1994 Fiscal Year Final Research Report Summary
Study on Gold Ore Genesis in Volcanic Island Arc
| Project/Area Number |
04402044
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| Research Category |
Grant-in-Aid for General Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Research Field |
資源開発工学
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| Research Institution | KYUSHU UNIVERSITY |
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Principal Investigator |
IZAWA Eigi Faculty of Eng., Kyushu Univ., Professor, 工学部, 教授 (50037751)
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| Co-Investigator(Kenkyū-buntansha) |
HARA Tsuyoshi Faculty of Eng., Kyushu Univ., Research Assoc., 工学部, 助手 (20159099)
NAKAE Yasuo Faculty of Eng., Kyushu Univ., Research Assoc., 工学部, 助手 (90253476)
WATANABE Koichiro Fac.of Eng., Kyushu Univ., Assoc.Prof., 工学部, 助教授 (10182916)
EHARA Sachio Faculty of Eng., Kyushu Univ., Professor, 工学部, 教授 (10002346)
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| Project Period (FY) |
1992 – 1994
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| Keywords | Volcanic arc / Hydrothermal system / Gold deposits / Magmatic material / Hydrothermal alteration zone / Laser-sampling ICP-MS |
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| Research Abstract |
During evolution of island arcs and associated magmatic activity, several kinds of metallic and nonmetallic mineral deposits are formed in the hydrothermal systems constructed in the upper crust. Recently it is recognized that epithermal deposits are an important source of gold. This study focused on Kyushu, which can be considered as an ideal example of volcanic arcs, and goal was to clarify the relation between igneous activity and gold mineralization. Results of this study show that the sites of gold mineralization are volcanic geothermal system and that the validity of exploration based on the geothermal model was confirmed.
1. Ages of volcanic activity and gold mineralization
(1) Age determinations for volcanic rocks in gold areas indicate that magnetite series magmatism in southern Kyushu begun about at 10 Ma.
(2) Age determinations for gold deposits in southern, central and western Kyushu clarified that gold mineralization in Kyushu occurred mainly in Pliocene and Pleistocene and that hydrothermal activity and mineralization occurred about 0.5 Ma after the initiation of volcanism in each volcanic center.
2. Hydrothermal alteration and geochemical studies of ore forming minerals
(1) Zonal arragements of hydrothermal alteration in several gold mineralized area show that mineralization occurred in the transitional part from the mixed layr mineral zone to the sericitecholorite zone in the center of a hydrothermal system.
(2) Trace gold was analyzed using laser-sampling ICP-MS for pyrite from the Akeshi and Kushikino deposits.
(3) Ar gas in the ore quartz from the Hishikari deposit was investigated and magmatic sign was not detected.
3. Models for epithermal gold deposits
(1) Possibility of the porphyry copper deposit existing beneath the Nansatsu deposits was examined.
(2) Problem of presence of gold rich basement/magma was investigated by analyzing trace gold in various rock samples from Kyushu using graphite furnace AA and LA-ICP-MS.
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