Pichekhol

This complex cuts Upper Proterozoic marbles and schists and consists principally of pyroxene nepheline syenites, that are albitized in several zones, and peralkaline syenites. It is thought that only the uppermost part of the massif is exposed, among which extensive areas of syenitized sandstones and marbles have been preserved. Both mesocratic and leucocratic nepheline syenites are present with nepheline contents of 15-25% in the central and southern parts of the massif but decreasing to only 5-15% towards the northern and northeastern outer contacts; there is a concomitant increase in pyroxene northwards to 30% and even 40%. Pegmatites of 0.5-3 m in thickness are intensively developed in the massif and are composed of nepheline, microcline, pyroxene, lepidomelane and titanite with accessory zircon, magnetite, rinkolite, uraninite, britholite, thorite and thorianite.