Mineralization and regional alteration at the Mons Cupri stratiform Cu–Zn–Pb deposit, Pilbara Craton, Western Australia
The Mons Cupri Cu–Zn–Pb deposit is hosted by conglomerate of the ca. 2,965 Ma Cistern Formation, which forms part of the Bookingarra Group in the Central Pilbara tectonic zone of the Pilbara Craton. The deposit has two distinct mineralized zones: a 5- to 10-m-thick, stratiform, Zn–Pb-rich semi-massive sulphide lens, which overlies a funnel-shaped Cu-rich stringer zone. The deposit is located 5–20 m stratigraphically below the contact of the Cistern Formation with the overlying Rushall Slate. A high-Mg basalt (the Comstock Member) is located near the base of the Rushall Slate. Regional alteration mapping indicates that feldspar-destructive alteration facies are restricted to the vicinity of the deposit, with intense chloritic alteration restricted to the stringer zone and a narrow cross-cutting zone that can be traced for 700 m to the east, in the footwall of the deposit. Feldspar-destructive zones are well developed in the Comstock Member, indicating that mineralization occurred after deposition of the Rushall Slate. The Mons Cupri stratiform semi-massive sulphide lens is hosted by a conglomerate, and textural evidence indicates that this lens formed by replacement. These observations, combined with Pb isotope data, suggest that the Mons Cupri deposit formed epigenetically, at least 30 Ma after deposition of its host rock.