Mining of alluvial cassiterite and its compositional diversity at the Mayo Darlé area, northern Cameron

Abstract

Cassiterite mineralization occurs in both the rock and the alluvial system in the Mayo-Darlé area of northern Cameroon. This study focuses on the morphology, mineral inclusions, and composition of alluvial cassiterite derived from Bambol and Mayo Seni localities, where active alluvial mining by artisans constitutes the most important rural economic activity. The cassiterite grains were primarily analyzed by backscattered electron (BSE) images to investigate their morphological characteristics and mineral inclusions. The composition was examined through electron microprobe analysis (EMPA). The cassiterite grains have an irregular to sub-rounded morphology, indicating proximity to the source, although most of the cassiterite grains display evidence of mechanical transport and abrasion. EMPA results show mainly high SnO2 content (93–103 wt. %), highlighting the predominance of cassiterite minerals in the humid tropical region. Among the Sn substituting elements, only Fe, Ta, and Mn were detected at very low concentrations (Fe = 0.02 to 0.3 FeO, Mn = 0 to 0.04 MnO, and Ta = 0 to 0.2 Ta2O5) all in wt. % respectively, suggesting little variation in the alluvial cassiterite compositions. This high SnO2 content indicates the purity of cassiterite in the area. Binary plots of compositional variation have similar trends, suggesting that cassiterite was derived from a single bedrock source, despite having a mixed signature of pegmatite- and hydrothermal-derived cassiterite. Mineral inclusions include quartz, hematite, and columbite group minerals (CGMs), which were similar in all the samples, suggesting a homogeneous source. The quartz inclusions highlight quartz veins associated with the mineralization and potential felsic plutonic bedrocks. The chemical signatures of the studied cassiterite grains are useful tools to explore the environment of an unknown primary source that can greatly help in mineral exploration in northern Cameroon.