Lithochemical Characteristics of Shungite-Bearing Fluidolites in the Paleoproterozoic Onega Structure

Studies of shungite-bearing fluidolites in the Onega structure were carried out within two dome- and sublayer-type deposits. Data on the composition of the mineral component of shungite-bearing fluidolites allow us to consider the Melnichny Dome as the most probable source of fluidolites. At the Shunga deposit, shungite rocks are divided into three groups according to lithochemical characteristics: shungite rocks of the shungite-bearing Horizon VIII (Na2O + K2O = 3.0–4.5%, AM = 0.10–0.15) and rocks similar to shungite-bearing fluidolites of the Melnichny deposit (Na2O + K2O = 5.0–6.0%, AM = 0.16–0.26 and Na2O + K2O = 6.0–7.5%, AM = 0.26–0.30). Fluidolites of shungite rock deposits are markers of different stages of the development of diapiric structures: formation of the stock-type body and its evolution into a diapiric hat.