Sea water basalt interaction in spilites from the Iberian Pyrite Belt |
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| Authors: | J Munhá R Kerrich |
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| Institution: | (1) Department of Geology, The University of Western Ontario, N6A 5B7 London, Ontario, Canada;(2) Present address: Faculdade de Ciencias, Mineralogia e Geologia, Lisboa, Portugal |
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| Abstract: | Low grade hydrothermally metamorphosed mafic rocks from the Iberian Pyrite Belt are enriched in 18O relative to the oxygen isotopic ratio of fresh basalt (+6.5±1 ). The observed 
18O whole rock values range from +0.87 to +15.71 corresponding to positive isotopic shifts of +5 to +10, thus requiring isotopic exchange with fluids under conditions of high water:rock ratios at low temperatures. The lowest
18O observed corresponds to an albitized dolerite still and is compatible with independent geochemical data suggesting lower water: rock ratios for the alteration of these rocks.The isotope data are consistent with the hypothesis that the spilites from the Pyrite Belt were produced by interaction of basaltic material with sea water.Significant leaching of transition metals from the mafic rocks during alteration coupled with available sulphur isotopic data for the sulphide ores also suggest that sea water may have played an important role in the formation of ore deposits in the Iberian Pyrite Belt. |
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