NUMERICAL SIMULATION OF BRINE REFLUX SYSTEMS AND THEIR POTENTIAL ROLE IN MINERAL DEPOSIT FORMATION

Sediment-hosted ore deposits account for a large fraction of the world’s base metal resources, yet the origin and migration of high-salinity brines from which metals precipitated remain poorly understood. Recent fluid inclusion studies demonstrate that the vast majority of ore-forming brines were sourced from residual brine produced by the evaporation of seawater rather than from dissolution of evaporite minerals. We use numerical modeling to examine processes that might produce and drive the large quantities of brines required to form these deposits in sedimentary basins. Our work builds directly upon previous models of brine reflux flow systems performed to investigate regional dolomitization and petroleum reservoir formation, which simulate the infiltration of evaporative brines on a basin-margin carbonate platform and their subsequent density-driven migration within the basin. To further explore these processes in the context of ore formation, a transient 2D thermohaline model of a generic brine reflux system was constructed using the finite element code FEFLOW, and potential flow rates, salinities, and temperatures of reflux brines were evaluated. The model domain (170 km by 6 km), boundary conditions (including an evaporative center reaching halite saturation), material properties, and initial conditions directly follow previous brine reflux models. However, alterations were made to the basin architecture to make it more representative of basins hosting world-class deposits. These include the addition of a high-K regional sandstone aquifer formed during active rifting in the early stages of basin formation, a low-K shale sequence formed during the sag-phase of basin development, and extensional faults. Results suggest that, in some cases, flow rates, temperatures, and salinities associated with brine reflux are adequate to produce base metal deposits. The modeling also shows that basin faults exert an important control the mineral potential of these flow systems. Our modeling therefore suggests that brine reflux may be important in the formation of sediment-hosted deposits when combined with active tectonism, and future work will focus on more realistic simulations of specific hypothesized flow systems in the geologic past.