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| Grasberg open pit mine at Tembagapura provinces of Papua Irian Jay seen from the heights |
The largest Gold Mine in world, Grasberg mine located some 60 miles north of Timika, at Tembagapura provinces of Papua Irian Jaya, and is the most eastern provinces at the country Indonesia. Grasberg mine is a joint venture between Freeport-McMoRan Copper & Gold (67.3%) and mining juggernaut Rio Tinto (13%), Government of Indonesia (9.3%) and PT Indocopper Investama Corporation (9.3%). Grasberg mine operator is PT Freeport Indonesia (a subsidiary of Freeport McMoRan Copper and Gold)
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| Grasberg open pit mine in the Jayawijaya Mountain glaciers at Papua Irian Jaya provinces Indoonesia |
The story of the Grasberg mine at Tembagapura provinces of Papua Irian Jaya began in the mid-1930s when Dutch colonists discovered copper deposits in the Jayawijaya Mountain glaciers in Papua Irian Jaya. PT Freeport Indonesia commenced mining operations in 1972 and in 1988 discovered the Grasberg mine. The Grasberg mining district contains one of the world’s largest recoverable copper reserve and the largest gold reserve. About 800 people working in mines Grasberg at Tembagapura provinces of Papua Irian Jaya
Grasberg mine have several projects in progress in the Grasberg minerals district related to the development of large-scale, long-lived, high-grade underground ore bodies located beneath and nearby the Grasberg open pit.
Development of the Grasberg Block Cave and Deep Mill Level Zone (DMLZ) is advancing to enable the DMLZ to commence production in late 2015 and the Grasberg Block Cave mine to commence production in early 2018.
Grasberg mine also has an underground mine development project for the long term in the area of " Kucing Liar " ore body, which lies on the southern flank of and underneath the southern portion of the Grasberg open pit.
MINERAL DEPOSIT IN GRASBERG MINE IRIAN JAYA
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| Mineral rock deposit in the Grasberg mine |
The Grasberg mine stands at the collision of the Indo-Australian and the Pacific tectonic plates. Two distinct phases of intrusion have led to the production of nested coaxial porphyry ore bodies and sulphide rich skarn at the margins, while sedimentary strata includes Eocene clastic carbonate limestone with siltstones and sandstones near the base.
Mineral deposits in the Grasberg mine, located in and around the two main igneous intrusions, Grasberg monzodiorite and diorite Hertzberg.
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
The igneous-hosted ore bodies (the Grasberg open pit and block cave, and portions of 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 (portions of the DOZ and all of Big Gossan) 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 dominated by chalcopyrite, but higher bornite concentrations are common. Moreover, gold occurs in significant concentrations in all of the district’s ore bodies.
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.
Mineral deposits in the Grasberg mine, located in and around the two main igneous intrusions, Grasberg monzodiorite and diorite Hertzberg.
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
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| The Grasberg complex the layout of the Grasberg/ Ertsberg minerals district reserves |
The igneous-hosted ore bodies (the Grasberg open pit and block cave, and portions of 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 (portions of the DOZ and all of Big Gossan) 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 dominated by chalcopyrite, but higher bornite concentrations are common. Moreover, gold occurs in significant concentrations in all of the district’s ore bodies.
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 PROCESS IN GRASBERG MINE
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| The transport of mineral rocks by Haul truck to processing plant |
Open pit operations in Grasberg mine, including drilling and blasting rock minerals. Ore mineral and waste rock are crushed at the surface facilities in the grasberg mine later in the shovel and put into trucks using 6.2m3 Caterpillar R1700 load-haul-dump vehicles (LHDs) . Then the next process, the transport of mineral rocks by Haul truck to stockpiles for processing plant
Grasberg mine provide the capacity to transport up to 150,000 mtd of ore to the mill and 75,000 mtd of overburden to the overburden stockpiles. The remaining overburden is moved by haul trucks.
PT Freeport Indonesia began production underground mine from the DOZ ore body in 1989 using open stope mining methods, but suspended production in 1991 in favor of production from the Grasberg open pit. Production resumed in September 2000 and is expected to continue through 2020, after the success of PT Freeport Indonesia for the development of DOZ, one of the largest underground mine in the world.
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| The activities of workers in underground mines |
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| The process of drilling in underground mines |
Other underground mines in the Grasberg mine is Big Gossan underground mine. The Big Gossan mine lies underground and adjacent to the current mill site. It is a tabular, near-vertical ore body. Production from the Big Gossan mine began in fourth-quarter 2010 and is designed to ramp up to 7,000 mtd in 2018.
The Big Gossan mine utilizes a blasthole stoping method with delayed paste backfill. Stopes of varying sizes are mined and the ore dropped down passes to a truck haulage level. Trucks are chute loaded and transport the ore to a jaw crusher. The crushed ore is then hoisted vertically via a two-skip production shaft to a level where it is loaded onto a conveyor belt. The belt carries the ore to one of the main underground conveyors where it is transferred and carried to the surface mill stockpile for processing.
Production equipment in Grasberg mine 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 plant, Raw materials ore are evenly and gradually conveyed into jaw stone crushing equipment for primary crushing via the hopper of vibrating feeder.
The crushed stone materials are conveyed to crushing plant by belt conveyor for secondary crushing before they are sent to vibrating screen to be separated.
After separating, qualified materials will be taken away as final products, while unqualified materials will be carried back to the stone crushing equipment for recrushing
After the crushing process, mineral ore is then transferred to the semi-autogenous grinding (SAG). A semi-autogenous grinding mill, or SAG mill, is responsible for grinding materials from large chunks into small, usable pieces for processing. The SAG mill is usually part of the primary stage in the grinding process, along with water, steel balls and the addition of lime to raise the pH of the ore. The grinding process reduces the rock to a slurry.
The slurry that remains after this Ball mill process has a very fine particle size. Then remaining slurry passes through a pre-leach thickener , to remove some of the water. The recovered water is reused in the grinding circuit while the thickened slurry moves into the leaching circuit.
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.
PROCESSING OF MINERAL ORE IN GRASBERG MINE
The processing of mineral ores, Grasberg mine in Papua Irian Jaya using flotation treatment system. The flotation process consists of producing a mineral concentrate through the use of chemical conditioning agents followed by intense agitation and air sparging of the agitated ore slurry to produce a mineral rich foam concentrate.
A flotation reagent is used to separate concentrate from the ore and either float (foam off) specific minerals or to depress the flotation of other minerals. Froth in a flotation cell is a combination of water, air and solid particles. The froth itself is quite unstable and you will often see bubbles breaking and coalescing into larger bubbles. Given this inherent instability, it is important to realise that there are limitations with how much material the froth phase can support and transport to the launder lip in a given period.
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 crushed stone materials are conveyed to crushing plant by belt conveyor for secondary crushing before they are sent to vibrating screen to be separated.
After separating, qualified materials will be taken away as final products, while unqualified materials will be carried back to the stone crushing equipment for recrushing
The slurry that remains after this Ball mill process has a very fine particle size. Then remaining slurry passes through a pre-leach thickener , to remove some of the water. The recovered water is reused in the grinding circuit while the thickened slurry moves into the leaching circuit.
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.
PROCESSING OF MINERAL ORE IN GRASBERG MINE
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| A processing plant of mineral ores in Grasberg mine in Papua Irian Jaya, Indonesia |
The processing of mineral ores, Grasberg mine in Papua Irian Jaya using flotation treatment system. The flotation process consists of producing a mineral concentrate through the use of chemical conditioning agents followed by intense agitation and air sparging of the agitated ore slurry to produce a mineral rich foam concentrate.
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| Process Flotation in Grasberg |
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.
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