Gulkhenskii

Gulkhenskii comprises minor, steeply dipping sheet-like bodies stretching for 4 km and cutting Proterozoic marbles intercalated with schists and gabbro-diorites. Two phases in the formation of the massif have been identified, the first involving emplacement of pyroxenites and gabbro-pyroxenites with minor peridotite schlieren, and the second intrusion of nepheline-pyroxene rocks of the urtite-jacupirangite series with small amounts of theralite. Olivine gabbro is composed of olivine, labradorite, augite and hornblende with occasionally hypersthene and Fe-Ti oxide minerals. Ijolites consist of nepheline and a pyroxene which is reported to be fassaite (30%), but hornblende (10%) and garnet are also present, together with calcite and apatite. In leucotheralites nepheline and andesine dominate over the mafic minerals (fassaite, hornblende, biotite). The rocks have been described by Sharackshinov (1984a) and Konev (1982); mineral compositions are given by Andre’E va and Troneva (1986).