In situ elemental and Sr-Nd isotopic compositions of hydrothermal apatite from the Shazhou U deposit in the Xiangshan complex: Implications for the origins of ore-forming fluids of volcanic related U deposits in South China

• Published in: Journal of Asian earth sciences Vol. 233; p. 105230
• Main Authors: Yu, Zhiqiang, Ling, Hongfei, Chen, Peirong, Chen, Weifeng, Fang, Qichun, Mavrogenes, John
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.08.2022
• Subjects: Halogens; Hydrothermal apatite; In situ Sr-Nd isotopes; The Xiangshan U deposits; Volcanic related U deposit; Halogens; Hydrothermal apatite; The Xiangshan U deposits; In situ Sr-Nd isotopes; Volcanic related U deposit
• ISSN: 1367-9120; 1878-5786
• DOI: 10.1016/j.jseaes.2022.105230

[Display omitted] •In situ Sr-Nd isotopes of apatite are effective in tracing origins of ore forming fluids in the Shazhou U deposit.•The reducing U-poor fluid was derived from mantle-derived magma which formed the mafic dikes in wall rocks.•The oxidizing U-rich fluid originated from percolation of meteoric water in the adjacent red-bed basins.•The Late Cretaceous mafic magmatism and red-bed basins are two key factors controlling U mineralization in South China. The origin of ore-forming fluids of volcanic related U deposits remains controversial. This study reports in situ elemental and Sr-Nd isotopic compositions of apatite associated with U mineralization from the Shazhou volcanic related U deposit in South China, which provides a new perspective to constrain the origin and evolution of its ore-forming fluids. Hydrothermal apatites from the hematized rocks and U-mineralized rocks show distinct textures and chemical features, indicating two types of fluids involved in the U mineralization process. The hematitization fluid was oxidizing and enriched in U and Cl. A reducing fluid with lower Cl/F and U was introduced and mixed with the oxidizing hematitization fluid to cause U precipitation. Apatite from the hematized rocks has a lower 87Sr/86Sr (0.709246–0.714383) than that of apatite in U ore veins (0.710383–0.719318). The εNd(t) of apatite in the hematized rocks is from −7.6 to −9.4, whereas apatite in U ore veins has higher εNd(t) ranging from −1.2 to −8.4, close to that of mafic dikes intruded into the volcanic rocks. In situ Sr-Nd isotopes of apatite indicate the oxidizing fluid originated from the red-bed basins, whilst the origin of the reducing fluid was related to the mantle-derived mafic dikes. The reducing fluid has experienced assimilation by the metamorphic basement rocks to gain higher radiogenic strontium. This study demonstrates that in situ elemental and Sr-Nd isotopic compositions of apatite are effective in identifying different ore-forming hydrothermal fluids and constraining their origins and chemical evolution.