Hanawa ( Sotoyama ) - Motoyama, Aketoshi, Onnataira

Honshu, Japan

Main commodities: Cu Zn Pb
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The Hanawa group of kuroko type Cu-Zn-Pb deposits are located on the western margin of the Sotoyama Basin (separated from the Hokuroko Basin to the west by a basement rise of Palaeozoic rocks).   It is within Akita Prefecture (close to the border with Iwate Prefecture), in northern Honshu, Japan.   Mining has been undertaken on the deposits from before to 1868 when it was known as the Sotoyama mine.

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

The geology of the Hanawa district can be summarised as follows:
Basement - slate, chert and sandstone of probable Permain age.
Natsujirisawa Formation - commences with a basal conglomerate at the unconformity with basement, and comprises overall a sequence of fine rhyolitic tuff, black mudstone and rhyolitic and/or andesitic lapilli tuff (andesitic pyroclastics predominate at the base and rhyolites at the top).   This unit corresponds to the regional Monzen Stage.
Shimokobesawa Formation - unconformably overlying the Natsujirisawa Formation, it corresponds to the regional Nishikuraswa Stage and represents the mineralised unit.   It is characterised by acidic volcanic and pyroclastics rocks subdivided as follows:
 i). Sotoyama member - which forms the footwall of the Hanawa ore deposits and comprises more than 550 m of rhyolitic lavas, fine tuff and pumice tuff.   The lava, the Sotoyama rhyolite, which is pale green to grey to white and commnly forms domes, is widespread in the district.
 ii). Aketoshi member - is the host to ore at the Aketoshi and Motoyama orebodies and is composed of pale grey-green rhyolitic tuff breccia, lapilli tuff, pumice tuff and fine tuff, with local basalt and mudstone, and is up to 350 m thick.
 iii). Iwanomesawa member - is the host to ore at the Onnataira orebodies and is composed of pale green rhyolite lava, lapilli tuff and pumice tuff intercalated with black mudstone, and is about 200 m thick.
 iv). Nakanosawa member - dacitic lapilli tuff and sandy tuff with local intercalations of fine tuff and varies from 50 to 200 m in thickness.   It is suggested this member corresponds to the regional Onnagawa Stage.
Sugisawa Formation - 100 to 250 m of dacitic welded tuffs, tuff breccia, lapilli tuff and sandy tuff of the regional Funakawa Stage.
Obesawa Formation - 50 to 500 m of dacitic to andesitic lapilli and sandy tuffs with siltstones, passing up into andesitic lava and interfingering locally with the Sugisawa Formation.
Intrusives - rhyolite, andesite, nevadite and basalt are found intruding various parts of the sequence at Hanawa.

The main orebodies at Hanawa have been divided into three groups, namely:
Motoyama Group - mostly either massive or lenticular in form.   This group has been further subdivided into the Old Motoyama [1 orebody], Santaira [3 orebodies], Ashiro [5 orebodies], Osaki [4 orebodies] and New Motoyama [4 orebodies].   The Old Motoyama and Santaira orebodies are cored by gypsum ore and are generally relatively large with lateral dimension of more than 100 m, up to nearly 200 m and grades of around 1 to 2% Cu Zn with little Pb.   The Ashiro and Osaki orebodies are much smaller, generally less than 100 m on their long axis, with grades of 0.4 to 1.2% Cu and 0.5 to 3% Zn, with little Pb.   The New Motoyama group have dimensions of 200x250+ m, 1%Cu and 28% S without Pb or Zn.
Aketoshi Group - comprises two orebodies which are small with long dimensions of less than 100 m and a maximum of 20 m width but are up to 10 m thick.   Grades average 2.4% Cu, 2% Pb, 6% Zn, 12% S.
Onnataira Group - are very small with a maximum dimension of 15 m by about 5 m wide but have grades averaging 1% Cu, 4% Pb, 20% Zn and 9% S.

Recorded production between 1937 and 1970 totalled:
    2.875 Mt @ 1.08% Cu, 0.78% Pb, 3.18% Zn, 18.01% S.

For detail of Kuroko style ore types and their composition see the Hokuroko Basin - Kuroko Deposits record.

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:
Kajiwara Y  1970 - Gypsum-Anhydrite ores and associated minerals from the Motoyama deposits of the Hanawa Mine: in Tatsumi T (Ed.), 1970 Volcanism and Ore Genesis University of Tokyo Press, Tokyo    pp 207-213
Ohtagaki T, Takahashi H, Obara K  1974 - Geology of the Hanawa Mine, Akita Prefecture: in Ishihara S (Ed.), 1974 Geology of Kuroko Deposits The Society of Mining Geologists of Japan   Mining Geology Special Issue 6 pp 157-168

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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