日本西南部四国增生复合体中的锰矿分布 Manganese Deposits Distributed in the Accretionary Complexes of Shikoku, Southwest Japan

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2012 年 10 月地球学报 Oct. 2012 第 33 卷增刊 1: 50-54 Acta Geoscientica Sinica Vol.33 Supp.1: 50-54 www.cagsbulletin.com www.地球学报.com doi: 10.3975/cagsb.2012.s1.25

Masaharu NAKAGAWA Department of Natural Science, Faculty of Science, Kochi University, Kochi 780-8520, Japan

Abstract: Bedded manganese ore deposits occur in many localities within the accretionary belts of the Shikoku region, SW Japan. The deposits occur mostly in bedded chert or its metamorphosed equivalent. These chert-hosted manganese deposits are considered to have been manganese nodule/crust-bearing siliceous sediments on deep-sea floor and have been converted to manganese ores by low-grade metamorphism through subduction-accretion process. The mineral assemblages of the ores reflect the metamorphic grade of the accretionary complexes. On the other hand, iron-manganese deposits and some manganese deposits occurring directly over basalt are considered to have been the hydrothermal precipitates associated with submarine volcanism. Key words: Manganese deposit; Accretionary complex; Shikoku; Metamorphism; Deep-sea manganese nodule/crust

Matsuoka et al., 1998; Isozaki et al., 2010). The Ryoke 0 Introduction metamorphic belt is distributed on the north of the Many bedded manganese and iron-manganese ore Median Tectonic Line (MTL) and is occupied by Cre- deposits occur in the accretionary complexes of the taceous granite and low-P/T type gneiss. The Sanba- Japanese Islands. These deposits are closely associated gawa metamorphic belt, on the south of MTL, is a with chert beds and accompanied by greenstone. Many high-P/T type regional metamorphic belt. It is com- workers studied the ore deposits in the 1950-1970’s posed of basic, quartz, pelitic and psammitic schists of (e.g. Yoshimura, 1952, 1969; Watanabe et al., 1970; the greenschist to eclogite facies. The southernmost Miyahisa and Sawamura, 1973; Nambu, 1980), and part of the Sanbagawa belt, which was once called considered that these were formed by hydrothermal Mikabu belt, is composed mainly of greenstone (me- alteration accompanied by greenstone volcanism, or tabasalt). The Chichibu belt is divided into the North were deposited accompanied by basic volcanismCAGS in Chichibu, Kurosegawa and South Chichibu belts. The geosynclines. Recently, based on the new concepts on North Chichibu belt comprises the Early-Middle Ju- accretion tectonics, we proposed a new model for the rassic accretionary complexes and has been subjected genesis of the Mn-bearing ore deposits in Japan (Na- to low-grade metamorphism of the prehnite-pumpe- kagawa et al., 2011). In the Shikoku region of SW Ja- llyite to pumpellyite-actinolite facies. The South Chi- pan, several accretionary belts are distributed and chibu belt comprises the Middle Jurassic to Early characterized by different grades of regional meta- Cretaceous accretionary complexes. These complexes morphism. Manganese ore deposits occur in many of North and South Chichibu belts are composed of localities within the accretionary belts. In the present terrigenous clastic rocks containing older oceanic study, the ore deposits have been re-examined based blocks of chert, limestone and greenstone. The south- on new field and laboratory investigations. ernmost region of the Shikoku is occupied by the Shimanto belt which comprises the clastics-dominated 1 Accretionary belts of Shikoku accretionary complexes. The Shimanto belt is divided The locations of the manganese and into the Cretaceous North Shimanto and Tertiary South iron-manganese ore deposits are shown together with Shimanto belts. the geotectonic subdivision of Shikoku in Fig. 1. The 2 Distribution, occurrence and age of Shikoku Island is composed of several accretionary belts which display various grades of regional meta- manganese deposits morphism. Many geologic studies were carried out on The bedded manganese and iron-manganese de- the accretionary complexes (e.g. Suyari et al., 1991; posits are distributed in the Sanbagawa, Mikabu, North

E-mail: [email protected]. Supp.1 Masaharu NAKAGAWA: Manganese Deposits Distributed in the Accretionary Complexes of… 51

Fig. 1 Distribution of manganese, iron-manganese and Besshi-type cupriferous deposits shown within the generalized geological framework of Shikoku, SW Japan (modified from Nakagawa et al., 2009). ●: manganese deposit. ●: iron-manganese deposit. ■: Besshi-type cupriferous deposit. 1-14: the mine number mentioned in Table 1. MTL: Median Tectonic Line. BTL: Butsuzo Tectonic Line. Ryoke: Ryoke metamorphic belt. Sanbagawa: Sanbagawa metamorphic belt. Mk: Mikabu greenstone. N. Chichibu: North Chichibu belt. Kr: Kurosegawa belt. S. Chichibu: South Chichibu belt. N. Shimanto: North Shimanto belt. S. Shimanto: South Shimanto belt. The geological subdivision is based on Suyari et al. (1991), Matsuoka et al. (1998) and GSJ (2010)

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Fig. 2 Plate tectonic model for the origin and accretion of Mn-formations along the Pacific-type consuming plate boundary (after Nakgawa et al., 2011)

Chichibu and South Chichibu belts (Fig. 1). The de- regular lenses. Some of the ores show layer structure. posits are abundant especially in the Chichibu belts Several biostratigraphic studies were carried out in the which contain abundant chert beds. Some manganif- accretionary belts. In the Chichibu belts, the microfos- erous iron deposits of small scale occur in the North sil ages of the chert are Permian to Triassic around the Shimanto belt. Besshi-type cupriferous iron sulfide deposits, whereas the ages of the clastic matrix of deposits are abundant in the Sanbagawa belt. olistostrome are Jurassic. In the North Shimanto belt, The manganese deposits occur mostly in bedded the ages of the chert are Early to Middle Cretaceous, chert or its metamorphosed equivalent. Most of the whereas those of the matrix sediments are Late Creta- deposits occur as small conformable, lenticular or ir- ceous.

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3 Mineralogy of manganese deposits Mn-bearing calcite and Mn-rich chlorite occur between greenstone and chert (No. 7). In the South Chi- The mineral constituents of the ores in the repre- chibu belt, many small manganese deposits occur in sentative manganese and iron-manganese deposits bedded chert. The manganese dioxide ore is abundant have been examined by XRD and EPMA analyses. The in this belt (Nos. 10, 11, 12). The ore consists of quartz, results together with the wall rock characteristics and todorokite, pyrolusite, cryptomelane and nsutite. available fossil age data are summarized in Table 1. Manganese carbonate ore consisting mainly of Piemontite-quartz schist is widely distributed in the fine-grained rhodochrosite also occur in several mines Sanbagawa metamorphic belt. In some small mines (No. 10) in this belt. In the North Shimanto belt, some (No. 1), quartz-piemontite-braunite ore occurs in the small deposits of manganiferous iron ore occur in red schist. In the Mikabu belt, manganese ores consisting chert (No. 13). The ore consists mainly of quartz, mainly of pyroxmangite, rhodonite, rhodochrosite, hematite and calcite with accessories of todorokite. ganophyllite and spessartine occur in quartz schist in On modern ocean floor, manganese and ferro- several mines (No. 2). In the North Chichibu belt, manganese nodules and crusts are known to occur and many manganese deposits occur in bedded chert, are considered to have formed by hydrogenetic pre- whereas iron-manganese deposits and some manga- cipitation from cold seawater. They are generally nese deposits occur between greenstone and red chert. composed of hydrous manganese oxide minerals such The manganese ores sandwiched between greenstone as vernadite, birnessite, todorokite and X-ray amor- and chert in the Ananai mines (Nos. 5, 6) contain phous Mn-bearing ferric oxyhydroxides (Hein et al., caryopilite, rhodochrosite, ganophyllite, strontio- 1997). piemontite, braunite, manganaxinite, barite, aegirine, hematite, Mn-bearing calcite, andradite and 4 Genesis of manganese deposits Ba-bearing orthoclase. The manganese ores embedded A schematic plate tectonic model for the origin within chert in many mines (Nos. 3, 4, 8, 9) consist and accretion of manganese formations is shown in Fig. mainly of rhodochrosite, caryopilite, rhodonite, 2. In the Shikoku region, the manganese deposits can braunite and quartz. Iron-manganese ore deposits con- be classified into two types based on the geological sisting of hematite, magnetite, Fe-rich caryopilite, setting, mineralogy and genetic characteristics. The

Table 1 Mineral constituents, wall rock characteristics and fossil age data of manganese and iron-manganese deposits in Shikoku No. Mine Location Wall rock Age of chert Type Main constituent minerals 1 Hakuryu Sanbagawa Quartz schist I Quartz, piemontite, braunite, spessartine, rhodochrosite, hematite, chlorite, sursassite, ardennite, phengite 2 Nobuki Mikabu Quartz schist I Quartz, pyroxmangite, rhodonite, rhodochrosite, ganophyllite, spessartine, tephroite 3 Dosu N. Chichibu Chert Permian I Quartz, rhodochrosite, caryopilite, rhodonite, gageite, apatite Quartz, rhodochrosite, caryopilite, chlorite, ganophyllite, rho- 4 Niro N. Chichibu Chert I CAGSdonite, greenalite, barite Quartz, caryopilite, rhodochrosite, ganophyllite, barite, 5 Ananai- N. Chichibu Greenstone, Middle Permian II braunite, aegirine, Fukinaro red chert rhodonite, hematite, kutnohorite, andradite, calcite, orthoclase Quartz, rhodochrosite, caryopilite, strontiopiemontite, manga- 6 Ananai- N. Chichibu Greenstone, Permian II naxinite, chlorite, barite, aegirine, ganophyllite, calcite, pumpelly- Honomori red chert ite-Mn2+, hematite 7 Kunimiyama N. Chichibu Greenstone, Early Permian II (FeMn) Hematite, Fe-rich caryopilite, magnetite, calcite, chlorite red chert Quartz, caryopilite, braunite, rhodochrosite, kutnohorite, 8 Tokoroyama N. Chichibu Chert Triassic I hematite, barite Quartz, rhodonite, rhodochrosite, braunite, ganophyllite, 9 Nakatsu N. Chichibu Chert Permian I caryopilite, barite 10 Okumiya S. Chichibu Chert I Quartz, nsutite, rhodochrosite 11 Ohira S. Chichibu Chert I Quartz, pyrolusite, cryptomelane, hematite 12 Tawaradu S. Chichibu Chert Triassic I Quartz, todorokite, cryptomelane 13 Hoshigoe N. Shimanto Red chert Early-Middle I-II (Fe) Quartz, hematite, calcite, todorokite Cretaceous The mine numbers are the same as those in Fig. 1. The age data for chert are based on the biostratigraphic studies by Suyari et al. (1982, 1983), Momoi et al. (1992), Ishida (1998), Fujinaga and Kato (2005), and others.

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manganese deposits occur mostly in bedded chert. In HEIN J R, KOSCHINSKY A, HALBACH P, MANHEIM F T, BAU these deposits classified as Type I, the ores consist M, KANG J K, LUBICK N. 1997. Iron and manganese oxide mainly of rhodochrosite, braunite, caryopilite and rhodonite. Radiolarian remains were found in some mineralization in the Pacific. In: NICHOLSON K, HEIN J R, ores suggesting the submarine origin of the manganese BUHN B, DASGUPTA S (Eds.). Manganese Mineralization: deposits. These chert-hosted manganese ores are Geochemistry and Mineralogy of Terrestrial and Marine De- con-sidered to have been manganese nod- posits. Geological Society Special Publication, 119: 123-138. ule/crust-bearing siliceous sediments on deep-sea floor and have been converted to manganese ores by ISHIDA K. 1998. Lithostratigraphy and radiolarian ages of the low-grade metamorphism through subduc- Shimanto Supergroup, East Shikoku. News of Osaka Micro- tion-accretion process. The mineral assemblages of the paleontologists, 11: 189-209 (in Japanese with English ab- ores reflect the metamorphic grade of the accretionary stract). complexes. Some manganese deposits were metamorphosed at the deeper levels. ISOZAKI Y, MARUYAMA S, AOKI K, NAKAMA T, MIYASHITA Iron-manganese deposits and some manganese A, OTOH S. 2010. Geotectonic subdivision of the Japanese deposits, classified as Type II, are associated with Islands revisited: categorization and definition of elements and greenstone and red chert. The mineralogy and texture boundaries of Pacific-type (Miyashiro-type) orogen. Journal of of these ores are different from those of the Geography, 119: 999-1053(in Japanese with English abstract). chert-hosted manganese ores. Geochemical similarities of these ores to those of modern submarine hydro- KATO Y, FUJINAGA K, NOZAKI T, OSAWA H, NAKAMURA K, thermal deposits were noted by Kato et al. (2005) and ONO R. 2005a. Rare earth, major and trace elements in the Fujinaga et al. (2006). These deposits occur directly Kunimiyama ferromanganese deposit in the northern Chichibu over basalt and are considered to have been the Belt, central Shikoku, Japan. Resource Geology, 55: 291-299. hydrothermal precipitates associated with the mid-oceanic ridge or oceanic island volcanism. MATSUOKA A, YAMAKITA S, SAKAKIBARA M, HISADA K. The mineral assemblage of the chert-hosted 1998. Unit division for the Chichibu Composite Belt from a manganese deposits in Shikoku shows a progressive view point of accretionary tectonics and geology of western change that can be correlated with the metamorphic Shikoku, Japan. Journal of Geological Society of Japan, 104: grades of the accretionary complexes. Manganese dioxide minerals such as todorokite and pyrolusite occur 634-653(in Japanese with English abstract). in the low-grade metamorphic terrane of South Chi- MIYAHISA M, SAWAMURA T. 1973. Manganese ore. In: chibu belt. Manganese silicate minerals such as WATANABE T, SAWAMURA T, MIYAHISA M (Eds.). Min- caryopilite (serpentine group), braunite and rhodonite eral deposits of Japan – the Shikoku district-. Asakura, Tokyo, (pyroxenoid group) occur in the higher-grade meta- 202-248(in Japanese). morphic terrane of North Chichibu belt. Manganese alumino-silicate minerals such as piemontite and MOMOI H, ISHIDA K, YAMASAKI T. 1992. Radiolarian geologic spessartine (garnet group) occur in the high-grade ages of some host cherts of bedded manganese ore deposits in metamorphic Sanbagawa and Mikabu belts.CAGS These the Chichibu belt of Ehime Prefecture, Japan. Memoirs of the manganese silicates and alumino-silicates are consid- Faculty of Science, Ehime University, 1: 71-89(in Japanese ered to have formed by the reactions of deep-sea manganese oxides, siliceous sediments and pelagic with English abstract). clays. NAKAGAWA M, SANTOSH M, MARUYAMA S. 2009. Distribu- tion and mineral assemblages of bedded manganese deposits in References: Shikoku, Southwest Japan: Implications for accretion tectonics. FUJINAGA K, KATO Y. 2005. Radiolarian age of red chert from Gondwana Research, 16: 609-621. the Kunimiyama ferromanganese deposit in the northern Chi- NAKAGAWA M, SANTOSH M, MARUYAMA S. (2011) chibu Belt, central Shikoku, Japan. Resource Geology, 55: Manganese formations in the accretionary belts of Japan: 353-356. Implications for subduction-accretion process in an active FUJINAGA K, NOZAKI T, NISHIUCHI T, KUWAHARA K, convergent margin. Journal of Asian Earth Sciences, 42: KATO Y. 2006. Geochemistry and origin of Ananai stratiform 208-222. manganese deposit in the northern Chichibu belt, central Shi- NAMBU M. 1980. Genesis and problems of the bedded manganese koku, Japan. Resource Geology, 56: 399-414. deposits and the bedded manganiferous iron deposits in the Geological Survey of Japan. 2010. Seamless digital geological map Kitakami mountainland, northeastern Japan. Mining Geology, of Japan (1:200,000). 30: 323-343(in Japanese with English abstract).

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SUYARI K., IWASAKI M., SUZUKI T(Eds.). 1991. Regional Ge- Journal of Science, University of Tokushima, 16: 143-167(in ology of Japan, Part 8 Shikoku. Kyoritsu Shuppan, Tokyo, Japanese with English abstract). 266(in Japanese). WATANABE T, YUI S, KATO A. 1970. Bedded manganese depos- SUYARI K, KUWANO Y, ISHIDA K. 1982. Stratigraphy and geo- its in Japan, a review. In: Tatsumi, T. (ed.), Volcanism and Ore logical structure of the Mikabu Greenrock terrain and its en- Genesis. University of Tokyo Press, Tokyo, 119-141. virons – II. Some informations about the Mesozoic stratigra- YOSHIMURA T. 1952. Manganese deposits of Japan. Man- phy of the North Subbelt of the Chichibu Belt -. Journal of gan-Kenkyukai, 567(in Japanese). Science, University of Tokushima, 15: 51-71 (in Japanese with YOSHIMURA T. 1969. Supplement to “Manganese Ore Deposits of English abstract). Japan”, Part II. The Science Reports of the Faculty of Science, SUYARI K, KUWANO Y, ISHIDA K. 1983. Biostratigraphic study Kyushu University, Geol., 9, Spec. Iss. 2, 487-1004(in Japa- of the North Subbelt of the Chichibu Belt in central Shikoku. nese).

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