Japan Geoscience Union Meeting 2019

Presentation information

[J] Oral

H (Human Geosciences ) » H-RE Resource and Engineering Geology

[H-RE16] Resource Geology

Wed. May 29, 2019 1:45 PM - 3:15 PM 106 (1F)

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

2:30 PM - 2:45 PM

[HRE16-08] Geochemical features of “invisible gold” in pyrites from the Akeshi and Kasuga deposits, Kagoshima, Japan

*Mizuki Ishida1, Rurik Romeo2,3, Mathieu Leisen2,3, Junji Torimoto4, Tatsuo Nozaki4,5,6,7, Kazutaka Yasukawa1,6, Koichiro Fujinaga6,1, Kentaro Nakamura1, Martin Reich2,3, Yasuhiro Kato1,6,5 (1.Department of Systems Innovation, School of Engineering, The University of Tokyo, 2.Department of Geology and Andean Geothermal Center of Excellence (CEGA), FCFM, 3.Millennium Nucleus for Metal Tracing Along Subduction, FCFM, Universidad de Chile, FCFM, 4.Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 5.Frontier Research Center for Energy and Resources, School of Engineering, The University of Tokyo, 6.Ocean Resources Research Center for Next Generation, Chiba Institute of Technology, 7.Department of Planetology, Graduate School of Science, Kobe University)

Keywords:Pyrite, Trace elements, Invisible gold, High-sulfidation deposit, Nansatsu-type

The occurrence of gold in ore is one of the most important information in gold deposit research. This information allows us to optimize beneficiation and smelting processes, as well as providing valuable insights into the mineralization mechanism, which can improve exploration strategies (e.g., [1]).

In hydrothermal gold deposits, gold is not always visible as native gold, electrum, caraverite (AuTe2) or other gold minerals. In many cases, it also exists as submicrometer-size inclusions and solid solution in other minerals, which is so-called “invisible gold” [2]. Pyrite is the most ubiquitous and well-known host mineral for this invisible gold, and its trace element geochemistry has been increasingly recognized as a useful tool to understand the mineralization processes (e.g., [3]).

In this study, we report the geochemical features of invisible gold in pyrites collected from the Akeshi and Kasuga deposits. These deposits, located in the southern part of the Kagoshima Prefecture, Japan, are currently under operation, and are classified as high-sulfidation gold deposits. In both Akeshi and Kasuga, gold minerals are only reported from high-grade ores, and other hosts of gold in lower-grade ores remain still uncertain [4]. Pyrite is the most common sulfide mineral in these deposits. Here, we report the results of EPMA (Electron Probe Micro Analyzer) and LA-ICP-MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry) trace element analyses of pyrite, in order to determine their mineralization processes.

[1] Morishita et al. (2018) Ore Geology Reviews, 95, 79-93.

[2] Cook and Chryssoulis (1990) Canadian Mineralogist, 28, 1-16.

[3] Román et al. (2019) Geochimica et Cosmochimica Acta, 246, 60-85.

[4] Nakamura et al. (1994) Resource Geology, 44(3), 155-171.