Patyn

This massif, of an area of some 50 km2, cuts Cambrian limestones, including dolomite, with layers of carbonaceous shale and sandstone. The intrusion is composed predominantly of gabbro, which contains small bodies and dykes of alkaline rocks, including dykes of melilite-nephelineand nepheline-sodalite rocks and peralkaline syenite. In the southwestern part of the massif a body of feldspathic melteigite-jacupirangite is present within recrystallized limestone and nepheline-melilite dykes are met with. The peralkaline syenites are coarse-grained rocks consisting mainly of orthoclase-perthite (65%), albite (30%), aegirine-augite (14%), biotite (1%) and accessory titanite, apatite and Fe-Ti oxides. The melilite-nepheline rocks usually contain garnet (25-60%) and admixtures of titanite, ilmenite, apatite, calcite, titanaugite and sulphides (up to 15-20%). Feldspathic melteigite consists of titanaugite (75%), plagioclase (12%) and nepheline (8%), as well as apatite, garnet and Fe-Ti oxide minerals. Pyrrhotite from a melilite rock gave d34S values of +3.5 to -0.5 and melilite rocks gave Ù18O values of +6.0 to +8.1 and Ù13C of +12.5 to +20.4 (Pokrovskiy and Andreeva, 1991). The same authors obtained 87Sr/86Sr ratios on gabbro of 0.7043 and 0.7047, on melilite rocks of 0.7065 and 0.7077, and on marble of 0.7078-0.7087. They concluded that 60-85% of the Sr in the melilite rocks was derived from the country rocks. Chemical analyses of these rocks are given by Bogatikov (1966).