Sedimentary basins provide about three-quarters of the Earth's base-metal resources. Three major types of lead-zinc mineralization are observed: 1) shale-hosted ore deposits of the SEDEX type, 2) limestone and dolomite-hosted ore deposits of the MVT type, and 3) limestone and dolomite-hosted ores of the Irish type. All three types of ores are known to have formed by the deep migration of metal-bearing brines in sedimentary basins where zinc and lead was leached from older sandstone and fractured crystalline basement. Major faults appear to have played an important role in guiding the transport of metal-bearing brines in both SEDEX and Irish ores, which are found in rifted tectonic environments. Unresolved issues regarding the origin of these lead-zinc deposits include the timing, rates and patterns of fluid flow, the geochemical and thermal aspects of fluid mixing and ore deposition, and the effects of faults on ore genesis. Until now, no group has tackled these issues for SEDEX-type ores so this topic forms the foundation of my project. The McArthur Basin in northern Australia hosts one of the world's largest SEDEX-type ores, the HYC deposit. To understand the effects of faults and rift-basin geology on ore formation, we plan to develop a series of numerical experiments wherein processes of hydrothermal fluid flow, heat transfer, and geochemical reactions are simulated for HYC using mathematical modeling. Basic parameters such as fault permeability, zinc concentration, etc. are poorly constrained for ancient rift settings like the McArthur Basin and so computer-based simulations allow us to explore parameter effects and couple complex processes like chemical reactions with the subsurface hydrology. I plan to collaborate with experts at the Centre for Ore Deposit Research in Hobart, Australia, who have been studying the geochemical and geological attributes of metal deposits in the McArthur Basin over the past decade. Together we hope to develop a better understanding of how these giant ore deposits form, and this in turn will help build better exploration models for rift basins in Australia, the USA, and Canada. I also hope that some of this research will benefit new studies by the US Geological Survey of the Red Dog deposit, Alaska, another giant SEDEX-type ore system.
