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| The Goldstrike mine property complex is located on the Carlin Trend |
Goldstrike mine is the largest gold mining in North America and a most prolific gold mining district in the Western Hemisphere. The Goldstrike mine property complex is located on the Carlin Trend in nor th-central Nevada, about 35 miles northwest of St. George and about 60 kilometers northwest of Elko, Nevada, USA
The Goldstrike mine complex owned and operated by the world's largest gold mining company, Barrick Goldstrike Mines Inc. The Goldstrike operation includes the Betze-Post the largest open pit gold mine and the Meikle and Rodeo underground gold mine which are located just north of the Betze-Post pit, along the same mineralized trend, and Goldstrike mine adjoins Newmont Mining's Carlin mine complex
Barrick, which is the biggest gold producer in the world, has operated the mine for over 20 years (since 1987). In 2014, the Goldstrike property operation produced 902,000 ounces of gold at average total cash costs of $854 per ounce. The Goldstrike property comprises approximately 4,197 hectares of surface rights ownership and approximately 3,535 hectares of mineral rights ownership on the Carlin Trend, a pro-lific gold producing region of North America. Goldstrike’s proven and probable mineral reserves as at December 31, 2014, were 9.6 million ounces of gold
MINERAL DEPOSIT IN GOLDSTRIKE DISTRICT
Like most Carlin type gold deposits in Nevada the gold was epithermally deposited in carbonate or silicate sedimentary rocks. The source of the heat was magmatic but the exact mechanism is still under debate. The Betze-Post deposits are up to 6,000 feet (1,800 m) long, 600 feet (180 m) thick and 800 feet (240 m) wide.
The bulk of the ore of these deposits was found in a sandstone host rock occurring at the base of the early Tertiary Claron Formation. High-angle faults appear to have been important in localizing ore in these deposits as well as in the other four deposits, where most of the ore occurred in brecciated and silicified Paleozoic limestone units.
The pre-Tertiary rocks in the district are complexly folded and faulted and record a long history of tectonic activity that culminated in extensive overthrusting of the Paleozoic rocks onto a sequence of clastic rocks of Mesozoic age. This overriding thrust is not exposed in the Goldstrike district but most likely underlies the en-tire district.
Following this period of thrusting the area was nearly beveled by erosion. The Claron Formation was then deposited across the beveled surface, followed by extrusion of large volumes of volcanic tuffs. Later high-angle faulting offset the Tertiary rocks and formed conduits for the mineralizing solutions that produced the gold-silver ore bodies
Betze-Post is the largest gold deposit in the Carlin trend, where the Goldstrike deposit is located. The Betze-Post open pit zone is a combination of five generations of pyrite mineralisation.
Diagenetic and coarse grained pyrites are contained in the metamorphic aureole of the Goldstrike. It also consists of micro-veinlets of arsenic and gold bearing pyrite of fourth generation. The arsenian pyrite is further divided into coarsely grained sulphides at 200µm diameter.
Gold mineralisation at Betze-post is controlled by favourable stratigraphy and structural complexity. The ore zone is extended in an area of approximately 1,829m. It has a width of 183m to 244m, while the thickness varies from 122m to 183m.
The mineralisation is divided into three categories - disseminated carbonaceous mineralisation, Siliceous stibnite breccias mineralisation and Seam mineralisation.
The disseminated carbonaceous mineralisation occurs as an upper tabular zone of the Popovich Formation, consisting of high grade gold. The breccias mineralisation takes a tabular zone, and is 300ft long with 150ft thickness. It represents partially brecciated and silicified limestone structure.
The seam mineralisation is rich in realgar and orpiment substance, and occurs as dark decalcified fractures and argillaceous zones.
MINING OPERATION AND PROCESSING IN GOLDSTRIKE MINE
Mining Operation Goldstrike mine
The Goldstrike mine operation consist of three distinct mines: the large Betze-Post open-pit mine, and the Meikle and Rodeo underground mines.
The Betze-Post pit is Open pit mining process consists of the stages of drilling for blasting, sorting, hauling, and crushing of ore. Method in mine includes the use of bulldozers to strip and develop the deposit, bulldozers and shovel loaders for loading and dump trucks to remove the ore from the open pit.
Shovels dig up material from different areas in the open-pit mine, and load the material onto trucks to be hauled out of the open-pit mining area. Then ore is placed into crushing machines and conveyed to an ore mill for processing.
Meikle is a high-grade ore body which is mined by transverse longhole stoping, underhand drift and fill mining methods. Long hole stoping uses holes drilled by a production drill to a predetermined pattern. Long hole stoping is a highly selective and productive method of mining and can cater for varying ore thicknesses and dips (0 - 90 degree).
Rodeo is a further extension of the mineralization found at Goldstrike and is a trackless operation, using two different underground mining methods, longhole open stoping and drift-and-fill.
Ore Processing In Goldstrike
The Goldstrike mine property consists of two processing facilities: (1) an autoclave circuit, which is used to treat the property’s non-carbonaceous sulfide (refractory) ore; and (2) the roaster, used for treating carbonaceous ore (not suitable for autoclaving).
Like most Carlin type gold deposits in Nevada the gold was epithermally deposited in carbonate or silicate sedimentary rocks. The source of the heat was magmatic but the exact mechanism is still under debate. The Betze-Post deposits are up to 6,000 feet (1,800 m) long, 600 feet (180 m) thick and 800 feet (240 m) wide.
The bulk of the ore of these deposits was found in a sandstone host rock occurring at the base of the early Tertiary Claron Formation. High-angle faults appear to have been important in localizing ore in these deposits as well as in the other four deposits, where most of the ore occurred in brecciated and silicified Paleozoic limestone units.
The pre-Tertiary rocks in the district are complexly folded and faulted and record a long history of tectonic activity that culminated in extensive overthrusting of the Paleozoic rocks onto a sequence of clastic rocks of Mesozoic age. This overriding thrust is not exposed in the Goldstrike district but most likely underlies the en-tire district.
Following this period of thrusting the area was nearly beveled by erosion. The Claron Formation was then deposited across the beveled surface, followed by extrusion of large volumes of volcanic tuffs. Later high-angle faulting offset the Tertiary rocks and formed conduits for the mineralizing solutions that produced the gold-silver ore bodies
Betze-Post is the largest gold deposit in the Carlin trend, where the Goldstrike deposit is located. The Betze-Post open pit zone is a combination of five generations of pyrite mineralisation.
Diagenetic and coarse grained pyrites are contained in the metamorphic aureole of the Goldstrike. It also consists of micro-veinlets of arsenic and gold bearing pyrite of fourth generation. The arsenian pyrite is further divided into coarsely grained sulphides at 200µm diameter.
Gold mineralisation at Betze-post is controlled by favourable stratigraphy and structural complexity. The ore zone is extended in an area of approximately 1,829m. It has a width of 183m to 244m, while the thickness varies from 122m to 183m.
The mineralisation is divided into three categories - disseminated carbonaceous mineralisation, Siliceous stibnite breccias mineralisation and Seam mineralisation.
The disseminated carbonaceous mineralisation occurs as an upper tabular zone of the Popovich Formation, consisting of high grade gold. The breccias mineralisation takes a tabular zone, and is 300ft long with 150ft thickness. It represents partially brecciated and silicified limestone structure.
The seam mineralisation is rich in realgar and orpiment substance, and occurs as dark decalcified fractures and argillaceous zones.
MINING OPERATION AND PROCESSING IN GOLDSTRIKE MINE
Mining Operation Goldstrike mine
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| Open pit mining process in Betze-Post |
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| Blasting mining process in Goldstrike mine |
The Goldstrike mine operation consist of three distinct mines: the large Betze-Post open-pit mine, and the Meikle and Rodeo underground mines.
The Betze-Post pit is Open pit mining process consists of the stages of drilling for blasting, sorting, hauling, and crushing of ore. Method in mine includes the use of bulldozers to strip and develop the deposit, bulldozers and shovel loaders for loading and dump trucks to remove the ore from the open pit.
Shovels dig up material from different areas in the open-pit mine, and load the material onto trucks to be hauled out of the open-pit mining area. Then ore is placed into crushing machines and conveyed to an ore mill for processing.
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| Long hole stoping uses holes drilled in Underground mine |
Rodeo is a further extension of the mineralization found at Goldstrike and is a trackless operation, using two different underground mining methods, longhole open stoping and drift-and-fill.
Ore Processing In Goldstrike
The Goldstrike mine property consists of two processing facilities: (1) an autoclave circuit, which is used to treat the property’s non-carbonaceous sulfide (refractory) ore; and (2) the roaster, used for treating carbonaceous ore (not suitable for autoclaving).
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| These processing plant facilities ores for both mine, the surface mining and underground operations. |
These facilities treat ores from both the surface and underground operations. Two haulage drifts connect the Meikle and Rodeo orebodies. The drifts are accessed from two shafts and by a decline at the bottom of the open pit mine.
Non-carbonaceous sulphide (refractory) ore is treated at an autoclave and carbon-in-leach (CIL) cyanidization circuit. Carbonaceous ore is treated at the roaster and CIL circuit, since the active carbon content in carbonaceous ore responds poorly to autoclaving. The two facilities treat ores from both the open pit and underground mines and, when combined, have a design capacity of 33,000 to 35,000 tons per day.
Recovered gold is processed into doré on-site and shipped to outside refineries for processing into gold bullion.
A modified pressure leach technology was successfully tested last year and it will be used to process ores that would otherwise have been treated at the roaster facility, consequently extending the life of the autoclave. The property also has a 115 megawatt natural gas-fired power plant, providing a significant portion of the operation’s power requirements off-grid
Barrick’s chemists, metallurgists and engineers have been working for more than two decades to perfect the process and bring it to commercial scale. They’ve honed the process in the lab and in a pilot test plant, but the unique chemistry of using a sodium thiosulfate compound instead of cyanide may pose additional and unforeseeable challenges when the autoclaves are scaled back into full production
The sustainability of the gold industry is being challenged by reducing grades, more complex ores and increasingly stringent environmental conditions. CSIRO is helping the industry reduce the risks and environmental impact of current processing operations by developing alternative processes that use less-toxic alternatives to cyanide.
The CSIRO-patented cyanide-free thiosulphate process is adding value to Barrick Gold Corporation‘s gold operation. The first gold bar produced with the thiosulphate process was poured in late 2014 at Barrick’s Goldstrike plant in Nevada, USA and operations are ramping up to recover gold from four million tonnes of stockpiled ore that was uneconomic to process by traditional methods.
Thiosulphate has long been seen as a potential alternative to cyanide for liberating gold from ores, but until now it has proved difficult to master. Cyanide is highly toxic and an environmental hazard.
As part of the thiosulphate process at Goldstrike, gold-bearing ore is heated as a thick slurry of ore, air, water and limestone in large pressure chambers or autoclaves and then pumped into the new ‘resin-in-leach’ circuit that takes place inside large stainless steel tanks.
Within the tanks, the slurry interacts with thiosulfate and a fine, bead-like material called resin that collects the gold.
At full capacity, 13,400 tons of ore can be processed daily, with leaching taking place simultaneously in two sets of seven tanks.
The thiosulphate process will enable Barrick to contribute an average of 350 to 450 thousand ounces of gold each year to their operation, allowing the large plant to keep operating, preserving jobs and bringing much needed income to the State.
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| Gold leaching process at the goldstrike factory |
Recovered gold is processed into doré on-site and shipped to outside refineries for processing into gold bullion.
A modified pressure leach technology was successfully tested last year and it will be used to process ores that would otherwise have been treated at the roaster facility, consequently extending the life of the autoclave. The property also has a 115 megawatt natural gas-fired power plant, providing a significant portion of the operation’s power requirements off-grid
Barrick’s chemists, metallurgists and engineers have been working for more than two decades to perfect the process and bring it to commercial scale. They’ve honed the process in the lab and in a pilot test plant, but the unique chemistry of using a sodium thiosulfate compound instead of cyanide may pose additional and unforeseeable challenges when the autoclaves are scaled back into full production
The sustainability of the gold industry is being challenged by reducing grades, more complex ores and increasingly stringent environmental conditions. CSIRO is helping the industry reduce the risks and environmental impact of current processing operations by developing alternative processes that use less-toxic alternatives to cyanide.
The CSIRO-patented cyanide-free thiosulphate process is adding value to Barrick Gold Corporation‘s gold operation. The first gold bar produced with the thiosulphate process was poured in late 2014 at Barrick’s Goldstrike plant in Nevada, USA and operations are ramping up to recover gold from four million tonnes of stockpiled ore that was uneconomic to process by traditional methods.
Thiosulphate has long been seen as a potential alternative to cyanide for liberating gold from ores, but until now it has proved difficult to master. Cyanide is highly toxic and an environmental hazard.
As part of the thiosulphate process at Goldstrike, gold-bearing ore is heated as a thick slurry of ore, air, water and limestone in large pressure chambers or autoclaves and then pumped into the new ‘resin-in-leach’ circuit that takes place inside large stainless steel tanks.
Within the tanks, the slurry interacts with thiosulfate and a fine, bead-like material called resin that collects the gold.
At full capacity, 13,400 tons of ore can be processed daily, with leaching taking place simultaneously in two sets of seven tanks.
The thiosulphate process will enable Barrick to contribute an average of 350 to 450 thousand ounces of gold each year to their operation, allowing the large plant to keep operating, preserving jobs and bringing much needed income to the State.
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