Geochronology and Petrogenetic Studies of Alagbede Gold Deposit, Southwestern Nigeria.
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Date
2018
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PhD dissertation published in ProQuest Number 10930135
Abstract
Geological mapping around the gold-bearing main quartz vein of Alagbede area, located about 25km northeast of the Kwara State University, Malete shows that the Basement Complex rocks comprised the biotite-gneiss, migmatitic gneiss, quartzite, quartz-mica schist, talc-tremolite-actinolite schist, porphyroblastic granite, porphyritic granite, porphyritic diorite, alkali granite, granodiorite, alkali syenite, pegmatite/aplite and vein quartz. The AFM chemical classification diagrams for common volcanic rocks revealed that the Alagbede granites exhibit volcanic arc granites (VAG) origin based on the (Rb) vs Log (Y+Nb) discrimination diagrams for tectonic interpretation. Electron Probe Micro Analysis (EPMA) and ore microscopic work has shown that Alagbede gold occurs mainly as small inclusions or microfracture-fillings in pyrite, chalcopyrite and arsenopyrite in the deposit and this suggest that the gold mineralization is coeval with the precipitation of the sulfide phases. The abundances of light REE relative to that of the heavy REE in the host quartzitic and granitic rocks, the presence of negative Eu anomaly on the chondrite-normalized REE spider diagram and the major element fractionation pattern argued for a metamorphic source accompanied by magmatic differentiation of granitic magma as the possible source for the ore fluids for the gold mineralization at Alagbede, consistent with other orogenic vein-type gold deposits. A process of fractional crystallization in which the latent heat of crystallization provides sufficient thermal energy to consume the wall-rock, is hereby proposed as the fractionation model for the major element chemistry of the igneous rocks in Alagbede area. The U-Th-Pb on zircon was dated by in situ Laser Ablation ICP-MS which yielded upper intercept crystallization ages with superimposed Pan African imprints for the gold mineralization. Alagbede gold deposit is hosted in the vein quartz (formed at 590+27 Ma) and fine grained syeno-granite (formed 596+28 Ma) that are sinistrally sheared by a NW-SE trending fault, linked to the transcurrent fault line of the Anka-Yauri-Iseyin schist belt. A Pan African age of 590+27 Ma is hereby proposed as the age of gold mineralization in Alagbede area.
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Ajadi Jimoh (2018). Geochronology and Petrogenetic Studies of Alagbede Gold Deposit, Southwestern Nigeria. PhD dissertation published. In ProQuest Number 10930135, 287p.