By Sergey M. Rodionov1, Alexander A. Obolenskiy2
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Kansk Metallogenic Belt of Au inShear Zone and Quartz Vein,REE-Li Pegmatite, amd W-Mo-Be Greisen,Stockwork, and Quartz Vein Deposits(Belt KN) (Southern Yenisei Ridge,North-Asian Craton Margin, Russia)This Early Neoproterozoic metallogenic belt occurs in the Kan cratonal terrane composed Archean crystalline rocks that crops out in the southern Yenisei Ridge. The western border of the belt is the Priyenisei major fault zone, the eastern border is a large fault between the Kan block anticlinorium and Angara-Taseev syncline. The northern border of the belt is the Angara-Viluy transform fault. The host are rocks are metamorphosed to amhibolite facies and are intruded by the Paleoproterozoic Taraksk gneiss and granitoid pluton with a Rb isochron age of 1850 to 1890 Ma, and a Rb-Sr isotopica age of 2.00 to 2.06 Ga). Also intruding the host rocks is the Neoproterozoic Nizhnekan granitoid pluton with a Pb isochron age of 850±50 Ma and a U-Th-Pb isochron age of 920±50 Ma (Kornev and others, 1996). Deposits are small in size and heterogenous. The major Au shear zone and quartz vein deposits, as at Kuzeevskoye and Bogunai, are predominant and occur in diaphthoresis zones in Archean rocks. Also occurring are W-Mo-Be greisen, stockwork, and quartz vein deposits, as at Kanskoye, and Li-Sn-Be and ceramic pegmatite, as at Barginskoye, that are related to granite intrusions. Ti-magnetite deposits occur in Riphean dunite, pyroxenite, and gabbro intrusions. Volcanic and sedimentary magnetite quartzite, as at Predivinskoy, is related to Riphean rhyolite and basalt. Three main districts occur in the belt: Kuzeevsk (Au), Bogunai (Au), and Predivinsk (Fe). The Sayan-Yenisei fault is the main structural control. (Brovkov and others, 1988). Bogunai Au in Shear Zone and Quartz Vein DepositThis deposit (Li, 1974; Bovin and Li, 1976; Serdyuk, 1997) consists of more than 40 quartz veins hosted in Archean metamorphic rock. The main host rocks are garnet and pyroxene plagiogneiss, granulite, migmatite, charnockite, and pegmatite, and diabase, diabase porphyry and gabbro dikes. Venis range up to several hundred meters length and are up to 1 km, and up to 2 m thick. Veins located in ares of greenschists facies metamorphism. Host rocks are altered to are silica, sericite, pyrite, chlorite, and carbonate. Main ore minerals are pyrite, sphalerite, and galena; and minor chalcopyrite, arsenopyrite, pyrrhotite, cubanite, magnetite, native gold, cassiterite, stannite, andmolybdenite. Gangue minerals are quartz (70 to 95%), calcite, siderite, chlorite, and sericite. Native gold is fine-grained and is associated with sulfides. Deposit is partly mined. A Pb-isotopic age of Au-sulfide deposits is 900±150 Ma. The deposit is small. Kanskoye W-Mo-Be Greisen, Stockwork, and Quartz Vein DepositThis deposit (Matrosov and Shaposhnikov, 1988) consists of quartz-molybdenite veins in the Neoproterozoic Nizhnekansk granitoid pluton. Veins range up to 270 to 300 m long and are from 0.16 to 0.38 m thick. Host rock is altered to greisen. Ore minerals are molybdenite, pyrite, chalcopyrite, and ilmenorutile. Molybdenite occurs irregular grains. Sparese disseminated molybdenite occurs along with wolframite, scheelite, and cassiterite in greisen, scheelite skarn, and pegmatite. The deposit is small. Barginskoye REE-Li Pegmatite DepositThis deposit (Matrosov and Shaposhnikov, 1988; Serdyuk and others, 1998) consists of pegmatite veins in Archean garnet-hypersthene gneiss. Host rocks along veins are altered to mica, staurolite-mica, and amphibole gneiss. 121 pegmatite veins occur and are generally conformable to host rock schistosity. Veins are layered, extend up to 400 m, and range from 1 to 2 m thick. The Giant vein is 2 km long and 10 to 50 m thick. Also occurring are lensoid pegmatite bodies. Major pegmatite minerals are quartz, K-feldspar, muscovite, biotite, garnet, beryl, epidote, and apatite. 15 veins contain commercial muscovite. Muscovite is low grade. Deposit has been mined. Pegmatite is genetically related to a Neoproterozoic granite sequence (Brovkov and others, 1985). The deposit is small. Origin and Tectonic Controls for Kansk Metallogenic BeltThe belt is interpreted as forming during tectonic and magmatic activation of the Angara-Kan block during orogenic development of the Riphean continental margin of the North Asian Craton. A direct relation between Au deposits and granitoid intrusions is not established. Au deposits are largely related to small mafic intrusions that intrude along the Sayan-Yenisei fault zone (Bovin and Li, 1976). W-Mo greisen and REE vein and pegmatite of presumed Late-Riphean age are interpreted as forming during early-stage intrusion of collisional granitoids (Li, 1982). REFERENCES: Bovin and Li, 1974; Li, 1982; Brovkov and others, 1988; Kornev and others, 1996. Tonodskiy Metallogenic Belt ofAu in Black Shale Deposits(Belt Tnd) (Russia, Northern Transbaikalia)This Riphean metallogenic belt occurs in the Paleoproterozoic Tonod greenschist terrane that comprises part of the basement of the North Asian Craton. The belt extends along a sublatitudinal trend for over 200 km is about 35 to 60 km wide. The belt occurs along the southeastern boundary of the North Asian Craton The terrane consists of quartz and quartz-feldspar metasedimentary rock (Albasinsky suite), turbidite sedimentary rock (rhythmically alternating black carbonaceous schist, quartz metasedimentary rock, chlorite-sericite and micaceous-quartz shale (Mikhailovsky suite) enclosing small bodies of metabasalt. The terrane is metamorphosed from greenschist to amphibolite facies and is deformed into linear and domal folds that are complicated by numerous thrusts. Most of the terrane consists of the accretionary Mesoproterozoic Chuya-Nechera granitoid and granite porphyry complex. The belt contains numberous Au deposits. Also occurring in the area are non-economic Fe, Sn, magnesite, U, and Ti-magnetite deposits. The major deposit is at Chertovo Koryto. Also occurring are promising large Au occurrences, as at Vostochny, Kevaktinsky, , and Osennee, that all occur on the periphery of the Kevaktinsky dome along major thrust zones in carbonaceous schist and metasedimentary rock. The belt is promising for undiscovered large Au deposits in the Kevaktinsky and Taimendinsky structures. Chertovo Koryto Au in Black Shale DepositThis deposit (B.V. Antonov and others wriiten commun. 1967; Ivanov and others, 1995; Kotkin, 1995) consists of three gently lying stockwork zones conformable with submeridional striking thrust. Zones contain quartz and sulphides in Paleoproterozoic carbonaceous schist and sandstone. Stockwork consists of variably-oriented veins and veinlets in fault zohes and range from 3 to 8 m thick (locally up to 300 m thick). Sulfides occur in quartz veins and enclosing rocks. Main ore minerals are arsenopyrite (0.1-0.5%), pyrrhotite, and pyrite, and lesser galena, chalcopyrite, sphalerite; ilmenite, apatite, rutile, garnet, zircon, and tourmaline. Fineness of gold is 870-904. Deposit occurs in central part of the Tonod uplift in the Patom district. The deposit is medium-size with an average grade of about 2.6 g/t Au. Origin and Tectonic Controls forTonodskiy Metallogenic BeltInitial gold deposition from hydrothermal-metamorphic processes that occurred during Proterozoic regional metamorphism related to accretion and generation of Chuya-Nechera granitoids. Subsequent economic concentration during late Riphean tectonism and magmatism. Subsequent economic concentration during late Riphean tectonism and magmatism with intrusion of magmatic rocks along transform microplate boundaries and within plate (plume) environment. REFERENCES: Kotkin, 1975; Ivanov and others, 1981; Ivanov and Ryazanov, 1992; Gusev and Khain, 1995; Ivanov and others, 1995. |