Macrotermes falciger termite mounds as indicators of lithogeochemical anomalies of metals of interest

Abstract

This study investigated the potential lithogeochemical filiation of Macrotermes falciger termite mound materials and the parent substrate materials sampled in both the Sakania and Tshisenda areas of the Haut-Katanga Province of the Democratic Republic of Congo. These geological areas with predominantly autochthonous cover are characterized by lateritic type profiles. Mineralogical characterization of Macrotermes falciger termite mound materials by infrared on 20–63 μm fractions indicated the presence of secondary minerals specific to tropical weathering. Further mineralogical analysis of 0–20 μm fractions using XRD also identified such primary and secondary minerals in these materials. A multi-element chemical analysis was performed on the <125 μm fractions of the different lithological substrates (granitic rock, feldspathic sandstone, and lateritic duricrust) as well as of the Macrotermes falciger termite mounds. Using log Fe2O3t/K2O vs logSiO2/Al2O3 ratios, all the samples were geochemically classified and lithogeochemical relationships were established. We showed that the yellow, grey and beige termite mounds were characterized by lithogeochemical facies of quartz-rich and slightly altered substrates (granite, arkose…) whereas the red termite mounds had lithogeochemical facies of clay formations associated with iron oxyhydroxides with less quartz. The accumulation of oxyhydroxides (Al, Fe, Mn) and the enrichment of low-mobility trace elements (Zr and Hf) in some mound materials allowed us to identify the Macrotermes falciger material supply zone between the accumulation horizon marked by chemical precipitation phenomena and the horizon of progressive transition to altered bedrock. Carrier phases of metals of interest, such as Cu, Co, Ni, Pb and Zn, were identified through scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX) on constitutive particles of Macrotermes falciger termite mounds. These 5 metals of interest were sorted into <63 μm, 20–63 μm and 0–20 μm fractions, then chemically analyzed to reveal their accumulation in the 0–20 μm fractions. These results, provide clear evidence that Macrotermes falciger termite mound materials are ideal for providing information on lithogeochemical anomalies in geochemical prospection.