A review of the Limerick Igneous Suite: links to base-metal mineralization in the SW Irish Orefield

The Limerick Igneous Suite (LIS) in SW Ireland consists of massive flows, hypabyssal intrusions, tuffs, agglomerates, and diatremes and is spatially associated with multiple base metal prospects, deposits, and historic mines in the Limerick Syncline. The LIS is subdivided into two igneous units: 1) the Knockroe, which is dominantly alkaline basalt to trachyandesite in composition, and 2) the Knockseefin, which forms a range of alkaline basalt to basanite compositions. Recent drilling has uncovered new, olivine-bearing porphyritic basalts that correspond to the Knockroe unit and may represent the highest degree of partial melting in the LIS. A new sulphide Re–Os isochron from the Ballywire prospect yielded an age of 340.9 ± 2.4 Ma and represents the first known mineralization age in the Limerick Syncline, which is contemporaneous with LIS emplacement. However, the 187Os/188Os of 0.48 is indicative of base metal derivation from crustal rocks akin to Palaeozoic basement as opposed to an igneous or mafic source. The LIS was not likely a source of metals, but the coeval emplacement between the LIS and mineralization in the Limerick Syncline suggests the LIS may have been a source of hydrothermalism in the region. Yet the intrusions themselves were emplaced in fault networks, hindering rather than enhancing hydrothermal fluid flow.