Property
Goldstrike Mine – Nevada’s Giant
Golden Goose
Goldstrike operation overview.
By Peggy Tsai
T
he 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.
How It All Started
Gold was first mined in an open-pit, heap leach operation by
PanCana Minerals Ltd, in 1976. Mining was focused on shallow
oxide deposits, specifically the Post deposit.
PanCana then entered into a 50/50 joint venture with
Western State Minerals Corporation in 1978. Reserves for the
Post deposit were delineated in 1986 and mining started in 1987.
By 1987, Barrick had acquired 100% ownership of the property
from both companies.
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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 Underground Operation
The Meikle and Rodeo underground mines are located 1.6
km north of the Betze-Post pit. The underground deposits are
hosted by carbonate breccias and limestone of the Devonian
Popovich Formation and various intrusive rocks. The deposits
follow the same mineralized trend as the open pit deposits.
The high-grade Meikle orebody was discovered in 1989 and
entered into production 7 years later in 1996. The moderategrade Rodeo orebody, located 0.5 kilometers northwest of the
open pit mine, was discovered in 1988. Production commenced
in 2002. The trackless underground operations use two different underground mining methods: long-hole open stoping and
drift-and-fill. The drift-and-fill method is chosen for flat-lying
mineralization or less competent ground conditions. The bulk of
the ore is hard and competent, since silification is the dominant
alteration.
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
Property
Betze open pit and Meikle underground mines.
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.
Processing
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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Environment
Water
In order to meet the rising demand for gold, extracting large
amounts of gold in Nevada comes with a price tag. Environmental
problems that come with gold mining in the desert include depletion of water reserves in aquifers, contamination of post–mining
artificial lakes, release of airborne mercury and the use of cyanide
in processing. Water is pumped from mines to keep them from
flooding, inherently removing water from surrounding aquifers.
The water is then used in the processing of ores, transported
into settling ponds for returning to the aquifer, or sent to sand
dune drainage/evaporation or used in irrigation. After the mines
are closed, water starts to fill in the pits and forms artificial
lakes. Water evaporates from these artificial lakes in the dry
desert at an accelerated pace. Some of the artificial lakes may
be poisonous due to the formation of acid from exposed rocks
and the leaching of metals such as arsenic and selenium into
the lakes. The long term implication of changing the hydrological
system is still uncertain.
Airborne Mercury and Cyanide from Processing
Mercury, produced from roasting ores and burning coal, is released into the air, which then bio-accumulates in the environment, specifically in the adjacent public ranch lands. Airborne
mercury is brought down by rain and enters into water bodies
such as lakes where it is taken up by organisms such as fish.
A dilute sodium cyanide solution is used in the leaching of ore.
Cyanide solution stored in tailing ponds can be released into
the outside environment if tailing ponds rupture.
However, in response to these environmental problems,
mining companies, including Barrick, have taken action to protect water quality, conserve water and control pollution. The
Goldstrike mine is equipped with air pollution control devices
on its facilities adhering to, and sometimes, exceeding legal
requirements. Various water reuse and conservation programs
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Above: Roaster plant.
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Below: Meikle underground drill
Property
have been implemented at the mine. To prevent cyanide spill or
seepage, the mine utilizes multiple levels of spill containment
procedures that are under routine inspection and monitoring.
In the last year, all activities at the Goldstrike property were in
compliance with environmental regulations and requirements
such as the International Cyanide Management Code. As at
the end of last year, the recorded amount of estimated future
reclamation and closure costs that were also asset retirement
obligations for the property was $98 million.
Current Activities 2007/2008
In 2007, a total of 20,774 meters of underground and surface
drilling were completed. Exploration and development drilling
focused on delineation of the Banshee underground reserve
and the Deep North Post resource. Results have demonstrated
continuity. Late in 2007, an exploration drift to access the Deep
North Post area commenced. In 2008, exploration drilling will
focus on delineation of the East Banshee reserve and the Deep
North Post and West Pit resource.
In addition, a 10-acre solar farm is to be located next to
the 115-megawatt natural gas-fired power plant. The farm will
generate one additional megawatt to meet state targets for renewable energy use.
At the open pit, overburden removal is ongoing until mid2008. Pit ore production will be limited and mill feed will be
supplemented by lower-grade stockpiled ore. At the underground mine, transitioning to zone mining in 2007 has lowered
production. However, in the second half of 2008, mines production is expected to increase when higher-grade ore is accessed.
In 2008, the Goldstrike property is expected to produce 1.66
to 1.72 million ounces of gold at average total costs of $410 to
$420 per ounce.
Links and References
Barrick Gold
Barrick Gold Annual Information Form 2007
Barrick Gold Annual Report 2007
Betze-Post Open Pit
Goldstrike Mine
Goldstrike Responsibility Report
In Nevada, Gold Mines Drink a Desert Dry
International Cyanide Code Report
Meikle and Rodeo Underground Mines
The Cost of Gold – Water Worries
Use of Cyanide
Use of Cyanide in Carbon-in-Leach Processing
Click here for full list of links:
http://go.mining.com/sept08-a12
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