Geochemical characterization of Gubanovskaya intrusion of rapakivi granites (Wiborg massif)

The paper presents new data on geology and composition of rapakivi granites of Gubanovskaya intrusion (Wiborg massif). Petrographic and geochemical characteristics of rapakivi granites of the second (ovoid) and third (trachytoid) phases of intrusion, as well as granites from the phase contact zone have been considered. Data on rock composition were obtained by XRF and ICP-MS methods. Ovoid granites are characterized by increased amounts of alumina and iron and calcium oxides, as well as high concentrations of barium and light rare earths, compared to trachytoid granites and rocks of the contact zone. Trachytoid granites are characterized by increased silica content compared to the granites of the second phase, and reduced barium and strontium values, which indicate the evolution of magma towards differentiation, typical for the late phases of intrusions of rapakivi granites. The contact zone rocks show the highest silica and REE contents. Anomalously high LREE content is comparable to rare-metal pegmatites of Olympic Dam, which may indicate the possibility of mineralization detection in them. The results of the study of rocks have shown that all studied granites by their geochemical characteristics belong to intraplate granites of A-type, namely A2-type rocks of crustal or mantle-crustal origin, and belong to calcareous-alkaline and shoshonite series.