Formation of the Fanshan lithocap and implications for exploration in the Luzong Basin, Anhui Province, China

Lithocaps in island-arc settings are genetically related to porphyry-epithermal systems and can be used to guide exploration for porphyry deposits. The Fanshan area of the Luzong basin in the eastern China, hosts a large lithocap but no porphyry or epithermal deposits have been found. The Fanshan lithocap in the Luzong basin is centred on the Dafanshan alunite mining district with vuggy quartz–alunite–pyrite, quartz–dickite–kaolinite ± alunite, quartz–kaolinite and kaolinite–illite ± smectite from northeast to southeast. The alteration zoning reflects the gradual decrease in the temperatures and acidities of the fluids. Four types of alunite including bladed alunite, needle alunite, granular alunite, and powdery alunite suggest that the Fanshan lithocap formed in the magmatic-hydrothermal and supergene environment. From the southwest to the northeast of the Dafanshan district, Pb and 10⁶ Pb/(Na + K) in the alunite samples gradually decrease, Au content gradually increases, but the Cu content does not change significantly. The peak positions at 1480 nm and the Na content of the magmatic-hydrothermal alunite gradually increase, whereas Pb and 10⁶ Pb/(Na + K) in the alunite minerals gradually decrease. This suggests that the source of the hydrothermal fluids and a potential zone of precious metal mineralization area may be in the northeast of the Dafanshan district, and the potential area of copper mineralization may be in the Huangtun area northeast of the Luzong basin.