Hydrothermal vein deposits

Hydrothermal vein deposits result from hydrothermal solutions. Hydrothermal solutions are essentially the residual hot solutions remaining after magmatic crystallisation (juvenile... 

Plutonic hydrothermal vein deposits, which can be found in China, (Jiangxi Guangdong Guangxi and Hunan provinces), Burma, countries of the former Sovient Union, Bolivia, Spain, and Portugal. 

Main hydrothermal ore deposit types of Neogene age that formed in and around the Japanese Islands are Kuroko deposits and epithermal vein-type deposits. This classification is based on the form of the deposits. 

Figure 1.18. Variation of Fe " /(Fe + Mg) and tetrahedral AI of chlorite from hydrothermal ore deposits Japanese Neogene Cu-Pb-Zn vein-type (open circle) and Kuroko deposits (solid circle). Localities 1 Ashio, 2 Yatani, 3 Toyoha, 4 Kishu, 5 Sayama, 6 Mikawa, 7 Furutobe, 8 Hanaoka, 9 Wanibuchi, 10 western Bergslagen (Shikazono and Kawahata, 1987).

Figure 1.83. Variation of Fe /(Fe + + Mg) and tetrahedral Al of chlorite from hydrothermal ore deposits Japanese Neogene Cu-Pb-Zn vein-type (open circle) and Kuroko deposits (solid circle). Localities 1 Ashio (Nakamura, 1960, 1963) 2 Yatani (Hattori, 1974) 3 Toyoha (Shikazono 1974a, Sawai, 1984) 4 Kishu (Shirozu, 1958) 5 Sayama (Shirozu, 1958) 6 Mikawa (Nagasawa, 1961) 7 Furutobe (Shirozu et al., 1975) 8 Hanaoka (Hayashi 1961, Hayashi and Oinuma, 1965 Tsuzuki and Honda, 1977 Shirozu et al., 1975) 9 Wanibuchi (Sakamoto and Sudo 1956, Iwao and Minato 1959, Katsumoto and Shirozu, 1973) 10 western Bergslagen (Baker et al., 1983) (Shikazono and Kawahata, 1987).

Consequently, the composition of chlorite in the discharge zone depends largely on the chemical nature of fluids (factors such as Fe "/Mg, SO /H2S, pH, aj 2+) and temperature. Movement of fluids may also be an important cause for the variability in the ratio of Fe " to Mg in hydrothermal chlorite. Wide compositional variations in chlorite from the hydrothermal ore deposits in Japan, including Kuroko and Neogene Cu-Pb-Zn vein-type deposits, are considered to reflect the variable chemical nature of ascending ore fluids and fluids that mix with ascending ore fluids at discharge zone. 

Therefore, the wider time range from middle Miocene to present is considered below based on available age data on hydrothermal ore deposits (Kuroko deposits, epithermal vein deposits) and hydrothermal alteration in the mine areas in Northeast Japan. 

Shikazono, N. (1973) Sphalerite-carbonate-pyrite assemblage in hydrothermal veins and its bearing on limiting the environment of their deposition. Geochem. J. 7, 97-114. 

In and nearby the Japanese Islands, which are situated close to plate boundaries (Pacific, Philippine, North American and Asian plates), many hydrothermal ore deposits were formed during the Miocene-present eras. Major deposit types are Kuroko and epithermal vein-types. Epithermal vein-type deposits are classified into precious (Au, Ag)-types and base-metal (Cu, Pb, Zn, Fe, Mn, Ag)-types. 

It is suggested that the mode of subduction of the Pacific Plate since the middle Miocene age related to Jackson s episode, hence oscillation of direction of lateral movement of Pacific plate. Synchronized igneous and hydrothermal activities and Jackson s episode indicate that the formations and characteristics of hydrothermal ore deposits (Kuroko and epithermal vein-type deposits) are largely influenced by plate tectonics (mode of subduction, direction of plate movement, etc.). For example, sulfur isotopic composition of sulfides is not controlled by /o and pH, but by of... 

Higgins, N.C. 1985. Wolframite deposition in a hydrothermal vein system The Grey River tungsten prospect. Economic Geology, 80, 1297-1397. 

If substantial arsenic is present in a sandstone or conglomerate, it may occur in hematite or other iron (oxy)(hydr)oxide cements or coatings on mineral grains. Arsenic may also be enriched in sandstones, conglomerates, and other clastic sedimentary rocks if hydrothermal or other secondary sulfide minerals are present (e.g. St. Peter Sandstone, (Gotkowitz et al., 2001) arsenian pyrite cement in the Marshall Sandstone of the Michigan Basin, USA, (Kolker et al., 2000 Szramek, Walter and McCall, 2004)). Sections of the St. Peter Sandstone in eastern Wisconsin, USA, are enriched in sulfide minerals and contain about 500 mg kg-1 of arsenic. In contrast, unmineralized portions typically have <10 mg kg-1 (Gotkowitz et al., 2001). If present in sedimentary rocks, hydrothermal sulfide deposits often tend to concentrate in veins and faults more than the rock matrices. 

Hydrothermal ore deposits can contain local zeohtes (e.g. the Andreasburg sulfide deposit in Germany) arising from circulating hot fluids. Similarly, zeolites arise in hydrothermal veins and cavities in felspathic rocks like the Adamello granite in Italy. 

At about the same time, the discovery of hot brine pools on the floor of the Red Sea indicated the possibility of direct precipitation of metalliferous sediments from high-temperature hydrothermal fluids on the seafloor (Miller et al. 1966 Bischoff 1969). This, more than any other discovery, resulted in a sweeping revolution in the field of ore genesis and a total reassessment of the origin of massive sulfide deposits, which were previously considered in many cases to be large mesothermal vein deposits that formed by replacement of country rocks deep in the earth. Moreover, in the first application of stable isotopes to seafloor hydrothermal processes, oxygen isotope studies of the Red Sea... 

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