Abstract

Platinum-bearing intrusives of forsterite dunite are the source rocks for several types of platinum deposit, broadly grouped as late magmatic and placer. Only minerals of the platinum group are of commercial value in the working of these deposits. The most productive platinum deposits genetically related to massifs of forsterite dunite are confined to the eugeosynclinal zone of folded regions, where they are associated with platinum-bearing massifs of two types: (1) dunite-clinopyroxenite-gabbro, in which platinum-group mineralization is concentrated in segregations of chrome spinellides within the forsterite dunites (Nizhnii Tagil type of platinum deposit), and (2) clinopyroxenite-gabbro, sparsely platiniferous, in which the platinum metals are contained mainly in titanomagnetite ores and in the neighboring apodunitic diallagites (Kachkanar type of platinum deposit). The Nizhnii Tagil type of platinum deposit is convergent with the Inagli type, which occurs in a zone of late Mesozoic tectono-magmatic activity in the Aldan shield. All the massifs whose primary platinum content is genetically related to forsterite dunites yield placer deposits. The assemblages of platinum-group minerals in these placers and in their bedrock source are identifiable. The fact is indicative of the primary endogene nature of platinum-group minerals both in the bedrock source and in placers. Some compositional differences in the association of subordinate and accessory platinum-group minerals reflect specific geologic-tectonic conditions of formation of platinum-metal mineralization.

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