Geochemical and mineralogical characterisation of the INCA Uranium mineralisation in the central zone of the Damara Belt, Namibia
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Date
2020
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Publisher
University of Namibia
Abstract
The Inca uranium deposit is situated about 40 km east of the town Swakopmund in the central Namib Desert within the Erongo region, in western Namibia. It is located within the uranium-endowed Central Zone of the Pan African Damara orogenic belt. The deposit is hosted in amphibolite facies grade metasedimentary rocks of the Lower Swakop Group of the Damara Supergoup. Characterisation of mineralogical and geochemical features of the Inca uranium mineralisation has been conducted to enhance the understanding of formation processes of the deposit. The objectives of the study were to characterise the occurrence of uranium mineralisation and to establish a genetic model of the deposit. This quantitative study has been conducted through whole-rock major and trace element geochemical analytical methods comprising ICP-OES and ICP-MS; and XRD method for mineral identification; as well as scanning electron microscopy and optical petrographic examination of selected drill core samples from three selected boreholes. Major element abundances of most samples are characterised by anomalous silica and iron oxides related to metamorphic and magmatic-hydrothermal alterations. Trace element abundances of some samples such as S, Pb, and Zn depict positive correlation with uranium mineralisation and is postulated to simultaneous and successive distinct processes. REE and uranium enrichment correlation particularly associated with magnetite skarn rocks suggests mobility of REE during hydrothermal uranium mineralisation. Uranium mineralisation is essentially made up of interstitially disseminated euhedral to subeuhedral primary uraninite and secondary, hydrothermal, massive to semi-massive and botryoidal coffinite occurring as fracture infills, veinlets and coatings around grain boundaries of gangue mineral assemblages of host metasedimentary and leucogranite rocks. Uraninite is intimately related to prograde metamorphic assemblages and magnetite skarn rock. Coffinite is derived from partial dissolution of uraninite under hydrothermal conditions and is associated with sulphide and REE mineralisation as fracture infills and along grain boundaries of host mineral assemblages of the iron skarn and calc-silicate rocks as well as leucogranites. Pervasive fracturing associated with secondary mineralisation suggests that fractures facilitated the remobilization of metals and served both as conduit for fluid transport and as deposition sites. The magnetite skarn rock served as a redox boundary for metal rich circulating hydrothermal fluids and triggered precipitation of uranium mineralisation and associated ore minerals such as galena, and xenotime. Botryoidal coffinite mineralisation together with opal and aragonite appear to be associated with late meteoric fluids under hydrothermal conditions. Partial oxidation of magnetite to hematite is suggested to be related to this later event. Further research work in mineral geochemistry, U-Pb geochronology and stable isotope is recommended to advance the understanding of the evolution and quantification of the ore forming processes involved in the formation of the Inca U deposit.
Description
A mini thesis submitted in partial fulfilment of the requirements for the Degree of Master of Science in Applied Geology
Keywords
Inca uranium, Mineralisation, Damara belt