Kyushu, Japan

Main commodities: Au
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Iwato is a relatively small low sulphidation acid sulphate alteration associated gold deposit in the Nansatsu District of southern Kyushu, Japan, some 7 km east of the Kasuga gold deposit.

The deposit is developed within the 300 m thick Nansatsu Upper Volcanics, composed of 6.4 to 5.9 Ma pyroxene-hornblende andesite flows and pyroclastics.   This unit has been strongly leached and variably silicified over a length of 2 km and widths of 200 to 400 m.   The eastern 750 m of the siliceous zone contains all of the orebodies, which occur exclusively within the zone of silification and are defined by a 2 g/t Au cut-off.   The larger of these bodies are around 100 to 200 m in diameter and persist to depths of 100 m.   In detail the orebodies look like upward coalesced mushrooms.

The siliceous rock is composed of fine grained quartz, minor rutile and secondary quartz crystals with finely disseminated pyrite throughout.   Other sulphides, sulphosalts and ore minerals are fine grained and disseminated and comprise native gold, electrum, argentite, pyrargyrite, canfieldite, chalcopyrite, bornite, chalcocite, enargite, native copper, sphalerite, galena, molybdenite, stannite, cassiterite, and native sulphur.

For detail, consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 1993.    
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:
Hayashi T  2001 - Geology and gold exploration in the Nansatsu district, southern Kyushu, Japan: in Feebrey CA, Hayashi T, Taguchi S, 1994 Epithermal Gold Mineralization and Modern Analogues, Kyushu, Japan Society of Economic Geologists, Guidebook Series   v. 34 pp 127-132
Hedenquist J W, Matsuhisa Y, Izawa E, White N C, Giggenbach W F, Aoki M  1994 - Geology, geochemistry, and origin of high sulfidation Cu-Au mineralization in the Nansatsu District, Japan: in    Econ. Geol.   v 89 pp 1 - 30

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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