Hokkaido, Japan

Main commodities: Cu Zn Pb Ag Au
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The Kunitomi cluster of kuroko type Cu-Zn-Pb-Ag-Au orebodies are hosted by middle Miocene volcanics on the southern part of the Shakotan Peninsular on south-western Hokkaido, Japan.

This part of Hokkaido had a similar Miocene geological history to northern Honshu where the large Hokuroko Basin Kuroko deposits were formed.

For background information on the geology and setting of the Hokuroko Basin see the Hokuroko Basin - Kuroko Deposits record.

A suite of at least eleven volcanic hosted massive and disseminated/stringer/stockwork sulphide deposits are hosted by middle Miocene dacitic pyroclastics in two parallel WNW trending lines over an area of 5x2 km.   Two types of mineralisation, which occur both separately and together, are recognised, namely:

i). massive and bedded sulphide Kuroko (black ore) and Oko (yellow ore) type lenses with associated siliceous ore, and
ii). stockwork/stringer and disseminated replacement mineralisation.

The most common sulphides in both styles are sphalerite, galena, chalcopyrite and pyrite.   Barite accompany the first style and gypsum veining the second.

Both types are associated with dacite domes which are overlain by pyroclastics and mudstones.

The largest of the orebodies/lenses is 350x150x10 m, the smallest 50x50x10 m.

Reserve figures quoted for the 11 lenses in 1975 total:
    3.4 Mt @ 0.3 to 1.9% Cu, 0.2 to 2.3% Pb, 2.5 to 9.7% Zn, 33 to 100 g/t Ag, 0.4 to 1.2 g/t Au.

Production 1935 to 1945:
    1 Mt @ 1.5 to 2.0% Cu

For detail consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 1975.    
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:
Ogura N  1974 - Geologic structure, igneous activity and mineralization of the Kunitomi Mine area, Hokkaido: in Ishihara S (Ed.), 1974 Geology of Kuroko Deposits The Society of Mining Geologists of Japan   Mining Geology Special Issue 6 pp 29-37

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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