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Geochemical Modeling of the Zoned Footwall Alteration Pipe, Hellyer Volcanic-Hosted Massive Sulfide Deposit, Western Tasmania, Australia


Schardt, C and Cooke, DR and Gemmell, JB and Large, RR, Geochemical Modeling of the Zoned Footwall Alteration Pipe, Hellyer Volcanic-Hosted Massive Sulfide Deposit, Western Tasmania, Australia, Economic Geology, 96, (5) pp. 1037-1054. ISSN 0361-0128 (2001) [Refereed Article]

DOI: doi:10.2113/gsecongeo.96.5.1037


The mineralogy of hydrothermal alteration assemblages (siliceous core, chlorite zone, sericite zone) in the footwall pipe of the Hellyer volcanic-hosted massive sulfide (VHMS) deposit is controlled mainly by the temperature, pH, and redox state of the hydrothermal fluids.

Based on the results of our numerical modeling, the zoned alteration system could have formed by a combination of water-rock interaction and cooling, with a siliceous core predicted to form at the center of the conduit, passing outward to a chlorite-dominated zone, a sericite-rich zone, and finally grading out to unaltered andesite. These mineralogical changes relate to a gradual evolution of fluid chemistry, water/rock ratio, pH, and temperature from the core to the margin of the system. Initial temperatures were probably close to 350C, and the hydrothermal fluids were reduced (H2S dominated). At low temperatures (<200C) a peripheral alteration zone, consisting mostly of K feldspar, chlorite, sericite, and hematite, is predicted to form. This low-temperature zone has not been recognized at Hellyer, but elevated K2O contents and local K feldspar development have been noted at other VHMS deposits, suggesting that this zone might form at low temperatures and low water/rock ratios in the footwall of VHMS deposits. If the existence of barren outer K feldspar alteration zones is confirmed, the findings could have important implications for exploration, specifically with regards to distinguishing ore-related alteration zones from barren alteration systems.

Item Details

Item Type:Refereed Article
Research Division:Earth Sciences
Research Group:Geochemistry
Research Field:Exploration geochemistry
Objective Division:Mineral Resources (Excl. Energy Resources)
Objective Group:Other mineral resources (excl. energy resources)
Objective Field:Other mineral resources (excl. energy resources) not elsewhere classified
UTAS Author:Schardt, C (Mr Christian Schardt)
UTAS Author:Cooke, DR (Professor David Cooke)
UTAS Author:Gemmell, JB (Professor Bruce Gemmell)
UTAS Author:Large, RR (Professor Ross Large)
ID Code:23259
Year Published:2001
Web of Science® Times Cited:34
Deposited By:Centre for Ore Deposit Research - CODES CoE
Deposited On:2001-08-01
Last Modified:2019-02-20

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