By Sergey M. Rodionov1, Alexander A. Obolenskiy2
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MIOCENE THROUGH QUATERNARYMETALLOGENIC BELTS (24 to 0 Ma)Northeast Hokkaido Metallogenic Beltof Au-Ag Epithermal Vein, Volcanic-Hosted Hg, Hg-Sb-W Vein and Stockwork,and Clastic Sediment-Hosted Hg±SbDeposits(Belt NEH) (Japan, Hokkaido)This Miocene to Quaternary metallogenic belt is related to veins and replacements in the Quaternary Japan volcanic belt and in the Japan Cenozoic sedimentary basin that overlies and intrudes the Hidaka zone of the Shimanto accretionarry wedge terrane. The metallogenic belt occurs in northeastern Hokkaido island in an area that is 250 km by 130 km and extends to the east of the study area Saito (1958) defined five districts in the Northeast Hokkaido belt. The Kitami metallogenic province of Urashima (1961) is similar to this study but excludes Quaternary deposits. Saito and others (1967) defined a Northeast Hokkaido metallogenic province for Neogene deposits in the area, and Yahata and others (1999) named the Northeast Hokkaido metallogenic province of Quaternary epithermal vein deposits. Most of deposits of the metallogenic belt occur in the Monbetsu-Kamishihoro Graben that ranges from 10 to 60 km wide and trends for 120 km north-south in the middle of the belt. The Kitami district of Saito (1958) covers the graben. The Utoro and Ohmu districts of Saito (1958) occur in the northwestern Northeast Hokkaido metallogenic belt and include the Motokura Pb-Zn-Cu deposit and some gold deposits. The districts also occur in the basins as indicated by gravity data (MITI, 1994). Au epithermal deposits also occur near the Quaternary volcanic front. Limonite and sulfur deposits are associated with the volcano but are not described in the mineral deposit database. Ages of epithermal deposits vary from 14.4 Ma to 0.3 Ma, and tend to young southward (Yahata and others, 1999). The ages of deposits indicate two stages of deposits in the belt, an early stage (14.4 to 11.2 Ma) and a late stage (8.1 to 0.3 Ma). The belt contains Au-Ag epithermal vein deposits (Konomai), volcanic-hosted Hg deposits (Itomuka), and Pb+Zn+Cu veins (Saito). Konomai Au-Ag Epithermal Vein MineThis mine (Kato and others, 1990; Mining and Materials Processing Institute of Japan, 1990; Maeda, 1990) consists of of east-west and northeast striking quartz veins. More than 18 veins occur in an area 15 by 5 km. One typical vein is 10 thick m and 2,100 m long. The veins mainly consists of quartz, chalcedony, calcite, and adularia. The main ore minerals are native gold, native silver, argentite, and miargyrite. Minor ore minerals are chalcopyrite, galena, and sphalerite. Theveins are hosted in Miocene rhyolitic tuff, mudstone and altered andesite. A K-Ar age isotope age for adularia from the vein is 12.9 + 0.4Ma. Deposit was discovered in 1915 and the mine closed in 1973. The deposit is medium size with production of 11,486,000 tonnes ore, 73.2 tonnes Au, 1,240 tonnes Ag from 1917-1973 with an average grade of 6.4 g/t Au and 108 g/t Ag. Itomuka Volcanic-Hosted Hg MineThis mine (Saito and others, 1967; Kishimoto, 1975) consists of disseminated and vein ore bodies that occur along faults. The ore bodies occur in a area 3 km east-west by 1.5 km north-south. A typical ore body has an average thickness of 6 m and length of 140 m. The main ore minerals are native mercury and cinnabar. Quartz, calcite, pyrite, and marcasite also occur. The deposit is hosted in altered Miocene andesite. Miocene rhyolite occurs near the deposit and is part of host rock sequence. The deposit was discovered in 1936, and was largest Hg mine in Japan. The mine is medium size with production of 3,300 tonnes Hg grading 0.35% Hg. Ryushoden Hg-Sb-W Vein and Stockwork MineThis mine (Mining and Metallurgical Institute of Japan, 1968; Kato and others, 1990) consists of dissemination that occur along faults. Pyrite, cinnabar, and calcite veins occur in the disseminated zone. The main ore mineral is cinnabar and minor ore minerals are native mercury and pyrite. Gangue mineals are quartz, chlorite, and calcite. The deposit is hosted in Miocene sandstone. Rhyolite is present southwest of the deposit and may be related to the deposit. The deposit is medium size with production of 880 tonnes Hg (from 1947-1974). Average grade is 0.27% Hg. Origin and Tectonic Controls for Northeast Hokkaido metallogenic beltThis belt is interpreted as forming along an island arc related to subduction of the Pacific Plate beneath eastern Hokkaido Island. Deposits in formed during Miocene and Quaternary island arc volcanism and related hydrothermal activity. REFERENCES: Saito, 1958; Urashima, 1961; Saito and others, 1967; Yahata and others, 1999. Northeast Japan Metallogenic Belt ofVolcanogenic Zn-Pb-Cu Massive Sulfide(Kuroko, Altai types),Au-Ag Epithermal Vein,Sulfur-Sulfide (S, FeS2),Polymetallic (Pb, Zn±Cu, Ba, Ag, Au)Volcanic-Hosted Metasomatite,Polymetallic Pb-Zn ± Cu (±Ag, Au) Vein andStockwork, Mn vein, Volcanogenic-Sedimentary Mn, Chemical-SedimentaryFe-Mn, and Limonite from Spring WaterDeposits(Belt NEJ) (Japan)This Miocene to Quaternary metallogenic belt is related to layers and veins in the Quaternary Japan volcanic belt and Japan Cenozoic sedimentary basin that overlie and intrude the Hiroshima granitic plutonic belt, and the Mino-Tamba-Chichibu and South Kitakami terranes. The belt occurs in the western part of northeastern Honshu and southwestern Hokkaido Islands, trends north-south for more than 1,300 km, and varies from 100 to 150 km wide. The belt extends into the Izu-Bonin island arc. Most of the associated deposits occur in Miocene volcanic rock in the Neogene sedimentary basin. The volcanic rock is mostly altered and is generally described as the Green Tuff. The southwestern margin of the belt in Honshu Island is bounded by the Itoigawa-Shizuoka tectonic line. The belt contains a large number of Kuroko deposits (Kosaka, Shakanai), Au-Ag epithermal vein deposits (Sado), polymetallic vein deposits (Hosokura), and sulfur-sulfide (S, FeS2) deposits. Iwasaki (1912) used the name Kosaka metallogenic province that covers most of the Northeast Japan metallogenic belt of this study. Watanabe (1923) also used the name Kosaka metallogenic province and slightly modified definition as the Ikuno-Kosaka metallogenic province. Tsuboya and others (1956) used the name Hokkaido-Northeast Japan Green Tuff metallogenic province with four provinces: Nemuro-Shiretoko province (in eastern Hokkaido Island); Kitami province (in northeastern Hokkaido Island); Inner Zone of Northeast Japan province; and Fossa Magna province (major graben in central Honshu Island). The Northeast Japan metallogenic belt of this study contains the Inner Zone of Northeast Japan province and the Fossa Magna province. Ishihara (1978) classified three metallogenic provinces in an area that is similar to this belt on the basis of metals in the deposits: Mn Au-Ag-Cu-Pb-Zn province in southwestern Hokkaido Island; Au-Ag-Cu-Pb-Zn province in northern Honshu Island; and Ag-Pb-Zn province for central Japan. Many Kuroko-type deposits occur in Hokuroku area in Akita Prefecture, northern Honshu. These deposits formed in the middle Miocene at around 13 Ma. Available K-Ar ages of vein deposits suggest two stages of ore formation: an early stage (15 to 10 Ma); and a late stage (8 to 2 Ma). Sulfur-sulfide (S, FeS2) and limonite deposits formed along with Quaternary volcanoes. Tsuboya and others (1956) defined sa eparate Pleistocene-Holocene metallogenic province around the volcanoes that is herein included in the Northeast Japan metallogenic belt. Ashio Polymetallic Pb-Zn ± Cu (±Ag, Au) Vein and Stockwork MineThis mine (Shibata and Ishihara, 1974; Omori and others, 1986) consists of northeast, east-northeast, and east-west striking veins. Eight main vein systems occur. Each vein system consists of 100-300 veins. About 1,400 veins were minned. The Main vein is 2,100 m long and 0.2 m thick. The host rocks are Miocene rhyolite (Ashio Rhyolite) that occurs as a slightly elongated circular shape (4.4 by 3.3 km) on the surface and isfunnel-shaped. Most of veins occur in the rhyolite. At depth the deposit extends into a Mesozoic accretionary complex. The main ore minerals are chalcopyrite, arsenopyrie, and pyrite. Minor ore minerals are bornite, chalcocite, covellite, pyrrhotite, sphalerite, galena, wolframite, cassiterite, stannite, bismuthinite, and native gold. Gangue minerals are mainly quartz, calcite, fluorite, and apatite. A zonal distribution of ore minerals occurs: a central zonewith Sn-W-Bi-Cu, an intermediate zone withCu-As-Zn, and a marginal zone with Zn-Pb-Cu-As minerals. Massive replacement ore bodies also occur Messozoic chert, and the ore minerals are similar to the veins. Wallrocks are altered to quartz, sericite, chlorite, and calcite. Quartz-sericite-calcite alteration is the most common. A K-Ar isotopic age for altered tuff is 14.8 + 1.1 Ma. The deposit was discovered in 1550, mining started around 1600 for Au, and the mine closed in 1973. The deposit is medium size with production of about 800,000 tonnes Cu, 4.5 tonnes Au, 600 tonnes Ag, and 22,000 tonnes Zn. Average grade is 20-30% Cu. Gumma Limonite MineThis mine (Geological Survey of Japan, 1954; Ota, 1957) occurs in the eastern foothill of Ksatsu-Shirane volcano above tuff breccia and andesite. The deposit is more than 10 m thick, and occurs along an old valley for 2,200 m long and is several tens to 200 m wide. The deposit formed by precipitation in the valley from a mineral spring from the Ksatsu-Shirane volcano. The ore mineral is limonite that is generally porous and reddish brown or dark brown. Jarosite occurs mainlyin the upstream part of the deposit. At the upper part of the deposit, mineral spring is still active. The deposit is small with production of 850,000 tonnes from 1950 to1955 , and resources of about 2,000,000 tonnes. Average grade is 49% Fe. Horobetsu Sulfur-Sulfide (S, FeS2) MineThis mine (Ota, 1954; Saito and others, 1967) consists of three ore connected bodies. The ore bodies are about 300 m long, 150 m wide, and 10-20 m thick. The host rock is Pliocene andesite lava. The ore minerals are native sulfur and pyrite. One ore body is consists of pyrite that occurs above the sulfur ore body. The deposit is surrounded by alteration zones, including opal, allunite, and kalonite. The deposit was discovered in 1902. The deposit is small production of 1,571,000 tonnes ore grading 39.7% S. Hosokura Au-Ag Epithermal Vein MineThis mine (Shikazono and Tsunakawa, 1982; Kawakami and others, 1986; Takahashi, 1988) consists of 13 main vein systems that strike east-west, north-south, and northwest. The veins occur in an area 4 km by 5 km. The Main Vein is 2,200 m long and 1.3 m thick. The main ore minerals are sphalerite, galena, chalcopyrite, tetrahedrite, pyrargyrite, stibnite, pyrite, marcasite, pyrrhotite, magnetite, hematite, chalcocite, covellite, native copper, and native silver. Gangue minerals are mainly quartz, chlorite, sericite, kaolin, calcite, montmorillonite, and fluorite. Wall rocks are latered to quartz, K-feldspar, albitized plagioclase, chlorite, sericite, kaolin, montmorillonite, and calcite. The host rocks are Miocene altered andesite and tuff. A K-Ar adularia age for the vein is 5.8 + 0.2Ma and for adularia from the host dacite is 9.7 U 0.5 Ma. The deposit was discovered in the early Ninth Century and the mine closed in 1987. The deposit is medium size with production of 26,000,000 tonnes ore, 775,000 tonnes Zn, 280,000 tonnes Pb, 400 tonnes Ag, 1 tonnes Au, and 9,500 tonnes Cu. Average grade is 4.12% Zn, 1.59%Pb, 0.05% Cu, 0.2 g/t Au, 40 g/t Ag. Kinjo Volcanogenic-Sedimentary Mn MineThis mine (Saito and others, 1967; Suzuki and others, 1969) consists of a horizontal stratiform ore body. Maximum thickness is 3 m. The deposit extends 120 m north-south and 100 m east-west. The ore body occurs between a lower greenish Miocene tuff breccia and an upper hornblende dacite and mudstone. Mn minerals were deposited in the Miocene. The ore minerals are psilomelane and pyrolusite. Gangue minerals are quartz and calcite. Deposit was discovered in 1952. The mine closed in 1961. The deposit is small with production of 2,289 tonnes MnO2 (from 1953-1955), and 4,699 tonnes Mn (from 1955-1958). Average grade is 53.79% MnO2. Kosaka Volcanogenic Zn-Pb-Cu Massive Sulfide (Kuroko, Altai types) MineThis mine (Oshima and others, 1974; Hashiguchi, 1983; Nakajima, 1989) consists of three main ore bodies, Motoyama, Uchinotai, and Uwamuki. The Motoyama body is 600 m long, 250 m wide, and 30 m thick. The Uchinotai ore body is 700 m long, 400 m wide, and 20 m thick. The kuroko deposit is divided into three type of ore, kuroko (narrow definition), yellow, and siliceous ores. The main ore minerals of the kuroko are chalcopyrite, pyrite, galena, sphalerite, and tennantite. The main ore minerals of the yellow and siliceous ores are pyrite, chalcopyrite, sphalerite , bornite, chalcocite, and covellite. Minor minerals are quartz and barite. Barite is enriched at the top of kuroko deposit. Host rocks are Miocene rhyolite and rhyolitic tuff. The Motoyama ore body was discovered in 1861. The Uchinotai ore body was discovered 1959. The deposit is medium size with production of 510,000 tonnes Cu, 520,000 tonnes Zn, 150,000 tonnes Pb, and reserves of 30 million tonnes. Average grade is 8.48% Zn, 2.84% Pb, 2.59% Cu, 1.15 g/t Au, 184.7 g/t Ag. Shakanai Volcanogenic Zn-Pb-Cu massive sulfide (Kuroko, Altai type) DepositThis deposit (Ohtagaki and others, 1974; Tanimura and others 1983; Nakajima, 1989) consists of eleven main bodies. The bodies are located in area of 4 km long, 2 km wide, with typical depth of 200 m. Main deposit minerals of the kuroko (black ore) are chalcopyrite, pyrite, galena, sphalerite, tetrahedrite and tennantite. Main deposit minerals of the yellow and siliceous ores are pyrite, chalcopyrite and small amont of sphalerite and galena. Siliceous and gypsum ore occurs below the unite of black ore and yellow ore. Minor minerals are quartz and barite. Host rock is Miocene rhyolite, rhyolite tuff and mudstone. Matsuki, Takadate, Takadate South deposits occur several hundred m W of the Shakanai deposit. Deposit was discovered in 1961. Mine closed in 1987. The deposit is medium size with an average grade of 3.3% Zn, 2.15% Cu, 0.9% Pb, 0.35 g/t Au, 77 g/t Ag. The deposit has produced 320,000 tonnes Zn, 130,000 tonnes Cu, 670,000 tonnes Pb, and has reserves of 30 million tonnes. Sado Au-Ag Epithermal Vein MineThis mine (Shikazono and Tsunakawa, 1982; Mining and Materials Processing Institute of Japan, 1994a) consists of seven main east-west striking veins. The main vein is 2,100 m long and 6 m wide. Host rocks are Miocene dacite tuff, andesitic tuff, and mudstone. The main ore minerals are native gold, argentite, pyrargyrite, pyroustite, miargyrite, chalcopyrite, tetrahedrite, pyrite, galena, and sphalerite. Gangue minerals are mainly quartz, chalcedony, calcite, barite, adularia, rhodochrosite, gypsum, and sericite. Wall rocks are altered to chlorite, albite, sericite, quartz, and pyrite. K-Ar adularia ages for the vein are 134 + 0.5 and 14.5 + 0.5 Ma. The deposit was discovered in 1601 and the mine closed in 1989. The deposit is medium size with production of 78 tonnes Au, 2,330 tonnes Ag, 5,400 tonnes Cu, and 15,300,000 tonnes ore. Average grade is 1-5 g/t Au, 30-100 g/t Ag, 0.1-0.3% Cu. Toyoha Au-Ag Epithermal Vein MineThis mine (Mining and Metallurgical Institute of Japan, 1968; Kuwahara and others, 1983; Kato and others, 1990) consists of east-west and northwest striking veins. About 50 veins are present in the area 2km east-west by 3km north-south. Veins have maximum thickness of 4m and about 1300m long. Main ore minerals are sphalerite, galena, pyrite, and rhodochrosite. Minor ore minerals are chalcopyrite, hematite, pyrrhotite, stibnite, and marcasite. Indium minerals are found in the ore. The gangue minerals are quartz and small amounts of chlorite and calcite. Wall rocks altered to quartz, chlorite, and sericite. The deposit was one of the largest mines in Japan. Deposit is hosted in Miocene pyroclastic rocks. K-Ar age of sericite in the vein is 2.2 Ma. The deposit is medium size with an an average grade of 9.6% Zn, 3.4% Pb, 179g/t Ag. The mine produces 12,000,000 tonnes ore with 1,400 tonnes Ag, 300,000 tonnes Pb, 780,000 tonnes Zn. Reserves of 13,000,000 tonnes ore grading 7.0% Zn, 2.1% Pb, 124g/t Ag. Origin and Tectonic Controls for Northeast Japan Metallogenic BeltThe volcanogenic massive sulfide deposits interpreted as forming in back-arc region of an island arc related to subduction of the Pacific Plate beneath eastern Hokkaido Island. Pliocene Au-Ag epithermal vein deposits on Izu Peninsula formed in the Izu-Bonin island arc that accreted to Honshu Island before the formation of the deposits. Sulfur-sulfide and limonite deposits formed in the active island arc. Island arc magmatism is related to subduction of Pacific Plate. REFERENCES: Iwasaki, 1912; Watanabe, 1923; Tsuboya and others, 1956; Ishihara, 1978. |