By Sergey M. Rodionov1, Alexander A. Obolenskiy2

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Pribaikalskiy Metallogenic Belt of

Carbonate-Hosted Pb-Zn

(Mississippi Valley Type) Deposits

(Belt PrB) (Russia, Western Transbaikalia)

This Riphean metallogenic belt occurs along the juncture of Paleoproterozoic Akitkan active continental margin volcanic-plutonic belt and sedimentary rock of the Patom fold and thrust belt, North Asian Craton. The belt extends along the northwestern coast of Lake Baikal for 170 km and ranges from 30 to 50 km wide. The tectonic setting of the belt is defined by tectonic and magmatic processes associated with the Akitkan volcanic-plutonic belt along the margin of Siberian Craton. This Paleoproterozoic volcanic-plutonic belt consists of subalkaline, siliceous lava, minor basalt porphyry, and subaerial volcanic and sedimentary sedimentary rock. Also occurring are comagmatic diorite, granodiorite, and granite, and rapakivi granitoids in the Primorsky Complex with an isotopic age of 1690±40 Ma. The overlap assemblage consists of clastic and carbonate sedimentary rock of the Baikal series (Goloustenskaya and Uluntuy suites) that extend the margin of the craton for 1000 km with monoclinal northwest dips. The sedimentary rocks consist of fine-grained limestone, unequigranular micro-and coarse-crystalline limestone with oolite-like internal structure, sedimentary and diagenetic dolomite, talc rock, and talc-carbonate rock. The monoclinal dip is complicated by longitudinal S folds and higher-order folds. Deposit controls are folds and regional shear zones that consist of lenses and sublaminated bodies of talc rock, and quartz and aragonite veins. The shear zones formed during overthrusting of the deposit-enclosing sequence over the older volcanic rock. The major deposit in the belt is at Barvinskoye.

Barvinskoye Carbonate-hosted Pb-Zn (Mississippi Valley type) Deposit

This deposit consists mainly of sulfides in layers, lenses, veins, and disseminations (Tychinsky and others, 1984) that occur along concordant ruptures and shears that controll the deposit. Also occurring are crossing verins. Sphalerite, galena, fluorite ore is most productive. Host rocks exhibit widespread are metasomatic alteration. The eposit is interpreted as forming during hydrothermal activity.

Origin and Tectonic Controls for

Pribaikalskiy Metallogenic Belt

The belt interpreted as forming along shear zones and faults that occur between an ancient active continental margin along the North Asian Craton.

REFERENCES: Tychinsky and others, 1984; Tychinsky and others, 1986.

Bokson-Kitoiskiy Metallogenic Belt of

Sedimentary Bauxite, Magmatic Nepheline,

Serpentine-hosted Asbestos, and

Au in Shear Zone and Quartz Vein Deposits

(Belt B-K) (Russia, East Sayan)

This Neoproterozoic through Silurian metallogenic belt is related to veins layers in plutons intruding, or in the Belaya-Kitoy metamorphic terrane, Hug accretionary wedge, and Tunka tonalite-trondhjemite-gneiss terranes, the Tannuola plutonic belt, and the Huvsgol-Bokson sedimentary overlap assemblage. The belt occurs in the central part of East Sayan Mountains in the upper parts of Irkut, Urik, and Kitoy Rivers, extends along a nearly sublatitudinal trend for 315 km, and is 150 km wide. Metallogenic belt is a composite that includes several mineral deposit types.

The Gargansky terrane consists of Archean plagio-granite-gneiss overlapped by a Riphean carbonates. The Ilchir terrane consists of a Riphean ophiolite, the Dibinsky suite of rhythmically-bedded sedimentary volcanic rock, the Sarkhoy suite of calc-alkaline and tholeiitic volcanic rock, and the middle Riphean Khugeinsky suite of clastic and volcanic rock metamorphosed at high-pressure. The Huvsgol-Bokson overlap assemblages consists of carbonate and clastic sedimentary rocks of the Vendian and Cambrian Bokson series, and clastic sedimentary rock of the Ordovian through Devonian Okinsky series.

Igneous suture complexes are the subduction-related tonalite Sumsunur complex with U-Pb and Rb-Sr ages of 790 Ma, and Devonian and Carboniferous granitoids of the Kholbinsky, Ognitsky, and Botogol complexes.

The major deposits are the Boksonskoye sedimentary bauxite, Botogolskoye magmatic nepheline, Ilchirskoye serpentinite-hosted asbestos, Bourun-Kholba Au in shear zone and quartz vein, Zun-Kholba Au in shear zone and quartz vein, and the Pionerskoye2 Au in shear zone and quartz vein deposits

Zun-Kholba Au in Shear Zone and Quartz Vein Deposit

This deposit (Feofilaktov, 1992; Zhmodik and others, 1994; Dobretsov and Ignatovich, 1989) consists of a steeply dipping zone (8000 x 200-600 m) that strikes northwest and contains over over 30 bodies of which 12 are economic. The bodies are divided into: (1) steeply-dipping quartz-polysulfide; (2) banded chalcopyrite-pyrite bodies; and (3) quartz veins. The first is economically important is hosted in talc-chlorite and carbonaceous-siliceous shales, are a combination of vein and dissemination with 20-50% sulfides. Major ore minerals are pyrite (up to 30-45%), pyrrhotite (up to 5-30%), chalcopyrite (up to 10%), galena (up to 5-8%), and sphalerite (up to 5%), and rare bornite, chalcocite, bismuthine, native silver, and Au and Ag tellurides. Gangue minerals are quartz, calcite, and talc, and rare albite, chlorite, muscovite, sericite, and graphite. Wall rocks contains zones of beresite, talc, graphitie, and listvinite alterations. Sulfide body dimensions are 150-300 by 0.2 by 0.4 m and occur in limestone. Sulfide grade ranges up to 50-80% and sulfides are mainly pyrite, sphalerite, galena, chalcopyrite, and pyrrhotite. Small quartz-sulfide veins 1-2% and rarely 5% sulfides with an average grade of 9.8 ppm Au and 13 ppm Ag. The deposit occurs in the central part of the Samarta-Kholba shear zone along the northern boundary of the Gargansky terrane. The deposit is medium size with an average grade of 26 ppm Au, 24-37 ppm Ag, and 1.7ppm Pt.

Boksonskoye Sedimentary Bauxite Deposit

This deposit (Il'ina, 1958; Orlova, 1958) consists of bauxite layers that occur over different dolomites (spotty, reef-generating, algae, banded, pink and red) in part of the thick Bokson suite in Archean and Proterozoic metamorphic and mafic igneous rock. Thickness of the bauxite beds average 5 m, locally up to 30 m. Bauxite occurs in contain dense, banded, thin-banded, and breccia varieties, locally as a sandy bauxites. The deposit contains 35 minerals and the primary minerals are bemite, kaolinite and dikkite, leptochlorite, and gallauzite, and rare dafite, montmorillonite, pyrophyllite, Fe oxides and hydroxide. Secondary minerals are sericite, muscovite, talc, serpentine, zeolite, hydrargillite, diaspore, chlorite, crysotile, quartz, calcite, and gypsum. The ore minerals are hematite, goethite, pyrite, magnetite. Terrigenous minerals are tourmaline, olivine, feldspar, quartz, rutile, leucoxene, and alunite. Varities of mineral assemblages are red-brown diaspore-hematite, gray-green diaspore chlorite, and intermediate diaspore-chlorite-hematite. The bauxite formed from coastal marine and lagoon sediments. The age of the deposit 540-600 Ma. This is the oldest bauxite deposit in Russia. The deposit is large with an average grade of 40% Al₂0₃.

Botogolskoe Magmatic Nepheline Deposit

This deposit (Solonenko, 1950) occurs in the Botogol alkaline nepheline syenite massif that forms an elongated oval that is 6 x 2 km and intrudes Proterozoic schist and carbonate rock. The massif formed in three stages: normal pyroxene and quartz syenite; alkaline pyroxene and nepheline syenite; and leucocratic nepheline syenite. Two deposit bodies occur, the Severny body of 0.6 km² size and the Yuzhny body of 0.2 km² size. The bodies are separated by a kilometer-wide zone of a low-grade deposit. The Severny body is mainly leucocratic nepheline syenite with local biotite and pyroxene. The Yuzhny body is mainly a pyroxene nepheline syenite. The deposit is interpreted as forming in a back-arc rift. The deposit is medium size with an average grade of 21% Al₂0₃.

Ilchirskoye Serpentinite-Hosted Asbestos Deposit

This deposit (Shamansky, 1945; Krutsko, 1964) occurs in the Ilchir lens-shaped massif (2.5 x 1 km) composed of Vendian peridotite and serpentinite. The deposit is an irregular lens with dimensions of 1700 by 100-380 by 150-550 m. The deposit has a concentric structure: a central part of asbestos-bearing serpentinite with a core of unaltered harzburgite; outward, serpentinite devoid of asbestos; and serpentinite-talc-carbonate rock. High-grade asbestos occurs in two tectonic zones of that cut the massif and vary from 100 to 400 m thick. Asbestos is a large network type with veinlets ranging from 20-30 mm thick (locally up to 70 mm), cutting in various directions, and occurring about 1-2 m apart. The ore mineral minerals are chrysotile-asbestos, bastite, serpentine, ophite, magnetite, talc, chromite, brucite, atagorite, carbonates, pyroxene, and olivine. Asbestos is silky, durable, useful for technological purposes. The deposit is small with an average grade of 2.5% asbestos fibre and from 0.08-0.25% textile grade asbestos.

Origin and Tectonic Controls for

Bokson-Kitoiskiy Metallogenic Belt

This belt is hosted in metamorphic, oceanic, accretionary wedge, and accretionary wedge, and tonalite-trondhjemite-gneiss terranes that underwent Cambrian through Silurian metamorphism, hydrothermal alteration, and plutonic intrusion. A younger suture complex is the subduction-related Sumsunur complex tonalite with a U-Pb and Rb-Sr isotopic age of 790 Ma. The deposits in the belt are interpreted as forming in multiple events.

REFERENCES: Solonenko, 1950; Orlova, 1958; Vinogradov, 1958; Il’ina, 1958; Krutsko., 1962; Krutsko, 1964; Levitsky, 1966; Dobretsov and Ignatovich, 1989; Feofilaktov, 1992; Mironov and others, 1995.

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