Geological and geochemical characteristics of lithocap in the Lu-Zong Basin, Anhui, China
Li, X and Zhang, L and Gao, C and Xie, J and White, NC, Geological and geochemical characteristics of lithocap in the Lu-Zong Basin, Anhui, China, Acta Petrologica Sinica, 33, (11) pp. 3545-3558. ISSN 1000-0569 (2017) [Refereed Article]
Lithocap is widespread in high-sulfidation epithermal gold deposits, and have obvious features to explore this deposit. Through studying geology, mineral assemblages and geochemistry of lithocap, it's better to understand the characteristics, developing and mineralization procedures of hydrothermal fluids. The Lujiang-Zongyang ore cluster is an important part of the Middle-Lower Yangtze mineralized belt. Lithocap represented by alunite is widespread in Lu-Zong Basin. The host lithocap has an area of >30km2, indicating Lu-Zong Basin maybe exist high-sulfidation epithermal systems. All previous studies in the area concentrated on the alunite deposit geology and alunite mineral reserves, geochemical characteristics need further research. Our study aims to determine the mineral assemblages present in the lithocap, and their geochemical characteristics. Lithocap is located in Zhuanqiao Formation, associated minerals are quartz kaolinite, dickite, minor sericite, illite and nacrite, jarosite and hematite, and few pyrite. The alunite and associated clay minerals are zoned horizontally away from Fanshan, assemblages are quartz + alunite, quartz + kaolinite/dickite, and kaolinite ± sericite ± illite outwards from the Fanshan district. Based on whole rock and SWIR analysis, lithocap can be divided into 3 types: siliceous altered rocks, alunite altered rocks and clay altered rocks. Except for SiO2, other major elements (K2O, Na2O, Al2O3, Fe2O3, TiO and P2O5) decrease in the siliceous rocks as a result of acid leaching. Other altered rocks show similar geochemical characteristics, but the contents of SiO2, Al2O3, Fe2O3 and P2O5 have a wider range; K2O and Na2O decrease, particularly Na2O, whereas TiO2 contents are mostly unchanged. Lithocap in Fanshan district is located in caldera, controlled by both volcanic structures and strata.