Noble gas mixtures in mineralizing fluids

Description and analysis of multi-component noble gas mixtures in ore fluids 

The procedure by which multi-component mixtures of noble gas (He and Ar) isotopes and halogens can be represented in terms of 2 and 3 dimensional linear mixing diagrams is described in this section. The treatment is not intended to be exhaustive but to illustrate how potentially useful pieces of mineral deposit information can be extracted from the data. 

Further insight into the magmatic component can be gained from the °Ar /Cl ratio obtained from irradiated samples (Kelley et al. 1986 Turner and Bannon 1992). Data from quartz vein samples from the Globe Miami porphyry copper deposit are plotted on a 40Ar/3 Ar versus Cl/ Ar diagram (Fig. 32, Kendrick et al. 2001b). The correlation 

Burgess et al. 2002). In contrast, typical crustal fluids exhibit °Ar7Cl values between 30 and 2,500 times lower (0.6-5x10, Turner and Bannon 1992) while ArVci of porphyry copper deposits are intermediate. Higher °Ar /Cl are predicted for metamorphic fluids which may acquire high concentrations of excess °Ar by thermal release from minerals without a concomitant release of Cl. 

Combined with the Cl abundance, the °Ar /Cl ratio obtained from irradiated samples can be used to calculate the concentration of excess °Ar in the inclusion fluids. After appropriate correction for radiogenic °Ar formed by in situ decay of K in the inclusions, the remainder is excess °Ar carried by the brines from which the host mineral was precipitated. The concentration of excess °Ar is useful as a measure of the extent of fluid-rock interaction (Kelley et al. 1986), residence time of the fluid in an aquifer (Turner 

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