Physico-Chemical Conditions of Crystallization and Ore Potential of Granitoids from the Boundary Zone of the Southern and Middle Urals

Abstract

Abstract—The paper briefly considers the geological structure of the boundary zone between the Southern and Middle Urals (Kunashak area), as well as the composition and conditions of formation of Devonian–Triassic granitoid complexes developed here. Thermobarometric studies of quartz from medium-grained biotite granites showed that the Poletaev (D₃), Shalkar (P₁), Sultayev (P₁), and Yugokonev (P₁–T₂) complexes were formed at water pressure of 2.2–2.7, 2.5 –3.0, 3.9–4.4 and 3.6–4.5 kbar and crystallization temperature of 800–840, 900–940, 840–900 and 940–980°С, respectively. This indicates a systematic increase in the crystallization depth of the granite massifs in this series from the hypabyssal–subsurface to the hypabyssal-abyssal facies. At the same time, the melt–fluid inclusion study revealed a decrease in fluid volume (–14.2–16.8, 8.1–14.3, 6.2–7.9 and 4.3–6.8 vol %), and concentrations of water (–3.7–4.8, 2.1–3.9, 1.8–2.3 and 1.3–1.9 wt %) and chlorine (–0.04–0.08, 0.03–0.07, 0.03–0.06 and 0.02–0.05 wt %) in this series. It has been shown that the granitoids of the Sultayev and Yugokonev complexes are very promising for tantalum, niobium, tungsten, molybdenum, and beryllium. The leucocratic aplitic and greisen granites of the final phases of the intrusions are most promising for the rare-metal mineralization. The erosion level of different structural and formation zones of the Kunashak area relative to each other has been established.