ABSTRACT

The utility of helium and neon isotopes as tracers of mixing in geothermal systems may be enhanced by employing an appropriate method of graphical analysis. On linear ³He/⁴He-²⁰Ne/⁴He diagrams mixing is revealed by straight lines. This is contrary to the current procedure of plotting ³He/⁴He against ⁴He/²⁰Ne, where mixing lines are curved. Construction of triangular mixing plots with such data allows an immediate quantitative assessment of the extent to which the measured isotopic ratios reflect those of different endmembers (e.g. atmospheric, radiogenic and magmatic) and allows one to use these plots to compare the sources of rare gases in geothermal systems from different parts of the globe.