The Grasberg minerals district includes open-pit and underground mines.
Did you know?
PT Freeport Indonesia (PT-FI) commenced mining operations in 1972 and in 1988 discovered the Grasberg mine. Today, after significant production, the Grasberg mining district contains one of the world’s largest recoverable copper reserve and the largest gold reserve.
The remote highlands of the Sudirman Mountain Range in the province of Papua, Indonesia, which is on the western half of the island of New Guinea.
Processes and facilities
The Grasberg minerals district includes the following underground mines that are being operated; the Grasberg Block Cave, the Deep Mill Level Zone (DMLZ) and Big Gossan. PT-FI also has several projects in progress in the Grasberg minerals district related to the development of the large-scale, long-lived, high-grade underground ore bodies located beneath and nearby the Grasberg open pit. In aggregate, these underground ore bodies are expected to produce large-scale quantities of copper and gold.
Grasberg Block Cave. The Grasberg Block Cave ore body is the same ore body historically mined from the surface in the Grasberg open pit. Undercutting, drawbell construction and ore extraction activities in the Grasberg Block Cave underground mine continue to track expectations. Monitoring data on cave propagation in the Grasberg Block Cave underground mine is providing confidence in growing production rates over time. As existing drawpoints mature and additional drawpoints are added, cave expansion is expected to accelerate production rates to an average of over 105,000 metric tons of ore per day in 2022 and 122,000 metric tons of ore per day in 2023. Production at the Grasberg Block Cave underground mine is expected to continue through 2041.
DMLZ underground mine. The DMLZ ore body lies below the DOZ underground mine at the 2,590-meter elevation and represents the downward continuation of mineralization in the Ertsberg East Skarn system and neighboring Ertsberg porphyry. During third-quarter 2018, PT-FI commenced hydraulic fracturing activities to manage rock stresses and pre-condition the DMLZ underground mine for large-scale production following mining induced seismic activity experienced in 2017 and 2018. Results to date have been effective in managing rock stresses and pre-conditioning the cave. Ongoing hydraulic fracturing operations combined with continued undercutting and drawbell openings in the two currently active production blocks are expected to expand the cave, supporting higher production rates that are expected to average approximately 68,000 metric tons of ore per day in 2022. Estimates of timing of future production continue to be reviewed and may be modified as additional information becomes available. Production at the DMLZ underground mine is expected to continue through 2041.
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. The 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 the ore is transferred and conveyed to the surface stockpiles for processing. Ore milled from the Big Gossan underground mine averaged 7,500 metric tons per day in 2021. Production at the Big Gossan underground mine is expected to continue through 2041.
Kucing Liar Underground Mine. PT-FI commenced long-term mine development activities for its Kucing Liar deposit in October 2021, which is expected to produce over 6 billion pounds of copper and 5 million ounces of gold between 2028 and the end of 2041. The Kucing Liar underground deposit lies on the southern flank of and underneath the southern portion of the Grasberg open pit at the 2,605-meter elevation level. Similar to PT-FI’s experience with large-scale, block-cave mines, pre-production development activities will occur over an approximate 10-year timeframe. At full operating rates of 90,000 metric tons of ore per day, annual production from Kucing Liar is expected to approximate 600 million pounds of copper and 500,000 ounces of gold, providing PT-FI with sustained long-term, large-scale and low-cost production.
DOZ underground mine. The DOZ ore body lies vertically below the depleted Intermediate Ore Zone. PT-FI began production from the DOZ ore body in 1989 and the ore body was depleted at the end of 2021.
Grasberg open pit. PT-FI began open-pit mining of the Grasberg ore body in 1990. The final phase of the Grasberg open pit was mined during 2019, including the removal of the open pit ramps. In aggregate, the Grasberg open pit produced over 27 billion pounds of copper and 46 million ounces of gold in the 30-year period from 1990 through 2019.
Description of Ore Bodies
Our Indonesia 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 Block Cave and portions of the DMLZ) occur as vein stockworks and disseminations of copper sulfides, dominated by chalcopyrite and, to a lesser extent, bornite. The sedimentary-rock hosted ore bodies (portions of the DMLZ and Kucing Liar and all of the 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, though rarely visible to the naked eye. These gold concentrations usually occur as inclusions within the copper sulfide minerals, though, in some deposits, these concentrations can also be strongly associated with pyrite.
48.8% of PT-FI owned by Freeport-McMoRan Inc.; 51.2% of PT-FI owned by PT Indonesia Asahan Aluminum (Persero) (PT Inalum), a state-owned enterprise that is wholly owned by the Indonesian government.
Note: FCX’s economic interest in PT-FI is expected to approximate 81.28% through 2022.