Environmental isotope investigations of New Zealand geothermal systems—A review

Abstract

Environmental isotope investigations of geothermal systems at the New Zealand Institute of Nuclear Sciences have concentrated in recent years on combining several isotopes with chemical analyses. Geothermal hydrology has been studied by the use of hydrogen and oxygen isotopes with chloride and other water analyses. Rocks and minerals in well cores have added information to the geology and chemistry through the use of oxygen isotope techniques. Oxygen, hydrogen, carbon and sulphur isotope geothermometry have been combined in an attempt to derive temperature profiles with depth. 222Rn measurements in soil indicate leakage through faults, while 222Rn measurement of well discharges show evidence of underground processes. Future work will include noble gas isotope measurements. Measurements of 1H and 14C are reported in an associated paper on tracing of underground water movements.