Abstract:

The western Hunan-eastern Guizhou area is an important Pb-Zn polymetallic ore district, some of which hosted in the algal limestone of the Lower Cambrian Qingxudong Formation. In this study, fluid inclusions and S, Pb, C isotope compositions were studied for four typical Pb-Zn deposits (Limei, Shizishan, Xiunao and Pukouchang) hosted in the Qingxudong Formation. The results show the ore-forming fluid with low temperature and medium to high salinity. The δ³⁴S values of sulfides are high. The δ¹³C and δ¹⁸O_V-SMOW values of wall-rock and calcite show the same characteristic with the normal marine carbonate. The Pb isotope of the wall-rocks and ore have a little variation scope, showing the linear distribution in the ²⁰⁷Pb/²⁰⁴Pb -²⁰⁶Pb/²⁰⁴Pb diagram. Our results indicated that ore-forming materials of the Pb-Zn deposits in the western Hunan-eastern Guizhou area mostly derived from the carbonate wall-rocks. Meanwhile, migrating fluid added Pb, Zn materials to the deposits as well. Pb, Zn and associated minerals were precipitated due to the changes of the physical and chemical conditions, resulted from mixing of two sources, indicating that the genesis type of our studied deposits is the Mississippi Valleytype (MVT) lead-zinc deposit

Key words: Qingxudong Formation, Mississippi Valley-type deposit, isotope, fluid inclusion, western Hunan eastern Guizhou