Khorninskii

This is one of the largest igneous complexes in the region, its area exceeding 650 km2. It is a heterogeneous pluton with a poorly defined zonal structure. The approximately circular outer zone is several hundreds of metres to 5 km wide. It is composed of moderately alkaline rocks, including syenites and quartz syenites (of the first stage), with subordinate amounts of granite (the second stage). The internal zone is more or less symetrical and here peralkaline granites (of the third stage) are predominant. Two to three phases of intrusion have been identified in each stage, each of which is completed by the intrusion of dykes. The country rocks are granodiorites, granites and Palaeozoic syenites, as well as trachytes and trachyrhyolites which are provisionally referred to the late Palaeozoic to early Mesozoic. The peralkaline granites of the first phase are coarse- and medium-grained and are characterized by an abundance of miarolitic cavities and by some heterogeneity of structure which manifests itself in the form of frequent schlieren of relatively finer grained or pegmatitic granites. Peralkaline granites of the second phase of intrusion are fine- and medium-grained and porphyritic.