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116 Geothermal Energy: Renewable Energy and the Environment

6.3 Listed below are three geothermometers (Fournier 1981; Henley et al. 1984), all con-
centrations are in mg/kg:

SiO 2 : T°C = [1032/(4.69 − log SiO 2 )] − 273.15
Na/K: T°C = [855.6/(log (Na/K) + 0.8573)] − 273.15

Na–K–Ca: T°C = [1647/(log (Na/K) + {0.33*[log(sqrt(Ca)/Na) + 2.06]} + 2.47)] − 273.15

Compute the temperatures for the waters listed in Table 5.1. Which samples have the
best agreement among the geothermometers?
6.4 Provide an explanation for the disagreement among the samples. Is there anything
systematic about the results?
6.5 Assuming that the water at The Geysers is mixing with “Primitive Magmatic Water,”
what proportion of magmatic water is in The Geysers sample with the highest oxygen
isotope ratio?
6.6 From the data in Figure 6.13, what would be the most likely circulation pattern of
water above the “hot spot” located at a depth of about 18 km and in the middle of the
Figure?
6.7 What might be the explanation for the lack of correspondence between the magnetic
and gravity surveys that was observed in the Fallon, Nevada study?

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