Deciphering the Complex History of Fluid Flow in Lower Carboniferous Carbonate Rocks, Irish Midlands: Geochemistry of Multiple Dolomitizing and Ore-Forming Events

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ABSTRACTDeciphering the Complex History of Fluid Flow in Lower Carboniferous Carbonate Rocks, Irish Midlands: Geochemistry of Multiple Dolomitizing and Ore-Forming EventsKevin L. Shelton & Jay M. GreggEAR-0106388 The Irish Midlands comprise a natural laboratory in which to study the physical, thermal and geochemical effects of fluid flow on dolomitization and zinc-lead ore deposition in an extensional/compressional tectonic setting. Our research addresses the relationships among sedimentary facies, early diagenesis and hydrothermal dolomitization, and their relationship to localized and regional fluid flow throughout Lower Carboniferous carbonate rocks in Ireland. Specific questions to be addressed are applicable to the Irish Midlands, as well as to similar extensional/compressional basinal settings worldwide: What are the sources of various multiple fluids and the extents of their flow systems?; What is the relative timing of each fluid system?; What are the critical fluid-fluid and fluid-rock interactions along flow paths that led to hydrothermal dolomitization and/or ore deposition?; What is the relative importance of regional-scale fluid flow through aquifers versus localized fracture-controlled flow for the development of mineral deposits? Our study will address these questions through combined application of carbonate petrology and a number of geochemical tools, including C, O and Sr isotopes, fluid inclusion microthermometry, and fluid inclusion halogen and trace element geochemistry, including new laser ablation-ICP-MS techniques. The impact of this study is profound and timely. Modelers are now expanding the capability of reactive flow hydrogeologic-geochemical models to simulate groundwater chemistry, patterns of rock alteration and ore mineralization in fractured rock. Geochemical data from our studies of chemical interactions of basinal fluids along stratigraphic and faulted pathways will provide an excellent basis for constraining theoretical models of deep fluid flow that are being developed for the Irish Midlands.