JpGU-AGU Joint Meeting 2017

Presentation information

[JJ] Oral

S (Solid Earth Sciences) » S-RD Resources, Mineral Deposit & Resource Exploration

[S-RD39] [JJ] Resource geology

Thu. May 25, 2017 10:45 AM - 12:15 PM A07 (Tokyo Bay Makuhari Hall)

convener:Tsubasa Otake(Division of Sustainable Resources Engineering, Faculty of Engineering, Hokkaido University), Tatsuo Nozaki(Research and Development Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology), Kenzo Sanematsu(Mineral Resource Research Group, Institute for Geo-Resources and Environment, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology), Ryohei Takahashi(Graduate School of International Resource Sciences, Akita University), Chairperson:Ryohei Takahashi(Graduate School of International Resource Sciences, Akita University)

11:15 AM - 11:30 AM

[SRD39-08] Mineralization of Ag-rich Sulfide Minerals in Chimney Samples at Bayonnaise Knoll, Izu-bonin Arc.

*Shinji Kawaguchi1, Kotaro Yonezu1, Thomas Tindell1, Jun-ichiro Ishibashi2, Kazuhiko Shiada2, Tatsuo Nozaki3 (1.Department of Earth Resources Engineering, Kyushu University., 2.Department of Earth and Planetary Sciences, Kyushu University., 3.Japan Agency for Marine-Earth Science and Technology (JAMSTEC))

Keywords:Beyonnaise Knoll, Chimney, Ag-sulfide Minerals

The Bayonnaise Knoll is located in the Izu-Bonin Arc, which forms an arc-trench system. In this study, the growth process of chimnies formed by hydrothermal fluid ejecting from hydrothermal vents, and mound ore formed around chimnies, is clarified based on geochemistry and mineralogy. Measured value for precious and base metals for the studied samples show Au (4.635 ppm), Ag (354 ppm), Cu (0.406 wt%), Pb (0.252 wt%), Zn (11.841 wt%) contents and used to compare with the average Kuroko-ore. In addition, the grade of Au and Ag are larger than that average value.

Chimney has a tubular structure and the growth axis is perpendicular to the chimney length. A manganese oxide is covered to the surface, 1) a white sulfate rich portion (G1), 2) followed by a gray portion containing sulfide (G2) and 3) a black porous portion containing sulfide (G3). This simillar classification can be also observed in the Kuroko-ore. Ba distribution are evenly confirmed in G1-G2 but only confiremed in G3 as a large crystalline portion in vug. It is known from previous studies that the formation temperature of barite (G1) is mainly estimated as 150-215 ℃ and the formation temperature of sphalerite (G2-G3) is around 205-225 ℃. Sphalerite, galena and chalcopyrite, which belongs to Kuroko-ore, were mainly observed in G2-G3. These similar mineralization can be obtained Kuroko-ore. From EPMA measurements, Ag-rich portion is distributed mainly on the outside of G2 and Ag-Cu-Pb, in which sulfide minerals were confirmed. It is presumed that Ag-rich-sulfide minerals were formed at around 200 ℃ because of the formation temperature of barite and sphalerite and that Ag-rich-sulfide distribution.Therefore, from the above point, chimney and mound ore in the Bayonnaise Knoll, is Au and Ag rich, but characterized by a similar concentration of major elements (Cu, Pb, Zn) to the Kuroko ores. And it was found that Ag-sulfide minerals were distributed in G2.