Chapter 2: The Dynamics of Permeability Enhancement and Fluid Flow in Overpressured, Fracture-Controlled Hydrothermal Systems

Many ore-producing hydrothermal systems form within intrinsically low permeability host rocks during fracture-controlled flow in overpressured fluid regimes. The generation and localization of fracture-controlled fluid pathways in these systems involves dynamic coupling between fluid flow, fluid pressures, stress states, and deformation processes. In high fluid flux settings, fracture-controlled permeability enhancement is driven largely by fluid pressurization rather than by tectonic loading. The orientation of the stress field plays a critical role in governing the orientations of activated fractures. Permeability destruction by fracture sealing and cementation of fragmented rock is rapid relative to the lifetimes of hydrothermal systems. Accordingly, repeated regeneration of permeability is necessary to sustain the high fluid fluxes required for ore formation. The evolution of permeability is thus controlled by a dynamic competition between permeability enhancement processes and permeability destruction processes.