LECTURES ON GEOCHEMICAL !N1 ERPRETATION OF ...
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LECTURES ON GEOCHEMICAL !N1 ERPRETATION OF ...

LECTURES ON GEOCHEMICAL !N1 ERPRETATION OF ... LECTURES ON GEOCHEMICAL !N1 ERPRETATION OF ...

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- 41 -CATION GEOTHERKOKETRYRobert O. FournierU.S. Geological Survey, Menla Park, California 94025 U. S.A.INTRODUCTIONcation geothcrmometers are widely used to interpret compositions ofwaters collected from hot springs and wells . At this time the~ are manydifferent geothcrmometers to choose from and it is rare when they all giveabout the same result, especially when applied to hot- spring waters. Thispresentation will discuss the bases for cation geothermometers and generalprecautions in their application. Equations for the various geothermometersthat are now in use are given in Table 1 .THE THEORETICAL BASIS FOR CATION GEOTHERKOKETRYCation geothermomet~is based on ion exchange reactions that havetemperature- dependent equilibrium constants. An example is exchange ofHa+and K+between coexisting alkali feldspars:(1)The equilibrium constant, K ,for reaction (1) iseqKeq[1CA1Si 30 S! [Na+![NaA1Si 30 S! [It!(2)wbere square brackets denote activities of the enclosed species. In theapplication of equation (2), usual simplifying assumptions are that theactivities of the solid reactions (in this case albite and K- fcldspar) areunity and that activities of the dissolved species are about equal to theirmolal concentrations in aqueous solution (generally a good assumption only

- 42 -TABLE 1. Equations fo~ cation geothc~omete~s (concent~ations in mg/kg).GeothermometerEquationSourceUa- I(t·c856=O:ss7-' -Iog(Hi/K) -273.15Truesdell (1976)Ha-Xt·C883O:7so-'-Iog(Hi/K) -273.15Tonani (1980)Ha- I(t·C933= O~993-+-Iog(ia7X)-273.15(2S- 250°C) A~orsson (1983)Ha- Kt·C1319= i~699 -+ - Iog(ia7K)-273.15(2S0- 350°C A~orsson (1983)Ha- Xt·C =1217i:483-;-Iog(ia/X) - 273.15Fournier (l983)Ha-Kt·C1178= i~470 - +- Iog(ia7K)-273 .15Nieva (1987)Ha-Kt·C1390= r:750-+-Iog(Ua/X) -273.15Giggenbach (1988)K-I!gt·C4410I4 :00 -' - Iog(K/~)- 273.15Giggenbach (1988)X- LttOe ~ -- ---- ~~~~ ---T---- - - 273 155. 470 - log(L,Iv'I!g) •Kharaka & Mariner(1988)Ha- Lit·cKharaka et al. (1982)Ha-Li(Cl0.3K)t·cFouillac & Hichard (1982)Fouillac & Kichard (1982)Na- CaTonani (1980)X-CaTonani (1980)Na-K- Cat·c1647= Iog(Hi7K)'~I Iog(lci/Ha)'2 :o6T'2 : 47 - 273.15Fournier &Truesdel1 (1913)~ = 4/3 for t 100°C

- 42 -TABLE 1. Equations fo~ cation geothc~omete~s (concent~ations in mg/kg).GeothermometerEquationSourceUa- I(t·c856=O:ss7-' -Iog(Hi/K) -273.15Truesdell (1976)Ha-Xt·C883O:7so-'-Iog(Hi/K) -273.15Tonani (1980)Ha- I(t·C933= O~993-+-Iog(ia7X)-273.15(2S- 250°C) A~orsson (1983)Ha- Kt·C1319= i~699 -+ - Iog(ia7K)-273.15(2S0- 350°C A~orsson (1983)Ha- Xt·C =1217i:483-;-Iog(ia/X) - 273.15Fournier (l983)Ha-Kt·C1178= i~470 - +- Iog(ia7K)-273 .15Nieva (1987)Ha-Kt·C1390= r:750-+-Iog(Ua/X) -273.15Giggenbach (1988)K-I!gt·C4410I4 :00 -' - Iog(K/~)- 273.15Giggenbach (1988)X- LttOe ~ -- ---- ~~~~ ---T---- - - 273 155. 470 - log(L,Iv'I!g) •Kharaka & Mariner(1988)Ha- Lit·cKharaka et al. (1982)Ha-Li(Cl0.3K)t·cFouillac & Hichard (1982)Fouillac & Kichard (1982)Na- CaTonani (1980)X-CaTonani (1980)Na-K- Cat·c1647= Iog(Hi7K)'~I Iog(lci/Ha)'2 :o6T'2 : 47 - 273.15Fournier &Truesdel1 (1913)~ = 4/3 for t 100°C

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