Microchemical characterization and stream sediment composition of alluvial gold particles from the Rafin Gora drainage system, Kushaka schist belt, North Western Nigeria

Abstract

Benjamin Odey Omang*, Akumbom Vishiti, Godwin Terwase Kave,  Enah Asinya Enah, Michael Ekuru Omeka, Cheo Emmanuel Suh   and Mohammed Ali Garba

The Proterozoic Kushaka schist belt of northwestern Nigeria is well known for its alluvial gold occurrence, although the primary source of gold is unknown due to the extensive thick weathering blanket. In this study, we integrate the morphology and microchemistry of alluvial gold to identify the probable primary source of gold in the area. Scanning electron microscope images of gold grains recovered by panning from the Rafin Gora drainage system indicated morphologies that vary from irregular, elongated   subrounded, which suggested that they belong to the proximal primary source.The grains shown scorched, pitted, and grooved surfaces  that were partly adorned with canals. These features coupled with gold fragments partially detached from the principal grains are indicative of gold grain transportation in a high-energy alluvial system. Polished gold grains show remarkable core-rim zonation with inclusions of galena and pyrite entombed in them. From EMPA analysis the BSe images that the gold grains are dominantly Au-Ag alloys although Cu levels may reach 1.12 wt%. The gold grain fineness values vary between 838 and 998.1 with an average of 933. These compositional characteristics are consistent with primary mineralization linked to orogenic processes. The Ag-rich rims attest to preferential Ag leaching from the margins of the grains, a feature common in alluvial gold grains. Reconnaissance stream sediment compositional data indicate elevated levels of Au-Ba-Ce-Hg-La-Cr-Cu-Mn-Pb-Th-V-Y-Zn a metal association suggestive of intrusion-driven hydrothermal quartz vein systems consistent with gold microchemical data. Results obtained in this study provide insight into the nature of gold mineralization and serve as a baseline exploration tool in the Kushaka schist belt in northwestern Nigeria.