Geochemistry of indium and other trace elements in biotite as an indicator of the formation conditions of the Gubanov intrusion (Wiborg rapakivi granite massif)

For the first time, the content of a wide range of trace elements, including indium, was determined for biotite from trachytoid granites of the Gubanov intrusion and host ovoid granites using the high-precision local SIMS method. It was established that indium in the biotite from granites of the Wiborg rapakivi massif was of magmatic nature and its accumulation was controlled by fractional crystallization. Indium behaved as a typical incompatible element, concentrating in the residual melt. The main elements associated with In during the magmatic stage were Sn, Sc, Sm, Nb, Rb, and Zn. These elements formed a reliable association, confirmed by both parametric and rank correlations. Chlorine likely participated in the transport of In in the form of chloride complexes, but this bond was not stable in mineral phases (biotite). The physicochemical conditions of indium accumulation — reducing conditions and moderately high pressure — favored the incorporation of In3+ into biotite, which began to crystallize from the melt under these parameters. The high In content (up to 5.8 ppm) in biotite, combined with the high Sn content (> 100 ppm) and a positive correlation with Zn, indicated that the Wiborg massif could be considered potentially promising for In-Sn-Zn mineralization.