ICDP Drilling into Seismogenic zones in South African mines (DSeis; 2016 – onwards)
- 1Ritsumeikan University, Kusatsu, Japan
- *A full list of authors appears at the end of the abstract
Limited access has hindered understanding of seismogenic zone and life at depth (e.g., ICDP Science Plan 2014-2019; 2020-2030). The 2014 M5.5 Orkney earthquake South Africa ruptured the entire vertical depth range, between 3.5 and 7 km of the West Rand Group (2.9 Ga metasedimentary formations with altered mafic/ultramafic sill/dyke complex). We could have a drilling rig at 2.9 km depth in hard-rock formations in West Rand Group at the Moab Khotsong gold mine. During 2017-2018, we accomplished NQ wireline full-core diamond drilling and downhole logging with a total length of 1.6 km (ICDP Thrill to Drill; Ogasawara et al. 2019; Nkosi et al. 2022). We could not make downhole logging at and below the intersections of the structure that hosted the Orkney main- and after-shocks. So, we exported the most critical section of the core to Center for Advanced Marine Core Research, Kochi University/Kochi Core Center (KCC) Japan to log and for further investigation. Mineral/geochemical studies (XRD, XRF, EPMA, SEM-EDS, X-ray CT, friction) at KCC, Hiroshima, Tohoku, Tokyo, and Kyoto Universities, as well as SPring8 elucidate the assemblage with talc and/or associated altered mafic minerals in greenschist facies and their mechano-chemical characteristics (e.g., Miyamoto et al. 2022; Yabe et al. 2023 GeoCongress). Our drilling also intersected the ancient hypersaline brine vein. US geomicrobiology team extensively investigated the brine (Oliver et al. 2022; Nisson et al. 2022). The outstanding outcomes include the age (>1Ga) and the salinity, the end-member in their research history since the 1990s. COVID-19 hindered, in particular, our research activity at 2.9 km depth at Moab Khotsong mine and access to the core during 2020-2021. However, we could log Holes A and B again in 2022 to compare with the previous logging data. This paper overviews the activity mentioned above, as well as prospects.
Our research is financially supported by ICDP, JSPS, JST-JICA, MEXT Japan, US NSF, German DFG, SA NRF, Ritsumeikan Univ., GFZ. Kochi Core Center, Astrobiology Center.
The ICDP DSeis team includes Y. Yabe, T. Ito, A. Funato, Y. Suzuki, A. Urai, T. Matsuzaki, A. Tsuchiyama, J. Matsuno (Japan); R. Durrheim, B. Liebenberg, J. Catillo, A. Gómez-Arias, M. Manzi, S. Mngadi, N. Nkosi, J. Matemela (South Africa); T. Kieft, D. Nisson (US); many others from the universities of Ritsumeikan, Tohoku, Witwatersrand, ETH Zurich, Free State, Princeton, New Mexico Inst. Min. Tech., Toronto, Oxford, Tokyo, Osaka, Osaka Metropolitan, Kochi, Kyoto, Hiroshima, Chinese Academy of Sciences, Berlin Free, Stanford, New Hampshire, W. Australia, and Tel Aviv; the institutes include CGS South Africa, GFZ, IITK, NASA, NIED, AIST, JAMSTEC, NGRI, IITH, IITK; The firms include Harmony Gold, AngloGold Ashanti, Sibanye Stillwater, Goldfields, Lesedi Drilling, Digital Surveying, Wireline Workshop, Geoline, iWater, Home Seismo, 3D GeoScience.
How to cite: Ogasawara, H. and the ICDP DSeis team: ICDP Drilling into Seismogenic zones in South African mines (DSeis; 2016 – onwards), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4104, https://doi.org/10.5194/egusphere-egu23-4104, 2023.
