Hydrothermal activity

The most significant deposits are in southern Nevada, in the Lake Mead area, and in the McDermitt caldera complex on the Nevada—Oregon border. In the McDermitt caldera, lithium probably originated from volcanic sedimentary rocks deposited in the caldera moat. There is evidence that areas of the caldera were hydrothermically active contributing to enrichment of lithium (14). This and other similar deposits are not economically viable as of this writing. These deposits do represent a significant lithium reserve, however, whenever large expansion in demand occurs. 

Edmond, J. M., Measures, C., McDuff, R. E. et al. (1979). Ridge crest hydrothermal activity and the balance of the major and minor elements in the... 

The great variety of mineral deposits of Japan reflects the complex geotectonic environments. An intimate relationship exists between igneous and hydrothermal activity, which in turn reflects the plate tectonic history of Japan. Many Japanese ore deposits have produced many different metals, and they contain almost all common and useful minerals, although many deposits are small in size. 

These different sites of hydrothermal and ore-forming activity may have resulted from the mode of subduction of the Pacific Plate. Mariana-type subduction (characterized by a steep angle of subduction and back-arc basin formation Uyeda and Kanamori, 1979) during middle Miocene caused WNW-ESE extension, submarine hydrothermal activity, thick accumulation of bimodal (basaltic and dacitic) volcanic activity (Green tuff) and Kuroko-type formation (Shikazono and Shimizu, 1993). Plio-Pleistocene Chilean-type subduction (shallow-dipping subduction zone, E-W compression Uyeda and Kanamori, 1979) and oblique subduction of the Pacific Plate beneath the North American Plate led to uplift and expansion of land area, subaerial hydrothermal activity accompanied by meteoric water circulation, subaerial andesitic volcanic activity and formation of vein-type deposits. 

Large epithermal gold vein-type deposits occur at major arc-arc junctions (Figs. 1.5 and 1.6) specifically, Chishima (Kurile)-Northeast Honshu, Northeast Honshu-Izu-Bonin and Southwest Honshu-Ryukyu. This may result from hydrothermal activities and mineralizations caused by intense volcanism at the arc-arc junctions. 

The REE study indicates that the concentrations of REE, particularly Eu and Ce in altered rocks and ore minerals are useful indicators of oxidation state, intensity of discharging hydrothermal solution and evolutionary stage of submarine hydrothermal activity. 

It is also noteworthy that major igneous and hydrothermal activities in the Japanese areas seems likely to have taken place almost at same times as the stress changes. The stress changes occurred at about 22 Ma, 15 Ma, 12 Ma and 8 Ma in the southern part of... 

The changes in stress fields, and intensities of igneous and hydrothermal activities seem to correlate to oscillatory motion of the Pacific plate (Jackson s episodes) (Jackson et al., 1975 Jackson and Shaw, 1975) (Masuda, 1984). Masuda (1984) and Takeuchi (1987) pointed out that the oscillatory motion of Pacific plate during the least 42 Ma correlates with magmatism, the intensity of tectonism, the change of stress field and the history of sedimentary basin in arc-trench system (Fig. 1.147). The above arguments also suggest that the mineralizations in arc and back-arc systems relate to the oscillatory motion of the Pacific plate. 

The causes for the different site of hydrothermal activity (submarine and subaerial environment) could be considered in terms of tectonic and geologic evolution of this metallogenic province from middle Miocene to Pleistocene. 

Geochemical features of sedimentary rocks formed in the Japan Sea as a proxy for hydrothermal activity... 

As noted already, intense submarine hydrothermal activity took place in the Japan Sea in 15-12 Ma, associated with Kuroko mineralization. However, it is uncertain that submarine hydrothermal activities associated with the Kuroko mineralization took place in the other periods from middle Miocene to present in the Japan Sea. Therefore, the geochemical features of sedimentary rocks which formed from the Japan Sea at these ages have been studied by the author because they are better indicator of age of hydrothermal activities than those of hydrothermally altered igneous rocks because the samples of continuous age of sedimentation are able to be collected and the ages are precisely determined based on microfossil data (foraminiferal, radioralian and diatom assemblages). 

Thick sedimentary pile from middle Miocene to late Pliocene is exposed in the Oga Peninsula, northern Honshu, Japan (Fig. 1.153). Age of the sedimentary rocks has been determined by microfossil data. Thus, the sedimentary rocks in the Oga Peninsula where type localities of Miocene sedimentary rocks in northern Japan are well exposed have been studied to elucidate the paleoenvironmental change of the Japan Sea (Watanabe et al., 1994a,b). Kimura (1998) obtained geochemical features of these rocks (isotopic and chemical compositions) and found that regional tectonics (uplift of Himalayan and Tibetan region) affect paleo-oceanic environment (oxidation-reduction condition, biogenic productivity). However, in their studies, no detailed discussions on the causes for the intensity and periodicity of hydrothermal activity, and temporal relationship between hydrothermal activity, volcanism and tectonics in the Japan Sea area were discussed. They considered only the time range from ca. 14 Ma to ca. 5 Ma. 

The geochemical features of the sedimentary rocks in the Oga Peninsula and the hydrothermal activity in Japan Sea deduced from these features are described below. 

High Zn, Cu and Ba contents of the Nishikurosawa Formation also indicate that the intense hydrothermal activity occurred at these ages. 

Magnetic susceptibility data are inferred to have been reflected by hydrothermal activity. The magnetic susceptibility data on the sedimentary rocks are shown in... 

It seems clear by comparing Fig. 1.159 with Table 1.26 that the ages of hydrothermal mineralization and alterations determined by K-Ar age dating are consistent with those of sedimentary rocks affected by hydrothermal activity in the Oga. Hydrothermal activities were intense at ca. 14-13 Ma, 12.6 Ma, 10.5 Ma, and 8.2 Ma. 

Matsuhisa, Y. and Utada, M. (1993) Hydrothermal activity responsible for the Kuroko mineralization inferred from oxygen isotopic ratios of altered rocks from the western area of the Hokuroku district, northern Japan. Bull. Geol. Surv. Japan, 44 (213/4), 155-168 (in Japanese). 

Oudin, E. and Cocherie, A. (1988) Fish debris record the hydrothermal activity in the Atlantic II Deep sediments (Red Sea). Geochim. Cosmochim. Acta, 52, 177-184. 

Shikazono, N. (1988a) Oxygen and carbon isotopic ratios of calcite and evolution of hydrothermal activities in the Seigoshi gold-silver mining district, Japan. Mining Geology Special Issue, 12, 1-16. 

Sulfates (barite and anhydrite) precipitate due to the mixing of discharging hydrothermal solution with cold seawater above the seafloor at an early stage of hydrothermal activity. Ca and Ba in hydrothermal solution react with SO in cold seawater, leading to the precipitations of anhydrite and barite. It is observed that anhydrite precipitated earlier than barite. This may depend on the initial Ca and Ba concentrations of end member hydrothermal solutions, temperature and degree of mixing of hydrothermal solutions and... 

The basic rocks in the Shimokawa area are metamorphosed up to green schist to amphibolite facies which are considered to be due to submarine hydrothermal activity (Miyake, 1988 Mariko, 1984 Mariko and Kato, 1994). 

Ishibashi, J. and Urabe, T. (1995) Hydrothermal activity related to arc-back-arc magmatism in the Western Pacific. In Taylor, B.C. (ed.), Backarc Basins Tectonics and Magmatism. New York Plenum Press, pp. 451-495. 

Nakamura, H. and Maeda, K. (1961) Thermal waters and hydrothermal activities in Arima hot spring area, Hyogo Prefecture (Japan). Japan Geol Surv. Bull, 12, AKl-VJl. 

It was shown in previous chapters that intense hydrothermal activities occurred in the Neogene age in and around the Japanese Islands under the submarine and subaerial environments. In this chapter the influence of these hydrothermal activities on the seawater chemistry, and the global geochemical cycle are considered. 

We saw in section 2.3.2 that present-day hot spring venting and sulfide-sulfate depositions have been discovered in back-arc basins in the Western Pacific. These intense hydrothermal activities indicate that seawater-volcanic rock interactions are taking place at these environments. 

Previous studies demonstrated that the CO2 fluxes by hydrothermal solution and volcanic gas from midoceanic ridges play an important role in the global CO2 cycle and affect the CO2 concentration in the atmosphere (e.g., Javoy, 1988). However, submarine volcanism and hydrothermal activity occur not only at midoceanic ridges but also at island arc and back-arc basins as already noted. 

Edmond, J., Measures, C., McDuff, E. et al. (1979) Ridge crest hydrothermal activity and the balances of major and minor elements in the ocean The Galapagos data. Earth Planet. Sci. Lett., 46, 1-18. Elderfield, H. and Schultz, A. (1996) Midocean ridge hydrothermal fluxes and the chemical composition of the ocean. Annu. Rev. Earth Planet Sci. Lett., 24, 191-224. 

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... 

Fluxes of volatile elements (CO2, S, As) and other elements (Hg, Mn, Ba) due to hydrothermal activities at back-arc basins were calculated. Probably the hydrothermal flux of minor elements concentrated in Kuroko deposits (Sb, Tl, etc.) is large compared with those from midoceanic ridges. CO2 flux from back-arc basins is estimated to be large compared with that from midoceanic ridges. 

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