Original paper

Morphology and electron-probe microanalysis of residual gold-grains at Dimako, Southeast Cameroon

Suh, C.E.; Lehmann, B.

Abstract

The morphology and chemistry of residual gold in the area around Dimako, Southeast Cameroon, are studied for the first time. The gold occurs in saprolite and nodular horizons of an extensive weathering blanket. The saprolite studied has 37 ± 22 ppm Au. The gold grains are irregular and dendritic in the deeper horizons but get progressively oblong, rounded, blunt, smooth and pitted up the profile. Gold grains from all horizons show remarkable core-to-rim zonation. The cores are relatively silver rich (11–15 wt % Ag) while the rims are very poor in silver (0 to ≈4 wt % Ag) and quite commonly attain fineness of close to 1000. Significantly, zoning is exhibited by grains from all horizons. Chemically purified silver-free homogeneous gold particles are not restricted to the higher, more evolved horizons. The gold particles are mostly residual. Reprecipitation of supergene gold as submicron/micron-sized gold adsorbed on clay contributes up to 50%.

Keywords

residual goldmorphologychemistryweathering blanketcore-to-rim zonationfinenesscameroon