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Mineralogy and stable isotope geochemistry of the Beaconsfield, Salisbury and Lefroy goldfields


Russell, DW and Van Moort, JC, Mineralogy and stable isotope geochemistry of the Beaconsfield, Salisbury and Lefroy goldfields, Geological Survey Bulletin, 70 pp. 208-226. ISSN 0082-2043 (1992) [Refereed Article]

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The quartz veins of the Tasmania Reef at Beaconsfield consist of auriferous microcystalline quartz with a central core of ankerite. Sulphides are distributed throughout the two to six metre wide reef, which has grades ranging from 14 g/t to 38 g/t Au. The host rock is the Ordovician Cabbage Tree Formation (quartzose sandstone and minor conglomerate).

The quartz veins at Lefroy usually contain less than 3 g/t Au. The host rock at Lefroy consists of Ordovician Mathinna Group (Powell and Baillie, in press) lutite.

Thin-section slides indicate eight phases of vein development of the Tasmania Reef. Most of these phases have been preceded by a period of brecciation. Quartz and pyrite developing phases precede, or are simultaneous with, two gold depositing phases and are followed by chalcopyrite-sphalerite-galena-ankerite veins, annealing quartz veins, and finally 'vuggy' ankerite veins.

Beaconsfield gold has an average fineness of 934 and Lefroy gold has an average fineness of 972. Both the high fineness values and the narrow fineness range indicate that these deposits are hypothermal. Arsenopyrite geothermometry indicates that the temperature of formation was between 370C and 440C. The δ34S of pyrite ranges from +7 to +24.7 % and the average δ18O values of the reef quartz is 17.90.8 %.

The Beaconsfield and Lefroy reefs are the result of precipitation from deep-seated fluids ascending through faults associated with the Devonian Tamar Fracture System

Item Details

Item Type:Refereed Article
Research Division:Earth Sciences
Research Group:Geochemistry
Research Field:Exploration geochemistry
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the earth sciences
UTAS Author:Van Moort, JC (Dr Jan Van Moort)
ID Code:103710
Year Published:1992
Deposited By:Earth Sciences
Deposited On:2015-10-26
Last Modified:2016-07-21

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