Archean Carbon and Oxygen Reservoirs: Their Significance for Fluid Sources and Circulation Paths for Archean Mesothermal Gold Deposits of the Norseman-Wiluna Belt, Western Australia
S. D. Golding, N. J. McNaughton, M. E. Barley, D. I. Groves, S. E. Ho, N. M. S. Rock, J. V. Turner, 1989. "Archean Carbon and Oxygen Reservoirs: Their Significance for Fluid Sources and Circulation Paths for Archean Mesothermal Gold Deposits of the Norseman-Wiluna Belt, Western Australia", The Geology of Gold Deposits: The Perspective in 1988, Reid R. Keays, W. R. H. Ramsay, David I. Groves
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Carbon and oxygen isotope studies of carbonate minerals from the two carbonate alteration styles that predate regional metamorphism and gold mineralization in the Norseman-Wiluna greenstone belt of Western Australia have significance for the sources of carbon and oxygen in ore fluids that produce Archean mesothermal gold deposits. The mantle-derived carbon reservoir in regional carbonation zones is the most likely source for auriferous ore fluids rather than the seawater-derived carbon reservoir in altered basalts. The wide range of δ13C values for gold-related carbonates reflects dissolution of different carbonate species and/or a variable input of organic and seawater-derived carbon.
The oxygen isotope compositions of auriferous ore fluids in the Norseman-Wiluna belt (δ18O = 4-9‰) indicate that these fluids (1) could have been in equilibrium with sea floor-altered basalts at 500° to 600°C, (2) derived from regional carbonation zones or interacted with them, or (3) derived from felsic porphyries or granitoids only if modified by subsequent fluid-rock interaction or changing P-T-X conditions.
There is a positive correlation between δ13C and δ18O for carbonates from gold-related alteration (both district and mine scale), with data for the two largest Archean mesothermal gold deposits in the world (Kalgoorlie, Western Australia; and Timmins, Ontario) plotting at the most positive end of this trend. Correlated δ13C and δ18O variations in gold-related carbonates on a district scale probably relate to source-conduit heterogeneities and host-rock compositional controls, whereas on a mine scale a model involving finite reservoir effects for carbon, temperature-controlled oxygen isotope fractionation, and possibly phase separation can account for the observed trends.