Geological and geochemical characteristics of lithocap in the Lu-Zong Basin, Anhui, China

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.