Pecularites of granite sistems including rare-metal pegmatites

Abstract

There are usually two generations of granitic pegmatites revealed in most of rare-metal pegmatite fields: beryl-bearing ones, often with tantalum-niobate, muscovite, inseparable from vein-shaped granite leucogranite complex, and sodium-lithium (Li, Ta, Cs, Be, Sn) pegmatites (or LCT-pegmatites), which are subdivided into «complex rare-metal» ones, with the pegmatite zonation and the major mineralization (large crystals of spodumene, tantalates, beryl, cassiterite, pollucite, petalite, amblygonite) in central parts of their body (Koktogay, Bernick Lake, Bikita, Karibib, Varutresk, Vishnyakovskoye, etc.), and «albite-spodumene» ones, composing numerous extensive pegmatite dykes without zoning, grouping in their fields as long as up to 10-15 km and more (Kings Mountain, Zavitinskoye, Goltsovoye, Kolmozero, Polmos Tundras, Tastygskoye, etc.). In some cases (Zavitinskoye, Vasin-Mylk, Shuckbjul), there are established complex rare-metal pegmatites occurring in «heads» of conveying dykes of «albite-spodumene pegmatites». The search of «parent granites» for «albite-spodumene pegmatites» is meaningless, because they are not pegmatites, but granites, although special ones (in fact, they are spodumene granites of the alakhinsky type). The terminological, as it seems to be, readjustment: «granite, not pegmatite», has its scientific (a) and prognostic (b) consequences. Firstly, there is resolving (a) the problem of parent granites, objections to the pegmatite status of «albite-spodumene pegmatites» become removed. This type of pegmatites occupies in history of magmatism over some pegmatite-bearing areas its independent, spodumene-rare- metal-granite stage, concluded by formation of their own - true - complex pegmatites. And secondly (b): it may be assumed that under such complex pegmatite fields as Koktogay, Bernick Lake, Bikita, Karibib, Vishnyakovskoye, there are occurring series of dikes of spodumene-rare-metal granites (i. e., Li ore deposits), which are differentiates of complex pegmatites.