Hydrothermal system

The authors realize the many problems inherent in their hypothesis and hope that someone will be inspired to solve the problem of how a transition from inorganic-based life to life as we know it could have taken place (Greenwell and Coveney, 2006). 

The variety of life forms to be found near hydrothermal vents does not, of course, mean that life itself originated there these geological systems are much too unstable for that. The dynamics of tectonic plates cause the vents to disappear after some decades, or at most after a few hundred years. According to Nils Holm from the Department of Geology and Geochemistry at the University of Stockholm, the discovery of the hydrothermal vents led to intense, and in some cases controversial, discussions of the question as to whether hydrothermal systems were the birthplaces of life around four billion years ago. Many geologists believe that hydrothermal activity on the primeval Earth was probably stronger than it is today, as the thick 

There are other arguments which support the assumption that biogenesis occurred at thermal sources  

The earlier assumption of a reducing atmosphere has been modified in favour of a neutral one. It is hypothetically possible that iron vapour and reduced forms of carbon from meteorite impacts on the ocean could have led to limited regions with reducing properties. 

The hydrothermal systems, hundreds of meters under the surface of the ocean, would have protected evolving systems from the high-energy cosmic radiation as well as from meteorite impacts. Even partial evaporation of sea water, due to gigantic impacts, could have been resisted by molecular systems present at great depths (Holm and Andersson, 1995). 

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A simple model can be used to describe this control of the concentration. In this model the input is from rivers and the output is uptake by reactions in the ocean crust under hydrothermal systems. (An application of this model is given in Section 13.5). Thus... 

Some applications of the coupled fluid flow-reaction model were carried out to the ore-forming process (e.g., Lichtner and Biino, 1992). However, a few attempts to understand quantitatively the precipitations of minerals from flowing supersaturated fluids in the submarine hydrothermal systems have been done (Wells and Ghiorso, 1991). Wells and Ghiorso (1991) discussed the silica behavior in midoceanic ridge hydrothermal system below the seafloor using a coupled fluid flow-reaction model. 

Amorphous silica and barite precipitate simultaneously from white smoker in midoceanic ridge hydrothermal system (Edmond et al., 1979). It is inferred that amorphous silica precipitates in the chimney at a later stage than sulfides and sulfates (anhydrite and barite) which constitute chimneys from which black smoker is emerging. 

Barite is abundant in back-arc basin hydrothermal system such as Okinawa, Manus and Mariana (Shikazono and Kusakabe, 1999). 

There is another opinion on the origin of Kuroko ore fluids. Sawkins (1982) thought that intrusive felsic magmas were the source of the metals and heat in Kuroko hydrothermal systems. He stressed the contributions of magmatic fluid and seawater in... 

Formation of albite which is characteristic mineral of propylitic alteration occurs by heating of rocks and descending fluids at recharge zone in the hydrothermal system (Giggenbach, 1984 Takeno, 1989). Thus, it is considered that the propylitic alteration takes place at recharge zone in the hydrothermal system, while potassic alteration at discharge zone. 

Hydrothermal system at discharge zone is composed of five reservoirs such as ore deposit/zone IV boundary, zone III/II boundary, zone II/I boundary, zone I/fresh country rocks boundary and temperature of each reservoir is 250°C, 220°C, 150°C, 100°C, and 25 °C, respectively. 

Evolution of tectonics and hydrothermal system associated with epithermal and Kuroko mineralizations... 

However, in contrast to these geologic and tectonic studies, very few studies on the relationship between tectonics and hydrothermal system in Neogene age have been carried out. Therefore, these studies are briefly summarized and then the relationship between geologic and tectonic evolution and evolution of hydrothermal system associated with the mineralizations (Kuroko deposits, epithermal veins) are considered below. 

Aoki, M. (1988) Gold mineralization in the Osorezan hydrothermal system — Rock alteration and hot spring precipitates. Mining Geology, 38, 64 (in Japanese). 

Aoki, M., Comsti, E.C., Florin, B.L. and Matsuhisa, Y. (1993) Evolution of the hydrothermal system with special reference to the geochemistry of alunite solid-solution. Baguio Report of Research and Development Cooperation 1717 Project, 8741, 42-63. 

Cathles, L.M. (1983b) An analysis of the hydrothermal system responsible for massive sulfide deposition in the Hokuroku basin of Japan. Econ. GeoL Mon., 5, 439-487. 

D Amore, F. and Panichi, C. (1980) Evaluation of deep temperatures of hydrothermal systems by a new gas geothermometer. Geochim. Cosmochim. Acta, 44, 2021-2032. 

Ellis, A.J. (1969) Present-day hydrothermal systems and mineral deposition. Commonwealth Mining Metall. Cong., 9th, London, Proc., pp. 1-30. 

Etoh, J., Taguchi, S. and Izawa, E. (2001) Gas compositions in fluid inclusions from the Hishikari epithermal gold deposit, southern Kyushu, Japan. Proceedings of International Symposium on Gold and Hydrothermal Systems, pp. 99-104. 

Giggenbach, W.F. (1997) The origin and evolution of fluids in magmatic-hydrothermal systems. In Barnes, H.L. (ed.). Geochemistry of Hydrothermal Ore Deposits. New York John Wiley and Sons, pp. 699-... 

Haas, L. Jr. (1971) The effect of salinity on the maximum thermal gradient of a hydrothermal system at hydrostatic pressure. Econ. Geol, 66, 940-946. 

Hedenquist, J.W. (1987) Volcanic-related hydrothermal systems in the Circum-Pacific basin and their potential for mineralization. Mining Geology, 37, 347-364 (in Japanese). 

Henley, R.W., Tmesdell, A.H. and Barton, RB. Jr. (1984) Fluid-mineral equilibria in hydrothermal systems. Reviews in Econ. Geol., 1, 115-127. 

Izawa, E., Tsujimoto, T. and Sano, M. (1987) Enrichment and depletion of elements in the hydrothermal system of the Kushikino gold mining district, Japan. Mining Geology, 37, 85 (in Japanese with English abst.). 

M.J. (1983) Metabasalts, axial hot springs and the structure of hydrothermal systems at midocean rides. 

Shikazono, N. (1974d) Present-day hydrothermal system associated with base metal precipitates — (II). 

Shikazono, N., Utada, M. and Shimizu, M. (1995) Mineralogical and geochemical characteristics of hydrothermal alteration of basalt in the Kuroko mine area, Japan Implications for the evolution of back arc basin hydrothermal system. Applied Geochemistry, 10, 621-642. 

Wells, J.T. and Ghiorso, M.S. (1991) Coupled fluid flow and reaction in midocean ridge hydrothermal system The behaviour of silica. Geochim. Cosmochim. Acta, 55, 2467-2481. 

White, D.E., Muffler, L.J.P. and Truesdeil, A.H. (1971) Vapor-dominated hydrothermal systems compared with hot water systems. Econ. Geol, 66, 75-97. 

Another interesting characteristic of the Osorezan hydrothermal system is that it is located at a volcanic front. This is different from low sulfidation epithermal Au-Ag veins... 

Such evolution of a hydrothermal system from acidic sulfate hydrothermal solution to neutral is common in the epithermal system associated with precious metal mineralization. For example, advanced argillic alteration and intense silicification occurred at earlier stage of hydrothermal system in the Seigoshi Au-Ag mine area. 

Pb, Zn) sulfides occur in deeper part as in Broadlands (New Zealand) and in Okuaizu (Japan). Pb and Zn sulfides occur dominantly at 400 m from the surface in Broadlands. In the boreholes of Broadlands, concentrations of precious and base metal elements in the boreholes change with depth as studied by Ewers and Keayse (1977), Au, As, Sb and T1 decrease with depth, but Ag increases with depth. In active geothermal systems in Japan, Au, Te, Se, T1 and Hg are enriched on the surface in the Osorezan hydrothermal system. 

Phase separation and segregation are occurring in some hydrothermal systems (Gamo, 1995) which modify the chemistry of initial hydrothermal solution. Von Damm and Bischoff (1987) and Butterfield et al. (1994) obtained high chloride concentration of more than twice of the seawater value for the hydrothermal solution at the North Cleft Segment and the South Cleft Segment of the Juan de Fuca Ridge. 

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