Grasberg Gold & Copper Mine
It is the largest gold mine and the
third largest copper mine in the
Products: Gold &
Deposit Type: Porphyry deposits
associated with the 3.2 to 2.7 Ma Grasberg Igneous Complex, porphyry ores of
the 4.4 to 3.0 Ma Ertsberg Diorite 2.5 km to the south, and a series of skarns
deposits.Together these deposits account for near 80 Mt of copper and around
3900 tonnes of gold (including inferred resources).
Mineralisation associated with the Ertsberg intrusive includes: The Ertsberg
stockwork which contained a resource of 122 Mt @ 0.54% Cu, 0.90 g/t Au in
2005.The skarn mineralisation, which includes the: i). GB (Gunung Bijah) - 33
Mt @ 2.5% Cu, 0.8 g/t Au (the original reserve on which mining in the district
was commenced), which is surrounded by Ertsberg Diorite near its NW margin;
ii). GBT Complex (the vertically stacked GBT, IOZ & DOZ), 1.5 km east of GB
on the northern contact, with reserves of >230 Mt @ 1% Cu, 0.8 g/t Au, iii).
Dom Skarn, 0.5 km south of GBT, partially enclosed by the intrusive near its SE
margin, with >70 Mt @ 1.4% Cu, 0.4 g/t Au, iv). Big Gossan within a fault
zone cutting sediments to the west of the Ertsberg Diorite with 33 Mt @ 2.81%
Cu, 1 g/t Au, v). Kucing Liar (dated at 3.42 Ma, the oldest mineralisation in
the district, predating the Dalam Diorite) is associated with a fault zone
between the two intrusive complexes, but close to the Grasberg complex,
contains >225 Mt @ 1.42% Cu, 1.57 g/t Au.
|Block diagram showing the Grasberg Igneous Complex and zoned alteration. Weak stockwork and potassic alteration associated with South Kali Dikes are not shown.|
The workings comprise an open pit mine, an underground mine and four concentrators. The open pit mine – which forms a mile-wide crater at the surface – is a high-volume low-cost operation, producing more than 67 million tonnes of ore and providing over 75% of the mill feed in 2006.
Designed to be fully mechanised, using 6.2m3 Caterpillar R1700 load-haul-dump vehicles (LHDs) at the extraction level with a truck haulage level to the gyratory crusher, the Deep Ore Zone (DOZ) block cave mine is one of the largest underground operations in the world.
After 2004, when the DOZ mine averaged 43,600 tonnes/day a second underground crusher and additional ventilation were installed to increase daily capacity to 50,000 tonnes.
Ore from both operations is transported by conveyor to centralized mine facilities, feeding a combined daily average total of some 225,000t of ore to the mill and 135,000t to the stockpiles.
Production equipment includes 30m3–42m3 buckets, a 170-strong fleet of 70t–330t haul trucks, together with 65 dozers and graders, with radar, GPS and robotics used in the mine’s state-of-the-art slope-monitoring system.
Ore undergoes primary crushing at the mine, before being delivered by ore passes to the mill complex for further crushing, grinding and flotation. Grasberg’s milling and concentrating complex is the largest in the world, with four crushers and two giant semi-autogenous grinding (SAG) units processing a daily average of 240,000t of ore.
“This is a high-grade resource, with averages of 1.5% copper and 2 g/t gold.”
A flotation reagent is used to separate concentrate from the ore. Slurry containing 60-40 copper concentrate is drawn along three pipelines to the seaport of Amamapare, over 70 miles away, where it is dewatered. Once filtered and dried, the concentrate – containing copper, gold and silver – is shipped to smelters around the world.
The facilities at the port also include the PT Puncak Jaya coal-fired power station, which supplies the Grasberg operations.