Vol 61, No 3 (2019)

With a view to reveal special characteristics of the transition stage from granite crystallization to rare-metal ore deposition it is studied Badzhal tin-bearing magmatic-fluid system of eponymously-named volcano-plutonic zone of the Middle Priamyrie. For that end the detail research of melt, fluid-melt and fluid inclusions and oxygen isotopes from minerals of granitoids from Verkne-Urmi massif from Badzhal volcano-plutonic zone and also minerals of Sn-W deposits Pravo-Urmi and Blizhnee have been carried out. The formation of greisens and hydrothermal veins were caused by the development of the integrated system associating with establishing of Verkne-Urmi granite massif which is one of a dome fold of Badzhal cryptobatholith. For the first time for tin deposits it has been followed up the transition from the magmatic phase of granite crystallization to the hydrothermal ore formation stage and the evolution of magmatic fluid from its separation from magmatic melt to Sn-W ore deposition. The direct evidence of tin-bearing fluid separation under melt crystallization is combined fluid-melt inclusions. Glass composition in inclusions shows that granites and granite-porphyry were crystallizing from acid and from limited to high-aluminous melts, that is value ASI changes from 0.95 to 1.33 and a content of alkalies varies from 6.02 up to 9.02 mass.%. Cl and F concentrations in glasses are according 0.03–0.14 and 0.14–0.44 mass.% and turned out to be higher of same in the total composition of rocks (0.02 and 0.05–0.13 mass.% in accordance). These differences indicate that Cl and F could be separated from granite melt under its crystallization and degasation. H₂O content made from total deficiency electron microprobe analysis is 8–11 mass.%. This evaluation was made inclusive of a probable effect of “Na loss” (Nielsen, Sigurdson, 1981) under aqueous glass crystallization. Considering a high error of a such estimation (Devine et al., 1995), it should take to obtained values as a very approximate evaluation and consider that examined melts contained about 9,5–10,0 mass.% of H₂O.

The results of melt inclusion examination show that at any rate a part of melt forming magmatic rocks of Badzhal Ore Magmatic System are crystallizing at about T = 650 °C. These melts were acid, limited fluoride and meta- and high aluminous. The reason of low temperatures of its crystallization are likely a high pressure of aqua and also a increased content of F. Most likely that examined inclusions characterize the final stage of establishing of the massif, herewith at the system crystals, residual liquor and magmatic fluid phase coexist.

The fluid from which greisens of Pravo-Urmi deposit formed is similar in properties to the supercritical fluid absorbing by magmatic minerals. The salinity of this fluid varying from ~9 to 12 mass.% equiv. NaCl, maximal T = 550 °C (with consideration for the temperature correction of T gom on a pressure ~1 кbar) are similar to such of magmatic fluid, which permit to connect its origin with pluton cooling. The formation of greisens and quartz-topaz veins of Pravo-Urmi deposit is related to fall of temperature of magmatic fluid from 550–450 up to 480–380 °C. The evolution of fluid deposited quartz-cassiterite veins of Blizhnee deposit, which based upon oxygen isotope composition (d¹⁸О_Н2О ≈ 8.5‰) also separated from magma, was going at more subsurface conditions under much lesser pressure. That led to the gas separation of a fluid with salinity ~13 mass.% equa. NaCl under T = 420–340 °C on thin low salinity vapour and brine with concentration 33.5–37.4 mass.% equiv. NaCl. The research of oxygen isotope system testifies that oxygen isotope composition of ore-forming fluid controlled by equilibrium with granites at wide interval tempera­tures (from ~700 °С up to the beginning of greisen crystallization). Correspondence of measured and calculation data of the offered model indicates that the considerable volume of external fluid with other isotope characteristics which did not reach the isotope equilibrium with Verkhne-Urmi massif did not come into the magmatic isotope system. The discovered differences of physico-chemical conditions for two studied deposits are not “critical” and support an idea about their formation as the single magmatic-fluid system.

Composition and genesis of arsenium-antimony sulfosalts of lead from the gold-bearing ores of the Berezitovoe deposit located in the eastern part of Mongol-Okhotsk orogenic belt (Upper Amur Area) were considered. Lead sulfosalts (Cu and Pb) are presented by tsugaruite, dufrenoysite, boulangerite, menehinite, bismuthic menehinite (with Bi up to 11.5 mass%), as well as minerals of jordanite-geocronite and bournonite-seligmannite series. The studies have revealed basic features of the lead sulfosalts relationship with ore and silicate minerals in different mineral association of vain ores and regularities in their composition variations. It was found that the composite arsenium-antimony sulfosalts form quasicontinuous series of solid compounds strongly differing from each other by the rate of semimetals as well as semimetals-Pb ratio in their composition.

The suggestion has been made that the main typomorphic features of composition of the arsenium-antimony sulfosalts of lead from ores of the Berezitovoe deposit were determined by the specific processes of partial melting of sulfides under the high temperature metamorphism of primary polymetallic ores.