An overpressured fluid system associated with the giant sandstone-hosted Jinding Zn-Pb deposit, western Yunnan, China

Abstract

The Jinding Zn-Pb deposit is hosted in continental clastic rocks in the Meso-Cenozoic Lanping-Simao Basin in western Yunnan. The deposit has been compared to SEDEX, MVT, and sandstone-hosted types (SST), all assuming intra-basinal origins for the ore-forming fluids. The driving forces of fluid flow and the pressure system have not been systematically investigated. This paper presents field and fluid-inclusion evidence to show that the Jinding mineralizing system was strongly overpressured. The common occurrence of CO₂-rich fluid inclusions and the high fluid pressures suggest a mineralizing system markedly different from most other sediment-hosted base metal deposits including SEDEX, MVT and SST. Numerical modeling of basinal fluid flow indicates that sediment compaction alone in the Lanping-Simao Basin cannot produce any significant overpressure. Tectonic thrusting can significantly increase fluid pressure, but is not enough to cause the high fluid overpressure indicated by fluid inclusions. Input of extra-basinal fluids (e.g. deepsourced CO₂) into the basin may have contributed to the development of the overpressured mineralizing system.