Tsugu deposit

The Tsugu gold-antimony deposit is located in the central part of Honshu, Japan (Fig. 1.171). Geologically, the Tsugu deposit occurs in the Ryoke metamorphic terrane. 

H Hotei vein, J Jirabo vein, S Shinsei vein, Y Yokoniabu vein, 

The previous studies on the Tsugu deposit (Tsuboya, 1936 Tatsumi, 1948 Shikazono and Shimizu, 1988b) demonstrated that  

Hg content of electrum ranges from nil to 8.5 wt%, and Ag content ranges from 

A frequency histogram of the Ag content of electrum from epithermal gold-silver vein-type deposits and the Tsugu deposit (Fig. 1.174) clearly indicates that the Au/Ag of electrum from the Tsugu deposit is higher than that from epithermal vein-type deposits. 

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From (1-79) it is clear that the Hg content of electrum is related to /sj and A l-vg. Using the thermochemical data for reaction (1-78) by Barton and Skinner (1979), isoactivity lines for Hg in electrum may be drawn on a log/sj-temperature diagram (Fig. 1.175). At a given temperature, the activity of Hg in electrum increases with a decrease in /sj. Therefore, the /sj for the mercurian gold of the Tsugu deposit is inferred to be relatively low. 

Microprobe analyses of sphalerite indicate that sphalerite from the Tsugu deposit is markedly higher in iron than that from the epithermal Au-Ag vein-type deposits in Japan. 

The ranges of /sj and temperature for epithermal Au-Ag vein-type deposits in Japan have been clearly defined based on the chemical composition of sphalerite and electrum, and homogenization temperatures of fluid inclusions (Shikazono, 1985d). Values of /s for the Tsugu deposit are lower than the typical ranges of values for the epithermal Au-Ag vein-type deposits in Japan (Fig. 1.176). Such a low f 2 is in accord with the high Hg content of electrum in the Tsugu deposit. 

Figure 1.174. Frequency (number of analyses) histogram for Ag (atomic %) of gold from the Tsugu deposit (solid) and epithermal gold-silver vein-type deposits in Japan (open). I sample I II sample II. Data sources Tsugu deposit (Shikazono and Shimizu, 1988b) epithermal gold-silver vein-type deposits in Japan (Shikazono 1981, 1986 Shikazono and Shimizu, 1988b).

It is generally accepted that Kuroko deposits formed under the submarine environment, while polymetallic vein-type deposits in central and Northwest Japan (Ashio, Tsugu, Kishu, Obira, etc.) under the subaerial environment. 

In contrast, in Southwest Japan, polymetallic veins (so-called xenothermal-type deposits in the sense of Buddington (1935) or subvolcanie hydrothermal type in the sense of Cissartz (1928, 1965) and Schneiderhohn (1941, 1955) occur. Examples of these deposits are Ashio, Tsugu, Kishu and Obira. All these vein-type deposits have formed at middle Miocene age in western part of Tanakura Tectonic Line under subaerial environment. In these deposits, many base-metal elements (Sn, W, Cu, Pb, Zn) and small amounts of Au and Ag are concentrated. These deposits are associated with felsic volcanic and plutonic rocks along the Median Tectonic Line (MTL) or south of MTL. 

Figure 1.171. Map showing location of the Tsugu gold-antimony deposit. 1 Green-tuff region, 2 outer zone of southwestern Japan, TTL Tanakura tectonic line, ISTL Itoigawa-Shizuoka tectonic line, MTL Median...

Figure 1.173. Relationship between mercury and gold contents of mercurian gold from the Tsugu gold-antimony deposit (Shikazono and Shimizu, 1988b).

Shikazono, N. and Shimizu, M. (1988b) Mercurian gold from the Tsugu gold-antimony deposit in Japan. Can. Min., 26, 423-428. 

Tsuboya, K. (1936) The geology and the ore deposits of the Tsugu gold mine, Aichi prefecture. J. Geol. Soc. Japan, 43, Ci-ll (in Japanese). 

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