Modeling of fluid pressure evolution related to sediment loading and thrust faulting in the Lanping basin:Implications for the formation of the Jinding Zn-Pb deposit,Yunnan,China

摘要

The Jinding Zn-Pb deposit occurs in Cretaceous and Paleocene siliciclastic rocks(mainly sandstones)in the Meso-Cenozoic Lanping basin,western Yunnan,China.With a reserve of approximately 200 Mt of ore containing 6.1% Zn and 1.3% Pb,Jinding is the largest sandstone-hosted Zn-Pb deposit in the world.Most previous studies assumed that the mineralizing fluids were derived from within the basin(including meteoric recharge),and the fluid flow was driven by topographic relief under a hydrostatic regime.In contrast,we propose that the mineralizing system was strongly overpressured based on observations of hydraulic fractures and fluid inclusion data.Numerical modeling results indicate that the overpressures could not have been produced by normal sediment compaction.Thrust faulting and input of mantle-derived fluids are likely responsible for the building-up of the high overpressures.The special hydrodynamic regime and potential contribution of mantle-derived fluids to the mineralizing system distinguish Jinding from other known sedimentary basin-related Pb-Zn deposits.