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Akeshi |
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Kyushu, Japan |
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Au SiO2
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Super Porphyry Cu and Au
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Akeshi is a small acid sulphate alteration associated gold deposit in the Nansatsu District of southern Kyushu, Japan, some 13 km north-east of the Kasuga gold deposit.
The deposit is developed within the 4.6 to 3.4 Ma Nansatsu Middle Volcanics and is younger than the ore at both Kasuga and Iwato which are similar gold deposits 6 to 13 km to the south-west. These volcanics are composed of 300 m of hornblende andesite flows and pyroclastics, and tuffaceous siltstone. Mineralisation has a much stronger structural control than at Iwato, reflecting the dominant fracture permeability in the host pyroxene andesite lavas.
The visible alteration consists of a quartz, varying from vuggy residual silica (with vugs often filled with sulphides and sulphur), to massive silica. Younger (<1 Ma) tuffs overlie most of the silica body, although the margin with argillised and weak silicification is observed on the northern margin.
There are three steeply dipping pipe like orebodies within the residual silica alteration. These have dimensions of: 1). 100 m NE-SW and 40 m wide dipping at 60° with a vertical extent of 150 m, 2). 50 m in diameter to a depth of 50 m below surface where it changes to a 40° plunge, and 3). a smaller isolated body. Underground exposures are more sulphide rich (up to 10%) compared to the lower sulphide contact in the oxidised zone of the open pit. Pyrite is the most common sulphide, followed by luzonite and then enargite, with covellite in late vugs. Primary gold is associated with luzonite and pyrite and varies from 1 to 100, averaging 15 microns.
For detail, consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 1999.
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.
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Selected References:
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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
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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
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Izawa E, Taguchi S, Kobayashi T, Watanabe K 1992 - Gold Mineralization in Volcano-Geothermal Areas of Kyushu: in Urabe T, Aoki M (Eds.), Mineral Deposits of Japan and the Philippines 29th IGC Field Trip C33 Guide Book, The Society of Resource Geology, Tokyo, Japan v6 pp 143-172
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Watanabe Y 2005 - Late Cenozoic evolution of epithermal gold metallogenic provinces in Kyushu, Japan: in Mineralium Deposita v40 pp 307-323
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Yukihiro Matsuhisa 1992 - Epithermal gold mineralization in Kyushu, Japan: in Epithermal Gold in Asia and the Pacific, Mineral Concentrations and Hydrocarbon Accumulations in the ESCAP Region UN Econ & Social Comm to Asia & the Pacific v6 pp 23-27
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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, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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