By Sergey M. Rodionov1, Alexander A. Obolenskiy2
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Wutai Metallogenic Belt ofBanded Iron Formation(BIF, Algoma Fe) Deposits(Belt WT) (North China)This Archean metallogenic belt is hosted in marine volcaniclastic and sedimentary basins and greenstone belts of West Liaoning-Hebei-Shanxi terrane in the Sino-Korean Craton. The significant BIF deposits are at Baizhiyuan and Jinganku. This metallogenic belt occurs in the Wutaishan area in western Shanxi Province. The belt is is 200 km long and ranges up to 20 km wide. BIF deposits occur in the Baizhiyuan Formation and Jinganku Formation of the Wutai Group with isotopic ages of >2500 Ma). The host units are mafic and felsic volcanic rock, and sedimentary rock. The significant deposit is at Baizhiyuan. Baizhiyan Banded Iron Formation (BIF, Algoma Fe) DepositThis deposit (Shen Baofeng and others, 1994) consists of several stratiform layers that are concordant to the host amphibolite, mica schist and gneiss. Individual Fe layers are 30 to 50 m thick and range up to 3 to 5 km long. The ores are mainly banded and are composed of an oxide facies (magnetite and quartz), a silicate facies (magnetite, quartz, and grunerite), and a carbonate facies (siderite, ferrodolomite, and other minerals). The host units are part of the Late Archean Wutai Group that is derived from mafic and felsic volcanic rock, sedimentary rock, and canbyite formation in a greenstone belt regionally metamorphosed to greenschist facies. In the area of the deposit is a group of similar, moderate to large Fe deposits that occur in a northeast-trending belt. The deposit is large with reserves of 179.7 million tonnes with average grade of 33.31% Fe, 0.26% S, and 0.06% P. Origin and Tectonic Controls forWutai Metallogenic BeltThe Wutai greenstone belt that hosts the BIF deposits is interpreted as forming in an immature to mature island arc. The southwestern Archean Liaoning-Hebei-Shanxi terrane (Wutaishan area) that hosts the Wutai metallogenic belt of BIF deposits consists of the following major units: (1) greenstone belts consisting of fine-grained biotite gneiss, plagioclase amphibolite, metamorphosed ultramafic rock; chlorite schist, chlorite-albite schist, plagioclase quartzite, quartzite, and phylllite (Wutai Group); and (2) tonalite, trondhjemite, and granodiorite. The Wutai greenstone belt is interpreted as forming in a rift along a continental margin (Shen Baofeng and others, 1994). However, Luo Hui and Li Zenhui (1986) interpret the Wutai greenstone belt and related BIF deposits as forming in an immature to mature island arc. REFERENCES: Hui and Li Zenhui, 1986; Shen Baofeng and others, 1994. PALEOPROTEROZOIC METALLOGENIC BELTS(2500 to 1600 MA)Uguy-Udokanskiy Metallogenic Belt ofZoned Mafic-Ultramafic Cr-PGE(± Cu, Ni, Au, Co, Ti, or Fe),Sediment-Hosted Cu, and Ta-Nb-REEAlkaline Metasomatite Deposits(Belt UU) (Russia, Aldan-Stanovoy Shield)This Paleoproterozoic metallogenic belt is hosted in the West Aldan cratonal terrane and Kodar-Udokan basin. The belt occurs in the Olekma-Vitim Mountains along the Kalar, Udokan and Kodar ridges, and Udokan, Verkhne-Kalar and Verkhne-Chara basins. The belt extends for 250 km and ranges from 25 to 225 km. The Western Aldan cratonal terrane, known in Transbaikalia as the Chara block, consists of a 12-km-thick sequence of schist, gneiss, quartzite, local marble and amphibolite, and zones of granitized and metamorphosed volcanic and sedimentary rock, mafic and ultramafic intrusions, plagiogranite gneiss, plagiogranite, granite, migmatite and metasomatite (Chechetkin and others, 1995). The Paleoproterozoic Kodar-Udokan basin is composed of a 9 to 12 km thick sequence of carbonate and clastic units in the Paleoproterozoic Udokan complex, and metasomatic and intrusive granitoids and gabbros. The Udokan complex consists of: (1) carbonaceous sandstone and shale flysch (Kodar series); (2) variegated carbonate and siltstone and sandstone molasse (Chiney suite); and (3) variegated siltstone and sandstone molasse (Kemensky series). Sedimentary rocks are regionally and contact metamorphosed during granitization and variable-age magmatic events including: migmatitic granite of Kuandinsky complex, Kodar complex granitoids, and dikes; gabbro, anorthosite, and norite of the Chiney complex; alkaline metasomatite of the Katuginsky complex (all Proterozoic); ultramafic, mafic, and alkaline rocks of the Paleozoic Ingamakit-Sakunsky complex in the Baikal rift system; Mesozoic alkaline granitoids and nepheline syenite magmatic units in the Transbaikalia sedimentary and volcanic-plutonic belt. The major sediment-hosted Cu deposits, that occur in part of the Olekma-Vitim Cu metallogenic province, are at Burpalinskoye, Krasnoye, Udokan, Pravo-Ingamakit, Sakinskoye, Sulbanskoye, and Unkurskoye. The major zoned mafic-ultramafic Cr-PGE (± Cu, Ni, Co, Ti, or Fe) deposit is at Chiney, and the major This Nb-REE alkaline metasomatite deposit is at Katuginskoye that is related to the Paleoproterozoic Kuandinsky migmatite and granite complex, and REE deposits related to the Paleoproterozoic Kadar granitoid complex. The belt is fairly promising for Cu, Ti, Ni, V, Pt, Au, Ni, Ta, and REE deposits. Udokanskoye Sediment-Hosted Cu DepositThis deposit (Chechetkin, and others, 1985, 1995; Volodin and others, 1994) occurs in the Kodar-Udokan basin and has an isotopic age of 2.0 to 1.8 Ga (Arkhangelskaya, 1998). The sedimentary rock of the Udokan complex in the basin contain Cu-bearing stratigraphic layers at Chitkandinsky, Alexandrovsky, Sakukansky, Ikabiisky, and Neminginsky. The Cu layers are composed of quartz sandstone with lenses and beds of calcareous sandstone, siltstone, and argillite. These layers are concordant with host rocks and extend from several hundred m to a few kilometers and up to 21.4 km at the Udokan deposit. Deposits occur in beds, parting, lenses, and nests. Ore minerals occur as disseminations, veinlets, nests, semi-massive, and massive. The main ore minerals are chalcocite, covellite, bornite, chalcopyrite, pyrite, and pyrrhotite. Also occurring are Pb, Zn sulfides, and native gold and silver (Chechetkin and others, 1995). The deposit size is unknown and has an average grade of 1.86-2.43% Cu, 13.6 ppm Ag, 0.51 ppm Au, 0.0004% Tl. Usuu Sediment-Hosted Cu DepositThis deposit (Davydov and Chiryaev, 1986) consists of Cu occurrences in the Goruoda Formation that extends for 25 km along the eastern flank of the Uguy basin. The formation exhibits lagoonal and bar facies. Three thick horizons of Cu deposits occur. The lower horizon contains carbonate rock and sandstone. The deposit consists of rare Cu-sulfides in disseminations. The middle horizon contains quartz sandstone bearing, and more abundant Cu-sulfides in disseminations. Thickness of the horizon ranges locally up to 60 m with Cu grades of up to 1%. The upper horizon contains disseminated Cu-sulfides in brecciated sandy dolomite and cross-bedded sandstone with a carbonate matrix. The upper horizon is 84 m thick, and Cu grade is 0.11 to 1%. Ore minerals are chalcopyrite, bornite, chalcocine, and pyrite, with subordinate magnetite and hematite, and rare fahlore, covellite, galena, and native copper. Hypergeneic malachite, azurite, and chrysocolla also occur. The deposit is small. Chineyskoye Zoned Mafic-UltramaficCr-PGE (± Cu, Ni, Co, Ti, or Fe) DepositThis deposit (Melnikova and others, 1983; Gongalsky and others, 1995) occurs in the Chiney stratified gabbro and anorthosite pluton in the Chiney complex bearing that contains both Ti-Fe-V, Cu, and PGE deposits (Gongalsky and others, 1995). The Chiney pluton occurs at an intersection of sublatitudinal system of faults along the southern margin of the Kodar-Udokan basin and the northwestern-striking faults along the margin of the Kodar-Udokan zone. Cu sulfides occur in (1) thin laminated Ti magnetite; (2) highly alkaline rocks in the endocontact of the pluton; (3) leucogabbro; (4) sandstone; (5) skarn; and (6) tectonic zones. Chalcopyrite is predominant (90%). Occurring are endocontact disseminations (pyrrhotite-chalcopyrite, pyrite-chalcopyrite), and exocontact disseminations and masses (pyrrhotite-chalcopyrite, bornite-chalcopyrite and chalcopyrite). Ores minerals are pentlandite, sphalerite, minerals of linnaeite, arsenides, and sulfoarsenides. Disseminated Cu sulfides (1-3%) occurs in all varieties units of the Chineisky massif. The deposit is large with an average grade of 0.40-16.75% Cu, 0.1-72.0 ppm Pt; 1-255 ppm Pd; 0.15-9.60 ppm Au, 0.027-0.260% Ni; 0.005-0.01% Co. Katuginskoye Ta-Nb-REE Alkaline Metasomatite DepositThis deposit (Beskov, 1995; Sobachenko, 1998) contains Zr and cryolite and has an isotopic age of 2.0 to 1.6 Ga (Arkhangelskaya, 1998). The deposit is related to the Katuginsky alkaline metasomatite complex that occurs along a thick structural zone at the junction of Archean Stanovik and Paleoproterozoic Kodar-Udokan structures. The structural zone contains major faults and numerous ruptures, intrusive and extrusive rock of various compositions and with a wide range of metamorphic facies (greenschist to granulite), and granitoids formed by palingenesis, granitization, and alkaline metasomatism. The alkaline-granite REE metasomatite deposits formed during the latter event (Arkhangelskaya, 1974). The deposit consists of microcline-albite-quartz metasomatite with finely impregnated REE minerals. Deposit is divided into two blocks (Western and Eastern) by a northeast-striking fault. The eastern block is uplifted 400 m relative to the western block. In plan view, the ore body is triangular with outcrops of rocks elongated in western and southeastern directions. The internal structure of metasomatite bodies is conformable with structure of enclosing gneiss and schist. The thickness of metasomatites in Eastern body is 600 m, and Western body is over 900 m. Dark mineral assemblages are biotite, biotite-riebeckite, riebeckite-arfvedsonite, arfvedsonite-aegirine varieties of microcline-albite-quartz metasomatite. The main ore minerals are pyrochlore, zircon, rare-earth fluorite, gagarinite, and cryolite. The content of pyrochlore increases 10-fold from biotite through arfvedsonite to arfvedsonite-aegirine metasomatites (from 700 to 63,100 ppm). Chemical composition and REE concentrations (Ta, Nb, TR, Zr) indicate a deep, possibly mantle origin of solution forming alkaline metasomatites and associated economic REE deposit. The deposit is large. Origin and Tectonic Controls forUguy-Udokanskiy Metallogenic BeltThe Udokan basin that hosts this metallogenic belt contains thick (up to 10,000 m) clastic and minor carbonate rocks that are intrude by zoned mafic-ultramafic plutons and granite with isotopic ages of about 2.0 to 1.8 Ga. The rocks are deformed, folded, and zonally metamorphosed up to amphibolite facies. The Cr and PGE deposits that occur in zoned mafic-ultramafic plutons, and Cu deposits that occur in clastic sedimentary rocks are interpreted as forming along a passive continental-margin rift. The younger Ta-Nb-REE alkaline metasomatite deposits are interpreted as forming during later collision and intrusion of anatectic granite. REFERENCES: Bogdanov and Apol'sky, 1988; Chechetkin and others, 1995; Arkhangelskaya, 1998; Parfenov and others, 1999, 2001. |