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The formation of magmatic-hydrothermal features in Sn-mineralized and barren Tasmanian intrusions, Southeast Australia: insights from quartz textures, trace elements, and microthermometry

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Hong, W and Cooke, DR and Zhang, L and Fox, N and Thompson, J, The formation of magmatic-hydrothermal features in Sn-mineralized and barren Tasmanian intrusions, Southeast Australia: insights from quartz textures, trace elements, and microthermometry, Economic Geology, 116, (8) pp. 1917-1948. ISSN 0361-0128 (2021) [Refereed Article]


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2021 Society of Economic Geologists, Inc

DOI: doi:10.5382/econgeo.4853

Abstract

Tasmania is the most important tin province in Australia, having been endowed with >0.65 Mt Sn. Some granitic intrusions in western Tasmania have distinctive tourmaline- and quartz-rich magmatic-hydrothermal features, whether they are mineralized (e.g., Heemskirk Granite) or barren (Pieman Heads Granite). The Devonian Heemskirk and Pieman Heads plutons crop out on the western coast of Tasmania and are characterized by similar mineralogical and geochemical compositions and ages. The magmatic-hydrothermal textural features include tourmaline patches, tourmaline orbicules, and tourmaline-muscovite veins, as well as miarolitic cavities and quartz-fluorite-sulfide veins in the Heemskirk Granite. Cathodoluminescence (CL) imaging, laser ablation-inductively coupled plasma-mass spectrometry, and microthermometric analyses of quartz have revealed the physicochemical evolution of the magmatic-hydrothermal fluids from which these tourmaline- and quartz-bearing assemblages precipitated. High Ti quartz (2028 ppm) in tourmaline patches, orbicules, and cavities typically have homogeneous CL-bright intensity, whereas CL-dark fractures have cut and/or offset the CL-bright and -gray domains that characterize low Ti quartz (3.48.5 ppm) from the tourmaline veins. The earliest fluid inclusion assemblages in the quartz-tourmaline orbicules and cavities have a salinity range from 3 to 14 wt % NaCl equiv with intermediate density and were probably trapped at lithostatic pressures of 1.57 0.2 kbar and temperatures of 550 to 570C, suggesting a depth of 5.9 0.8 km. Prolonged depressurization and cooling may have led to the evolution of a brine (~39 wt % NaCl equiv salinity) from the primary magmatic liquid, which formed halite-bearing hypersaline inclusions in the tourmaline orbicules. Continuous pressure decrease explains the intense brittle failure and fluid migration outward from the apical portions of the pluton, where magmatic fluids partially mixed with and were cooled by external meteoric water. These mechanisms triggered the formation of tourmaline-muscovite-quartz veins and local cassiterite-bearing greisens from a moderate-salinity fluid (~12 wt % NaCl equiv) at temperatures of ~300C and hydrostatic pressures of 120 bars. Retrograde dissolution textures evident from CL-bright quartz cores surrounded by oscillatory growth zones with gray CL response characterize the low Ti (<1 ppm) and high Al (5001,000 ppm) quartz from the fluorite-sulfide veins that precipitated from a low-salinity (5.7 wt % NaCl equiv) acidic fluid at temperatures of 200 25C and hydrostatic pressures of <50 bars. High Sb concentrations (up to 80 ppm) in quartz may be an indicator of low-temperature base metal mineralization related to granitic intrusions. Abundant fluid percolation, protracted fractional crystallization, and high tin concentrations in exsolved hydrothermal fluids may explain why the Heemskirk Granite is well endowed in Sn and base metal deposits, whereas the Pieman Heads Granite is barren.

Item Details

Item Type:Refereed Article
Keywords:tin, granite, fluid, inclusion, quartz, laser ablation
Research Division:Earth Sciences
Research Group:Geology
Research Field:Resource geoscience
Objective Division:Mineral Resources (Excl. Energy Resources)
Objective Group:Mineral exploration
Objective Field:Mineral exploration not elsewhere classified
UTAS Author:Hong, W (Mr Wei Hong)
UTAS Author:Cooke, DR (Professor David Cooke)
UTAS Author:Zhang, L (Dr Lejun Zhang)
UTAS Author:Fox, N (Dr Nathan Fox)
UTAS Author:Thompson, J (Mr Jay Thompson)
ID Code:147315
Year Published:2021
Funding Support:Australian Research Council (IH130200004)
Deposited By:CODES ARC
Deposited On:2021-10-25
Last Modified:2022-06-22
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