By Sergey M. Rodionov1, Alexander A. Obolenskiy2
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Malo-Khingan Metallogenic Belt ofPorphyry Sn and Rhyolite-HostedSn Deposits(Belt MKh) (Russia, Far East)This Late Cretaceous metallogenic belt is related to granitoids in the Khingan-Okhotsk volcanic-plutonic belt. The intrusive rocks of the Khingan-Okhotsk belt in this area are dominantly granite and are comagmatic with the volcanic rock. The granitoids are interpreted as subduction-related, calc-alkalic igneous rocks and include both S-and I-type granite. The major deposit is at Khinganskoe. Khingan Porphyry Sn MineThis deposit (Ognyanov, 1986) occurs in a pipe-shaped, hydrothermal explosion breccia that intrudes felsic volcanic rock. The deposit occurs in15 areas in a zone that ranges from 10 to 50 m across, varies from 100 to 400 to 500 m long, and at depth occurs in a symmetrical breccia zone that is about 250 to 300 m wide across. The zone extends to depths of over 1,200 m. At the upper levels, the breccia is replaced by chlorite, and at the depths of 700 to 800 m, the breccia is replaced by quartz-muscovite (sericite)-topaz greisen. Most of the district consists of quartz, fluorite, and cassiterite with subordinate arsenopyrite, marcasite, loellingite, chalcopyrite, and Bi-minerals. The deposit is interpreted as probably genetically related to a subalkaline potassium granite with a K-Ar isotopic age of 80 to 90 Ma, a Rb-Sr whole-rock isochron age of 78 Ma, and an initial Sr isotopic ratio of 0.7123. The deposit has been mined since the 1960's. The deposit is medium size and averages 0.6 to 0.7% Sn. Origin and Tectonic Controls for Malo-Khingan Metallogenic BeltThe belt is interpreted as forming during generation of granitoids along along the Khingan transform continental-margin arc consisting of the Khingan-Okhotsk volcanic-plutonic belt that is tectonically to oblique subduction of the ancestral Pacific Ocean plate. The southwest part of Khingan-Okhotsk volcanic-plutonic belt occurs in a post-accretionary Cretaceous volcanic-tectonic basin in the eastern Bureya continental-margin arc superterrane. The basin is filled with mid-Cretaceous, intermediate volcanic rock and overlying Late Cretaceous tuff and rhyolite lava that range from 1.5 to 3.0 km thick. The basin overlies a Proterozoic metamorphic rock of the Bureya superterrane. The Khingan-Okhotsk belt is part of the Khingan continental-margin arc that is interpreted as forming from oblique subduction of the ancestral Pacific Ocean plate. Fragments of this plate are interpreted as occurring in tectonically interwoven units of the Amur River, Khabarovsk (younger Early Cretaceous part), and Kiselevka-Manoma accretionary-wedge terranes. This tectonic linkage of the arc to the subduction units is based on: (1) occurrence of accretionary-wedge terranes outboard (oceanward) of, and parallel to the various parts of the Khinghan arc; (2) formation of melange structures during the Early and mid-Cretaceous; and (3) where not disrupted by extensive Cretaceous movement, dipping of melange structures and bounding faults toward and beneath the igneous units of the arc. Formation of the Khingan arc and related subduction is generally interpreted as ending in the late mid-Cretaceous when oblique subduction changed into sinistral-slip faulting along the outboard margin of the arc. REFERENCES: Ognyanov, 1986; Vrublevsky and others, 1988; Natal'in, 1991, 1993; Nokleberg and others, 1994, 1997, 1998, 2000, 2003; Nechaev and others, 1996; Sengor and Natal'in, 1996; Gonevchuk and others, 1998. Badzhal-Komsomolsk MetallogenicBelt of Sn-W Greisen, Stockwork, andQuartz Vein, Cassiterite-Sulfide-SilicateVein and Stockwork, Cu (±Fe, Au, Ag, Mo)Skarn, and Porphyry Mo (±W, Sn, Bi)Deposits(Belt BKS) (Russia, Far East)This Late Cretaceous metallogenic belt is related to veins and replacements in the Khingan-Okhotsk volcanic-plutonic belt. The major deposits are at Pravourmiyskoe, Solnechnoe, Festivalnoe, and Sobolinoye. Solnechnoe Sn-W Greisen, Stockwork, and Quartz Vein MineThis mine (Ognyanov, 1986) consists of highly altered quartz-tourmaline zone numerous apophyses and occurs along, and is related to a long north-south-striking, left-lateral, strike-slip fault. The zone ranges varies from 0.5 to 15 m thick, is 800 m long, and extends deep more than 500 m deep. Five vertically-zoned mineral assemblages occur, from bottom to top: (1) quartz-tourmaline; (2) quartz-arsenopyrite-cassiterite with wolframite, bismuthinite, and scheelite; (3) quartz-sulfide (pyrrhotite, chalcopyrite, and marcasite); (4) quartz-galena-sphalerite; and (5) quartz-carbonate. The deposit is closely related to a K-rich granite phase of a gabbro, diorite, granodiorite complex with a K-Ar isotopic age of 75 to 86 Ma. The deposit is medium size with an average grade of 0.56% Sn, 0.05% W, and 0.1% Cu. The deposit has been mined since 1960's and is mostly exhausted. Sobolinoye Sn-W Greisen, Stockwork, and Quartz Vein DepositThis deposit (G.E. Usanov, written commun., 1987; Onikhimovskiy and Belomestnykh, 1996) occurs in the northern part of Amutsk volcanic basin in a fault-bounded district that covers an anrea of 5.4 km2. The deposit is bounded by the Leningradskiy thrust that dips west at a low angle (48o) and contains mylonite tectonic breccias. Along the thrust, folded Jurassic flysh is overthrust by Late Cretaceous andesite, dacite, and rhyolite. Units along the thrust are intruded by Late Cretaceous a diorite and quartz-diorite stock and dikes. Sedimentary and volcanic, and intrusive rocks are cut by generally steeply-dipping (60 to 80o) fracture zones that occur in or near the thrust in feathering, strike-slip faults. The deposit contains about ten fracture zones quartz-tourmaline, quartz-sericite, and quartz-chlorite. Zones range up to 1.1 km long and about 3 to 7 m thick, with some ranging up to 60 m thick. The deposit contains Sn, W, Cu, Bi, Ag, and economic In. Quartz-tourmaline forms an older mineral assemblage that grades upward into: (1) quartz-cassiterite with arsenopyrite; (2) quartz-pyrrhotite-chalcopyrite with stannite, fluorite, and magnetite; (3) quartz-galena-sphalerite; and (4) quartz-fluorite-calcite. Host rocks are generally altered to quartz-sericite and quartz-chlorite alteration in the upper parts of the deposit. The deposit is large with an average grade of 0.3-0.7% Sn, 0.53% Cu, 0.06% WO3, 0.014% Bi. Pravourmiskoe Sn-W Greisen, Stockwork, and Quartz Vein DepositThis deposit (Ognyanov, 1986) consists of disseminations and veins that occur in a linear area over 1,500 m long, 5 to 25 m thick, and extends several hundred m down dip. An earlier ore assemblage consists of quartz-topaz-cassiterite with fluorite, and a later assemblage consists of quartz-arsenopyrite-chalcopyrite, and quartz-tourmaline with cassiterite and stibnite. The deposit contains Sn, W, and Cu; Bi, Pb, and Sb. Gangue mineral assemblages are quartz-siderophyllite (zwitters) with quartz-topaz greisen. The deposit occurs along an east-west-trending thrust fault with small offset, and is hosted in, and is genetically related to Late Cretaceous felsic volcanic rock that overlie the large, shallow, granite and leucogranite complex of the Verkhneurmiisky batholith with K-Ar isotopic ages of 75 to 85 Ma. The granite has a Rb-Sr isochron age of 95 to 83 Ma and an initial Sr ratio of 0.703 to 0.708. The deposit is medium size with an average grade of 0.1 to 5% Sn, 0.05% W03, and 0.5% Cu. Origin and Tectonic Controls for Badzhal-Komsomolsk Metallogenic BeltThe belt is interpreted as forming during generation of granitoids along the Khingan transform continental-margin arc that is related to oblique subduction of ancestral Pacific Ocean plate. The Khingan-Okhotsk volcanic-plutonic belt that hosts the metallogenic belt, is divided into two main sequences: (1) Berriasian to Cenomanian calc-alkalic andesite and minor tholeiitic basalt, with coeval gabbro, diorite. and granodiorite; and (2) Late Cretaceous (mainly pre-Senonian) K-rich felsic volcanic rock, tuff, and ignimbrite, and coeval subvolcanic intrusive and granitoids plutons. The Cretaceous granitoids include granite, leucogranite, and composite gabbro, diorite, granodiorite that are coeval and comagmatic with volcanic rock. Both suites exhibit high K contents. The Khingan-Okhotsk belt overlies the Turan and Malokhingask terranes of the Bureya continental-margin arc superterrane, and Badzhal and Ulban accretionary-wedge terranes. REFERENCES: Ognyanov, 1986; Nokleberg and others, 1994, 1997, 1998, 2000, 2003; Lebedev and others, 1994; Rodionov, 2000. |