Groundwater meteoric

Oxygen isotopic fractionation factors used for the calculation were taken from Taylor (1997). Initial 8 0 value of hydrothermal solution (0%o) was estimated from 8 0 values of K-feldspar and quartz in the veins and homogenization temperatures (Shikazono and Nagayama, 1993), and that of groundwater (—7%c) was estimated from meteoric water value of the south Kyushu district (—7%c) (Matsubaya et al., 1975). 

Uranium is readily mobilized in the meteoric environment, principally as the highly soluble uranyl ion (U02 ) and its complexes, the most important of which are the stable carbonate complexes that form in typical groundwaters (pH > 5, pC02 = 10 bar) (Gascoyne 1992b Grenthe et al. 1992 see also Langmuir (1997) for review). Uranium is... 

Analysis for such isotopes as carbon and deuterium has been conventionally used to assess the relative age of groundwater, and in evaluating its origin (i.e., meteoric, juvenile, formation, etc.), chemistry, and total salinity. Isotope composition of ground-water and surface water has also been used to correlate between areas of precipitation and groundwater, thus providing an indication of source area(s) of recharge. 

Fig. 2. Stable isotopes of S and O in groundwaters, Spence porphyry Cu deposit, Chile. These data are consistent with mixing between deep saline waters and regional dilute meteoric waters.

Noble gases in rainwater are in solubility equilibrium with air and, although we know of no investigations addressed to the question, there is no reason to believe any differently for river and lake water. Most work on meteoric water has thus been on groundwater, which is removed from contact with air, especially geothermal water (see review by Mazor, 1975). Matters of interest are the temperature at which the water was last equilibrated with air, whether it has behaved as a closed system since air equilibration, and indeed whether or not it is actually meteoric. 

The chemistry of the groundwaters of Bermuda was investigated in detail by Plummer et al. (1976). To date this investigation still remains one of the few major integrative studies of phreatic meteoric water diagenesis in the literature (see also, e.g., Harris and Matthews, 1968, Barbados Back and Hanshaw, 1970, Florida and Yucatan Plummer, 1977, Florida Budd, 1984, 1988, Bahamas). A summary of the conclusions of this work is given here. 

Figure 7.33. Geochemistry of the Devonshire, Bermuda groundwater lens. (A) Log of partial pressure of CO2 (PCO2X (B) strontium concentration in ppm, (C) calcium and (D) magnesium derived from the rock because of diagenesis in the meteoric realm. (After Plummer et al., 1976.)...

The meteoric line is a convenient reference line for the understanding and tracing of local groundwater origins and movements. Hence, in each hydrochemical investigation the local meteoric line has to be established from samples of individual rain events or monthly means of precipitation. A specific example of a local meteoric line, from northeastern Brazil, is given in Fig. 9.5. A local meteoric line is obtained 5D = 6.4 <5180 + 5.5 (Salati et al., 1980). Examples of equations of local meteoric lines reported from various parts of the world are given in Table 9.1. 

In Fig. 9.7 the groundwater data fall distinctly below the relevant meteoric line, indicating that secondary fractionation has occurred, or that the waters are ancient and were recharged in a different climatic regime that... 

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