Epithermal gold deposits

Recently, epithermal gold deposits were divided into several types based on gangue minerals, and physicochemical environment of ore deposition (pH, H2S concentration of ore fluids). They are hot spring-type (Silberman, 1982 Berger, 1983a Berger and Eimon,... 

Tonnages of gold, silver and the other associated metal, silver/gold ratio, K-Ar ages and host rocks for the Te-type and Se-type epithermal gold deposits (Shikazono et al., 1990)... 

Figure 1.117. Map showing the distribution of Se-type and Te-type epithermal gold deposits in Japan. 1 Green-tuff and subaerial volcanic region of Tertiary/Quaternary ages, 2 Main Paleozoic/Mesozoic terrane, 3 Main metamorphic terrane, 4 Te-type deposits, 5 Se-type deposits, 6 Te- and Se-bearing deposits, ISTL Itoigawa-Shizuoka tectonic line, TTL Tanakura tectonic line, MTL Median tectonic line (Shikazono et al.,I990).

Figure 1.133. The normal order in other epithermal gold deposits in Japan (Nagayama, 1993a).

Etoh, J., Taguchi, S. and Izawa, E. (2001) Gas compositions in fluid inclusions from the Hishikari epithermal gold deposit, southern Kyushu, Japan. Proceedings of International Symposium on Gold and Hydrothermal Systems, pp. 99-104. 

Hayashi, K., Maruyama, T. and Satoh, H. (2000b) Precipitation of gold in a low-sulfidation epithermal gold deposit Insights from a submillimeter scale oxygen isotope analysis of vein quartz. Econ. Geol, 96, 211-216. 

Hedenquist, J.W., Izawa, E., Arribas, A. and White, N.C. (1996) Epithermal gold deposits styles, characteristics, and exploration. Resource Geology Special Publication No. 1. 

Shikazono, N., Nakata, M. and Shimizu, M. (1990) Geochemical, mineralogic and geologic characteristics of Se- and Te-bearing epithermal gold deposits in Japan. Mining Geology, 40, 337-352. 

Yajima, T., Matsumoto, T, Yoshioka, K. and Nakayama, K. (1997) Geology and exploration of the Seta low sulfidation epithermal gold deposit, eastern Hokkaido, Japan. Mining Geology, 47, 45-58. 

Fig. 2.23 shows the distributions of major geothermal systems and epithermal gold deposits of Japanese Islands. It is interesting to note that their distributions are similar and they are distributed close to the volcanic front. 

Fig. 2.23. The major geothermal system and epithermal gold deposits of Japan. Epithermal gold deposits are represented by gold mines or mining areas that have produced more than 10 metric tons of gold (Izawa and Aoki, 1991).

Spatial relationship between back-arc deposits and epithermal gold deposits... 

Aizu geothermal field, with genetic relation to the epithermal gold deposits. Mining Geology, 38, 291-301 (in Japanese). 

Heated meteoric waters are a major constituent of ore-forming fluids in many ore deposits and may become dominant during the latest stages of ore deposition. The latter has been documented for many porphyry skam-type deposits. The isotopic variations observed for several Tertiary North American deposits vary systematic with latitude and, hence, palaeo-meteoric water composition (Sheppard et al. 1971). The ore-forming fluid has commonly been shifted in 0-isotope composition from its meteoric 5 0-value to higher 0 contents through water-rock interaction. Meteoric waters may become dominant in epithermal gold deposits and other vein and replacement deposits. 

Hydrothermal activity associated with volcanism introduces into the environment high quantities of heavy metals, and in some cases, this activity can even produce ore deposits. Classic examples are porphyry copper and epithermal gold deposits (Bodnar, 1995 Hedenquist and Lowenstem, 1994). For the Bagnoli area, this scenario is confirmed both by research carried out on the waters in front of Bagnoli (Damiani el al., 1987 Sharp and Nardi, 1987) and by recent studies... 

Gold (Appendix, Plate 18) is frequently enriched in active geothermal system and epithermal gold deposits (Appendix, Plates 19-23). 

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