GEOLOGICAL STRUCTURE, COMPOSITION, AND AGE OF THE PYALOCHNOOZERO ULTRAMAFIC-MAFIC MASSIF, NORTHEASTERN BALTIC SHIELD

Abstract

The finding of low-sulfide PGE mineralization in the Sumian layered peridotite–pyroxenite–gabbronorite massifs located in the Pechenga–Varzuga and North Karelian riftogenic system of the Baltic Shield sparked increased interest in other, less studied similar objects. One of them is the Pyalochnoozero Massif 90 km2 in area located in the eastern Belomorian Block. The massif was traditionally combined with Ondomozero and Peschanoozero massifs into the Sumian pyroxenite–peridotite–gabbronorite [2] or gabbroanortho site complexes. Though geochemical PGE anomalies were found in the rocks of the Pyalochnoozero Massif during large-scale geological survey, the internal structure, rock associations, composition, age, and metallogenic potential of the intrusion remained poorly studied. Detailed study of the massif helped us to significantly refine its geological structure and composition and determine its formation age.