Greisenized Alteration-Mineralization Geochemistry of the Tin Deposit Related to A-Type Granite: Case Study on the Kamusite and Ganliangzi Deposits, Xinjiang

The typical tin ores related to A-type granite have been discovered in Kalamaili region, east of the Junggar, North Xinjiang. However, little has been known about the metallogenetic mechanism of the tin ores so far. This study on petrology and geochemistry of four mineralization-alteration zones from the Kamusite and Ganliangzi tin deposits show that the ores and metallogenic rock body are the products of the fractional crystallization of homologous magma with the ores forming at the later stage, and there are two alteration zoning patterns:(1) (red) fine-grained Bt-granite→greisenized fine-grained granite→tin-bearing quartz veins; (2) fine-grained Bt-granite→tin-bearing greisen→tin-bearing silicification veins. The elements migration of the altered zone show that SiO₂ was externally supplied, Na₂O and K₂O moved out in varying degrees, more Fe₂O₃ was supplied than lost, and Th/U ratios kept decreasing in the whole mineralized process, which suggests that the on-going silicification and alkali metasomatism in the whole process result in the changes of metallogenic environment from basic to acidic and the increases of oxygen fugacity. The migration of trace elements (eg. W, Cu, Bi, In) was significantly positively associated with the enrichment of tin, while that of others (eg. Pb, Rb, Nb, Ta) was negative, together with the most active component of F and Cl, and these elements played important roles in the process of migration, enrichment and precipitation of tin. This indicates that the elements from the metallogenic rock body were lost while the fluid played an important role in the process of Sn mineralization, and the enrichment and mineralization of Sn was probably caused in the transition stage from magmatic to hydrothermal system.