The Formation of Magmatic-Hydrothermal Features in Sn-Mineralized and Barren Tasmanian Intrusions, Southeast Australia: Insights from Quartz Textures, Trace Elements, and Microthermometry

Abstract Tasmania is the most important tin province in Australia, having been endowed with >0.65 Mt Sn. Some granitic intrusions western have distinctive tourmaline- and quartz-rich magmatic-hydrothermal features, whether they are mineralized (e.g., Heemskirk Granite) or barren (Pieman Heads Granite). The Devonian Pieman plutons crop out on coast of characterized by similar mineralogical geochemical compositions ages. textural features include tourmaline patches, orbicules, tourmaline-muscovite veins, as well miarolitic cavities quartz-fluorite-sulfide veins Granite. Cathodoluminescence (CL) imaging, laser ablation-inductively coupled plasma-mass spectrometry, microthermometric analyses quartz revealed physicochemical evolution fluids from which these quartz-bearing assemblages precipitated. High Ti (20–28 ppm) typically homogeneous CL-bright intensity, whereas CL-dark fractures cut and/or offset -gray domains that characterize low (3.4–8.5 veins. earliest fluid inclusion quartz-tourmaline orbicules a salinity range 3 to 14 wt % NaCl equiv intermediate density were probably trapped at lithostatic pressures 1.57 ± 0.2 kbar temperatures 550° 570°C, suggesting depth 5.9 0.8 km. Prolonged depressurization cooling may led brine (~39 salinity) primary magmatic liquid, formed halite-bearing hypersaline inclusions orbicules. Continuous pressure decrease explains intense brittle failure migration outward apical portions pluton, where partially mixed cooled external meteoric water. These mechanisms triggered formation tourmaline-muscovite-quartz local cassiterite-bearing greisens moderate-salinity (~12 equiv) ~300°C hydrostatic 120 bars. Retrograde dissolution textures evident cores surrounded oscillatory growth zones gray CL response (<1 high Al (500–1,000 fluorite-sulfide precipitated low-salinity (5.7 acidic 200° 25°C <50 Sb concentrations (up 80 be an indicator low-temperature base metal mineralization related intrusions. Abundant percolation, protracted fractional crystallization, exsolved hydrothermal explain why Granite Sn deposits, barren.