ABOUT ONTOGENY OF GRAPHITE AND MUSCOVITE IN RARE-METAL PEGMATITES OF BAKENNOYE DEPOSITE, THE KALBINSKY RIDGE

摘要

Unusual black mica-like aggregates, appearing to be xenoliths of the host graphite-bearing schists, have been remarked in veins of rare-metal granite pegmatites. They turn out to be the saturated by graphite pseuromorphs of oncosine after spodumene. When it is free of graphite inclusions, oncosine is the apple-green aggregate of later muscovite representing the last generation of mica within pegmatites of Bakennoye deposit. Inside ore bodies, graphite is paragenetically related only to this muscovite: it was observed, without exception, as syngenetic microinclusions within aggregates and crystals of the mica, e.g. in druses of the muscovite crystals overgrowing walls of small cavities. In crystals of this type graphite microinclusions occur in epitaxial intergrowth with muscovite by two laws and, thus, become the reason of a skeletal growth of muscovite at final stages of the druse formation. The mere fact of the close graphite and muscovite coexistence, with their epitaxy, may be regarded as one more example of the structurally ordered mineral paragenesis.