Morphological and microchemical signatures of alluvial gold and electrum grains from the Tcholliré gold district, northern Cameroon: Insights to potential epithermal gold system in the area

Abstract

The Tcholliré district, located in the Adamawa-Yadé Domain (AYD) of the Neoproterozoic Fold Belt of Cameroon (NFBC), hosts some alluvial gold mining sites. The morphological and chemical signatures of the alluvial gold grains from these mining sites are yet to be described. Thus, we describe for the first  time the morphology, microtexture, and chemical features of gold and electrum grains and other heavy minerals, notably cassiterite, recovered from stream sediments from the Tcholliré district drainage system, discuss distance-to-source, and trace the possible source(s) of gold mineralization and type. A total of 33 gold-electrum grains recovered from the gravel layer in two pits dug along stream channels were analysed by scanning electron microscopy (SEM)-energy dispersive spectroscopy (EDS) and electron probe microanalyses (EMPA). The gold grains display angular, irregular to sub-rounded morphologies,  ndicating a close distance hypogene source. Gold in the concentrate is associated with phases such as zircon, cassiterite, and sulfides (e.g., anglesite and tetrahedrite). Inclusions such as quartz, clay minerals, and ilmenite occur in the gold grains and point to a granitoid-related host. Gold grains are mainly alloyed with Ag and Cu with contents as high as 67.17 wt. % Ag (electrum) and 23.54 wt. % Cu. These are the
highest combined Ag and Cu values reported in gold grains in Cameroon thus far. The variation in the concentration of Au and Ag from core to rim is slightly heterogeneous. Such elevated Ag contents in the rim section reflects recently liberated grains from the source. The compositional range of Ag and Cu coupled with the presence of electrum and cassiterite are consistent with a single high-sulfidation and high- temperature magmatic-hydrothermal origin possibly linked to epithermal activity of the Cameroon Volcanic Line.