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Petrology and geochemistry of sphalerite from the Cambrian VHMS deposits in the Rosebery-Hercules district, western Tasmania: Implications for gold mineralisation and Devonian metamorphic-metasomatic processes

Citation

Zaw, K and Large, RR, Petrology and geochemistry of sphalerite from the Cambrian VHMS deposits in the Rosebery-Hercules district, western Tasmania: Implications for gold mineralisation and Devonian metamorphic-metasomatic processes, Mineralogy and Petrology, 57, (1-2) pp. 97-118. ISSN 0930-0708 (1996) [Refereed Article]

Copyright Statement

Springer-Verlag 1996

DOI: doi:10.1007/BF01161624

Abstract

Sphalerite is the major ore mineral in the Zn-rich, volcanic-hosted massive sulphide deposits of western Tasmania. These deposits have been affected by regional metamorphism to upper greenschist facies, and associated tectonic deformation related to the Devonian Tabberabberan Orogeny. The southern end of the Rosebery deposit has undergone metasomatic replacement related to a post-orogenic Devonian granite intrusion.

Sphalerite from VHMS deposits in the Rosebery district varies widely in colour, grain size and texture. Compositional variation of the sphalerites was studied for three purposes (1) to investigate effects of the Devonian overprinting, (2) to provide pressure (depth) estimates at the time of Fe-S-O replacement during the Devonian, and (3) to deduce the effect ofa FeS(a S 2) on gold deposition and subsequent remobilisation.

Sphalerite from the Rosebery deposit shows an FeS range from 2.0 to 20.0 mole%, with a bimodal distribution; a mode of 16.0 mole% FeS was noted for the F(J) lens where Devonian metasomatism prevailed, whereas a mode of 2.44.0 mol% FeS was found for the other lenses. Sphalerite from the Hercules deposit has a range of 2.010.0 mole% FeS, whereas sphalerite from the South Hercules deposit ranges from 4.0-12.0 mole% FeS. VHMS sphalerites also contain minor copper, manganese and cadmium.

The bimodal distribution of FeS content in Rosebery sphalerite suggests that the primary VHMS mineralisation underwent at least two periods of post-depositional re-equilibration. The FeS content in sphalerite in equilibrium with hexagonal pyrrhotite and pyrite indicates that the Devonian replacement occurred at a pressure off 3.0 0.5 kb, corresponding to 8.0 0.1 km depth.

The relationship between FeS content in sphalerite and gold grades at Rosebery, Hercules and South Hercules displays complex patterns that reflect either variations in the initial depositional conditions an the seafloor (pH, temperature anda S 2), or later Devonian metamorphic and metasomatic recrystallisation.

Item Details

Item Type:Refereed Article
Research Division:Earth Sciences
Research Group:Geology
Research Field:Ore Deposit Petrology
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Earth Sciences
Author:Zaw, K (Professor Khin Zaw)
Author:Large, RR (Professor Ross Large)
ID Code:8262
Year Published:1996
Web of Science® Times Cited:14
Deposited By:Earth Sciences
Deposited On:1996-08-01
Last Modified:2016-08-23
Downloads:0

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