Quartz veins

Quarz-gang, m. quartz vein, -gefass, n. quartz vessel, -gerat, n. quartz apparatus, quartz ware, -glas, n. quartz glass, -gut, n. quartz ware. 

Figure 1.6. Di.stribution and temporal and spatial relationship of late Cenozoic gold deposits in the Japanese Islands. 1 Quartz vein-type gold deposits with little to no base metals. 2 Gold-silver deposits with abundant base metals. 3 Distribution boundary of gold deposits formed during the Miocene. 4 Location of Plio-Pleistocene gold deposits at the actual island arc junctions. 5 Location of Plio-Pleistocene gold deposits in front of the actual island arc junctions. Numbers in the figure are K-Ar ages of epithermal Au-Ag veins (Kubota, 1994).

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 formation of epidote, K-feldspar, prehnite, wairakite and calcite in the geothermal area is considered to be due to the loss of CO2 gas and rapid precipitation from the solution supersaturated with respect to quartz (Browne, 1978). The widespread occurrence of these minerals in the Seigoshi district seems to be consistent with the above-mentioned consideration, namely that these minerals usually occur as veinlets rather than the replacements of original minerals and filling amygdule. In particular, many veinlets of epidote, prehnite and wairakite are found near the Au-Ag-quartz veins. 

Morishita (1993) showed based on carbon isotopic composition of carbonates that carbon of carbonates in the gold-bearing quartz vein in southern Kyushu was derived from the Shimanto Supergroup shale. Imai et al. (1998) considered that hydrogen in the ore fluids was derived from the Shimanto Supergroup shale based on 5D (—60%o to — 100%c) of inclusion fluids in quartz and adularia of the Hishikari veins. These isotopic... 

Figures 1.137 and 1.138 show the change in elemental contents (Si02, K2O, CaO, MgO) of altered andesitic rocks away from the quartz vein system. Figure 1.139 shows the relationships between (CaO - - Na20) content and K2O content. These data indicate the following features of compositional variation of altered rocks.

The dependence of concentration of K+, Na+, Ca + and H4Si04 in equilibrium with common alteration minerals (K-feldspar, Na-feldspar, quartz) on temperature is shown in Fig. 1.140 (Shikazono, 1988b). This figure demonstrates that (1) chemical compositions of hydrothermal solution depend on alteration minerals, temperature and chloride concentration, and K" " and HaSiOa concentrations increase and Ca + concentration decrease with increasing of temperature. In this case, it is considered that potassic alteration adjacent to the gold-quartz veins occurs when hydrothermal solution initially in... 

Therefore, it is thought that the mixing of acidic solution with hydrothermal solution occurred and andesite near the gold-quartz veins suffered superimposed potassic and advanced argillic alterations. 

Figure 1.142 shows the dependence of solubility of Si02 minerals (quartz, cristobalite) on temperature. As described already, cristobalite occurs in peripheral and shallower part of hydrothermal alteration zone. Quartz is present in zones occurring in deeper and closer to the gold-quartz veins. Such zoning from quartz to cristobalite is also common in main active geothermal systems (Hayashi, 1973 Takeno et al., 2000). 

Gold-quartz vein-type deposits (mesothermal-hypothermal vein-type deposits)... 

Gold-quartz vein-type (mesothermal-type and hypothermal-type deposits in the sense of Lindgren (1928)) occur in sedimentary terrane associated with Cretaceous felsic... 

Main opaque minerals include native gold, electrum, pyrite, pyrrhotite, chalcopy-rite, cubanite, sphalerite, arsenopyrite and tellurobismutite. The amounts of these sulfide minerals are poor, compared with those in epithermal Au-Ag vein-type deposits. It is noteworthy that silver minerals are abundant in epithermal Au-Ag vein-type deposits, whereas they are poor in gold-quartz veins. 

I.6.3.2. Gold-quartz vein-type deposits in Yamizo Mountains, central Japan... 

Gold-quartz veins ranging in width from several centimeters to several ten centimeters are situated in shale and/or sandstone of the Yamizo Formation and rarely in granitoids. The strike and dip of the veins are various. For example, the veins of the Kuryu, Shiozawa, and Daigo deposits strike N40°W, N20-30°W, and N30°E, respectively, and dip 60°E, 30-50°W, and 20°W, respectively. 

In the Yamizo Mountains, the correlation between A Ag and a kind of the host rocks is found A Ag of gold from gold-quartz veins in shale is lower than that in sand.stone. 

Ishihara, S., Sakamaki, Y., Sasaki, A., Teraoka, Y. and Terashima, S. (1986) Role of the basement in the genesis of the Hishikari gold-quartz vein deposit, southern Kyushu. Japan. Mining Geology, 36, 495-510. 

Izawa, E., Yoshida, T. and Sakai, T. (1981) Fluid inclusion studies on the gold-silver quartz veins at Kushikino, Kagoshima, Japan. Minig Geol., Spec. Issue, 10, 25-34. 

Izawa, E., Kurihara, M. and Itaya, T. (1993) K-Ar ages and the initial Ar isotopic ratio of adularia-quartz veins from the Hishikari gold deposit, Japan. Resource Geology Special Issue, 14, 63-69. 

Nakayama, E. and Enjoji, M. (1985) Au-Ag-quartz vein from Nebazawa mine, Gunma Prefecture. In Mining and Metallurgical Institute of Japan (ed.), Gold and Silver Ore in Japan, pp. 89-112 (in Japanese). 

Takahashi, M. Ishiyama, T. and Mizuta, T. (1998) Structure and environment of formation of the Hosen No. 5 and Ryosen No. 5 gold-quartz veins, Hishikari mine. Japan. Rep. Inst. Appl. Earth Sci. Dep. Geosci. Akita U., 63, 55-72 (in Japanese with English abst.). 

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. 

The five types of molybdenum deposits include (i) molybdenum and copper porphyry deposits (ii) Quartz vein and pipes (iii) Pegmatites and apatites dikes (iv) Contact-meta-morphic rocks and tactite bodies of silica bearing limestone and (v) Sedimentary rocks containing bedded deposits. 

Group 2 Cassiterite from quartz veins. Cassiterite from this group contain about 1% (Nb,Ta)205 and about 03-0.4% wolframite. 

The granitoid pluton is mostly massive, with some isolated off-shoots of the pluton in the east show foliation in the NW-SE direction with moderate dips towards SW (Fig.1), which is parallel to the schistosity of the country-rock metapelites. Pegmatites and pegmatitic quartz veins occur in metasediments, spatially associated with the granites. 

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