East Tuva

Numerous alkaline complexes are known in eastern Tuva, where they form an approximately north-south arc in the eastern part of the Tuva region adjacent to the border with Mongolia. Three subprovinces can be identified (Fig. 2_168). The first is located on the southern slopes of an anticlinorium of East Sayan and extends into the northeastern part of Tuva (Fig. 2_168, area A). Although these occurrences are adjacent to those of East Sayan they are traditionally included in the East Tuva province, principally because they are located on the same Caledonian structures. The second subprovince lies in eastern Tuva and is part of the Okinskii block (Fig. 2_168, area B), and the third subprovince is in the Sangilen Upland (Fig. 2_168, area C). The occurrences vary in area from 1-2 to 55-65 km2 but the largest, the Kadyross complex, covers approximately 150 km2. The first two subprovinces have much in common in so far as the structures and rock types are concerned. Two or sometimes three magmatic phases are distinguished. During the first, and principal, intrusive phase peralkaline syenites are predominant with less frequently miaskitic nepheline syenites, juvites and feldspathic urtites. The second intrusive phase is generally represented by peralkaline and mildly alkaline granites, granosyenites and quartz syenites but, according to some authors, peralkaline granites are likely to be found as a third phase also. The alkaline complexes of southeastern Tuva, the third subprovince, are rich in nepheline syenites with urtites, ijolites and juvites also common.
The province of East Tuva extends across the international border into Mongolia and the province as a whole is reviewed, in English, by Pavlenko (1974) under the name of the 'Mongol-Tuva province.