Clumped C-O isotope temperature constraints for carbonate precipitation associated with Irish-type Zn-Pb orebodies

Ireland hosts the greatest concentration of discovered zinc per square kilometre on Earth, with production from 5 carbonate-hosted deposits, including the giant Navan deposit. Clumped C-O isotope analyses of carbonates offer a powerful new technique to directly deliver accurate fluid temperatures and precise calculations of fluid O isotope compositions, offering a significant opportunity to refine the evolving genetic models, and develop new vectoring tools for exploration. We present the first clumped C-O isotope results for parageneticallyconstrained carbonate generations from a number of Irishtype Zn-Pb deposits. Preliminary analysis of hanging-wall white matrix breccias from Lisheen show non-systematic temperature variation (~100 to 170°C), with fluid d18OV-SMOW increasing with temperature. Significant variations in temperature at the thin section scale may be indicative of fluid mixing and/or multiple phases of WMB dolomite brecciation. Post-ore pink dolomite at Lisheen, and crosscutting calcite veins formed at significantly lower temperatures (67 to 42°C). Temperatures of 61 to 110°C were obtained for sphalerite-bearing calcite veins in the hanging-wall of the Randalstown Fault near Navan. These veins contain coarse sphalerite interpreted to have been remobilised from the nearby Navan orebody by a single, cool fluid (Marks, 2015). Clumped C-O data will also be presented for samples from Galmoy, Kilbricken and Castlegard ("Pallas Green"), from which existing fluid inclusion constraints are available.