Carboniferous basin evolution of central Ireland - simulation of structural controls on mineralization

Much is known about the Carboniferous-hosted, hydrothermal, zinc-lead deposits of central Ireland, including temperatures, geochemistries and fluid properties at the mineralised sites. However, this knowledge is insufficient to force a unique genetic interpretation of the palaeo-hydrogeological system responsible for mineralisation. Two hypothetical flow systems survive previous mass-balance testing: a deep, topographically-driven, regional flow, and deep, convective-flow systems local to each deposit. In order to develop models of these flow systems, we have created a 4-D, Early Carboniferous restoration of basin development in central Ireland. The structural style is one of tilted fault blocks of the pre-Carboniferous “basement”; the Carboniferous sedimentary rocks are deposited in the accommodation space created by movement of the basement. Fluid- and heat-flow simulations based on the geological restorations show that most of the rising, hot flows are focused on faults. The 4-D restorations suggest that such faults are at active, syn-depositional, fault-block corners. Buoyancy-driven convective flow systems, operating within both the fractured basement and its sedimentary cover, are a viable mineralisation system that agrees with the geological interpretation. Topographically-driven flow systems developed from the geological interpretation do not reproduce the important characteristics of hydrothermal flow as deduced from evidence at the deposit sites.