Archaean carbon reservoirs and their relevance to the fluid source for gold deposits
| Autor: | Neal J. McNaughton, David I. Groves, Nicholas M.S. Rock, Suzanne D. Golding, M. E. Barley |
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| Rok vydání: | 1988 |
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| Zdroj: | Nature. 331:254-257 |
| ISSN: | 1476-4687 0028-0836 |
| DOI: | 10.1038/331254a0 |
| Popis: | It is commonly assumed1,2 that seawater-derived carbon in altered volcanic rocks is the only major pre-metamorphic carbon-in-carbonate reservoir in Archaean greenstone belts. Thus carbonates from Archaean gold deposits with stable isotope ratios too negative (median δ13C ≈ −3‰) to have been derived from such carbon (δ13C usually assumed to be near 0‰) have been interpreted as being derived from a local felsic magmatic source1. Barley and Groves3, however, recognize two carbonate-alteration styles that predate regional metamorphism and gold mineralization in the Norseman–Wiluna greenstone belt of Western Australia: evidence is summarized below. These are seafloor alteration and fault-controlled regional alteration, which, as shown below, have completely different carbon isotope compositions. The latter (median δ13C = −4.8‰) implies a major juvenile carbon (CO2) flux from the mantle during greenstone-belt evolution, and is thus of fundamental importance in itself. However, here we show why the mere existence of two carbon-in-carbonate reservoirs and variation in carbon isotope ratios of carbonates between individual gold deposits in one area, negate some of the fundamental assumptions used to support magmatic-fluid models1. |
| Databáze: | OpenAIRE |
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