Grasberg is a world-class mining complex in Indonesia, where Freeport-McMoRan Copper & Gold is engaged in exploration and development, mining and milling of ore containing copper, gold and silver.
PT Freeport Indonesia commenced mining operations at this site in 1972 and in 1988 discovered the Grasberg mine. Today, after significant production, the Grasberg mining district contains the world's largest recoverable copper reserve and the largest gold reserve.
The Grasberg mine is located at Tembagapura in Irian Jaya, which is Indonesia's easternmost province, on the western half of the island of New Guinea. The mine is about 60 miles north of Timika, a town of about 100,000 people. There are about two million people living in this region. The Lorentz National Park, which has several glaciers on its peaks, lies to the east of the mine.
The mine is 96 km north of the southwest coast of Indonesia at elevations of 2,500 to 4,200 m above sea level. PT Freeport has constructed an airport, a port at Amamapare, a 119 km road, an aerial tramway, a hospital and related medical facilities, two town sites with housing, schools, and other facilities sufficient to support more than 17,000 persons.
The Grasberg deposit is the main deposit in the Grasberg complex. The deposit originally formed the core of a 4,100 m high mountain, which has been mined by open pit methods to the 3,000 m level (1998). The Grasberg mine includes a high-grade core and the main Grasberg deposit which are currently being mined, as well as the underlying Heavy Sulfide and Deep Grasberg deposits.
Ore bodies are located within and around two main igneous intrusions, the Grasberg monzodiorite and the Ertsberg diorite. The host rocks of these ore bodies include both carbonate and clastic rocks that form the ridge crests and upper flanks of the Sudirman Range, and the igneous rocks of monzonitic to dioritic composition that intrude them. The igneous-hosted ore bodies (the Grasberg open pit and block cave, and the DOZ block cave) occur as vein stockworks and disseminations of copper sulphides, dominated by chalcopyrite and, to a much lesser extent, bornite. The sedimentary-rock hosted ore bodies occur as "magnetite-rich, calcium/magnesian skarn" replacements, whose location and orientation are strongly influenced by major faults and by the chemistry of the carbonate rocks along the margins of the intrusions.
The copper mineralization in these skarn deposits is also dominated by chalcopyrite, but higher bornite concentrations are common. Moreover, gold occurs in significant concentrations in all of the district's ore bodies, though rarely visible to the naked eye. These gold concentrations usually occur as inclusions within the copper sulphide minerals, though, in some deposits, these concentrations can also be strongly associated with pyrite.
Mining & Operation
Freeport began open-pit mining of the Grasberg ore body in 1990. Open-pit operations are expected to continue through 2015, at which time the Grasberg underground mining operations are scheduled to begin. Production is currently at the 3,295-to 4,285-m elevation level and totaled 49.0 million metric tons of ore in 2008 and 57.5 million metric tons of ore in 2007, which provided 67 percent of our 2008 mill feed and 75 percent of our 2007 mill feed. Remaining mill feed comes from our DOZ mine. The current Grasberg equipment fleet consists of over 500 units. At December 31, 2008, the larger mining equipment directly associated with production included an available fleet of 157 haul trucks with payloads ranging from approximately 215 metric tons to 330 metric tons and 19 shovels with bucket sizes ranging from 30 cubic meters to 42 cubic meters, which in 2008 moved an average of 669,000 metric tons per day.
Ore from the open pit and from underground block-caving operations is transported by conveyor through adits to centralized mine facilities. Mine facilities include a power plant, several mills, crushing and screening operations, concentrators, thickeners, and a pump station. Three pipelines deliver concentrate (slurry) composed of 65% solids-by-weight from the mill to the port site at Amamapare 74 miles away.
Facilities include several mills, crushing and screening operations, concentrators, thickeners, and a pump station. This is also the base of a 2,000 foot tram that transports workers and equipment up to the mine. Three pipelines deliver concentrate composed of 65% solids-by-weight from the mill to the port at Amamapare, 74 miles down the mountain. The facilities at Amamapare include a coal-fired power plant.
Grasberg crushing and conveying systems are integral to the mine and provide the capacity to transport up to 225,000 metric tons per day of Grasberg ore to the mill and 135,000 metric tons per day of overburden to the overburden stockpiles. The remaining ore and overburden is moved by haul trucks.
The milling complex is at the 9,000 foot elevation. After primary crushing at the mine, ore is delivered by ore passes to the mill where it receives further crushing, grinding, and flotation.
The mill's four crushing units process an average of 240,000 tons of ore daily. Two giant Semi-Autogenous Grinding (SAG) units pulverize the rock material into fine gravel. Semi-Autogenous Grinding (SAG) units, including a 34-foot SAG mill (Concentrator #3) and a 38-foot SAG (Concentrator #4), helped the operations achieve record volumes and improved metals recovery.
A flotation reagent used in the flotation process to separate the concentrate from the ore evaporates rapidly and cannot be detected even a short distance from the mill.
Slurry containing a 60-40 copper concentrate is shipped by pipelines to the seaport at Amanapare where it is dewatered. The rock and water slurry is agitated in the tanks and alcohol based reagents are added to cause the copper and gold-bearing minerals to adhere to air bubbles, which are collected as copper concentrate. The process at PT Freeport Indonesia does not involve the use of cyanide or mercury, nor does it involve chemical alteration of the ore.
Once the concentrate is filtered and dried, it is shipped to a smelter around the world.
The PT Puncak Jaya coal-fired power plant beside the port supplies power to the Grasberg operations.