Abstract

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Dutsen Bakura hill amethyst mineralization is located within a sheared granitic gneiss in the PanAfrican basement complex of northcentral Nigeria. The zone of mineralization is within a shear zone that trend NE-SW consistent with Pan-African structural trend. Mineralization consists of bands of milky quartz and amethyst, apparently formed from two stage sequence of silicification. Major, trace and rare earth element (REE) distribution patterns are used to distinguished host rock and mineralization characteristic. SiO2 content ranges generally between 76.77 – 79.25 wt % ; Al2O3 content ranges between 11.61 – 11.85 wt %; Fe2O3(T) content ranges between 1.49 – 2.26 wt %; Na2O content ranges between 2.91 - 4.99 wt % in the granite gneiss. The sheared granite gneiss has SiO2 content ranging between 82.09 w % - 99.21 wt %; Al2O3 content ranging between 7.42 - 10.34 wt % which is slightly lower than that of the granite gneiss; Fe2O3 (T) content ranges between 0.67 – 3.90 wt %; Na2O content ranges between 0.01 - 0.02 wt %. Major element content distribution within the mineralised zone is as follows: The SiO2 content in the amethyst ranges from 98.95 - 100 wt %; Al2O3 ranges between 0.06 – 0.18 wt %; Fe2O3 (T) ranges between 0.63 – 0.67 wt %; Na2O content ranges between 0.01 -0.02. However, SiO2 in the milky quartz ranges from 97.43 to 99.22 wt%; Al2O3 content ranges between 0.05 – 0.22 wt %; Fe2O3 (T) content ranges between 0.56 – 0.66 wt %; Na2O content ranges between 0.01 -0.02 wt %. This paper reports the geological and chemical characteristics of amethyst mineralization of Dutsen Bakura hill with the general view of chemically characterizing Nigerian amethyst.Dutsen Bakura hill amethyst mineralization is located within a sheared granitic gneiss in the PanAfrican basement complex of northcentral Nigeria. The zone of mineralization is within a shear zone that trend NE-SW consistent with Pan-African structural trend. Mineralization consists of bands of milky quartz and amethyst, apparently formed from two stage sequence of silicification. Major, trace and rare earth element (REE) distribution patterns are used to distinguished host rock and mineralization characteristic. SiO2 content ranges generally between 76.77 – 79.25 wt % ; Al2O3 content ranges between 11.61 – 11.85 wt %; Fe2O3(T) content ranges between 1.49 – 2.26 wt %; Na2O content ranges between 2.91 - 4.99 wt % in the granite gneiss. The sheared granite gneiss has SiO2 content ranging between 82.09 w % - 99.21 wt %; Al2O3 content ranging between 7.42 - 10.34 wt % which is slightly lower than that of the granite gneiss; Fe2O3 (T) content ranges between 0.67 – 3.90 wt %; Na2O content ranges between 0.01 - 0.02 wt %. Major element content distribution within the mineralised zone is as follows: The SiO2 content in the amethyst ranges from 98.95 - 100 wt %; Al2O3 ranges between 0.06 – 0.18 wt %; Fe2O3 (T) ranges between 0.63 – 0.67 wt %; Na2O content ranges between 0.01 -0.02. However, SiO2 in the milky quartz ranges from 97.43 to 99.22 wt%; Al2O3 content ranges between 0.05 – 0.22 wt %; Fe2O3 (T) content ranges between 0.56 – 0.66 wt %; Na2O content ranges between 0.01 -0.02 wt %. This paper reports the geological and chemical characteristics of amethyst mineralization of Dutsen Bakura hill with the general view of chemically characterizing Nigerian amethyst.

Keywords: Amethyst, Geology, Mineralization, Characterization, Shear Zone, Silicification