Genesis and Uranium Sources of Leucogranite-hosted Uranium Deposits in the Gaudeanmus Area, Central Damara Belt, Namibia： Study of Element and Nd Isotope Geochemistry

• Published in: Acta geologica Sinica (Beijing) 2017-12, Vol.91 (6), p.2126-2137
• Main Authors: FAN, Honghai, CHEN, Jinyong, WANG, Shengyun, ZHAO, Jingyang, GU, Dazhao, MENG, Yanning
• Format: Article
• Language: English
• Subjects: Barium; Damara Belt; Earth; Gallium; Gaudeanmus; Geochemistry; Isotopes; Lead; leucogranites; Magma; Mineralization; Minerals; Nd isotopes; Niobium; Rare earth elements; Ratios; Samarium isotopes; Silicon dioxide; source of uranium; Strontium; Tantalum; Trace elements; Uranium
• ISSN: 1000-9515; 1755-6724
• DOI: 10.1111/1755-6724.13453

This paper presents a systematic study of major and trace elements and Sm-Nd isotopes in leucogranites closely related to uranium mineralization in the Gaudeanmus area, Namibia. The results illustrate that the uraniferous leucogranites possess high SiO2 （68.8wt%-76.0wt%, average 73.1wt%） and K （4.05wt%-7.78wt%, average 5.94wt%） contents, and are sub-alkaline and metaluminous to weakly peraluminous, as reflected by A/CNK values of 0.96-1.07 with an average of 1.01. The leucogranites are rich in light rare earth elements （LREE/HREE = 2.53-7.71; （La/Yb）s = 2.14-10.40）, have moderate Eu depletion and high Rb/Sr ratios （2.03-5.50 with an average of 4.36）; meanwhile, they are enriched in Rb, K, Th, U and Pb, and depleted in Ba, Nb, Ta, and Sr. The tNd（t） values of uraninites range from -14.8 to -16.5, and the two-stage Nd model ages are 2.43-2.56 Ga. Detailed elemental and Sm-Nd isotopic geochemical characteristics suggest that the leucogranites were formed in a post- orogenic extensional environment. The U-rich pre-Damara basement was the main source of uranium during the primary mineralization event, which is disseminated in leucogranites, whereas the uranium mineralization in veins possibly resulted from remobilization of the primary uranium minerals.