GEOLOGY, MINERALOGY AND PROVENANCE OF ALLUVIAL GOLD MINERALIZATION IN RIVER GAGARE DRAINAGE BASIN, WONAKA SCHIST BELT, NORTHWESTERN NIGERIA

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Date
2017-11
Authors
GREMA, HARUNA MUHAMMED
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Abstract
Gold occurrence in Nigeria is known to be associated with the schist belts in the western half of the country. Amongst these is the Wonaka schist belt that has widespread occurrence of placer Au without identified primary sources, which has remained puzzling. This study applied morphological and mineral chemistry analyses of gold grains to characterize and determine the provenance of gold grains within the River Gagare drainage basin and also estimate the transport distances and provide insight into the possible mineralization style. Analytical techniques and methods employed include transmitted light microscopy, sieve analysis, binocular microscopy, scanning electron microscopy, and energy dispersive spectroscopy. These were used to carry out petrographic examination of the rocks, sedimentological studies of the gold-bearing stream sediments and heavy mineral concentrates and also to determine gold grain surface characteristics such as roundness, flatness, outline, surface texture and composition. The study area comprises of metasediments (quartz-mica schist, phyllite, metasandstone), granitoids (porphyritic granite, and diorite) and granitic gneiss, with aplite, quartz and quartzo-feldspathic veins as the minor rock occurrences. The dominant tectonic fabric within the metasediments and the granite gneiss are the steeply dipping, N-S, NW-SE and NE-SW trending, phyllitic cleavage, schistose foliations (S1) and gneissocity respectively. Gold grains from class 1, 4, and 5 are all of the B and C types, with similar flatness indices ranging from 2.5 to 11. Most of the gold grains from these classes are equant and elongated having moderately smoothen surfaces and regular outlines, suggesting short to moderate transport distances (300 m – 15 km). Rivers Kutiri and Gagare have 75% of the gold grains within them belonging to the Ctype group, with catchment area consisting of all the classes, and flatness indices between 3 and 46. Primitive and trunk placers give them a multisource. The sources may be more distant than indicated by the ratios of A-type to B-type and B-type to C-type grains determined by the morphological characteristics. Lack of delicate secondary growth, pristine type, sharply crystalline Au grains, and Au overgrowth are indicative of detrital origin. All the representative gold grains plotted in the mesothermal field of the ternary Au- Agx10-Cux100 plot with low Cu and enriched Ag contents. Additionally, 70% of the recovered Au grains were less than 60 μm in size typical for Au from Archean granitegreenstone terrains.
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A THESIS SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES, AHMADU BELLO UNIVERSITY, ZARIA; IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF MASTER OF SCIENCE DEGREE IN GEOLOGY DEPARTMENT OF GEOLOGY, FACULTY OF PHYSICAL SCIENCES, AHMADU BELLO UNIVERSITY, ZARIA - NIGERIA
Keywords
GEOLOGY,, MINERALOGY,, PROVENANCE,, ALLUVIAL GOLD MINERALIZATION,, RIVER GAGARE DRAINAGE BASIN,, WONAKA SCHIST BELT,, NORTHWESTERN NIGERIA
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