By Sergey M. Rodionov1, Alexander A. Obolenskiy2
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Hidaka Metallogenic Belt ofCyprus Cu-Zn Massive Sulfide andBesshi Cu-Zn-Ag Massive SulfideDeposits(Belt HD) (Japan, Hokkaido)This Middle Cretaceous to Eocene metallogenic belt is related to stratiform units in in the Hidaka belt of the Shimanto accretionary wedge terrane. The belt occurs in the central part of the Hokkaido island, trends north-south for more than 350 km, and ranges from 20 to 70 km wide. The belt is hosted in a Cretaceous and Paleogene accretionary complex. The northern Hidaka belt contains mainly clastic rocks, and the southern Hidaka belt contains the Hidaka metamorphic rock. Saito (1958) defined this belt as the Main Central Hokkaido belt, and Tsuboya and others (1956) used the name Hidaka metallogenic province that also contained the Kamuikotan metallogenic belt of present study. Saito and others (1967) used the name Central Hokkaido metallogenic province with similar definition as for the Hidaka metallogenic province. The Hidaka metallogenic belt contains at least ten Cyprus type massive sulfide deposits (Saito, 1958), but most are small and not included in the database. The major deposit is the Shimokawa Besshi Cu-Zn-Ag massive sulfide deposit. Besshi Cu-Zn-Ag Massive Sulfide DepositThis deposit (Suyari and others, 1991; Watanabe and others, 1998) consists of four srtratiform ore bodies. The Main Motoyama body extends 1,600 m along strike and 2,000 m down dip, and has dimensions of 3,000 by 11,000 m. Average thickness is 2.4 m with a maximum thickness of 15 m. The ain ore minerals are pyrite, chalcopyrite, bornite, and magnetite. Gangue minerals are chlorite, hornblende, glaucophane, and quartz. Deposit hosted in pelitic schist of Cretaceous Sambagawa Metamorphic Rocks. Mafic schist and piedmontite schist occur the ore zone. Geochemistry indicates mafic schist derived from basalt that formed in an oceanic intra-plate or constructive plate margins. Age of peak of metamorphism is 110 Ma according to Rb-Sr and K-Ar isotopic studies. Possible age for submarine basaltic volcanism and deposit formation is 200 Ma (Late Triassic) to 140 Ma (Jurassic). Deposit was discovered in 1690. The deposit is large with a grade of 1.0-1.8% Cu, 0.1-1.4% Zn, 11.9-40% S, 0.3-0.7g/t Au, 7-20g/t Ag. The deposit has produced 706,000 tonnes Cu, and has reserves of 8,000,000 tonnes. Shimokawa Besshi Cu-Zn-Ag Massive Sulfide DepositThis deposit (Mining and Metallurgical Institute of Japan, 1965; Kato and others, 1990; Mariko and Kato, 1994) consists of of seven sulfide bodies that occur along the same stratigraphic horizon. The horizon strikes north-south, and dips 50 to 60oeast. The sulfide bodies occur along a 1,800 m long zone. Average thickness of the bodies is 5.2 m with a maximum of 30 m. The main ore minerals are pyrite, chalcopyrite, pyrrhotite, sphalerite, and magnetite. Minor ore minerals are cubanite, valleriite, cobalt-bearing pentlandite, and cobaltite. Gangue minerals are quartz, chlorite, sericite, and cabonate minerals. The deposit occurs between tholeiitic pillow basalt and slate of the Cretaceous Hidaka Group. Tholeiitic rocks show geochemical similarity to mid-ocean ridge basalt or marginal basin basalt. Host rocks are altered from zeolite to amphibolite facies. The deposit is medium-size with average grade of 2.3% Cu, 0.8% Zn, 0.22%Co, and 20.3% S. 6,800,000 tonnes ore was produced from 1941-1982. The main mining occurred from 1941 to 1982. Origin and Tectonic Controls for Hidaka Metallogenic BeltThe belt is interpreted as forming in basalt generated along the Kula-Pacific ridge. Subsequently, the host rocks and deposits were structurally incorporated into the Shimanto accretionary wedge terrane. The basalt associated with the deposits has geochemical characteristics of N-type MORB (Miyashita and others, 1997). The ages of basalt are interpreted as mid-Cretaceous to Eocene. The basalt occurs in clastic sedimentary rock, suggesting occurrence of a spreading ridge near a subduction zone (Miyashita and others, 1997). The deposits in the belt are interpreted as forming during this magmatism along the Kula-Pacific ridge that was being subducted under the East Asia continental margin REFERENCES: Tsuboya and others, 1956; Saito, 1958; Saito and others, 1967; Miyashita and others, 1997. Inner Zone Southwest Japan MetallogenicBelt of Zn-Pb (Ag, Cu, W) Skarn, W-Mo-BeGreisen, Stockwork, and Quartz Vein,W±Mo±Be skarn, Cu (±Fe, Au, Ag, Mo) Skarn,Porphyry Mo (±W, Sn, Bi), PolymetallicPb-Zn ±Cu (± Ag, Au) Vein and Stockwork,Fluorspar Vein, and Metamorphic GraphiteDeposits(Belt ISJ) (Japan)This Cretaceous to Paleogene metallogenic belt is related to veins and replacements in Nohi rhyolitic volcanic belt and Hiroshima granitic belt that overlie and intrude the Hida, Sangun-Hidagaien-Kurosegawa, Akiyoshi-Maizuru, Mino-Tamba-Chichibu terranes (some too small to show at 15 M scale). The metallogenic belt occurs in the western part of Honshu Island and northern Kyushu Island, trends east-northeast to west-southwest for more than 1,000 km, and ranges up to 150 km wide. The eastern margin is bounded by the Tanakura tectonic line, and the Kitakami metallogenic belt is interpreted as eastern extension of the Inner Zone Southwest Japan metallogenic belt. The belts contains a large number of skarn deposits (Kamioka Tochibara deposit), and polymetallic veins (Ikuno deposit). Tsuboya and others (1956) used the name Inner Zone Southwest Japan metallogenic province in a similar as in this study. However, Ikuno and Akenobe deposits were excluded because being interpreted as Neogene at that time. The Ikuno and Akenobe deposits are included in the Inner Zone Southwest Japan metallogenic belt. Kamioka Mozumi Zn-Pb (Ag, Cu, W) Skarn MineThis mine (Akiyama, 1980; Akiyama, 1981; Nagasawa and Shibata, 1985; Sato and Uchiumi, 1990; Kato, 1999) consists of more than 18 skarn bodies that occur in masses, stratiform layers, and veins. The Main ore body is 300 m long, 400 m wide, and 10 m thick. The ain ore minerals are sphalerite, galena, chalcopyrite, magnetite, pyrite, and pyrrhotite with miner molybdenite and scheelite. The skarn minerals are hedenbergite,actinolite, diopside, garnet, wollastonite, and epidote. The skarn is clinopyroxene skarn that is replaced by garnet or by magnetite, calcite, and quartz. Replacements are likely related to deposition of Zn-Pb sulfides. Host rocks are crystalline limestone, diopside gneiss, amphibole gneiss, and amphibolite of the Hida Metamorphic Rock. K-Ar age for sericite from the Kamioka Tchibora and Kamioka Mozumi deposits are 63.8-67.5 + 0 Ma and a K-Ar age isotopic for hastingsite from skarn near the Kamioka Tchibora deposit is 63.3 + 1.6 Ma. Those ages suggest mineralization during the Late Cretaceous to Paleogene. Mineralization is related to the quartz porphyry or granite intrusion. The deposit was discovered in 1589. The deposit is medium size with production of 815,000 tonnes Zn, 52,000 tonnes Pb, 190 tonnes Ag. Average grade is 7.9% Zn, 2.68% Pb, 31 g/t Ag. Bandojima Cu (±Fe, Au, Ag, Mo) Skarn MineThis mine (Geological Survey of Japan, 1956; Mining and Metallurgical Institute of Japan, 1965) consists of nine skarn bodies that occur in masses and sheets. The Main ore body is 150 m long, 85 m wide, and 4 m thick. The main ore minerals are sphalerite, galena, chalcopyrite, and pyrrhotite. Skarn minerals are garnet and epidote. Host rocks are crystaline limestone, calcareous shale, and chert of the Hida Metamorphic Rock. Mineralization is related to intrusion of Mesozoic quartz diorite that occurs under the deposit. The deposit found before 1900. The deposit is small with production of 1,723 tonnes Zn, 1,464 tonnes Pb, and 105 tonnes Cu from 1952 to 1961 grading 10-15% Pb, 5-7% Zn, 1-2% Cu. The mine contains reserves of 600,000 tonnes ore. Kamioka Tochibora Zn-Pb (Ag, Cu, W) Skarn MineThis mine (Akiyama, 1980; Akiyama, 1981; Nagasawa and Shibata, 1985; Sato and Uchiumi, 1990; Kato, 1999) consists of more than 34 skarn bodies with local massive ore. The main ore body is 250 m long, 500 m wide, and 60 m thick. The main ore minerals are sphalerite, galena, chalcopyrite, matildite, magnetite, pyrite, and hematite. The minor minerals are molybdenite native silver, argentite, and scheerlite. Skarn minerals are hedenbergite,actinolite, diopside, garnet, wollastonite, and epidote. Host rocks are crystaline limestone, diopside gneiss, amphibole gneiss, and amphibolite of the Hida metamorphic rock. K-Ar ages of sericites from Kamioka Tchibora and Kamioka Mozumi deposits are 63.8-67.5 Ma and a K-Ar age of hastingsite from skarn near the Kamioka Tchibora deposit is 63.3 +/- 1.6 Ma. Those ages suggest mineralization took place at late Cretaceous-Paleogene. The mineralization may be related to the quartz porphyry. The deposit was discovered in 1580. Ikuno Polymetallic Pb-Zn ±Cu (± Ag, Au) Vein and Stockwork MineThis mine (MITI 1988; Shimizu and others, 1998) consists of more than 50 northwest and north-south striking polymetalic veins. The Main vein is 1,900 m long and with average width of 1.4 m. Veins occur in a area 8 km (east-west) by 6 km (north-south). The host rocks are rhyolite, andesite, and associated pyroclastic rock, and minor sedimentary rocks of Cretaceous-Paleogene Ikuno Group. A zonal distribution of metals occurs. From the center of the deposit to marginal are Cu, Cu-Zn, Zn, Pb-Zn, and Au-Ag assemblages. Sn and Sn-W zones also occur. Ore minerals are pyrargyrite, stephanite, native silver, native gold, and scheelite. Rare Se-bering benjaminite and matildite occur. Gangue minerals are quartz, calcite, fluorite, chlorite, siderite, and feldspar. Wall rocks are altered to quartz, chlorite, and sericite. A K-Ar isotopic age for adularia from the vein is 65.6 + 2.0 Ma and 63.0 + 1.9 Ma. The deposit was discovered in 807 and the mine closed in 1972. The mine is medium size with production of 47,000 tonnes Cu, 92,000 tonnes Zn, 19,000 tonnes Pb, 1,500 tonnes Sn grading 0.3 g/t Au, 60 g/t Ag, 1.4% Cu, 5% Zn, 0.8% Sn, 1.5% Pb. Otani W-Mo-Be Greisen, Stockwork, and Quartz Vein MineThis mine (Mining and Metallurgical Institute of Japan, 1968; Shibata and Ishihara, 1974; Imoto and others 1989) consists of northeast striking veins. The Main vein is 700 m long with average thickness of 1.5 m. The host rocks are Cretaceous granodiorite. The main ore minerals are scheelite, cassiterite, chalcopyrite, arsenopyrite, pyrite, pyrrhotite, sphalerite, and stannite. Gangue minerals are mainly quartz, calcite, muscovite, and fluorite. Greisen alteration occurs in the wall rocks. Deposit formed during intrusion of Cretaceous granite. K-Ar isotopic age of muscovite from the vein is 91 Ma. Deposit was found in 1912 and mine closed in 1983. The mine is medium size production of 776,000 tonnes ore (from 1951-1971) with an average grade of 0.46% WO3, 0.26% Cu, 0.11% Sn. Origin and Tectonic Controls for Inner Zone Southwest Japan Metallogenic BeltThe belt is interpreted as forming during generation of granitoids along the East Asia magmatic arc related to subduction of of Kula and Pacific plates. The deposits in the belt are interpreted as forming during siliceous granitoid magmatism. Granitoids in the Inner Zone of Southwest Japan are classified into three belts, from south to north, the Ryoke, Sanyo, and Sanin belts. Granitoids in the Ryoke and Sanyo belts are typically ilmenite-series, and those in the Sanin are magnetite-series (Ishihara and others, 1992). Ages of granitoids from the Ryoke and Sanyo belts are Cretaceous, however, those of the Sanin belt are mostly Paleogene. Deposits are not related to granitoids of Ryoke belt. Granitoids in the Sanyo belt host W-Sn-Cu skarn or veins deposits. Ishihara (1978) defined a W-Sn-Cu metallogenic province for this belt. Mo-Pb-Zn deposits characterize the Sanin belt, and were defined as a Mo-Pb-Zn metallogenic province by Ishihara (1978). The Inner Zone Southwest Japan metallogenic belt is thereby be divided into two units, the southern W-Sn-Cu Sanyo belt, and the Mo-Pb-Zn Sanin belt. REFERENCES: Tsuboya and others, 1956; Ishihara, 1978; Ishihara, Sasaki, and Sato, 1992. |