Reconnaissance Exploration for Gold in the Misaki Area within the Iramba Sekenke Greenstone Belt, Central Tanzania

Abstract

Combinations of geological, geophysical and geochemical techniques have been used to explore for gold deposits at Misaki within the Iramba‑Sekenke Greenstone Belt in Singida region. The Misaki area is occupied by different rocks including homogeneous coarse-grained granite containing numerous xenoliths (> 5 vol. %), tonalite, K-rich granite, pegmatite and dolerite dykes. All granitic rocks have been intruded by dolerite dykes, cut by epidote veins and are found juxtaposed to a tonalitic rock. Granitic rocks contain mainly anhedral to subhedral K‑feldspar, plagioclase, quartz, biotite, hornblende, muscovite and opaque minerals, whereas tonalite contains similar minerals with relatively large amounts of plagioclase and mafic minerals (> 10 wt. %; biotite, hornblende and opaque minerals) and no K-feldspar. The rocks are weakly foliated to massive and poikilitic. K‑feldspar is perthitic, whereas plagioclases have cores with rim overgrowths. Chlorite, epidote and sericite in the rock formed at the expense of primary minerals under greenschist facies conditions. Geophysical datasets managed to identify lineaments that crosscut different rocks at Misaki, from which three (3) major structural trends have been recognized, which are NE-SW, NW-SE and ESE-WNW. Results from radiometric data mapped different lithological units by their different radiometric element contents (U, Th and K), distinguishing areas occupied by sediments or sedimentary rocks and those underlain by granitoid rocks. Soil geochemical survey have identified gold anomalies of up to 0.2 ppm Au that in parts show strong affinity with Pb. Bismuth and arsenic were also found to be associated with Au in the soil. Gold anomalies when overlaid with magnetic lineaments indicate an association of gold with NE-SW trending lineaments. Results of this work call for a follow-up detailed geological mapping that would involve trenching and sampling of unweathered rocks, and documentation of geological structures to uncover potential gold deposits of the Misaki area within the Iramba‑Sekenke Greenstone Belt.