FCX's 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 DOZ) 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 DOZ 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.

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.

After mining the final phase of the Grasberg open pit during 2019, the Grasberg minerals district includes the following underground mines that are being operated or in advanced development; the Grasberg Block Cave, the Deep Mill Level Zone (DMLZ), Big Gossan and the Deep Ore Zone (DOZ).

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 30,000 metric tons of ore per day in 2020, over 60,000 metric tons of ore per day in 2021 and 130,000 metric tons of ore per day in 2023 from five production blocks spanning 335,000 square meters.

The Grasberg Block Cave fleet consists of approximately 460 pieces of mobile equipment. The primary mining equipment directly associated with production and development includes an available fleet of 52 LHD units and 35 haul trucks. Each production LHD unit typically carries approximately 11 metric tons of ore and transfer ore into 55 to 60 metric ton capacity haul trucks. In addition, the Grasberg Block Cave has a rail haulage system currently operating with 3 locomotives and 27 ore wagons that haul the ore to the first of the 3 planned gyratory crushers located underground via an automated rail system. Each ore wagon typically carries 30 metric tons.

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.

The DMLZ has continued its ramp-up of production. Hydraulic fracturing operations have been effective in managing rock stresses and pre-conditioning the cave following mining-induced seismic activity experienced in 2017 and 2018. Ore extraction continues to exceed expectations, averaging 14,900 metric tons of ore per day in fourth-quarter 2019 and reached approximately 16,000 metric tons of ore per day at year-end 2019. 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 29,000 metric tons of ore per day in 2020, approach 60,000 metric tons of ore per day in 2021 and 80,000 metric tons of ore per day in 2022 from three production blocks.

The DMLZ fleet consists of over 290 pieces of mobile equipment, which includes 22 LHD units and 9 haul trucks used in production and development activities.

The Big Gossan ore body lies underground and adjacent to the current mill site. It is a tabular, near vertical ore body with approximate dimensions of 1,200 meters along strike and 800 meters down dip with varying thicknesses from 20 meters to 120 meters. 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.

The Big Gossan fleet consists of over 88 pieces of mobile equipment, which includes 12 LHD units and 9 haul trucks used in development and production activities.

The DOZ ore body lies vertically below the now depleted Intermediate Ore Zone. PT-FI began production 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 2000 using the block-cave method and is at the 3,110-meter elevation level.

The DOZ is a mature block-cave mine that previously operated at 80,000 metric tons of ore per day. Current operating rates from the DOZ underground mine are driven by the value of the incremental DOZ ore grade compared to the ore from the DMLZ and Grasberg Block Cave underground mines.

The DOZ fleet consists of 186 pieces of mobile equipment. The primary mining equipment directly associated with production includes an available fleet of 40 LHD units and 19 haul trucks. The trucks dump into two gyratory crushers, and the ore is then conveyed to the surface stockpiles for processing.

The mill produces copper and gold concentrate from mined ore through a process to separate valuable minerals from the impurities covering them. The main steps in the process are crushing, grinding, flotation, and dewatering. Crushing and grinding transform ore size into fine sand in order to release particles containing copper and gold.

Flotation is a separation process to produce copper-gold concentrate. Concentrate slurry consisting of finely ground ore and water mixed with reagents is introduced into a series of mixing tanks called flotation cells, where air is pumped into the slurry.

The reagents used are lime, frothers and collectors. Frothers form stable bubbles that float to the surface of the flotation cell as froth. Collectors react with valuable metal sulfide mineral particle surfaces. rendering these surfaces hydrophobic. The hydrophobic sulfide mineral particles adhere to the air bubbles rising from the slurry zone into the froth floating on the surfac ........