By Sergey M. Rodionov1, Alexander A. Obolenskiy2
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Kukhtuy-Uliya Metallogenic Belt ofAu-Ag Epithermal Vein, Porphyry Mo(±W, Sn, Bi), Porphyry Sn, andPolymetallic (Pb, Zn±Cu, Ba, Ag, Au)Volcanic-Hosted Metasomatite Deposits(Belt Kul) (Russia, Far East)This Late Cretaceous and to Paleocene metallogenic belt is related to veins that are associated with the Okhotsk-Chukotka volcanic-plutonic belt that intrudes and overlies the Okhotsk terrane. The metallogenic belt occurs in the Uliya volcanic zone of Okhotsk-Chukotka volcanic-plutonic belt and in the overlapped Okhotsk cratonal terrane. The metallogenic belt contains several Au deposits and occurrences. The main deposits are at Khakandzha and Yurievka. Khakandzha Au-Ag Epithermal Vein DepositThis deposit (Onikhimovkiy, and Belomestnykh, 1996) occurs in the Uliya volcanic zone that overlaps the Okhotsk terrane is hosted in a large domal volcanic-plutonic structure that overlies a Late Triassic clastic sequence. The lower part of volcanic-plutonic structure is andesite and the upper part is dacite and rhyolite. The subjacent and the volcanic rock are intruded by a Late Cretaceous brecciated latite sill and granosyenite porphyry dikes, and by Paleocene basalt, diabase, and andesite dikes. The deposit consists of a gently dipping (15 to 30o southwest) zone of breccia and silica alteration that ranges from 7 to 52 m thick. The zone is cut by numerous branching veins and veinlets of quartz and quartz-adularia that contain the Au-Ag minerals. The ore is low-sulfide (0.5 to 3.0%), and the main ore minerals are native gold, pyrite, galena, sphalerite, chalcopyrite, electrum, and native silver. Gangue minerals are: quartz, adularia, rodhochrosite, rhodonite, and calcite. Gold fineness ranges from 532 to 774. The deposit contains from 0.1 to 1806 g/t Au (average of 8 to 10 g/t Au), and from 0.1 to 32,676 g/t Ag (average of 350 to 600 g/t Ag). Au/Ag is 1:44. A high Mn content is typical for the deposit. NOTE: Need latitude and longitude. Yurievka Au-Ag Epithermal Vein DepositThis deposit (Onikhimovkiy, and Belomestnykh, 1996) is hosted in the Uliya volcanic zone that consisits of Late Cretaceous andesite, basalt, dacite, rhiolite, and dacite. The deposit occurs along a tectonic zone that strikes sub-latitudinally and dips steeply. The host rocks are altered to propilite. Gold ores are high-sulfide. Average grade is about 10 to 25 g/t Au, and the deposit contains about 7.1 tonnes gold. NOTE: Need latitude and longitude. Origin and Tectonic Controls for Kukhtuy-Uliya Metallogenic BeltThe belt is interpreted as forming during generation of granitoids along an active continental margin arc consisting of the Albian to Late Cretaceous Okhotsk-Chukotka volcanic-plutonic belt. REFERENCES: Korol'kov and others, 1974; Vel'dyaksov and Umitbaev, 1976; Avchenko, 1977; Chikov, 1978; Verzkhovskaya and Krichevets, 1987; Pavlov, 1993; Moiseenko and Eirish, 1996; Onikhimovsky and Belomestnykh, 1996. Bakcharsk Metallogenic Belt ofSedimentary Siderite Fe, BandedIron Formation (BIF, Superior Fe), andSedimentary Fe-V Deposits(Belt BCh) (Russia, Eastern Siberia)This Cretaceous and Paleogene metallogenic belt is hosted in stratiform units in the Northern, Eastern, and Western Siberia sedimentary basins. The belt extends south to the north and is part of the West Siberian Fe basin that is exposed over an area more than 50,000 km2 (Shakhov, 1964; Kuznetsov, 1982). Huge reserves of oolitic brown Fe deposits are hosted in a thick sequence of Cretaceous and Paleogene marine clastic sedimentary rock. The four Fe horizons are recognized and consist of goethite-leptochlorite and hydrogoethite-leptochlorite. The horizons vary from 30 to 45 m thick. Along strike and downward the horizons grade into ferruginous quartz sandstone. The overlying sedimentary section ranges from 150 to 260 m thick. The largest Bakcharsk deposit has been studied in detail by 56 deep boreholes (Orlov, 1998; Roslyakov and Sviridov, 1998) Bakcharskoye Sedimentary Siderite Fe DepositThis deposit (Shachov, 1964; Sviridov, 1988; Rosljakov and Orlov, 1998) consists of brown ironstone beds hosted in loosely or weakly cemented marine shallow-water Late Cretaceous and Paleogene sedimentary rock that overlies the Siberian Platform. The deposit covers an area of 1,200 km2 and occurs in three stratigraphic levels. (1) The Eocene Bakcharsk horizon consists of by dense hydrogoethite with siderite cement with an average thickness of 12.8 m. (2) The Maastrichtian Kolpashevsk horizon consists of brown ironstone and oolitic ferruginous sandstone. The average thickness is 3.1 m. (3) The Santonian-Campanian Narimsk horizon consists of hydrogoethite-leptochlorite oolite and averages 2.3 m thick. The major Fe reserves are in the Bakcharsk horizon. Grades range from 30.32 to 53.48% Fe, up to 0.33% V2O5, and 0.055% S. The deposit is large with reserves of 28,000,000,000 grading 37.4% Fe. Origin and Tectonic Controls for Bakcharsk Metallogenic beltThe belt is interpreted as forming in a nearshore environment during rewashing of laterite crust weathering material during rewashing in a shallow-water, near-shore environment. The laterite crust is interpreted as derived from trapp basalt plateaus of the North Asian Craton (Shakhov, 1964; Kuznetsov, 1982). REFERENCES: Shakhov, 1964; Kuznetsov, 1982; Orlov, 1998; Roslyakov and Sviridov, 1998. Verkhoturovsk Metallogenic Belt ofBauxite (Karst Type), Talc (Magnesite)Replacement, andSedimentary BauxiteDeposits(Belt VT) (Yenisei Ridge, Russia, EasternSiberia)This Cretaceous to Paleogene metallogenic belt is related to weathering of units in North Asian Craton, North Asian Craton Margin (East Angara fold and thrust belt), and Central Angara terrane. The belt occurs in the southern part of Yenisei Ridge. The bauxite deposits are related to humid hypergenesis during the Cretaceous and Paleogene. The belt occurs in the southern Chernorechensk-Kamensk synclinorium and the Central anticlinorium of Yenisei Ridge. The belt extends latitudinally for about 200 km and ranges from 120 km wide in the west (Sokhatinoe, Murlinoye, Sredne-Tatarskoye deposits) to 40 km wide in the east (Kirgiteiskoye, Verkhoturovskoye, and Porozhninskoye deposits). The majority of deposits occur in karst basins and are derived from diagenetically altered weathering crust. The weathering crust ranges from 60 to 80 m thick and is developed over Proterozic shale, argillite, carbonaceous rock, and limestone. Bauxite fills karst and structural or erosional basins that occur along contact zones between limestone and amphibolite (Tatarsk group deposits, Ivanovskoye deposit), or in argillaceous schist (Kirgiteiskoye, Verkhoturovskoye, and Porozhninskoye deposits). Bauxite basins are valley-shaped and isometric. The bauxite-bearing horizon ranges up to 130 m thick and consists of light or mottled kaolinite and kaolinite-gibbsite clay with admixtures of hydromica, hydrogoethite, and bauxite. The deposits are lensoid or bedded. Grade ranges from 34 to 48% Al2O3 and 2 to 6% SiO2. The bauxite consists of gibbsite with intermixed kaolinite, boehmite, diaspore, and fine-grained corundum. The largest deposits contain mottled clays and occur in deep (up to 250 m) karst cavities. The deeper karst cavities occur in uplifted areas of the anticlinotium (Tatarskoye deposit) (Peltek, 1971). Most of the bauxite deposits are small except for the medium-size Porozhninskoye deposit. Porozhinskoye 2 Bauxite (karst type) DepositThis deposit (Peltek, 1967, 1969; Smirnov, 1978) consists of karst bauxite deposits that occur in the contact zone of Proterozoic clastic and carbonate rocks. Bauxite horizon consists of variegated bauxitic clays, earthy and stony clayey bauxite. Ore horizon is 15 km long and 12 to 45 m thick. Separate deposits are from 120 to 1200 m long, 50 to 150 m width, and 12 to 37 m thick. Bauxite are pisolitic, of gibbsite composition, and enriched in Fe oxides. Main ore minerals are gibbsite, kaolinite, corundum, magnetite, hematite, goethite. The deposit is medium size with an average grade of 43.6% Al2O3. Origin and Tectonic Controls for Verkhoturovsk Metallogenic BeltThe belt is interpreted as forming during Cretaceous and Paleogene tropical weathering and regional peneplane formation on the Yenisei Ridge (Kozlovskaya and Adamenko, 1971) in a humid mesothermal climate (Sergeeva, 1971). Bauxite deposits occur in the middle part of a Cretaceous and Paleogene sedimentary sequence. Underlying strata contain mainly hydromica and kaolinite-hydromica clays and weathered fragments of host rocks. The upper bauxite strata consist of kaolinite and kaolinite-hydromica clay and various types of bauxite (Pasova and Spirin, 1970). However, some researchers interpret the bauxite deposits as forming during deposition of lateritic weathering crust that developed on alumosilicate rock (Peltek, 1967; Cykin, 1981, 1994). REFERENCES: Peltek, 1967, 1971; Pasova and Spirin, 1970; Kozlovskaya and Adamenko, 1971; Sergeeva, 1971; Cykin, 1988, 1994. |