TITLE:
Mineralogical and Geochemical Characterization of Gold-Bearing Minerals from Placers in the Les Saras Area (Mayombe, Congo Republic)
AUTHORS:
Isidore Nguelet-Moukaha, Noël Watha Ndoudy, Jean de Dieu Nzila, Claude Dipakama, Ulrich Verne Matiaba Bazika, Anne-Sylvie Andre-Mayer, Florent Boudzoumou
KEYWORDS:
Mayombe, Placers, Mineralogy, Geochemistry, Gold
JOURNAL NAME:
Open Journal of Geology,
Vol.15 No.5,
May
30,
2025
ABSTRACT: With the aim to contribute to the search for the source of placer gold, the Les Saras sector, located in the south-western part of the Republic of the Congo in the Mayombe chain, has been the subject of a study aimed to characterize the mineralogical composition of artisanally mined gold placers. Sediment samples collected from the local drainage system were analyzed using scanning electron microscopy (SEM) and electron microprobe techniques. Results show that the placers are mainly composed of oxides (ilmenite, cassiterite, columbo-tantalite and rutile), followed by silicates (garnets), rare earths (monazite) and native elements (gold). The ilmenites exhibit high TiO2 (54 - 57 wt%) and FeO (37 - 43 wt%) content, while rutiles are chemically pure. Garnets are classified as almandine- and pyrope-type, and monazites show enrichment in lanthanum (21 - 28 wt%) and cerium (8 - 11 wt%). The angular morphology of gold grains suggests limited transport. Geochemical analyses reveal the presence of Ag, Bi, and Cu as associated elements, along with a peripheral enrichment in gold attributed to selective silver leaching. Two distinct types of gold grains were identified based on fineness: 1) high-fineness grains (up to 988) with low Ag content (