Bugutuiskii

Bugutuiskii is situated in the central part of an area of alkaline granites. All told, about 30 occurrences have been identified in this area and rare-metal mineralization is associated with some of them. The Bugutuiskii intrusion is elliptical in shape and extends in a northeasterly direction for some 20 km. It is intruded into Proterozoic gneisses, early Palaeozoic granites and Permian-Triassic trachyrhyolites. The massif is composed of peralkaline granites and quartz syenites of two stages of intrusion which differ chiefly in grain size, the earlier rocks being characteristically coarser. Peralkaline granites of the first stage, which are coarse- and medium-grained, are composed predominantly of alkali feldspar, quartz (about 25%), aegirine and alkali amphibole. The rocks of the second stage – quartz syenites and granites – are fine- and medium-grained, with mafic minerals represented by aegirine and riebeckite (1-5%). There are dykes of granite porphyry, quartz syenite porphyry and syenite, which extend for up to 1 km from the main complex.