Invited Paper:The Physical Hydrogeology of Ore Deposits

摘要

Hydrothermal ore deposits represent a convergence of fluid flow, thermal energy, and solute flux that ishydrogeologically unusual. From the hydrogeologic perspective, hydrothermal ore deposition represents acomplex coupled-flow problem—sufficiently complex that physically rigorous description of the coupled thermal(T), hydraulic (H), mechanical (M), and chemical (C) processes (THMC modeling) continues to challengeour computational ability. Though research into these coupled behaviors has found only a limited subset to bequantitatively tractable, it has yielded valuable insights into the workings of hydrothermal systems in a widerange of geologic environments including sedimentary, metamorphic, and magmatic. Examples of theseinsights include the quantification of likely driving mechanisms, rates and paths of fluid flow, ore-mineral precipitationmechanisms, longevity of hydrothermal systems, mechanisms by which hydrothermal fluids acquiretheir temperature and composition, and the controlling influence of permeability and other rock properties onhydrothermal fluid behavior. In this communication we review some of the fundamental theory needed to characterizethe physical hydrogeology of hydrothermal systems and discuss how this theory has been applied instudies of Mississippi Valley-type, tabular uranium, porphyry, epithermal, and mid-ocean ridge ore-formingsystems. A key limitation in the computational state-of-the-art is the inability to describe fluid flow and transportfully in the many ore systems that show evidence of repeated shear or tensional failure with associateddynamic variations in permeability. However, we discuss global-scale compilations that suggest some numericalconstraints on both mean and dynamically enhanced crustal permeability. Principles of physical hydrogeologycan be powerful tools for investigating hydrothermal ore formation and are becoming increasingly accessiblewith ongoing advances in modeling software.