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 over 105,000 metric tons of ore per day in 2022 and 122,000 metric tons of ore per day in 2023 from five production blocks spanning 335,000 square meters. As of December 31, 2021, the Grasberg Block Cave underground mine had 336 open drawbells.

The Grasberg Block Cave fleet consists of approximately 580 pieces of mobile equipment. The primary mining equipment directly associated with production and development includes an available fleet of 88 LHD units and 33 haul trucks. Each production LHD unit typically carries approximately 11 metric tons of ore and transfers ore into the rail haulage system.

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