Water meteoric origin

Oxygen and hydrogen isotopes are a powerful tool in the study of the origin of subsurface waters. Prior to the use of isotopes, it was generally assumed that most of the formation waters in marine sedimentary rocks were of connate marine origin. This widely held view was challenged by Clayton et al. (1966), who demonstrated that waters from several sedimentary basins were predominantly of local meteoric origin. 

Meteoric water Water recently originating from the atmosphere. 

Fig. 9.7 Isotopic composition of groundwaters of northern Chile. The values lie below the meteoric line of local precipitation, explained by the investigators (Fritz, et al., 1979) as reflecting secondary fractionation by evaporation prior to infiltration, or the presence of ancient waters that originated in a different climatic regime. The large variations in the groundwater compositions are useful in local groundwater tracing.

The presence of volatile-bearing phases such as phlogopite, apatite, and carbonates in kimberhtes testify to the volatile-rich nature of the parental magma (e.g., Mitchell, 1986). The ubiquitous serpentization present in kimberlites cannot be used as evidence of magmatic water, with the exception of groundmass serpentine that is interpreted to be primary in nature. As discussed by Mitchell (1986), there are hmited stable isotopic data consistent with a meteoric origin for some of the water in the serpentine. However, it is unclear if these results could be attributed to postemplacement exchange of deuteric serpentine with meteoric fluids. 

This important and useful metal occurs very abundantly in nature. It is occasionally found in the uncombined state in masses, most probably of meteoric origin but its most common form is that of oxide, frequently uncombined, frequently also combined with carbonic acid. It is found, likewise, abundantly as sulphuret. There is hardly a rock, a soil, or a mineral which does not contain some proportion, generally a small one, of oxide of iron and the carbonate is a frequent ingredient in mineral waters, which are then termed chalybeate waters. 

However, it cannot be decided at present which processes (degree of seawater-rock interaction or mixing ratio of seawater, igneous water and meteoric water) are important for the generation of Kuroko ore fluids solely from the isotopic studies. But experimental and theoretical considerations on seawater-volcanic rocks interaction and origin of hydrothermal solution at midoceanic ridges suggest that Kuroko ore fluids can be produced dominantly by seawater-volcanic rock interaction. 

These detailed studies on individual mine district suggest that carbon in carbonates was derived from the country rocks underlying the ore deposits and oxygen in ore fluids is controlled by origin of ore fluids (mostly meteoric water) and boiling of ore fluids. 

Mixing of high temperature hydrothermal solution with high salinity and low temperature solution with low salinity of meteoric water origin seems the most likely mechanism for the base-metal vein-type deposition. 

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