Age and geochemical evolution of granite magmatism in Olkhon region from Caledonian syncollisional ore-free granite to the rare metal granite and pegmatite of Middle Paleozoic intraplate setting

Abstract

The detailed description of two granite complexes in the Olkhon subterrane is given. The Early Paleozoic Sharanur complex was formed by granitization of gneisses of the Olkhon series. It includes migmatites, granite-gneisses, granites and pegmatites of normal alkalinity; they belong to the type of syncollisional granites. The Middle Paleozoic Aya granite complex includes mother Aya massif of amazonite-bearing granites and several types of rare-metal pegmatites. They have elevated alkalinity, low of Ba, Sr, and high LILE and HFSE elements contents. The Aya pegmatites lie in northwest cracks of stretching and associated with the rise of the territory under the influence of the North Asian plume. These cracks and pegmatites mark the beginning of a new intraplate geodynamic setting. Two geochemical types are distinguished among the pegmatites of this complex. These are amazonite pegmatites of Li-F type with Ta mineralization and complex type pegmatite with Be-Rb-Nb-Ta and Li-F mineralization (the Ilixin vein). The Tashkiney pegmatite vein is similar to Ilixin, but lies in the gneisses of the Olkhon series. It shows high concentrations of Be, Nb, Ta, as well as W, Sn, but lacks Li and F, due to a greater depth and higher temperature of the melt crystallization of this pegmatite.

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