Greenschist facies regional and contact metamorphism of the Thalanga volcanic-hosted massive sulfide deposit (northern Queensland, Australia)

The conditions of two separate greenschist facies metamorphic events have been reconstructed at the syn-genetic Thalanga massive sulfide deposit (northern Queensland, Australia) using scarce garnet-biotite and garnet-chlorite-bearing samples from the felsic volcano-sedimentary host-rock succession. Regional metamorphism (peak temperature: 440 to°) generated a foliation defined by aligned chlorite, muscovite and biotite, and rare, euhedral spessartine-almandine (-grossular)-rich garnets. The emplacement of a post-tectonic diorite pluton was associated with contact metamorphism and scarce anhedral spessartine-almandine-rich garnet poikiloblasts crystallized within a -e1650-m wide aureole at temperatures of -e1500°C. Both metamorphic stages occurred under pressure conditions of ≤ 3.5 kbar. Our study documents a useful method for geothermobarometric reconstruction of metamorphosed, syn-genetic ore deposits where calculations based on sulfide assemblages failed to produce unequivocal constraints. Furthermore, we show that hydrothermally altered footwall rhyolite have higher Xchlorite and Xbiolite than unaltered rocks, which may help to identify fossil, metamorphosed, hydrothermal systems associated with massive sulfide deposits similar to Thalanga.