Morphologic and placer features were used to characterize, determine the provenance, and transport distances of gold grains within the River Gagare drainage basin of the Wonaka Schist Belt. Field studies, scanning electron examination coupled with energy dispersive spectrometry and binocular microscopy were utilized to study the spatial distributions, shape, size, inclusions, primary and fluvial transport-induced deformations, as well as Cailleux flatness indices . The grains are dominantly sub-rounded (71%), with length between 35 800 µm and width of 10 778 µm while the rounded grains have a mean length of 292.5 µm and width of 179 µm. Circularity and sphericity are similar (2.2) within the sub-rounded grains, however, variations exist in the rounded grain type (2.7, 2.6). The Cailleux flatness index ranges from 2.5 to 9 for sub-rounded grains and 2 15.5 for the rounded, indicating the multisource nature of the grains. The grains are consistent with short to moderate transport distances from the lode sources. The similarities in physical features, lack of delicate secondary growth structures and irregular grain outlines point to a detrital source for the placer deposits. Evidence of emulsion crystallisation type is indicated by presence of sub- to anhedral inclusions within the Au grains.
Key words: Placer gold; Cailleux flatness indices; Wonaka Schist Belt; River Gagare; Scanning Electron Microscopy; Provenance; Northwest Nigeria.
|