Zimov’E Chinskii

About 80 % of the massif is composed of medium- and coarse-grained hastingsite syenites, which sometimes contain quartz. It cuts limestone intercalated with siltstones and sandstones, which are altered to hornstones in the vicinity of the contact, and early Palaeozoic gabbro and gabbro-diorites. Porphyritic granites and syenites are extensively developed in the region. Nepheline syenite bodies, which can reach 100 m across, occur at the boundary between hastingsite syenites and limestones. Within most areas of the peralkaline syenites a large number of country rock xenoliths occur which vary in size up to 500 x 200 m. Nepheline syenites are grey and dark-grey rocks, which are often trachytic and banded. They consist of microcline perthite (23-70%), albite (7-39%), nepheline (16-30%), hastingsite (16-30%), aegirine-augite (0-10%) and biotite (0-5%). Accessory minerals include apatite, zircon, titanite, calcite and Ti-Fe oxide minerals. Postmagmatic alteration caused the development of garnet (grossularite-andradite), cancrinite and zeolite. Porphyritic urtites and monmouthites, with phenocrysts up to 2 cm across, and congressites are also found in the massif, and are distinguished by their dark minerals with monmouthites characterized by the presence of hastingsite, urtites by clinopyroxene and congressites by biotite.