Mineralogy and Geochemistry of Shale-Hosted Copper of the Middle Buanji Group, Chimala Area, South-Western Tanzania

Abstract

The mineralogical and geochemical assessments are presented in this paper to constrain the mineralogy and copper concentrations of the shale-hosted copper in the Middle Buanji Group of the Upper Paleoproterozoic (1.67 Ga). The XRD analysis revealed that illite and chamosite are the major clay minerals present in the shales together with pseudomalachite, quartz, and muscovite that constitute over 95% by proportion of the sample. The minerals biotite, birnessite, ferroselite, bearsite, chloritoid, and anatase are present in association with shale-hosted copper in low amounts (i.e., <5% by proportion of the sample). The pseudomalachite [Cu5(PO4)2(OH)4] is considered as ore mineral of copper in the shales of the Middle Buanji Group. Field observations revealed the presence of different shale layers within the Middle Buanji Group such as red, grey and green/blue in which copper mineral is distributed. On average, the copper concentrations in the shale layers were unevenly distributed throughout the red-grey-green shales layers with values of 0.31 wt%, 5.2 wt% and 13.19 wt%, respectively. A noticeable amount of copper mineralization up to 25.7 wt% was restricted within the green shale layer as compared to red (0.31 wt%) and grey (10.9 wt%) layers.

Keywords: Pseudomalachite; Supergene enrichment; Shale-hosted copper; Green shale layer