Hydrothermal vent chimneys mineral precipitation

Modem hydro- High-temperature hydrothermal vents currently active at mid-ocean ridges offer a thermal mineral- unique opportunity to study a hydrothermal mineral deposit in the process of ization at formation. The current working model assumes that cold seawater sulphate is mid-ocean ridges drawn down into sea-floor basalts, where it is heated in the vicinity of a magma chamber. Some sulphate is precipitated as anhydrite whilst the remainder is reduced to sulphide by reaction with the basalt. The fluid is vented back onto the seafloor at about 350 C laden with sulphides. On mixing with seawater these are precipitated onto the sea floor as a fine sulphide sediment whilst at the vent site itself the sulphides are built into a chimney a metre or so in height. 

In the 1970s black smokers (Fig. 2.2) were detected. These are chimney-like structures above hydrothermal vents. In these smoker chimneys sulfides of iron, copper and zinc are found. At the mixture of the hot mineral rich water with cold water, these sulfides are precipitated and the vent water therefore appears black in color. The most striking discovery was that these warm chemical rich environments are the living space for many species. Huber and Wachtershauser, 1998 [166], modelled volcanic or hydrothermal settings. They showed that amino acids were converted into their peptides by use of precipitated (Ni, Fe)S and CO in conjunction with H2S (or CH3SH) as a catalyst and condensation agent at 100°C and pH 7 to 10 under anaerobic, aqueous conditions. Thus a thermophilic origin of life seems plausible. 

Farrell and Holland (1983) cited ba,sed on Sr isotope study on anhydrite and barite in Kuroko deposits that the most appealing model for the formation of Kuroko strata-bound ores would seem to entail precipitation of the minerals from a hydrothermal solution within the discharge vent or in the interior of a hydrothermal plume formed immediately below above the vent exit in the overlying seawater (Eldridge et al., 1983). The study on the chimney ores from Kuroko deposits support this model which is discussed below. 

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