By Sergey M. Rodionov1, Alexander A. Obolenskiy2
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Tatarsko-Tyradinsk Metallogenic Belt ofREE-Li Pegmatite, W-Mo-Be Greisen,Stockwork, and Quartz Vein, andTa-Nb-REE Alkaline Metasomatite Deposits(Belt TT) (Yenisei Ridge, North-AsianCraton Margin, Russia).This Late Neoproterozoic metallogenic belt is related to veins and replacements in the Central Angara passive continental margin and Isakov island arc terranes. The belt is about 400 km length and ranges up to 150 km wide, has an irregular structure, and contains three main REE deposits, from south to north, at Sredne-Tatarsk, Enashiminsk, and Sredne-Vorogovsk. The deposits are generally small and genetically related to late Riphean and Vendian collisional, subalkalic, leucocratic granite and coeval nepheline syenite, alkali syenite, and granosyenite. The largest deposit is the Tatarskoye Nb apatite-pyrochlore carbonatite deposit that is hosted in alkali metasomatite and carbonatite. Deposits occur along intersections of sublatitudinal and northwest-trending faults with longitudinal major faults (Ishimbinsk and Tatarsk deep-faults). Granitoid-related REE deposits occur in anticlinal domes, and the alkali metasomatites occurs along deep-faults zones. Sn, W, and Mo occurrences occur in large granitoid plutons and small companion granite plutons and pegmatite bodies. The host rocks are contact metamorphosed, altered to greisen, and metasomatized (Brovkov and others, 1985). Tatarskoye REE (±Ta, Nb, Fe) Carbonatite DepositThis deposit (Brovkov and others, 1985) consists of phosphate and Ni minerals in carbonatite and alkali metasomatite that occur in an exocontact zone of a granitoid pluton that intrudes interbedded Proterozoic quartz-micaceous schist, marble, quartzite, amphibolite, and amphibole-chlorite schist. The district containing the deposit extends more than 20 km and ranges from 50 to 300 to 400 m wide. Twelve lensoid and sheet-like deposits occur in the district. Carbonatite is interpreted as a metasomatic unit and consists of dolomite-amphibole-biotite and calcite-amphibole-biotite carbonatite. Dolomite carbonatite has highest grade. The deposit minerals are Fe-dolomite, phlogopite, alkali amphibole, apatite, magnetite, pyrochlore, columbite, pyrrhotite. Also occurring are minor pyrite, chalcopyrite, ilmenite, molybdenite, zircon, rutile, and sphene. Deposit is interpreted as a near-fault type of alkaline metasomatite related to alkali basalt magmatism. Weathered surface rocks containg up to 5% Nb2O5, is widespread and contains complex Ni and phophorus minerals and vermiculite. The deposit is large. Oleniya Gora W-Mo-Be Greisen, Stockwork, and Quartz Vein DepositThis deposit (Matrosov and Shaposhnikov, 1988) consists of scheelite-bearing quartz veins cutting Neoproterozoic metamorphic rock that is intruded by Tatarsk-Ayachtinsk granitoid complex. The deposit occurs along the contact of quartz-carbonate-mica and quartz-micaceous schist with quartzite. The deposit extends along strike for about 900 m long, varies from 1 to 60 m thick, and contains numerous quartz veins from 15 to 18 m long and 0.8 to 4 m thick. Quartz veins also occur concordant to quartzite and hornfels. The ore minerals occur in streaks, nests, and disseminations. The principal ore mineral is scheelite, and associated minerals are pyrrhotite, pyrite, arsenopyrite, chalcopyrite, stibnite, berthierite, native silver, and gold. Antimony and Au deposits superimposed on W deposits. Ore shoots are common. The deposit is medium size with an average grade of 0.1% WO3. The deposit is medium-size with an average grade of 0.1% WO3. Enashiminskoye 3 REE-Li Pegmatite DepositThis deposit (Brovkov and others, 1985) consists of Sn-bearing pegmatite veins in carbonate and micaceous schist adjacent to small bodies of Late-Proterozoic leucocratic granite. Veins vary from tens of meters to few hundreds of meters long and 0.2 to 4 m thick. Veins are intensely altered to albite and consist of quartz, albite, and microcline with subordinate lepidolite, zinnwaldite, fluorite, spodumene, tourmaline, spessartine, apatite, cassiterite, and magnetite. Columbite-tantalite, beryl, pyrrhotite, arsenopyrite, and pyrite occur rarely. Cassiterite is more abundant in areas of more intensely albite-altered pegmatite. The deposit is small. Origin and Tectonic Controls forTatarsko-Tyradinsk Metallogenic BeltThe belt and hosting magmatic occur along major fault zones separating major tectonic blocks. The host coeval granitoid and alkaline magmatic complexes interpreted as intruding during collision and local extension along major fault zones during oblique collision. The belt formed in a short time span in the late Riphean and Vendian and is hosted in leucogranite, alkali-leucogranite, alkali-granite-syenite, and nepheline syenite plutons that intruded along major fault zones. The isotopic age of the Tatarsko-Tyradinsk metallogenic belt is 675 to 620 Ma and during this time, four host magmatic complexes formed (Kornev and others, 1996): (1) the Gurakhtinsk complex of subalkali granite and leucocratic granite with aplite and pegamatite veins; (2) the Glushikhinsk complex of subalkalic leucocratic granite that is interpreted as a post-collisional intraplate granite; (3) the Srednetatarsk complex of nepheline syenite; and (4) the Srednevorogovsk alkali-granite-syenite complex that consists of A-type intraplate granite that formed in an extension regime (Kornev and others, 1996). REFERENCES: Nozhkin, Trofimov, 1982; Brovkov and others, 1985; Lapin and others, 1987; Dacenko and others, 1994; Kornev and others, 1996. Vorogovsko-Angarsk Metallogenic Belt ofSedimentary-Exhalative Zn, Pb (SEDEX),Carbonate-hosted Pb-Zn (Mississippi Valley type),and Fe Skarn Deposits(Belt VA) (Yenisei Ridge, North-Asian Craton Margin, Russia).This Early Neoproterozoic metallogenic belt (also known as Yenisei Ridge polymetallic belt) occurs at the western margin of the Yenisei Ridge in the West Angara passive continental margin terrane in the Bolshepit synclinorium. The belt is about 450 km long and varies from 100 km (to the south) to 25 km (to the north) wide. The largest Pb-Zn deposits occur in the southern belt in the Priangarsk ore district. The main types of deposits in this district are: hydrothermal-sedimentary deposits with pyrite, pyrrhotite, and sphalerite that are conformable with host clastic and carbonate rocks (Gorevskoye); and galena and sphalerite streaks and disseminations that occur in algal limestone and dolomite (Moryanikhinskoye, Merkurikhinskoye, and others). To the north, in the Rassokhinskoye district (Lineinoye, Krutoye), and Bolshepitsk and Teneginsk districts are more than 300 deposits and occurrences that are mostly hosted in middle and late Riphean carbonaceous and clastic rock in a graben or syncline. Also occurring in this area are: Pb-Zn silicate and oxide deposits in carbonate rock (Teneginskoye); polymetallic vein deposits adjacent to porphyry deposits; and large Fe-skarn deposits (Enashiminskoye, Lendakhskoye, Polkan Gora) that occur near a central anticlinorium. These deposits and occurrences are related to middle and late Riphean volcanism and eruption of rhyolite and andesite-basalt, and subsequent formation of skarn along contacts with the granitoid plutons (Matrosov, Shaposhnikov, 1988). Three environment are defined for the various hydrothermal-sedimentary and polygenic stratiform Pb-Zn deposits: (1) deposition of proximal massive Pb-Zn sulfide deposits in local fault basins in clastic and carbonate sedimentary rock (Gorevskoye); 2) deposition of distal pyrite and polymetallic deposits in carbonaceous schist in deeper parts of basins (Lineynoye); and (3) deposition of carbonate-hosted Pb-Zn deposits hosted in carbonate reefs and sedimentary carbonate breccia horizons (Moryanikhinskoye, Merkurikhinskoye) (Ponomarev and others, 1991). Gorevskoye Sedimentary Exhalative Pb-Zn (SEDEX) DepositThis deposit (Distanov, 1985; Brovkov and others, 1985; Kuznetsov and others, 1990; Avdonin, 1997) consists of concordant lensoid masses of Pb-Zn sulfides hosted in late Riphean clastic and carbonate rock. The deposit occurs in a small synclinal fold on the limb of a larger anticline that is cut by the Main fault and associated fracture and shear zones on the northeast limb. Host rocks consist of a uniform sequence of dark-gray lenticular limestone with thin interbedded marl and shale. Host rocks are intensely deformed and metamorphosed to greenschist facies. Also occurring are numerous diabase dikes up to 10 m thick and several hundred meters long occur. Three separate deposits occur and range from 20 to 150 m wide, extend northwest for up to 1200 m, form an en-echelon system, and dip at 75 to 85°. The deposits extend to 1000 m depth at the southeastern flank of the deposit. Host rocks are siliceous siderite rocks and siderople. The ore mineral structures are lenticular, layered, streaky, massive, breccia, and disseminated. Main ore minerals are galena, pyrrhotite, and sphalerite, and lesser pyrite, marcasite, burnonite, boulangerite, jamsonite, arsenopyrite, ilmenite, rarely chalcopyrite, tennantite, argentite, pyrargirite, prustite, sternbergite, diskrasite, native silver, and lollingite. In decreasing abundance, th gangue minerals are quartz, siderite, ankerite, dolomite, calcite, biotite, muscovite, and garnet. Sphalerite occurs mainly on hanging wall of the district, whereas galena is concentrated on the footwall. Ag, Cd, Ta, and Te occur in solid solution. A model Pb isotopic age for the deposit is 834 to 852 Ma. The deposit is a large, world class deposit and has an average grade of 7.02% Pb and 1.36% Zn. Moryanikhinskoye Carbonate-Hosted Pb-Zn (Mississippi Valley type) DepositThis deposit (Ponomarev and others, 1991) consists of layered bodies of disseminated, streaky, disseminated, and massive Pb-Zn sulfides hosted in late Riphean dolomite and limestone. The deposit occurs in a southeastern periclinal closing of an anticline complicated by a shear zone. Host rocks are are 320 m thick and consist of dark-grey dolomite and algal ferruginous limestone with interbedded shale, marl and tuffaceous siltstone, with. single beds of schistose metabasalt porphyry and blastoporphyritic quartz-sericite schist. A spatial relation between Pb-Zn deposits and organic carbonate units exists. Five concordant layered deposits occur, and extend more than 500 m along strike and range up to 600 m deep. The thickness of deposits ranges from 3.0 to 8.7 m, occasionally up to 33 m. Boundaries of deposits are gradational, particularly for disseminated ores. Main ore minerals are galena, sphalerite, and pyrite, and rare pyrrhotite, chalcopyrite, burnonite, and fahl. The main gangue minerals are quartz and Fe-carbonate. Galena and sphalerite with a Zn:Pb ratio of 2:5 are predominant. Chalcopyrite and fahl are typical minerals in veins along with sphalerite, galena and pyrite. The deposit is interpreted as forming under polygenous hydrothermal and sedimentary conditions. A model Pb isotopic age for the deposit is 740 to 849 Ma. The deposit is medium size with an average grade of 2.5% Pb and 1.1% Zn. Enashiminskoye 2 Fe Skarn DepositThis deposit (Matrosov and Shaposhnikov, 1988) consists of layers and lenses deposits of magnetite in metamorphosed middle Riphean volcanic, carbonate, and clastic rocks. Host rocks and Fe-ores are intruded by Chirimbinsk granitoid pluton. The contact zone is contact metamorphosed, carbonate-altered, and silicified and contains epidote-amphibole-garnet skarn. The district containing the deposit extends up to 4.7 km along strike and contains more than 20 deposits that vary from 5 to 70 m thick, are up to 700 m long, and are up to 650 m deep. Deposit minerals are magnetite, epidote, and amphibole. Deposit contains anomalous Ti, V, Cr, and Mn, and anomously low S and P. Deposit formation was polygenetic with initial formation of primary siliceous-carbonate and ferruginous sedimentary rocks that were regionally metamorphosed, contact-metasomatized. The deposit is large with resources of 450,000,000 tonnes grading 36 to 51% Fe. Origin and Tectonic Controls for Vorogovsko-Angarsk Metallogenic BeltThe SEDEX deposits in the belt are interpreted as forming along major fault depressions along transcrustal block in pericratonal subsidences. Carbonate-hosted Pb-Zn deposits formed in carbonate reefs. Volcanogenic-sedimentary Fe deposits are interpreted as forming during marine volcanism and sedimentation. Formation of the metallogenic belt is interpreted as forming during convergence along a middle to late Riphean continental margin (Obolenskiy and others, 1999). The principal structural control for the Gorevskoye deposit was the intersection between a system of northwest block-bounding faults and the transversal Irkeneevsk plate boundary fault. Host rocks and the coeval deposits have model Pb isotopic age of about 950 Ma. Approximate coeval units are collision-related granite plutons (Tatar-Ayakhta complex) and dolerite dikes. REFERENCES: Matrosov, Shaposhnikov, 1988; Distanov, 1985; Ponomarev and others, 1991; Obolenskiy and others, 1999. |