Timing of vein-hosted copper mineralization and its structural setting in the Upper Paleozoic sedimentary rocks of SW Ireland

This study provides new insights into the genetic and chronological development of the vein-hosted Cu sulfide mineralization in the Late Paleozoic Munster basins of SW Ireland. Field mapping of selected historical mining sites in West Cork, supported by drone photogrammetry, petrography, microthermometry and geochronology, provided elementary data for a reinterpretation of the mineralization processes. Our structural investigations defined two distinct ore-forming episodes. The initial vein precipitation is directly related to synbasinal, extensional east–west- to ENE–WSW-striking normal faults. Smaller sediment-hosted Cu sulfide occurrences are related to the extensional fault systems. The second mineralization phase occurred during the early stage of the Late Carboniferous Variscan compression via the reactivation of the early extensional basinal fault systems. Molybdenite samples related to Cu mineralization from the historical Ballycummisk Mines on the Mizen Peninsula produced Re–Os dates of 315.5 ± 1.6 and 311.8 ± 1.6 Ma. This Pennsylvanian (Upper) Carboniferous sulfide emplacement is related to the second-stage syn-Variscan compressional mineralization event. The discovery of the two distinct Cu mineralizing events in SW Ireland provides an important contribution to our understanding of the development of the Irish Ore Field, including the Irish Midlands Pb–Zn deposits.