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.

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.

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.