Sedimentary rock-hosted ore-forming systems: structural setting and paleohydrology

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Sedimentary rocks deposited in intracontinental and passive margin basins host a wide variety of hydrothermal ore-deposits that contain a significant percentage of global metal resources, especially lead, zinc, copper, and gold. These deposits form in a variety of ore-forming systems that operate at different periods of time as the basins progress through sequential stages of rifting, sedimentation, collision, deformation, erosion, and exhumation. The potential for ore-forming systems to generate deposits at any stage is strongly dependent on the overall hydrogeological framework of the basin, which is largely controlled by basin geometry, the permeability of sedimentary layers, and the density, geometry and permeability of cross-cutting structures. The long-term goal of my proposed research program is to evaluate how the physical and chemical evolution of sedimentary basins and their constituent sediments affects the potential for generating different types of sedimentary rock-hosted ore-deposits. This will be accomplished by comparing ore-forming systems operating at three different stages in the life cycle, from deposition to exhumation, of passive margin sediments: (1) sedimentary exhalative (SEDEX) Pb-Zn ore systems active during basin sedimentation prior to extensive lithification; (2) orogenic Au-systems active during deformation and low-grade metamorphism accompanying the incorporation of passive margin sediments into a foreland fold and thrust belt; and (3) Carlin-type Au-systems active nearly 300 million years after the host passive margin sediments were incorporated into a fold and thrust belt. My proposed research program will provide new constraints in understanding how the evolution of passive margin sedimentary basins influences the type of sedimentary rock-hosted ore-deposit that will form. The program encompasses field sites in the lower Paleozoic Selwyn Basin of the Yukon and Northwest Territories, and the laterally equivalent basin of central and eastern Nevada. First-order constraints on the hydrogeological framework under which the deposits formed will be provided by integrating extensive geological field observations, careful structural mapping, geochronology and geochemistry, taking advantage of recent advances in micro-analytical techniques and geochemical imaging. The extent to which the primary sedimentological character and subsequent diagenetic and structural evolution of host rocks is controlled by hydrothermal fluid flow and how early formed ore-deposits are modified by subsequent stages of collision and basin deformation will also be evaluated. The results will be used to advance conceptual models for the formation of sedimentary rock-hosted ore-deposits and their link to the life cycle of sedimentary basins, with implications for the exploration and discovery of metals vital to society.