Characterisation of the hydrothermal fluids of the Guelb Moghrein iron oxide-Cu-Au-Co deposit, Mauritania: ore mineral chemistry, fluid inclusions and isotope geochemistry.

The 2492 Ma deposit occurs on the margin of the West African craton in an Archaean carbonate-facies banded iron formation, having formed during regional shearing in upper-greenschist/lower-amphibolite facies rocks. The hydrothermal mineralisation, hosted by breccias and shear zones that focused the ore fluids, comprises magnetite, pyrrhotite, chalcopyrite, Fe- Co-Ni arsenides, arsenopyrite, cobaltite and Bi-Au-Ag-Te minerals. The meta-carbonate has three types of fluid inclusions, which indicate that the IOCG deposit resulted from complex hydrothermal evolution, with Au transported as AuCl2(-) complexes in undersaturated ore fluids and concentrated in co-existing Bi melt-droplets so that an assemblage of Au- Bi was precipitated during cooling.
The 2492 Ma deposit occurs on the margin of the West African craton in an Archaean carbonate-facies banded iron formation, having formed during regional shearing in upper-greenschist/lower-amphibolite facies rocks. The hydrothermal mineralisation, hosted by breccias and shear zones that focused the ore fluids, comprises magnetite, pyrrhotite, chalcopyrite, Fe- Co-Ni arsenides, arsenopyrite, cobaltite and Bi-Au-Ag-Te minerals. The meta-carbonate has three types of fluid inclusions, which indicate that the IOCG deposit resulted from complex hydrothermal evolution, with Au transported as AuCl2(-) complexes in undersaturated ore fluids and concentrated in co-existing Bi melt-droplets so that an assemblage of Au- Bi was precipitated during cooling.