Examination of thousands of fluid inclusion gas analyses has led us to question some working hypotheses associated with interpretations of N2/Ar ratios in geothermal volatiles. Fluid inclusion gas analyses, some confirmed by analyses of present fluids, indicate that geothermal fluids have N2 and Ar concentrations about 10 times greater than in air saturated water. Also, high N2/Ar ratios are associated with lower concentrations of Ar, rather than increased N2 in all geothermal systems we have studied. These observations contradict commonly held ideas about how geothermal systems operate and there are no apparent explanations. We introduce a CO2/CH4 vs. N2/Ar diagram. It illustrates fluid sources and processes better than a ternary diagram, and defines fluid compo-sitions that have organic nitrogen.

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