Chromitite formation—a key to understanding processes of platinum enrichment

摘要: AbstractThe mafic layered suite of the 2050 m.y. old Bushveld Complex hosts a number substantial platinum-group element (PGE)-bearing chromitite layers, including UG2, within Critical Zone, together with thin stringers platinum-bearing Merensky Reef. Until 1982 only Reef was mined for platinum, although it has long been known that chromitites also host PGE-bearing minerals (PGM). Three groups occur: (i) Lower Group up to seven major layers hosted in feldspathic pyroxenite; (ii) Middle four by pyroxenite or norite; and (iii) an Upper Group, usually two packages, pyroxenite, norite anorthosite. There is systematic chemical variation from bottom top layer terms Cr : Fe ratio abundance proportion PGE.Detailed studies 87Sr/86Sr isotope variations undertaken on interstitial plagioclase different silicate rocks sh...