Abstract
The apogranitoid fenites in the exocontact parts of the Gorodnytsa intrusion of alkaline-ultrabasic rocks (northwestern part of the Ukrainian Shield) are considered. Those alkaline-ultrabasic rocks are represented by magnesian (primitive) olivine jacupirangites and melanocratic olivine melteigites. Frequently fenitization zones have a small thickness (up to several meters). The fenitization more intensively appeared in the upper level of this intrusion in comparison to the lower one. The most fenitized rocks of granitoid composition are presented by syenites. The external part of the intrusion is contaminated by hosted granitoid rocks as a result the hybrid rocks of albite-diopside composition or melanocratic syenites (without feldspathoid) are formed similar to tvaitosite. The role of SiO2 and Na2O + K2O in the condition of the fenite generation is considered.
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