The authors analyze the geodynamic settings of large fields of spodumene pegmatites hosting Li and complex (Li, Cs, Ta, Be, and Sn) deposits of rare metals within the Central Asian Fold Belt. Most of the studied fields show a considerable time gap (from few tens of Myr to hundreds of Myr) between the spodumene pegmatites and the associated granites, which are usually considered parental. This evidence necessitates recognition of an independent pegmatite stage in the magmatic history of some pegmatite-bearing structures in Central Asia. The Precambrian–Late Mesozoic interval is marked by a close relationship between the large fields of spodumene pegmatites and extension settings of continental lithosphere. They occur either as (1) zones of long-lived deep faults bordering on trough (rift) structures experiencing the tectonic-magmatic activity or as (2) postcollisional zones of shearing and pull-apart dislocations. Thus, large fields of spodumene pegmatites might serve as indicators of continental-lithosphere extension. Important factors favoring the formation of rare-metal pegmatites both in collision zones and continental-rift settings are the presence of thick mature crust dissected by long-lived, deeply penetrating (down to the upper mantle) fault zones. They ease the effect of deep sources of energy and substance on crustal chambers of granite and pegmatite formation.

The results of the determination of Rb, Sr, Cs, Ba, and Pb in K-feldspars by total reflection X-ray fluorescence analysis using 0.05 g sample in mass are presented. Prepared suspensions of the rock Certified Reference Materials and the K-feldspar samples were chosen as the sample preparation method. Studying the particle sizes of the K-feldspar sample powders was carried out. The concentrations of the elements were evaluated using the internal standard method. As internal standard, either a Se solution was added to the sample or the concentration of Rb was preliminary determined or known, have been used. The accuracy of the element determinations was estimated by comparison between obtained and certified values of the elements determined in the Certified Reference Materials of the K-feldspars, such as JF-1 and JF-2.

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On the background of Early Paleozoic precollisional, syncollisional, and late collisional igneous rocks prevailing in the region (Khaidai and Shara-Nur granitoids and Birkhin gabbroid complex), rare-metal pegmatoid granite bodies and pegmatites along the southern edge of the Ol’khon region are of particular interest. They have a Middle Paleozoic age (390–391 Ma), cut the Caledonides, and belong to different geochemical types. The Anga unit includes amazonite-containing Li–F–B pegmatites, which are also enriched in Ta, Nb, and W. In the Ol’khon Group, only one K-feldspathic body rich in Rb, Be, Nb, W, Sn, Sc, U, and Th, with large crystals of aquamarine, has been found. The compositions of granite–pegmatite bodies and accessory rare-metal minerals have been studied. The rare-metal granite–pegmatites probably form a peripheral zone of the Hercynian within-plate setting widespread in the eastern Baikal area and related to the influence of the Siberian hot spot.