Platinum-Group Element systematics in the North Atlantic Igneous Province: new insights from Northern Irish and Irish magmatism

Anna Morrison, Michael Stock, Mark Cooper, Jens Andersen, Hannah Hughes, Elliot J Carter, Jack Beckwith, Iain McDonald, Andrew Kerr, Paul Mohr

The North Atlantic Igneous Province (NAIP) is one of the most prospective regions for Ni-Cu-Platinum-Group Element (PGE) mineralisation in Europe, and recent studies have discovered elevated PGE concentrations within its early lavas and minor intrusions comprising the British and Irish Palaeogene Igneous Province (BIPIP). This study presents an extended digital map of the regional mafic dyke swarms associated with the BIPIP in Northern Ireland and Ireland and a comprehensive new geochemical dataset of these magma conduits, the Antrim Lava Group and associated minor intrusions, including PGE and Au analyses. Digital mapping using aerial electromagnetic data reveals a high density of dyke-related anomalies on the island of Ireland. Dyke density and orientation indicate at least one swarm originating from an onshore Palaeogene igneous centre (Slieve Gullion, Carlingford, possibly Dromore High), whilst others are likely propagating from submarine igneous centres in the North Atlantic. The origins and evolution of dyke swarms provide context for interpreting variations in PGE abundances. Previous authors have highlighted that early NAIP magmatic rocks (e.g., Greenland and Scotland) had high Pt/Pd ratios (~1.9), while younger sequences (e.g., Iceland) trend towards lower ratios (~0.4). Our data reveal that Irish BIPIP centres record a similar transition with an average Pt/Pd ratio of 1.6 ± 0.8, reflecting an evolving geodynamic setting where the magmatic conditions transitioned from intra-plate volcanism through to the inception of continental rifting and ocean opening. A close spatiotemporal association between variable Pt/Pd in BIPIP rocks in Ireland and high Pt/Pd in BIPIP rocks in Scotland suggests that the geodynamic transition occurred within a geologically short time interval (<1 Myr). Results from our samples attest to widespread sulphide saturation, supporting the potential for orthomagmatic Ni-Cu-PGE mineralisation within related central complexes or magmatic feeder networks.