ИСТИНА

Composition of mineral-forming fluids is a critical parameter for an identification of genesis of a mineral deposit. One may be expected that gold deposits within the same metallogenic province were formed from a similar fluid at similar physical and chemical conditions. Fluid inclusions were studied in quartz from 10 world class (productions+reserves more 100 t Au) and several ordinary gold deposits located in Lena (PR), Sayan-Yenisei (PR), Urals (Pz), Verkhoyansk (Mz), Kolyma (Mz), Okhotsk-Chukotka volcano-plutonic belt (Mz) and Eastern Transbaikalian (Mz). Deposits under consideration are Sukhoi Log, Olimpiada, Sarylakh, Sentachan, Nezhdaninskoye, Maiskoye, Natalkinskoye, Berezovskoye, Kochkarskoye, Darasun. Some of them are located in the metasedimentary sequence, while others are intrusion-hosted deposits. Four main types of fluid inclusions are recognized in quartz at room temperature in orogenic (mesothermal) deposits from Lena (PR), Sayan-Yenisei (PR), Urals (Pz), Verkhoyansk (Mz), Kolyma province: (1) two-phase aqueous inclusions, containing liquid and vapor; (2) type II, two- or three-phase, (H2O)L + (CO2)V or L + (CH4)V or L fluid inclusions, including IIa, H2O-CO2-inclusions; (3) type III, vapour-rich inclusions, rarely with small liquid rims or meniscus, including IIIa, (CO2)V + (CO2)L, and IIIb (CO2)V + N2 +NH4; and (4) type IV, multi-phase inclusions containing (H2O)L-(H2O)V, and solid-daughter mineral identifying as halite on the basis of habit and optical characteristics. The data obtained indicate that the commercial ore bodies in orogenic (mesothermal) deposits studied were deposited from the H2O+CO+NaCl±CH4±N2 fluid with low- to moderate salinity. A mineral formation occurred at 100 to 450oC and 1 to 3 kbars. Dilute aqueous fluids recorded in the late gold-sulphosalts-bearing veins. Such a fluid regime is typical for orogenic gold deposits. Compositionally contrasting fluids are responsiple for a formation of gold deposits in the the Darasun district (Transbaikalian). Brines with salinity 56.3–29.9 wt % NaCl- equiv. formed early metasomatites. Auriferous quartz -base metal-sulphosalt veins crystallized from aqueous fluids with salinity 22.2–0.4 wt % NaCl-equiv. Such fluids are characteristic for porphyry or “intrusion related” deposits. Dilute aqueous fluids with salinity of 9.2–0.4 wt % NaCl- equiv. formed epithermal gold deposits within Okhotsk–Chukotka volcanic belt and Transbaykalia.