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

Camborne School of Mines, University of Exeter, Redruth TR15 3SE, UK

^* Author for correspondence: M.Power{at}csm.ex.ac.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 ³⁴S values ( – 9.2 to – 18.3 ) 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 ³⁴S values between – 10.8 and – 15.0 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.

Key Words: Rum • platinum-group element • mineralization