Botogol

Botogol occupies an area of 10 km2. The intrusion comprises nepheline and peralkaline syenites containing a variety of xenoliths including limestone, quartzite and schist. The country rock limestones near the contact with the alkaline massif are metamorphosed with the formation of andradite, diopside andorthoclase while nepheline, apatite, zircon and cancrinite are present in some rocks. The massif has a zonal structure with nepheline syenites, together with small juvite and ijolite bodies, towards the centre and nepheline-free syenites at the margins. The nepheline syenites have a trachytic texture and comprise microcline (40-60%), nepheline (20-40%) and aegirine-hedenbergite (15-30%). The syenites are predominantly leucocratic rocks, with modal aegirine-hedenbergite varying from 15 to 30%,but in the vicinity of the outer contact the proportion of dark minerals increases and they become more melanocratic. Within the massif large concentrations of graphite have been discovered, the majority of these occurrences being related to xenoliths of carbonate rocks and localized in nepheline syenites and occasionally in peralkaline pyroxene syenites. For a detailed account of rock and mineral compositions see Lobzova (1975) and Kost'uk and Bazarova (1966).