Comportement de l'or dans les magmas calco-alcalins – Approche expérimentale et géochimique sur le magmatisme adakitique de Nord-Luzon (Philippines).

Abstract : Au-Cu-Mo deposits represent major metal resources known to be spatio-temporally associated with intrusive arc magmatism, and especially adakitic magmatism whose petrogenesis is particular. Although the bulk of the ore metals seem to originate from the magmas, there is as yet no consensus on processes responsible for their concentration. The fact that primary ore minerals are predominantly sulfides has led to the suggestion that sulfur may play an important role in metal enrichment processes at the magmatic stage. Previous experimental studies have shown that sulfides can largely fractionate gold from the melt, and therefore concluded that oxidized magmas are more likely to be Au-enriched. Here, we conducted high-pressure temperature experiments on five natural magmas from the Philippines, over a range of fO2 going from reducing to strongly oxidizing conditions. The experiments were carried out in gold capsules, in the presence of variable amounts of H2O, and with or without addition of sulphur. Our data show that gold solubility in S-free charges is low but globally increases with fO2. Gold solubility in S-bearing charges appears much higher in reduced and moderately oxidizing conditions. In very oxidizing conditions, Au solubility is low, nearly constant, and does not seem affected by the presence of sulphur ; it only shows a dependence on fO2 by following the same trend than S-free charges. This study shows conclusively that Au transport and concentration in silicic melts can be dramatically enhanced by the presence of sulphur. Gold enrichment in porphyry- and epithermal-type deposits can be directly linked with sulphur incorporation and abundances in magmas.
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Mineralogy. Université d'Orléans, 2007. French


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Submitted on : Thursday, January 17, 2008 - 3:54:52 PM
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  • HAL Id : tel-00207524, version 1

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Sébastien Jégo. Comportement de l'or dans les magmas calco-alcalins – Approche expérimentale et géochimique sur le magmatisme adakitique de Nord-Luzon (Philippines).. Mineralogy. Université d'Orléans, 2007. French. <tel-00207524>

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