This paper presents new data for historical vein-hosted copper sulfide deposits in the Late Paleozoic Munster and South Munster basins of SW Ireland. Detailed mapping, 3D modelling, fluid inclusion microthermometry and geochronology from the Allihies area of the Beara Peninsula have led to a new interpretation of the timing and development of ore mineralization. Macro- and microstructural studies reveal that the ore-bearing, mainly east–west-striking quartz veins are directly related to early extensional, basinal normal faults. Molybdenite Re–Os dating of the main-stage Cu lode yields ages from 367.3 ± 5.5 to 366.4 ± 1.9 Ma. This early vein system experienced subsequent late Carboniferous Variscan deformation, including cleavage development, sinistral SW–NE strike-slip faulting, cataclastic deformation and recrystallization. The new timing of Cu mineralization in SW Ireland has major implications for its relationship to the base metal deposits of the Irish Midlands. Supplementary material: A video file showing a 3D model of the major lodes and the underground workings at Mountain Mine, and Excel spreadsheets showing fluid inclusion measurements and sample locations of the Allihies Copper Mining District are available at https://doi.org/10.6084/m9.figshare.c.4875015