Cobalt of the Tyrone Igneous Complex: geochemistry of mafic hosted sulphides and remobilisation

Abstract

Primary sulphide mineralisation in mafic rocks and secondary remobilised sulphides contain significant cobalt and relate to early Palaeozoic ocean closure and arc-continent collision in the Irish Caledonian terrane. This study presents new laser ablation data, portable Xray diffraction (pXRF) geochemistry, and the recent mineral exploration of Shackleton Resources Ltd whole rock analyses, to study sulphide mineralisation within the Tyrone Igneous Complex (TIC); and the study investigates geochemical similarities and temporal association between sulphide showings. A sulphide mobility event of the TIC can be dated to 455.8 ? 3 (mega annum) Ma age (Rice 2016), or 325 Ma (Parnell 2000), while LA ICP-MS sulphide mapping (Stratford 2019) records element zonation, possibly uniting the origins of sulphides and cobalt. The TIC mineralisation history is complex, the tectonics of terrane accretion and metamorphism may have increased sulphide mobility into adjacent rocks via extensional structures. On the TIC, sulphide showings of different types may be related. Individual sampled cobalt values are locally high at 0.12% Co, indicating an undiscovered economic concentration of the metal, while sulfosalt elements show a close association of bismuth-silver, gold, and copper. Volcanogenic massive sulphide (VMS) type mineralisation is well understood in the adjacent terrane of Newfoundland and Nova Scotia. But no VMS economic metal deposits are found in the Laurentian half of Ireland and Britain. In addition, increasing awareness of resource responsibility, provenance, and critical elements, a domestic supply of cobalt is aligned to the WHO sustainable development goals (https://www.who.int/europe/about-us/our-work/sustainable-development-goals). Therefore, understanding sulphide mineralisation of the TIC may identify a source of metals, metal mobilisation, and metal traps in syn-mineralisation structures. Furthermore, it is hoped the structural concept of northwest striking, large basement fractures and the migration of sulphide hosted metals into cover units may help to explain the lack of discovered VMS or VMS-orogenic mineralisation, economic or otherwise.