Carbonate alteration at the Mulgarrie gold mine in the Eastern Goldfields of Western Australia, is represented by porphyroblasts, veins and pervasive, texturally destructive, carbonatisation. Two foliations, S 1M and S 2M , were produced by two separate deformation events at the mine‐scale, D 1M and D 2M . D 1M and D 2M both occurred in response to regional D 2 tectonism. Carbonate alteration was the product of two separate episodes of fluid ingress: the earlier produced magnesite and the latter Fe‐dolomite. Both periods of carbonate alteration occurred pre‐ to early syn‐D 2M , when mafic to ultramafic komatiitic rocks reacted with fluids that moved along regional faults and pre‐date the alteration associated with regional peak metamorphism. Gold at Mulgarrie overprints pre‐ and late syn‐D 2 quartz veins in zones of massive carbonate alteration, suggesting it has a late‐ to post‐D 2 timing. This late timing agrees with the generally accepted syn‐D 3 (and younger) age for gold mineralisation in the Eastern Goldfields. We suggest that carbonate alteration at Mulgarrie is not a product of the hydrothermal event responsible for the gold mineralisation. Rather, the different relative timing of magnesite, Fe‐dolomite and gold indicates there were two carbonate‐producing fluid systems and a fluid transporting the gold overprinted these. Similarly, early carbonate alteration may play a role in localising auriferous vein deposits throughout the Yilgarn and other Archaean cratons.
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Document Type: Research Article
Delta Gold Ltd, PO Box 152, Kalgoorlie, WA 6430, Australia
Mineral Deposit Research Unit, Department of Earth and Ocean Sciences, University of British Columbia, Vancouver BC, Canada, V6t 1Z4
Publication date: February 1, 2001