Regional-scale geochemical analysis of carbonate cements: Reconstructing multiple fluid interactions related to dolomitization and mineralization in Lower Carboniferous rocks of the Irish Midlands.

摘要

Previous studies of the dolomitization history of Viséan rocks of the Irish Midlands focused on ore fluids in and near ore zones. In order to provide a regional context within which to place studies of individual ore deposits/ore districts, I undertook a regional-scale petrologic and geochemical study of Lower Carboniferous rocks in the Irish Midlands.; Three distinct fluids were present outside of mineralized areas: (1) a low-temperature, high-salinity fluid generated from seawater evaporated beyond the point of halite precipitation. This fluid was enriched in 18O relative to Lower Carboniferous seawater, had variable Sr concentrations, and 87Sr/86Sr ratios that were slightly higher than Lower Carboniferous seawater; (2) a low-temperature, moderate-salinity fluid generated from seawater evaporated to the point of gypsum precipitation. This fluid was enriched in 18O relative to Lower Carboniferous seawater, had very high Sr concentrations, and high 87Sr/ 86Sr ratios; and, (3) a high-temperature, moderate-salinity fluid generated from seawater evaporated to the point of gypsum precipitation. This fluid was enriched in 18O relative to Lower Carboniferous seawater, had low Sr concentrations, and 87Sr/86Sr ratios that were slightly higher than Lower Carboniferous seawater.; A comprehensive knowledge of the distribution of multiple fluids in the Lower Carboniferous rocks of the Irish Midlands allows us to recognize ore-related hydrothermal fluids outside of mineralized zones. Mapping the distribution of ore fluids in non-mineralized areas may allow us to determine the extent of the ore-forming system and to locate potential new exploration targets by identifying areas in which fluids of appropriate ore-forming character were present.