Kamaishi - Shinyama, Sahinai, Nippo, Rasa-Omine

Honshu, Japan

Main commodities: Cu Fe
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The Kamaishi iron-copper skarn deposits are located in north-eastern Honshu, 20 km WNW of Kamaishi City and ~450 km NNE of Tokyo in Japan.   It lies close to the Hayachine-Goyozan tectonic zone in a district composed of Palaeozoic and Mesozoic formations and igneous rocks (#Location: 39° 18'N, 141° 41'E).

The Sahinai and Shinyama ore deposits are the largest within the mine. At least 13 other orebodies were mined, including Nippo and Rasa-Omine. Shinyama is the largest largest Fe "skarn" orebody in Japan, had was 400 x 80 m with vertical dimensions of 550m.

The Palaeozoic sequence includes andesitic pyroclastics, slates and sandstones and limestones, while the overlying Mesozoic succession is composed of shales and sandstones and andesitic pyroclastics. Intrusives include granodiorites and diorites with minor quartz monzonite in two complexes, the 122 Ma Kurihashi and 119 Ma Ganidake intrusions.

A series of orebodies are developed within Carboniferous and Permian limestones over a length of 4 km adjacent to diorite to diorite porphyry intrusions of the Cretaceous Ganidake intrusive complex. Deposits are clustered on both the eastern and western margins of the intrusive complex. The larger Cu and/or Fe deposits are on the western flank, within the Carboniferous Nagaiwa-Onimaru limestone. The Kurihashi intrusion cuts the ores and is taken to be younger than the mineralisation.

The mine operates on 4 ore deposits, each of which is composed of a number of orebodies.   Orebodies are classified as:  i) Copper - on the limestone side  ii) Iron-copper and  iii) Iron on the intrusive side.

Skarn zonation outwards from the intrusive contact is from plagioclase-amphibolite → epidote-amphibolite → epidote-clinopyroxene → garnet-clinopyroxene → garnet → clinopyroxene → limestone.   The outer three garnet and/or clinopyroxene skarns assemblages are exoskarns within the limestone protolith, while the inner three are endoskarns within the intrusive.  Garnets are of the grossular-andradite series, while clinopyroxenes belong to the diopside-hedenbergite series, with the hedenbergite component decreasing towards the intrusive contact.

The Cu rich ores are within the clinopyroxene skarns, while the more iron rich ores are located between the garnet and garnet-clinopyroxene zones closer to the intrusive contact.

The paragenesis is skarn minerals → magnetite → pyrrhotite → chalcopyrite and cubanite → pyrite.

Magnetite-garnet skarns were worked for iron since 1727 during the Tokugawa shogunate era, with Japan's first modern blast furnace built there in 1857 (late Edo era). Peak production was in the 1970s. The production in 1958 had been 1.06 Mt of ore averaging 28.6% Fe (Mindat website, 2013).

In 1980 production was 7800 t Cu and 0.29 Mt Fe. Copper orebodies contained up to 2.8% Cu, while the iron-copper orebodies have grades of around 0.6% Cu, 36% Fe (Uchida and Iiyama, 1982).

Iron ore reseves in 1987 at the Kamiashi operation were 10 Mt of Fe ore. Average Fe grades are quoted as 33% Fe. Nippo, the largest of the Cu mines, had remaining serves of 4.4 Mt in 5 orebodies with grade of 1.1 to 1.6% Cu (Ochiai, 1987).

Most of the mines were abandoned in the late 1980's after the closure of the steel works in Kamaishi City in 1980.

For detail see the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 1987.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information
   Selected References:
Ochiai K  1987 - A reaction model relating skarn zones and ore formation at the Nippo Copper ore deposit, Kamaishi Mine, Northeastern Japan: in    Econ. Geol.   v82 pp 1001-1018
Uchida E, Iiyama J T  1982 - Physicochemical study of skarn formation in the Shinyama iron-copper ore deposit of the Kamaishi Mine, northeastern Japan: in    Econ. Geol.   v77 pp 809-822

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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