Typomorphism of rock-forming minerals of andesites from the Karaburan Complex of the Polovinkinskaya Depression (Aldan-Stanovoy shield)

This study presents an inaugural analysis of rock-forming mineral chemistry within andesites from the Polovinkinskaya Depression, situated at the junction of the Tynda and Nimnyr terranes in the central Aldan- Stanovoy Shield. Utilizing microprobe data processed through MagMin PT, WinPyrox, and COMAGMAT, we evaluated the systematics, thermodynamic crystallization conditions, and potential metallogenic significance of these rocks. The mineral assemblage includes plagioclase (oligoclase and two generations of andesine), groundmass andesine microlites, pyroxenes (augite and diopside), Ca-amphiboles (edenite and pargasite), and Mg-biotite. Our findings indicate that plagioclase crystallization occurred under conditions analogous to those found in island arcs and active continental margins, characterized by high oxygen fugacity (logfO 2 =-5.04 to -6.86), temperatures ranging from 1090°C to 1124°C, and pressures decreasing from 12 to 4,5 kbar. These data support the hypothesis that subducted oceanic crust from the Mongol-Okhotsk Basin contributed to the Mesozoic Aldan magmatic sources. Furthermore, the identified P-T depth intervals (36–24, 24–12, 12–6, and 6–2 km) suggest the presence of intermediate Mesozoic magma chambers. Finally, an assessment of amphibole and biotite typomorphism, combined with the geological evolution of the andesites, indicates a high potential for epithermal gold mineralization in the region.