Diversity of platinum-group element mineralization styles in the North Atlantic Igneous Province: New evidence from Rum, UK

Two generations of sulphide-hosted platinum-group element mineralization occur in the West Sgaorishal ultramafic plug, Rum. Disseminated Cu and Ni sulphides around the margin of the plug host a restricted platinum-group mineral assemblage that is dominated by Pd bismutho-tellurides and sperrylite (PtAs2) with subordinate electrum (AuAg), froodite (PdBi2) and unidentified Pt-Bi-Te phases. Later sulphide-rich dykes cross-cut the plug and host an assemblage dominated by Pd bismutho-tellurides, sperrylite and locally very abundant paolovite (Pd2Sn). Whole rock combined platinum-group element + Au concentrations are proportional to the sulphide abundance with slightly elevated values in disseminated sulphide lithologies (> 400 ppb) and very high values (> 2000 ppb) in the sulphide-rich dykes. Both generations have relatively flat chondrite-normalized plots indicating a primitive magmatic source. Negative delta(34)S values (-9.2 to -18.3parts per thousand) indicate that the disseminated mineralization is due to contamination probably derived from Jurassic sedimentary rocks leading to sulphur saturation and collection of platinum-group elements. The sulphide-rich dykes must have entrained a platinum-group element-rich sulphide liquid collected from a much larger volume of magma. The presence of platinum-group elements and sulphide-rich dykes with delta(34)S values between -10.8 and -15.0parts per thousand indicates that parts of the Rum Layered Suite became sulphur saturated through magmatic contamination. It appears likely that platinum-group element mineralization styles within the southern North Atlantic Igneous Province are diverse and may be present in a wider variety of mineralogical associations than previously recognized.