Mechanisms for anhydrite and gypsum formation in the Kuroko massive sulfide–sulfate deposits, north Japan (original) (raw)

Abstract

The Sr, Ba, and rare earth elements (REEs) concentrations and Sr isotopic composition of anhydrite and gypsum have been determined for samples from the Matsumine, Shakanai, and Hanaoka Kuroko-type massive sulfide–sulfate deposits of northern Japan to evaluate the mechanisms of sekko (anhydrite and gypsum) ore formation. The Sr isotopic compositions of the samples fall in the range of 0.7077–0.7087, intermediate between that for middle Miocene (13–15 Ma) seawater (0.7088) (Peterman et al., Geochim Cosmochim Acta, 34:105–120, 1970) and that for country rocks (e.g., 0.7030–0.7050) (Shuto, Assn Geol Collab Japan Monograph 18:91–105, 1974). The Kuroko anhydrite samples exhibit two types of chondrite-normalized REE patterns: one with a decrease from light REEs (LREEs) to heavy REEs (HREEs) (type I), and another with a LREE-depleted pattern (type II).

Based on the Sr content and isotopic ratio (assuming an Sr/Ca (mM/M) of 8.7 for seawater), anhydrite is considered to have formed by mixing of preheated seawater with a hydrothermal solution of Sr/Ca (mM/M) = ca. 0.59–1.36 under the condition in which the partition coefficient (Kd) ranges between ca. 0.5 and 0.7. This results in the formation of anhydrite with higher Sr content with an Sr isotopic value close to that of seawater under seawater-dominant conditions.

Larger crystals of type II anhydrite are partly replaced by smaller ones, indicating that anhydrite dissolution and recrystallization occurred after or during the formation of sekko ore. Gypsum, which partially replaces anhydrite in the Kuroko deposits, also exhibits two distinct chondrite-normalized REE patterns. Because LREEs are likely to be more readily mobilized during dissolution and recrystallization, it is hypothesized that LREEs are leached from type I anhydrite, resulting in the formation of type II anhydrite with LREE-depleted profiles.

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Acknowledgments

We thank Dr. O. Matsubaya of Akita University and Dr. A. Okamoto of Tohoku University for their useful advice. We also thank the University Museum, University of Tokyo, for giving anhydrite and gypsum samples to us for this study. This manuscript was greatly improved by the valuable comments from Drs. D. Lentz, D.H.A. Teagle, and D. Vanko.

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  1. Yasumasa Ogawa
    Present address: Graduate School of Environmental Studies, Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai, Miyagi, 980-8579, Japan

Authors and Affiliations

  1. Department of Applied Chemistry, Faculty of Science and Technology, Keio University, Hiyoshi 3-14-1, Kohoku-ku, Yokohama, Kanagawa, 223-8522, Japan
    Yasumasa Ogawa & Naotatsu Shikazono
  2. Division of Applied Earth Science, Department of Earth Science and Technology, Faculty of Engineering and Resource Science, Akita University, Tegatagakuen-machi 1-1, Akita, Akita, 010-8502, Japan
    Daizo Ishiyama, Hinako Sato & Toshio Mizuta
  3. Research Institute for Humanity and Nature, Inter-University Research Institute, Ministry of Education, Culture, Sports, Science, and Technology, Takashima-cho 305, Marutamachi-dori, Kawaramachi Nishi-iri, Kamigyo-ku, Kyotom, Kyoto, Kyoto, 602-0875, Japan
    Takanori Nakano

Authors

  1. Yasumasa Ogawa
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  2. Naotatsu Shikazono
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  3. Daizo Ishiyama
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  4. Hinako Sato
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  5. Toshio Mizuta
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  6. Takanori Nakano
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Correspondence toYasumasa Ogawa.

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Editorial handling: D. Lentz

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Ogawa, Y., Shikazono, N., Ishiyama, D. et al. Mechanisms for anhydrite and gypsum formation in the Kuroko massive sulfide–sulfate deposits, north Japan.Miner Deposita 42, 219–233 (2007). https://doi.org/10.1007/s00126-006-0101-7

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