Fossil Hydrothermal Systems

The best-studied example of a hydrothermal system associated with a gabbro is the Skaergaard intrusion (Taylor and Forester 1979 Norton and Taylor 1979). The latter authors carried out a computer simulation of the Skaergaard hydrothermal system and fonnd a good match between calculated and measured 8 0-values. They further demonstrated that most of the subsolidus hydrothermal exchange took place at very high temperatnres (400-800° C), which is compatible with the general 

Taylor (1988) distinguished three types of fossil hydrothermal systems on the basis of varying water/rock ratios, temperatures, and the length of time that fluid/rock interaction proceeds  

Type /. Epizonal systems with a wide variation in whole rock 0-contents and extreme oxygen isotope disequilibrium among coexisting minerals. These systems typically have temperatures between 200 and 600°C and life-times 10 y. 

Type II. Deeper-seated and/ or longer-lived systems, also with a wide spectrum of whole rock ratios, but with equilibrated ratios among coexisting 

Type III. Equilibrated systems with a relatively uniform oxygen isotope composition in all lithologies. These systems require a large water/rock ratio, temperatures between 500 and 800°C, and life times around 5 x 10 y. 

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In Chapter 2, a geochemical, geological and mineralogical summary of active subaerial and submarine back-arc basin hydrothermal systems and mineralizations is given. The characteristic features of above-fossil and active subaerial and submarine hydrothermal systems are compared with fossil hydrothermal systems (epithermal vein-type and Kuroko deposits), and the causes for the differences in the characteristic features are considered. Characteristic features of Paleozoic-Mesozoic volcanogenic stratiform Cu deposits (Besshi-type deposits) are compared with those of midoceanic ridge deposits and Kuroko deposits. 

Smith CN, Kesler SE, Klaue B, Blum J (2005) Mercury isotope fractionation in fossil hydrothermal systems. Geology 33 825-828... 

Taylor HP, Epstein S (1962) Relation between 0/ 0 ratios in coexisting minerals of igneous and metamorphic rocks, I Principles and experimental results. Geol Soc Am Bull 73 461 80 Taylor HP, Forester RW (1979) An oxygen and hydrogen isotope study of the Skaergaard intrusion and its country rocks a description of a 55 M.Y, old fossil hydrothermal system. J Petrol 20 355 19... 

Yang, S.X. and Blum, N. (1999a) A fossil hydrothermal system or a source -bed in the Madiyi formation near the Xiangxi Au-Sb-W deposit, NW Hunan, PR China Chemical Geology, 155(1-2), 151-69. 

Craw, D., Chappell, D. and Reay, A. (2000a) Environmental mercury and arsenic sources in fossil hydrothermal systems, Northland, New Zealand. Environmental Geology, 39(8), 875-87. 

Schiffman P. and Smith B. M. (1988) Petrology and oxygen isotope geochemistry of a fossil seawater hydrothermal system within the Solea Graben, northern Troodos ophiolite, Cyprus. J. Geophys. Res. 93, 4612-4624. 

The fi O-Pj system has also recently been applied to phosphates associated with ferric iron oxyhydroxide precipitates in submarine ocean ridge sediments (Blake et al., 2000, 2001). The gi O-Pj signature of phosphate associated with these authigenic Fe-oxyhydroxide precipitates indicates microbial phosphate turnover at elevated temperatures. The latter observation suggests that phosphate oxygen isotopes may be useful biomarkers for fossil hydrothermal vent systems. On the basis of this work, Blake et al. (2001) also hypothesize that authigenic phases extant on other planets may retain imprints of primitive biospheres, in the form of detectable and diagnostic fi O-Pj composition, imparted by biochemical, enzymatic processes. 

The transition elements are useful tracers in many geological systems. They are industrially important and form economic ores, especially in hydrothermal systems where they are often present as sulfide minerals. Cd, Hg, Zn, and Pb are persistent industrial pollutants and determination of low levels of these elements in ores and fossil fuels is critical as processing of ores or burning of fuels may concentrate and release toxic elements. The concentration of such toxic trace elements may affect the economic value of an ore or fossil fuel deposit significantly. 

Deactivation of zeolite-based SCR systems can be divided into two main categories hydrothermal deactivation by steam in the exhaust system or chemical deactivation by different chemicals found in an exhaust stream of typical fossil fiiel engine. Steam is present in the exhaust, since it is a by-product of burning fossil fuels, while different chemicals might be present due to lubrication oil, contaminants in the fuel, or they may be originating from a different catalyst in the exhaust system. 

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