Hydrothermal vent chimneys

Tivey MK (1995) Modeling chimney growth and associated fluid flow at seafloor hydrothermal vent sites. In SE Humphris, RA Zierenberg, LS Mullineaux, RE Thomson (eds) Seafloor Hydrothermal Systems ... 

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. 

Figure 7,27 Schematic representation of 5 S values in a modern mid KJcean ridge hydrothermal vent system. Most values are taken from Kerridge cr al. (1983) but with additions, from Btuth and Ohmoto (1988) and Woodruff and Shanks (1988). The enlargement of the chimney wall shows changing 5 S values and sulphide composition from inner to outer wall.

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. 

Deposits which are forming are frequentiy characterized by venting streams of hot (300°C) mineralized fluid known as smokers. These result in the local formation of metalliferous mud, rock chimneys, or mounds rich in sulfides. In the upper fractured zone or deep in the rock mass beneath the vents, vein or massive sulfide deposits may be formed by the ckculating fluids and preserved as the cmstal plates move across the oceans. These off-axis deposits are potentially the most significant resources of hydrothermal deposits, even though none has yet been located. 

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. 

Woodruff, L.G. and Shanks, W.C. Ill (1988) Sulfur isotope. study of chimney minerals and vent fluids from 21°N East Pacific Rise Hydrothermal sulfur sources and disequilibrium sulfate reduction. J. Geophys. Res., 93, 4562-4572,... 

The ridge crest is a dynamic setting in which volcanic activity creates new vents while old ones die. On fast-spreading centers, hydrothermal circulation supports focused discharges through chimneys that have an average life span of a few decades. 

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