Morphological and microchemical characterization of gold grains in stream sediments around Eseka (Nyong Unit), Cameroon: insights into Au origin and exploration

Abstract

Gold in stream sediments at Eseka located within the metasedimentary Nyong Unit (Ntem Complex) is known as an artisanal mining site. The primary source of gold remains unknown, and an adequate exploration model is of concern. This study uses the morphology and microchemistry of the gold grains and trace element geochemistry to constraint its primary source. Scanning electron microscopy, electron microprobe analysis, inductively coupled plasma optical emission/mass spectrometry, and multivariate statistics were used for these investigations. The results show that gold grains are irregular, elongated, or angular and display a size variation of 0.5 to 1.4 mm. Au count in the studied sediments ranges from 2 to 5, and a few sub-rounded grains with groovy surface topography are observed. These indicate a short transportation distance (~ 1000 m) through fluvial system and proximity to the Au primary source. Eseka sediments contain Au (> 1000 ppb), Ag (0.1–1.1 ppm), and Hg (< 0.05 ppm), and two main element associations (Hg-La-Mo-Pb-Th and Ba-Co-Cr-Cu-V) have been determined. Au (93.32–100.01 wt%) is alloyed with Ag (0.119–2.660 wt%), Cu (0.010–0.378 wt%), Hg (0–0.037 wt%), and Te (0–0.011 wt%) with a narrow fineness (935–999). The mineralization in Eseka is classified as very high grade Au which is linked to a mesothermal/orogenic source similar to some Au deposits of the Ntem Complex. A prospective zone has been identified and can be explored using field geologic mapping, pitting-trenching, geophysical method, and soil and stream sediment geochemistry.