Genesis of the Mount Colin Cu-Au deposit, NW Queensland: Evidence from geology, multi-mineral U–Pb geochronology, S-, O- and C-isotope constraints

Abstract

The Mount Colin Cu-Au deposit is located in the Mary Kathleen Domain of the Mount Isa Inlier, NW Queensland. The deposit is hosted in the Corella Formation, which transitions into the Burstall Granite at a depth of ~400 m. The host rocks of the deposit are overprinted by Na-Ca alteration and a Ca-Mg-Fe skarn assemblage. Na-Ca alteration yields a titanite 207Pb/206Pb weighted mean age of 1717 ± 8 Ma (MSWD = 0.32) and is composed of albite, actinolite, zircon, titanite and scapolite with retrograde calcite, prehnite and sericite. The Ca-Mg-Fe skarn yields a titanite 207Pb/206Pb weighted mean age of 1712 ± 7 Ma (MSWD = 1.2) and is composed of hastingsite, K-feldspar, clinopyroxene, albite, titanite, calcite, biotite, and zircon with retrograde quartz and chlorite. Based on temporal relationships, Na-Ca alteration and the Ca-Mg-Fe skarn is interpreted to have formed from a hydrothermal magmatic fluid during late-stage magmatism of the (1740–1710 Ma) Wonga-Burstall plutons. A second generation of titanite (denoted titanite II) is present within Na-Ca alteration and the Ca-Mg-Fe skarn assemblage. Titanite II yields a 207Pb/206Pb weighted mean age of 1576 ± 7 Ma (MSWD = 0.37), and is interpreted to have formed from an external metamorphic hydrothermal fluid during widespread deformation associated with the (1610–1500 Ma) Isan Orogeny. The Mount Colin Cu-Au deposit consists of a predominantly coarse-grained, mineralogically zoned assemblage that infills along the NW-striking Mount Colin Fault. The centre of the deposit comprises a largely unmineralized core composed of calcite and/or quartz ± apatite ± microcline. Cu-Au mineralization is positioned along the outer margins of the deposit and consists of biotite, actinolite, chalcopyrite and pyrrhotite with trace abundances of magnetite, pyrite, galena, melonite and arsenopyrite. Apatite from the core of the deposit yields a U–Pb age of 1523 ± 16 Ma (MSWD = 1.2). The δ34SCDT values of chalcopyrite and pyrrhotite range from 0.1–2.1 ‰ and 0.9–1.5 ‰ respectively. The δ13CVPDB values of calcite range from −5.54 ‰ to −4.54 ‰ with corresponding δ18OVSMOW values ranging from 8.16–11.26 ‰. Based on the temporal and isotopic constraints presented in this study, a hydrothermal magmatic origin for Cu-Au mineralization is favoured. The timing of Cu-Au mineralization is coeval with a regional-scale metamorphic/hydrothermal event throughout the Mary Kathleen Domain and widespread magmatism throughout the Eastern Fold Belt of the Mount Isa Inlier.