Mineralogy and Geochemistry Zonation of the DMLZ Cu-Au deposit, Potential Exploration Target in the East Erstberg Skarn System (EESS), Papua

Mineralisation Styles

Mr Utreck Frans Frisco Rumbiak

Padjajaran University

The Deep Mill Level Zone (DMLZ) skarn Cu-Au deposit is a mining zone within the lower part of the East Ertsberg Skarn System (EESS). The DMLZ is hosted in an upper Cretaceous to lower
Tertiary siliciclastic and carbonate succession adjacent to the 3 Ma Ertsberg pluton. A combination of NW structural features and lithological contact created weakness zones that created fluid pathways responsible for the Cu and Au deposition in the EESS. Mineralization is hosted within potassic altered quartz monzodiorite and Ca-Mg silicate skarns respectively. In the horizontal direction, mineralogical studies show that diopside, forsterite, and anhydrite (prograde skarn) are dominant near the intrusive body. The dominant prograde skarn assemblages are controlled by composition of the Waripi Carbonates, notably the relative abundance of quartz, dolomite, and calcite within the protolith. Magnetite is commonly associated with these calc-magnesian silicate mineral, and the intensity of magnetite-anhydrite assemblages within this zone commonly associated with high concentration of copper and gold mineralization. Serpentine and talc present as an overprinting retrograde alteration for the earlier prograde skarn. In the intrusive part, secondary biotite is increased to the contact with sediment and shifted to chlorite to the center of the Ertsberg pluton body. Garnet locally present as the prograde mineral in the endoskarn. Sericite also present as temperature decreased and overprints earlier potassic, propylitic, and prograde endoskarn. Copper sulphides mineral are dominated by chalcopyrite disseminated within the potassic and exoskarn body, and bornite that deposited within the magnetite-anhydrite zone only. Although not significant, chalcopyrite also deposited together with quartz, anhydrite, and pyrite as a vein in the intrusive body. Geochemical patterns indicate that Cu, Au, Ag, Bi, Te, and Co concentrated in the magnetite-anhydrite zone, whereas Pb, Zn, and Sb is depleted and pushed away from this zone. As is widespreadly distributed either in intrusive or exoskarn body, therefore could not be used as a proximitor for metal sources.

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