Goryachegorskii

The stock-like Goryachegorskii intrusion of 0.9 km2 cuts volcanic rocks of Lower Devonian age. It is composed, from west to east, of theralite and leucotheralite, which comprise the first phase, feldspathic ijolite and urtite, the second phase, and nepheline syenite, the third phase. Theralite is the most abundant rock type and consists of nepheline (56-60%), plagioclase of basic and intermediate composition (20-25%), alkali feldspar (2-3%), clinopyroxene, mainly fassaite, (15%), olivine, alkali amphibole, biotite and Fe-Ti oxide minerals. Feldspathic urtites (nepheline-rich nepheline syenite) are characterized by dominant nepheline (61%) with sodic plagioclase (21%), clinopyroxene (13%), olivine, alkali amphibole and Fe-Ti oxide minerals. The nepheline syenites comprise alkali feldspar and sodic and sodic-calcic plagioclase (55-65%), nepheline (20-25%) and mafic minerals, including aegirine.