Numerical modelling of deformation and fluid flow in the Shuikoushan district, Hunan Province, South China

摘要

The Shuikoushan district, in Hunan Province, South China, contains major Pb-Zn-Au-Ag polymetallic mineralisation. Two groups of numerical models have been constructed to study the interactions between deformation and fluid flow in the district Suring the Yanshanian compression event (180 to 90 Ma). The first group includes district-scale conceptual models of coupled deformation and fluid flow during folding. The models show that fluid flow patterns are controlled by deformation within the fold system inferred for the district. During regional shortening and folding, fluids are generally focused towards the fold hinge/core areas along higher permeability layers (in particular Permian limestone units), in preference to flowing across the low permeability seal units (Permian and Jurassic terrestrial sequences). The efficiency of this fluid focusing can only be significantly increased if these folded seal units are allowed to undergo permeability increase as a result of tensile failure. The modelling results show that permeability enhancement localises mostly at fold hinges, dominantly within the silicified zone on the top of the Permian limestone unit. This process results in increased flow velocities and facilitates fluid focusing towards fold hinge/core locations at this silicified rock horizon. The second group includes deposit scale models for the Kangjiawan deposit, which is one of the two major deposits in the Shuikoushan district. The models show patterns of tensile failure, permeability creation, fluid focusing and mixing, and fracture development along a selected exploration cross section through the deposit. These results are consistent with the observed brecciation and mineralisation features. Regions of maximum brecciation in the district are associated with: (1) a combination of fold hinge and fault intersection locations (structural); and (2) the silicified zone and Permian limestone unit (lithological). Such brecciation zones are associated with extensive fluid focusing and mixing, and therefore represent the most favourable locations for mineralisation in the district. On the basis of this work, ideas for future research work and mineral exploration in the district are proposed.