Polymetallic vein-type deposits

87sr/86sr ratio of volcanic rocks and granitic rocks (Shibata and Ishihara, 1979) (Fig. 1.166) and 5 S and sulfur content of Quaternary volcanic rocks (Ueda and Sakai, 1984) are different in two provinces (Fig. 1.167). 

As for the mineralization at the middle Miocene age in the Northeast Japan, Kuroko and epithermal base-metal veins have been formed. No enrichment of Sn and W is found in these deposits. 

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. 

According to Ishihara (1977), these granitic rocks are ilmenite-series while granitic rocks in Green tuff region are magnetite-series.  

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Polymetallic vein-type deposits occur in middle Miocene volcanic terrain in central and western Japan. 

Figure 1.124. Ag/Au total production ratio from each mine and Ag content of electrum. Solid circle epithermal Au-Ag vein-type deposits. Open circle epithermal base metal vein-type deposits. Solid square hypo/mesothermal polymetallic vein-type deposits. Open. square epithermal Au disseminated-type deposits. I Tada, 2 Toyoha, 3 Omidani, 4 Innai, 5 Ikuno, Oe-Inakuraishi, 7 Nebazawa, 8 Kawazu, 9 Todoroki, 10 Yatani, 11 Seigoshi, 12 Sado, 13 Takeno, 14 , awaji, 15 Yugashima, 16 Takadama, 17 Handa, 18 Konomai, 19 Sakoshi-Odomari, 20 Toi, 21 Sanru, 22 Arakawa, 23 Taio, 24 Chitose, 25 Hokuryu, 26 Okuchi, 27 Fuke, 28 Yamagano, 29 Akeshi, 30 Kasuga (Shikazono, 1986).

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. 

This spatial difference is consistent with the distribution with that of hydrothermal deposits of middle Miocene (Kuroko and polymetallic vein-type deposits in Japan). 

The relationship between the iron content of stannite in equilibrium with sphalerite and pyrite or with sphalerite and pyrrhotite was derived based on thermochemical data by Scott and Barnes (1971), Barton and Skinner (1979) and Nakamura and Shima (1982). These types of deposits are skam-type polymetallic (Sn, W, Cu, Zn, Pb, Au, Ag) vein-type and Sn-W vein-type deposits. As shown in Fig. 1.181, the /s -temperature range for each type of deposits is different at a given temperature, /sj increases from Sn-W vein-type through skam-type to polymetallic vein-type deposits. It is interesting to note... 

Figure 1.185. Locations of hypo/mesothermal vein-type deposits in Japan. Abbreviations are the same as those in Fig. 1.62. Open circle hypo/mesothermal Au vein-type deposits. Solid circle hypo/mesothermal polymetallic vein-type deposits (Shikazono and Shimizu, 1988a).

Sawai, O. (1999) Wall rock alteration of the Toyoha polymetallic vein-type deposits,. southwestern Hokkaido, Japan. Resource Geology Special Issue, 20, 99-112. 

As noted already, the formation of polymetallic vein-type deposits and Kuroko deposits occurred under the subaerial and submarine environments, respectively, at nearly the same time (middle Miocene). 

During the middle Miocene, Kuroko deposits, polymetallic vein-type deposits, gold-quartz vein-type deposits and Sb and Hg vein-type deposits were formed (see sections 1.3 and 1.6). Many vein-type deposits were formed not only in and nearby the Japanese Islands, but also at middle Miocene in northwest USA (Basin and Range Lipman, 1982), and elsewhere in the circum-Pacific regions (e.g., Peru). It is probable that large amounts of CO2 effused into the atmosphere from hydrothermal solution associated with this widespread mineralization and volcanic gas from subduction zones, causing an increase in temperature. 

For instance, polymetallic vein-type deposits formed under the subaerial environment influenced by igneous and sedimentary components. 

During the Miocene age, polymetallic vein-type (xenothermal-type, subvolcanic-type) and gold-quartz vein-type (mesothermal-hypothermal-type) mineralizations occurred mainly in middle to western part of Japan. They are described in section 1.6.1. In section 1.6.2, Hg and Sb vein-type deposits are described. 

The other important deposit types of the Neogene age are polymetallic (Cu, Pb, Zn, Sn, W, Au, Ag) (xenothermal or subvolcanic type deposits) vein-type deposits, hypo/mesothermal Au vein-type deposits, disseminated-type (hot spring type) Au deposits, and Hg-Sb disseminated and vein-type deposits. 

The Mount Pleasant Mine Property is located in Charlotte County, southwestern New Brunswick, Canada. The mineralization is divided into two main groups consisting of porphyry-type tungsten-molybdenum deposits, and vein and replacement-type tin polymetallic bodies. The deposits at Mount Pleasant are described in some detail in Kooiman et al. (1986) and Sinclair et al. (2006). Their petrogenetic character is discussed in Yang et al. (2003), Inverno Hutchinson (2006) and Sinclair et al. (2007). 

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