agnew Gold Mine and and previously named Emu Mine , is a gold mine located 375 kilometres north of Kalgoorlie, 3 kilometres west of Agnew, Western Australia. Agnew Gold Mine is Acquired in 2001 by Gold Fields, mining company from South Africa, and It is one of two mines the Gold Fields company an operates in Australia, the other mine being the St Ives Gold Mine.
The Agnew gold deposit was first discovered in 1895, and the first mining operation by Waroonga Gold Mines, which then often changed ownership. As the legal entity holding and conducting mining activity on the Agnew mine mineral leases then in 2001 was incorporated The Agnew Gold Mining Company Proprietary Limited (AGMC)
Agnew controls over a total area of 69,269 hectares (total of granted tenements) for exploration and mineral rights, has security of tenure for all current exploration and mining leases that contribute to future Mineral Reserves in Agnew mine. The Gold Fields Limited Group holds 100% of the issued shares of AGMC through its 100% holding in the issued shares of Orogen Holding (BVI) Limited.
MINERAL DEPOSITS IN AGNEW MINE
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| Minerals in the Agnew mine |
The gold mineralisation in Agnew is mainly found in the Kim and Main ore bodies, in the quartz breccia lodes which are 4m to 9m wide, and Main North lodes that are accessed via declines. Mineralisation at the Main ore body occurs in steeply north dipping axial planar structures.
Agnew is part of the Norseman – Wiluna Greenstone Belt which is highly mineralised with gold and nickel. The mine area largely contains tholeiitic and komatiitic volcanic rocks, and albitic sedimentary rocks. It features a series of distinct felsic volcanic centres. The structure of the mine is linear with north trending strike-slip faults.
Orogenic greenstone gold deposits hosted in a number of different styles of lodes. Although all of the Agnew deposits broadly occur at the intersections between structures and stratigraphy, there are subtle differences in alteration and mineralisation, that are controlled in part by the local host rock chemistry
The greenstone belt of the Agnew area has been metamorphosed to upper greenschist and lower amphibolite metamorphic grades. Gold mineralisation is found in quartz, breccia lodes, quartz tensional (rock stressed in opposite directions) veining, and disseminated arsenopyrite-pyrite-biotite mineralisation along the contacts between a sandstone and ultramafic conglomerate, and other contacts within the conglomerate package. High grade gold ore shoots plunge steeply to the north along these contacts.
MINING METHODS AND MINERAL PROCESSING IN AGNEW GOLD MINE AUSTRALIA
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The process of drilling in underground mines Agnew
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Mining at the main orebody is divided into two zones – the northern and southern. Ore from the northern zone is extracted by transverse stoping and from the southern zone by open stoping.
New Holland mining occurs in two primary areas Genesis 500 and Sheba that are accessed via declines.
The underground workings are accessed from the old Waroonga Pit, via the Kim decline which extends to more than 850 metres below the surface. Stopes are mined by mechanised sub-level stoping and backfilled using paste fill
The mining areas also include the Songvang North openpit. Access to the underground mine is through the Waroonga openpit, which includes an access portal, emergency egress and ventilation drive.
The Rajah Lode was mined in 2012 using the modified Avoca Method. This is a variation of bench-stoping methodology where the fill typically consists of uncemented waste rock that is introduced to control wall stability at intervals from 20 to 30 metres.
During 2012 the Main Lode North ore body was extracted using transverse stoping, with mining commencing at the footwall and retreating to the hangingwall. The stopes were accessed via a tramming drive developed in the hangingwall sandstone. The final northern cutback of the Songvang pit was completed in February 2012.
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| Process of transporting the material rock from the underground mines toward the processing plant |
The Agnew process plant mineral ore has a capacity of 1.3 million tonnes per annum.
The comminution for mineral ore circuit comprises a contractor-owned and operated three-stage crushing plant, feeding a fine ore stockpile, ahead of a two-stage closed circuit ball milling circuit.
The gravity circuit includes a Knelson concentrator and an in-line leach reactor which recovers approximately 40% of total gold production in the Agnew gold mine.
A Knelson concentrator is a type of gravity concentration apparatus, The apparatus is used for the recovery of fine particles of free gold, the gold that does not require gold cyanidation for recovery
The key components of the unit include: a cone shaped "concentrate" bowl, which is rotated at high speed by an electric motor and a pressurized water jacket encompasses the bowl.
Feed material, typically from a ball mill discharge or cyclone underflow bleed, is fed as a slurry toward the center of the bowl from above. The feed slurry contacts the base plate of the vessel and, due to its rotation, is thrust outward.
The outer extremities of the concentrated bowl house a series of ribs, and between each pair of ribs is a groove. During operation the lighter material flows upward over the grooves and the heavy mineral particles (usually of economic value) becomes trapped within them.
Pressurized water is injected through a series of tangential water inlets along the perimeter of each groove to maintain a fluidized bed of particles in which heavy mineral particles can be efficiently concentrated.
The Knelson concentrator typically operates as a batch process, with lighter [gangue] material being continuously discharged via overflow and a heavy mineral concentrate periodically removed by flushing the bowl with water.
In the process plant at Agnew mine, there is also a conventional Carbon-in-Pulp (CIP) circuit.
The CIP circuit includes leach and absorption tanks followed by a pressure Zadra carbon elution circuit. Currently, the overall metallurgical recovery averages around 93.5%.
The stockpiled ore, comprising the large blasted rock from underground, is crushed to under , and transported by conveyer to the grinding mill where water and lime are added prior to the ore being reduced in size by grinding to fine sand particles with a width of 0.1 millimetres.
The slurry is then pumped through a series of six large tanks where additional chemical substances are added to further dissolve the gold. Carbon is added to the tanks to absorb and concentrate the gold, and later the gold is extracted from the carbon by a final chemical and electrowinning process before it is smelted into gold ‘ dore ’ bars.
The mineral reserves in the Agnew mine at the mine are expected to be depleted by 2017.
The comminution for mineral ore circuit comprises a contractor-owned and operated three-stage crushing plant, feeding a fine ore stockpile, ahead of a two-stage closed circuit ball milling circuit.
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| Stage crushing plant |
A Knelson concentrator is a type of gravity concentration apparatus, The apparatus is used for the recovery of fine particles of free gold, the gold that does not require gold cyanidation for recovery
The key components of the unit include: a cone shaped "concentrate" bowl, which is rotated at high speed by an electric motor and a pressurized water jacket encompasses the bowl.
Feed material, typically from a ball mill discharge or cyclone underflow bleed, is fed as a slurry toward the center of the bowl from above. The feed slurry contacts the base plate of the vessel and, due to its rotation, is thrust outward.
The outer extremities of the concentrated bowl house a series of ribs, and between each pair of ribs is a groove. During operation the lighter material flows upward over the grooves and the heavy mineral particles (usually of economic value) becomes trapped within them.
Pressurized water is injected through a series of tangential water inlets along the perimeter of each groove to maintain a fluidized bed of particles in which heavy mineral particles can be efficiently concentrated.
The Knelson concentrator typically operates as a batch process, with lighter [gangue] material being continuously discharged via overflow and a heavy mineral concentrate periodically removed by flushing the bowl with water.
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| Process plant conventional Carbon-in-Pulp at Agnew mine |
The CIP circuit includes leach and absorption tanks followed by a pressure Zadra carbon elution circuit. Currently, the overall metallurgical recovery averages around 93.5%.
The stockpiled ore, comprising the large blasted rock from underground, is crushed to under , and transported by conveyer to the grinding mill where water and lime are added prior to the ore being reduced in size by grinding to fine sand particles with a width of 0.1 millimetres.
The slurry is then pumped through a series of six large tanks where additional chemical substances are added to further dissolve the gold. Carbon is added to the tanks to absorb and concentrate the gold, and later the gold is extracted from the carbon by a final chemical and electrowinning process before it is smelted into gold ‘ dore ’ bars.
The mineral reserves in the Agnew mine at the mine are expected to be depleted by 2017.
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