Wednesday, April 29, 2015

The Goldstrike Mine.

Barrick Goldstrike Mine

It is owned and operated by the world's largest gold mining company, & it is the largest gold mine in North America.
The Goldstrike Mine.
The Goldstrike Mine.

Location: Eureka County, Nevada, United States.
Products: Gold , Silver.
Ore Type: Epithermal gold deposite in carbonate or silicate sedimentary rocks.
Owner: Barrick Gold.
Ounces of gold produced in 2014 >> 902,000
Ounces of proven and probable gold reserves >> 9,614,000
Overview: The Goldstrike mine, one of the top five gold-producing mines in the world, is Barrick Gold’s largest producing mine. The mine consists of both the Betze-Post open-pit and the Meikle and Rodeo underground mines (the “Goldstrike Mine”). Barrick, which is also the biggest gold producer in the world, has operated the mine for over 20 years (since 1987). The mine is located on the Carlin Trend in north-central Nevada, USA, about 40 kilometers northwest of the city of Elko. In 2007, the Goldstrike operation produced 1.63 million ounces of gold at average total cash costs of $373 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 prolific gold producing region of North America. The northwestsoutheast trend is an 80 km long, 8 km wide belt that contains more than 20 major gold deposits. The operation employs approximately 1,600 employees.

Geological settings & Mineralization : The Goldstrike mine complex (including the Betze-Post-Screamer and Meikle Rodeo deposits). 
Betze-Post Open Pit
After Barrick took over the operation, two sulphide ore zones were identified as the Betze and Deep Post deposits in 1987. Since it entered production in 1993, the Betze-Post pit has been a truck-and-shovel operation using large electric shovels. The Betze-Post ore zones extend for 1,829 meters northwest and average 183 to 244 meters in width and 122 to 183 meters in thickness. The Post oxide orebody occurs in the siliceous siltstones, mudstones, argillites and minor limestones of the Rodeo Creek Formation. The Betze and Post oxide deposits are hosted in sedimentary rocks of Silurian to Devonian age. The mineralization of the Betze-Post pit was captured by structural traps developed by Mesozoic folding and thrust faults. Volcanic and sedimentary rocks filled ranges and basins formed by Tertiary faulting. The Tertiary volcanism initialized gold mineralization approximately 39 million years ago.
In 2007, the open pit mine produced 1,215,000 ounces of gold from 136.9 million tons mined and 10.5 million tons processed. The average grade processed is 0.136 oz/ton with a recovery rate of 85.5%. The average total cash cost was $355 per ounce. The open pit mine has proven and probable reserves totaling 12.19 million ounces from 94.9 million tons grading 0.128 oz/ton. The mine is expected to sustain the current production level for approximately 8 years, based on existing reserves. Most of the open pit mine is subject to a net smelter return of up to 4% and a net profits interest of up to 6%. 

Meikle Rodeo deposits
The Meikle deposit occurs in hydrothermal and solution collapse breccias in the Bootstrap Limestone of the Roberts Mountains Formation. The gold at Goldstrike was carried into the various orebodies by hot hydrothermal fluids, and deposited with very fine pyrite and silica. Over time, the pyrite oxidized, freeing the gold and making its extraction relatively easy, as in the Post Oxide deposit. In the deeper deposits – Betze, Rodeo and Meikle – the gold is still locked up with the iron sulphide and an additional processing step (autoclaving or roasting) is required to free the gold. 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. In the year ended December 31, 2007, the underground mine produced 413,186 ounces of gold at an average total cash cost of $431 per ounce. Proven and probable reserves underground are estimated at 7.42 million tons at 0.364 oz/ton, containing 2.7 million ounces. The Goldstrike’s total (open pit and underground) proven and probable mineral reserves as of December 31, 2007 are estimated at 14.9 million ounces of gold. The underground mine, which originally produced at a rate of approximately 2,000 tons of ore per day, averaged 3,562 tons per day in 2007. Based on current reserves and production capacity, the expected mine life is 9 years. The maximum royalties payable on the Meikle deposit are a 4% net smelter return and a 5% net profits interest.

Mining Processing & operations: The Goldstrike complex consist of three distinct mines: the large Betze-Post open pit mine, and the Meikle and Rodeo underground mines. The ore from all three mines is milled and leached by the cyanide process. Carlin-type gold deposits host gold mainly as microscopically fine grains. Refractory non-carbonaceous sulphide ore is treated in an autoclave followed by a carbon-in-leach (CIL) cyanidation circuit. Carbonaceous ore, also refractory, is treated with a roaster followed by a CIL circuit. The two treatment facilities treat ores from both the open pit and underground mines. Recovered gold is processed into doré on-site and shipped to outside refineries for processing into gold bullion.
In 2008 the Betze-Post open-pit mine produced 1,281,450 oz (36,328 kg) of gold and 152,886 oz (4,334.2 kg) of silver, while the Meikle-Rodeo underground operations yielded 424,687 oz (12,039.7 kg) of gold and 51,438 oz (1,458.2 kg) of silver. This was 30% of the total 5,698,000 oz (161,500 kg) output of all gold mining operations in Nevada.
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.

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