Abstract:
We examined a paragenesis of platinum-group mineral phases in ore-bearing metasomatic rocks occurring in a Lower Proterozoic sequence of shungite-bearing metaschist. These metasomatic rocks exhibit no signs of genetic affinity with igneous complexes, and thus are of interest as a new, uncommon type of rock bearing platinum-group ores. In terms of the composition of the platinum-group mineral phases, we identified five groups of palladium-containing phases and two groups of platinum-containing phases that constitute different systems. We believe that the platinum-group mineralization in the metasomatites sprang from volcanosedimentary shungite-bearing sequences of the Karelian complex. During sedimentation of carbon-containing rocks, basalt igneous activity was significant; its pyroclastic component is identifiable in all the varieties of the sedimentary material. Oxidation of organic matter gave rise to 'background' concentrations of heavy-metal catalysts. Superimposed epigenetic processes were the main factor causing the redistribution and local deposition of the 'background' concentrations, producing the mineralization described above. It appears that this type of platinum-group mineralization is a new and perhaps promising mineral form.