Аннотация:The Uderei Au-Sb deposit located in the central Enisei Ridge; orebodies of the deposit are hosted in metamorphosed (green schist facies) siltstone and carbonate-clay rocks of the Late Proterozoic Uderei Formation. The orebodies are numerous quartz veins and veinlets of variable thickness (up to 1 m) and length (up to 100 m).
Two types of wall-rock alteration were indentified at Uderei: (1) early beresite (quartz+muscovite+carbonate±chlorite±pyrite±arsenopyrite) and (2) late argilic. The first type altered rock accompanies gold mineralization, whereas the second type, antimony mineralization. Frequently, antimony mineralization spatially overlaps the gold ore. According to Nevol’ko and Borisenko (2009), the gold ore is of ~712 Ma age, whereas antimony mineralization, ~670 Ma.
In addition to quartz, muscovite (sericite) and siderite are gangue minerals of the gold ore stage. The ore minerals of the stage are pyrite-I enriched in As, arsenopyrite, Fe-rich sphalerite-I, gersdorffite, tetrahedrite, chalcopyrite, and native gold as nanoinclusions in arsenopyrite. The ore minerals of the antimony stage are stibnite, berthierite, zinkenite, ulmanite, chalcostibite, and rare free native gold probably remobilized from early arsenopyrite.
The fluid inclusions are negative crystals or irregular shaped of 2 to 25 microns in size. The primary fluid inclusions are evenly distributed in crystal body; pseudosecondary inclusions heal fractures within crystal, and secondary fluid inclusions heal fractures rising at the crystal surface. At room temperature on the basis of phase composition, the following types of fluid inclusions are recognized: (1) two- or three-phase CO2-H2O with large (20-30 vol %) gas bubble; (2) two- or three-phase gas-dominated inclusions with small CO2 gas bubble and water rim; and (3) two-phase inclusions aqueous solutions. Microthermometry was performed for 305 fluid inclusions. Homogenization temperature of primary and pseudosecondary CO2-H2O inclusions (type 1) ranges from 228 to 338oC. Salinity varies from 4.1 to 7.1 wt % equiv NaCl. Two-phase fluid inclusions of type 3 homogenize into liquid at 136-194oC and contain aqueous solution with salinity of 2.9 to 6.9 wt % equiv NaCl. The primary and pseudosecondary CO2-H2O inclusions (type 1) correspond to the gold mineralization, whereas the secondary fluid inclusions (type 3) studied here probably correspond to the antimony stage of the Uderei formation.
The Ptot/PH2O values of fluids of the Uderei deposit indicate the shallow (hypabyssal) formation of the deposit in closed system with tectonic activity. Tectonic activity was expressed as local opening and closing fractures resulting in boiled gas-saturated fluid (Prokof’ev, 1998).