Scanning electron microscopy and energy-dispersive X-ray investigations of gold grains in quartz veins from the Seiga gold mine, south Egypt

Abstract

Seiga Au mineralization is located in the Wadi Seiga which intersected the Wadi Allaqi in Southeast Egypt. It has had a long history of ancient Au working since 4000B.C. and discontinzuous mining until 1950s. This study presents a detailed microchemical characterization of Au grains in quartz veins and veinlets, aiming to obtain further understanding of Au occurrences, chemistry of Au bearing phases, their internal structure, inclusions and genesis, and type of source mineralization for evaluation and exploration purposes. The scanning electron microscope fitted with energy dispersive X-ray spectrometer techniques has been applied to achieve this paper.The results revealed that the Au mineralization is considered as a single major episode of mineralization formed by hydrothermal ore bearing fluid rich in sulfides, epithermal character and metamorphic origin. It formed through four stages, including four mineral phases varied in their dimensions, distribution and composition. The first two phases were homogeneous and included Au+Ag and Au+Ag±Cs±Rb phases that derived from two separated homogeneous ore bearing fluids. They existed as discrete individual grains in quartz veins and veinlets, caged in secondary iron oxides pseudomorphed after early formed Au bearing pyrites and as zoned Au grains including the cores of Au+Ag phase and the rims of younger Au+Ag±Cs±Rb phase. The third phase was represented by pyrites and chalcopyrites, whereas the fourth phase included carbonate (ankerite and calcite) and muscovite minerals. Both the last two phases were barren and free of Au signals. Seiga Au mineralization has been subjected to dissolution, remobilization and re-precipitation processes that control the dimension and distribution of both Au phases. The obtained results give a complete image of quantitative and qualitative characterization of Au alloy phases and their associated minerals for genetic history of Au mineralization.