Ore-Forming Fluids of the Aleksandrovskoe and Davenda Deposits (Eastern Transbaikalia)

Abstract

A study of the composition of fluid inclusions in ore minerals of the Davenda Mo–porphyry deposit and the Aleksandrovskoe sulfide–quartz–gold ore deposit, as well as of fluid inclusions in minerals of igneous rocks, showed that ore-forming fluids inherit the salt and gas composition of magmatic fluids generated during crystallization of ore-bearing rocks of the Amudzhikan–Sretensky Igneous Complex, which formed simultaneously with the Au and Mo mineralization. The gold-bearing sulfide–quartz veins of the Aleksandrovskoe deposit formed with the participation of two types of hydrothermal fluids, differing in the composition of salts and the gas phase: homogeneous Ca–Na chloride fluids with CO2 and heterophasic Na–K–Fe-chloride fluids, which indicates two sources of ore-forming fluids during the formation of Au-mineralization. Na–K–Fe-chloride fluids in terms of salt and gas composition were similar to the ore-forming fluids of the Mo-mineralization of the Davenda deposit. Ore-forming Ca–Na-chloride with CO2 The fluids of the Aleksandrovskoe field are comparable in salt and gas composition with the magmatogenic fluids of quartz diorite porphyries and diorite porphyrites. Ore forming Na–K–Fe carbonate-chloride fluids of the Davenda and Aleksandrovskoe deposits show great similarity in composition to magmatic fluids of granite porphyry and emphasize the genetic identity of Mo mineralization in both deposits. The data obtained confirm the widespread opinion that a genetic relationship exists between gold mineralization and dikes of intermediate and mafic composition, and molybdenum–porphyry mineralization with granite–porphyry of the Amudzhikan–Sretensky Igneous Complex. The real agents of this genetic link are metalliferous magmatogenic fluids, the salt and gas composition of which inherit ore-forming fluids. The formation depth of productive ore mineral assemblages in veins of the Aleksandrovskoe and Davenda deposits is estimated at 7.9–7 and 8–6.3 km, respectively, which is not typical of porphyry deposits, the formation of which is characterized by shallower depths.