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 open pit and block cave, and portions of the DOZ block cave) 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 and is currently mining the final phase of the Grasberg open pit, which contains high copper and gold ore grades. PT-FI expects to mine high-grade ore over the next several quarters prior to transitioning to the Grasberg Block Cave underground mine in the first half of 2019.

Production from the ore stockpiles, which are located outside of the pit limits, is expected to continue through the end of 2019. Production in the open pit is currently at the 3,200- to 3,400-meter elevation level and totaled 37 million metric tons of ore in 2017.

The current open-pit equipment fleet consists of over 500 units. The larger mining equipment directly associated with production includes an available fleet of 99 haul trucks with payloads of 218 metric tons and 15 shovels with bucket sizes ranging from 17 to 42 cubic meters, which are capable of moving an average of 340,000 metric tons of material per day.

The Big Gossan mine was first brought into production in 2010. The Big Gossan underground mine was on care-and-maintenance status during most of 2017 and production restarted in fourthquarter 2017.

The Big Gossan mine 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 mine fleet consists of over 72 pieces of mobile equipment, which includes 9 LHD units and 9 haul trucks used in development and production activities.

The DOZ is a mature block-cave mine.

The DOZ mine fleet consists of 159 pieces of mobile equipment. The primary mining equipment directly associated with production and development includes an available fleet of 45 LHD units and 22 haul trucks. Each production LHD unit typically carries approximately 11 metric tons of ore. Using ore passes and chutes, the LHD units transfer ore into 55-metric ton capacity haul trucks. The trucks dump into two gyratory crushers, and the ore is then conveyed to the surface stockpiles for processing.

Production at the DOZ underground mine is expected to continue through 2021.

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 surface of the cell. The froth containing valuable minerals, resembling metallic detergent froth spills over the top of the flotation machine into launders where valuable minerals collect. The valuable minerals collected in the launders are called concentrate. Concentrate (in the form of slurry containing 65% solids by weight) is pumped to Portsite through four 115 km-long slurry pipelines. Upon reaching Portsite, the concentrate is dewatered until only 9% moisture content remains, and is then shipped for sale.

Crude and free gold particles do not react well in the flotation process. The Knelson concentrator, a gravity recovery system uses centrifugal force to separate and recover the crude and free gold. Gold recovery from ore is thus enhanced overall.

Crushing and conveying systems are integral to the Grasberg mine and provide the capacity to transport more than 250,000 metric tons of ore per day. Ore milled from the Grasberg open pit averaged 101,800 metric tons per day in 2017, 119,700 metric tons per day in 2016 and 115,900 metric tons per day in 2015.

Ore milled from the Big Gossan underground mine averaged 600 metric tons of ore per day in 2017 and 900 metric tons of ore per day in 2016.

Ore milled from the DOZ underground mine averaged 31,200 metric tons of ore per day in 2017, 38,000 metric tons of ore per day in 2016 and 43,700 metric tons of ore per day in 2015.

Ore milled from the DMLZ underground mine averaged 3,200 metric tons of ore per day in 2017, 4,400 metric tons per day in 2016, and 2,900 metric tons per day in 2015.