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.