In Grasberg Block Cave (GBC) Mine area, anhydrite-gypsum and sulfur mineral distribution can be traced in Grasberg Intrusive Complex (GIC), skarn, and Heavy Sulphide Zone (HSZ). GIC and Skarn contain abundant of anhydritegypsum as product of alteration. Potassic alteration in GIC are characterized by anhydrite appearance within the rock or as intense stockwork veins associate with quartz-pyritechalcopyrite. In the skarn, anhydrite mineral appear as dominant alteration mineral especially if the skarn occurred between contact of igneous rock and Waripi Dolomite with enough temperature to form anhydrite. Not only within the rock anhydrite also as vein and fill the fracture associated with suphide mineral pyritechalcopyrite. This anhydrite add by water become gypsum as result. Gypsum is easier to dissolve in water so can caused high sulfate content in water. Both potassic alteration GIC and skarn contain gypsum associated with 3-5% pyrite and 1-2% chalcopyrite content as disseminated. Even locally up to 5-10% pyrite and 3% chalcopyrite also minor sphalerite as replacement sulphide alteration or intense patchy.

Heavy Sulphide Zone in GBC area is characterized by more than 20% pyrite content and strong-pervasive replacement sulphide alteration. Locally pyrite content could up to more than 50%. The dominant sulphide content comprises of pyrite-chalcopyrite-pyrhotitesphalerite and easily oxidized if contact with ground water especially for pyrite.

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 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 ........