Platinum-group element mineralization within ultramafic rocks at Corrycharmaig, Perthshire: implications for the origin of the complex

Alloys and complexes of the platinum-group elements (PGE) Pt, Pd, Ru, Ph, I r and Os occur as discrete platinum-group minerals (PGM) throughout the chr omite-dominant lithologies of the Corrycharmaig ultramafic body. PGM are ei ther enclosed by chromite or occur in association with secondary Ni sulphid e (heazlewoodite). The PGM enclosed by chromite are large (up to 40 mum), e uhedral and interpreted to be primary magmatic in origin. Those that occur in association with heazlewoodite are small (<2 <mu>m) and appear to have p artitioned into the sulphide phase during alteration and metamorphism and s ubsequently exsolved. The dominance of Ru, Ir and Os (Ir PGE or IPGE) sugge sts that either the Corrycharmaig protolith was enriched in these elements relative to Rh, Pd and Pt (Pt PGE or PPGE) or that primary PPGE have been r emoved from the system. Previous interpretations for the genesis of the Cor rycharmaig body have included ophiolite complexes or, more recently, komati itic intrusions. The nature of the chromite mineralization and chemistry al ong with the presence of large laurite (IPGE-rich) grains enclosed by chrom ite are more indicative of an ophiolitic origin.