Abstract
The aim of this study was to define the part played by organic matter in Au ore genesis. The possible associations and relations between carbonaceous matter and Au were studied at various observation scales (drill-hole, rock sample and microanalysis) in an early-stage Au shear zone type deposit, the West Viges prospect, Creuse Department, France. Prior work had shown that, in this type of deposit, Au mainly occurs within the structure of arsenopyrite. The study of three cores from drill-holes revealed a relation between the distribution of the mineralization and the presence of moderately brecciated anthracitic layers within the host volcanosedimentary tuffs. Chemical assays for Au performed on the rock samples after destruction of the carbonaceous material by calcination showed that the Au content is nearly always higher after calcination. This may indicate that part of the Au initially contained in the rock is trapped in the organic phase. X-ray diffraction spectra on carbonaceous phases isolated from some samples indicated the presence of elemental Au. These results indicate that, like arsenopyrite, organic matter is the bearer of Au and retains it during conventional acid treatment of the ore.
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