Mass Transfer during Hematitization and Implications for Uranium Mineralization in the Zoujiashan Deposit, Xiangshan Volcanic Basin

• 作者: Teng Deng Guoxiang Chi Xiongjie Zhang Zenghua Li Deru Xu Shengmiao Li Pengfei Du Pei Shang Shaohao Zou Wanpeng Zhou Ke Xu Hai Yan Ma Wen Zhengpeng Ding
• 来源期刊: 地球科学学刊（英文版）
• 年，卷（期）: 2022,（2）
• 所属期刊栏目: Special Issue on Sandstone-Type Uranium Mineralization and Its Metallogenic Background
• 页码范围: 422-434
• 页数: 13页
• 语种: 英文

摘要

The Zoujiashan uranium deposit in the Xiangshan ore field is the largest volcanic-related uranium deposit in China. Hematite-and fluorite-type ores are the predominant mineralization styles. Hematitization in the Xiangshan ore field is closely associated with uranium mineralization, mainly oc- curring as hematitized rocks enclosing fluorite-type vein ores developed in pre-ore illitized porphyritic lava. Detailed petrographic and mass balance calculation studies were conducted to evaluate the mech- anisms for uranium precipitation and mass transfer during hematitization. Petrographic observations suggest that in the hematitized rocks, orthoclase is more altered than plagioclase, and quartz dissolu- tion is common, whereas in the illitized rocks, pyrite commonly occurs within the altered biotite grains, and chlorite grains are locally found. Mass balance calculations indicate that Na2O and U were gained, K2O, CaO and SiO2 were lost, whereas Fe2O3-t remained more or less constant during hematitization. These observations suggest that the hydrothermal fluids were Na-and U-rich and Ca-K-poor, and the Fe2+used for hematitization was locally derived, most likely from biotite, pyrite and chlorite in the host rocks. The Fe2+is inferred to have played the role of reductant to precipitate uranium, and calculation indicates that oxidation of Fe2+ provided by host rocks is sufficient to form ores of economic signifi- cance. Consequently, the hematite-type ore is interpreted to be generated by the reaction between oxi- dized ore fluids and reduced components in host rocks. The development of calcite and pyrite in the flu- orite ores suggests that perhaps mixing between the U-rich fluid and another fluid carrying reduced sulfur and carbon may have also contributed to uranium mineralization, in addition to temperature and pressure drop associated with the veining.