Geology, alteration geochemistry, and exploration geochemical mapping of the Ertsberg Cu-Au-Mo district in Papua, Indonesia

The Ertsberg-Grasberg district hosts the world's largest Cu-Au(Mo) skarn system. The mineralization is related to the Pliocene Ertsberg- and Grasberg intrusive complexes, which intruded the Jurassic-Cretaceous Kembelangan Group siliciclastics and Cenozoic New Guinea Limestone Group. Despite previous studies, elemental migration across the porphyry-skarn system and across the different ore stages is still unclear. Here, we attempt to tackle this issue by integrating ore deposit geology, alteration/mineralization paragenesis, whole-rock geochemistry of the Ertsberg granitoids and carbonate wallrocks, together with spatial mapping of hydrothermal minerals and target/pathfinder trace elements at the Deep Mill Level Zone of Ertsberg. Ores at Ertsberg are mainly skarn-hosted, whose formation comprises five stages: (I) prograde skarn; (II) retrograde alteration; (III) massive anhydrite replacement; (IV) late hydrothermal veining; (V) supergene alteration. Massive magnetite and main CuAu mineralization occurred in Stage II and III, respectively, although minor Cu mineralization persisted to Stage IV.