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Conditions of formation for magmatic-hydrothermal features in the Sn-mineralized Heemskirk Granite, Western Tasmania, SE Australia

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Hong, W and Cooke, DR and Zhang, L and Fox, N, Conditions of formation for magmatic-hydrothermal features in the Sn-mineralized Heemskirk Granite, Western Tasmania, SE Australia, SEG 2017 Ore Deposits of Asia: China and Beyond Programme, 17-20 September 2017, Beijing, China (2017) [Conference Extract]


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Abstract

Abundant Sn skarn, greisen, and vein-type Ag-Pb-Zn deposits are spatially associated with the Heemskirk Granite from western Tasmania, southeastern Australia. Significant cassiterite deposits include the Federation, St Dizier, Severn, Queen Hill, and Montana Sn deposits, which are estimated to host at least 1.07 Mt at 0.98 to 1.91% Sn. We have investigated the CL characteristics, trace elements, and microthermometry of quartz from tourmaline patches, tourmaline-quartz orbicules, tourmaline miarolitic cavities, tourmaline-quartz-muscovite cassiterite veins, and Pb-Zn sulfide veins from the Heemskirk Granite. SEM-CL analyses reveal that CL-bright quartz cores are typically cut by dark to gray CL patches, CL-dark streaks, and healed fractures, offset by cobweb-like networks and jigsaw puzzle pieces, and/or overprinted by gray to bright CL growth zones. LA-ICP-MS analyses show that Al, Li, Ti, Na, K, Fe, Ge, and Rb are the most abundant trace elements in the quartz, although sub-microscopic fluid inclusions in quartz can contribute trace elements (especially Na, K, Rb, and Ca) to these analyses. The average Ge/Ti and Al/Ti ratios in quartz increase progressively from 0.04 in tourmaline patches, to 0.18 in tourmaline veins, indicating that evolved fluids were responsible for formation of these distinctive tourmaline-quartz features within the granite carapace. Increasing Sn concentrations in quartz from tourmaline patches (median = 0.115 ppm) to tourmaline-muscovite veins (median = 0.174 ppm) have been detected, consistent with Sn contents being gradually enriched in the evolved, late-stage magmatic-hydrothermal fluids. Quartz grains associated with Pb-Zn sulfide veins have much higher Sb concentrations (median = 2.73 ppm) than other types of quartz (medians < 0.06 ppm), which may be useful for base metal exploration. Liquid-rich (type I), vapor-rich (type II), and halite-bearing (type III) fluid inclusions have been identified in quartz from the tourmaline-rich textural features and sulfide veins. Microthermometric measurements show that fluid inclusions have homogenization temperatures and salinities ranging from 156 to 460C and 2 to 15 wt % NaCl equiv (type I), 334 to 550C and 6 to 8 wt % NaCl equiv (type II), and 170 to 530C and 31 to 56 wt % NaCl equiv (type III). Combined microthermometry and Ti-in-quartz geothermometry demonstrate that tourmaline patches, orbicules and cavities formed at temperatures of 500 to 565C and lithostatic pressures of 0.6 to 1.3 kbar (depth of 2.8 to ≥ 5 km). Tourmaline-muscovite cassiterite veins formed at temperatures of 310 20C and hydrostatic pressures of 0.1 to 0.3 kbar (depth of ca. 1 km). Pb-Zn sulfide quartz veins precipitated under lower temperature-pressure conditions (280 40C; hydrostatic pressure of 80 bar). Depositional mechanisms, including decompression, decreasing temperature, and/or mixing with external water could have played a positive role in the generation and precipitation of the quartz-rich features and related Sn-sulfide mineralization.

Item Details

Item Type:Conference Extract
Keywords:tin, granite, tourmaline, quartz, cathodeluminescence, fluid inclusions
Research Division:Earth Sciences
Research Group:Geology
Research Field:Ore Deposit Petrology
Objective Division:Mineral Resources (excl. Energy Resources)
Objective Group:Mineral Exploration
Objective Field:Mineral Exploration not elsewhere classified
Author:Hong, W (Mr Wei Hong)
Author:Cooke, DR (Professor David Cooke)
Author:Zhang, L (Mr Lejun Zhang)
Author:Fox, N (Dr Nathan Fox)
ID Code:122945
Year Published:2017
Funding Support:Australian Research Council (CE0561595)
Deposited By:CODES ARC
Deposited On:2017-12-06
Last Modified:2017-12-07
Downloads:0

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