The Big Gossan Cu-Au skarn deposit is the highest grade copper deposit in the world-class Ertsberg district, Irian Jaya. Current reserves are 37.4 million metric tons (Mr), grading 2.69 percent Cu, 1.02 g/t Au, and 16 g/t Ag. Mineralization is associated with a series of 3 to 4 Ma granodioritic dikes which have intruded close to the near-vertical faulted contact between the Shale Member of the Cretaceous Ekmai Formation and the stratigraphically overlying Paleocene Waripi and Eocene Faumai Formations. Most mineralization and alteration occurs in the purer carbonate rocks of the Waripi Formation, although biotite and calc-silicate hornfels alteration also occurs in the footwall rocks adjacent to mineralization.Prograde skarn alteration consists dominantly of pyroxene and garnet with an overall ratio of approximately 2:1. The average pyroxene and garnet compositions are Di73Hds4Joa and Ads47Gr•a5Sp•.sPy0..•, respectively. The skarn is zoned in three dimensions relative to the main fluid conduit along the Ekmai-Waripi contact. Proximal zones are garnet rich and the garnet has a dark red-brown color, whereas the pyroxene is pale in color and is iron poor. Intermediate zones contain subequal amounts of relatively coarse-grained, green pyroxene and brown garnet. Distal skarn zones are dominated by dark green, iron-rich (up to Hd75) pyroxene. Garnet in distal zones typically is pale green to greenish brown. At the skarn-marble contact, retrograde alteration (mostly amphibole and epidote) and sulfide minerals (mostly pyrite and pyrrhotite) are abundant. Chalcopyrite and anhydrite are present in all skarn zones. Although the skarn-marble contact is sharp, tiny dark veinlets (containing chlorite, serpentine, clay, sulfides, and/or carbon) which locally resemble stylolites record the passage of hydrothermal fluids for tens to hundreds of meters beyond the skarn. Skarn zonation in terms of mineral ratios, colors, and compositions can be used for exploration on both a local and district scale.In addition to mineralogy, Big Gossan is zoned with respect to metals. Cu, Au, Ag, Pb, Zn, As, and Co in the skarn all increase toward the top of the system, whereas Mo increases with depth. Similarly, Cu, Au, Ag, Pb, Zn, As, and Co increase (for a given elevation) toward the western and in most cases, toward the eastern margin of the system. Only Mo is inverse to this trend, defining a central core zone xvhich is interpreted to represent the main locus of fluid flow overlying the source pluton. Relative to the host rocks (Kembelangan and Waripi Formations), minera]ized skarn is enriched in Si, Fe, S, Cu, Ag, Au, As, Co, Se, and W. Both the host rocks and mineralized skarn are significantly depleted in rare earth elements relative to typical Phanerozoic sedimentary rocks. Particularly striking is the deep negative curopium anomaly, mostly < 1 ppm Eu.Fluids associated with prograde skarn are high-temperature, low COs (<0.05 mole %), NaC1-KC1 brines. Pressure-corrected temperatures for fluid inclusions in prograde skarn range from 360 ø to...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.