Huang, R; Yuan, G; Wang, G; Qiu, K; Shao, H; Gong, N
The Husab uranium deposit is a typical pegmatite-hosted ore deposit located in the southern Central Zone of the Damara orogenic belt, Namibia, which is one of the largest uranium deposits in the world. The enriching and precipitating mechanism of uranium in different ores is still in debate. In order to reveal the relationship between magma evolution and uranium mineralization, petrology, mineralogy, as well as geochemistry of E-type pegmatite ores are studied. The results of field and microscopic identification show that the uraniferous E -type pegmatites can be divided into two categories, including " simple-type" and " complex-type" ore bodies. The former has granitic-pegmatitic texture, and its main industrial uranium minerals are uraninites (with few thorites), which are disseminated distributed among quartzs, feldspars and biotites with low to medium mineralization degree. The latter is characterized by heterogeneous texture with extremely high mineralization, in which uraninites and a large number of biotite agglomerates are spatially related in genesis. Geochemical analysis results show that in the "simple-type" pegmatite, the enrichment of uranium is controlled by fractional crystallization process, while in the "complex-type" pegmatite, uranium mineralization is closely related to assimilation process. The mineral-melt phase equilibrium simulation of pegmatite ores concludes that the mixing of external source of mafic components (FeO, MgO, TiO2) led the change of mineral crystallization sequence in "complex-type" melts. Compared with "simple type" melts, the initial crystallization temperature of biotite increased and that of potassium feldspar decreased, which provided more adequate crystallizing time and growing space for biotite, promoting it to be produced in the form of massive aggregation. This process would consume lots of F ions in magma and induced the hydrolysis of UFm4-m complex, resulting in precipitation of uraninites near the biotite agglomerates and the formation of high-grade uranium mineralization. Therefore, the study of " simple-type" and " complex type" pegmatite ores in this case effectively reveals the uranium mineralization process, enriches the knowledge about the pegmatite type uranium deposit, and also provides a scientific basis for the exploration and development of uranium resources.