Proskurovskii

The Proskurovskii massif was discovered by drilling in 1978 (Tsarovsky et al., 1980). It is located 43 km south of the town of Khmelnitsky and lies within Chudnovo-Berdichev garnet granitoids (with hypersthene and biotite). It has a symmetrical outline and is elongated to the northwest. Syenites and granosyenites are the most widely developed rocks of the complex, occupying 75-80% of the total area, and these prove to be fenites. Nepheline-rich rocks, including ijolite-melteigite and nepheline syenites (juvite, pulaskite), are considered to be intrusive. Malignites, which are a feldspathic facies of the ijolites and melteigites, alkaline pyroxenites, jacupirangites and tveitasites are occasionally encountered. It is thought that carbonatites are likely to be present. The first explorers of the massif (Tsarovsky et al., 1980) thought that all the alkaline rocks were metasomatites which had been generated by nephelinization of the enclosing heterogeneous granitoids and pyroxenites. There is a certain regularity in the distribution of the nepheline rocks in the massif: thus, melanocratic rocks of ijolite-melteigite composition develop predominantly in the central area and form a core which seems to be bounded on the south and northeast by elongate, horseshoe-shaped bodies of feldspathic ijolite and nepheline syenite. Varieties of nepheline syenite include biotite-pyroxene, biotite-amphibole-pyroxene, amphibole-biotite and biotite types. Apart from the common nepheline-pyroxene rocks of the ijolite-melteigite series, types of pyroxenite with primary biotite also occur. Certain features of the Proskurov complex, notably the presence of jacupirangite-melteigite-ijolite and nepheline syenite, the abundance of calcite and apatite, and also the extensive fenitization of the enclosing granitoids, indicate that the massif is a representative of an alkali-ultrabasic association (in the sense of the Soviet literature). It remains to be considered whether some specific compositional properties, such as the low Ti content of the rocks of the jacupirangite-ijolite series, the presence of amphiboles of a composition transitional from hastingsite to katophorite, and aegirine-salitic pyroxenes in jacupirangites and ijolites are characteristic of the Proterozoic alkali-ultrabasic (carbonatite) complexes.