Abstract:
In the early stages of geothermal exploration, with the help of ground-truthing via outcrop or coring examination, Ground Penetrating Radar (GPR) has proven a successful technique in mapping the lateral and vertical extent of hot spring siliceous sinter deposits up to depths of 10 meters. Alkali chloride fluid is the fluid we seek for our geothermal power plants, making sinters important in geothermal exploration. Sinters are important as they provide evidence of sites where alkali chloride fluid discharged at the surface. They are preserved for thousands of years after hot spring flow discharge ceases. Sinter samples were collected from Opal Mound, and Steamboat Springs, USA, and from Pukemoremore and Horohoro, New Zealand. Samples were specifically chosen to represent the opal-A to opal-A/CT to opal-CT ± opal-C to quartz silica phase diagenetic sequence and to include both trace element-poor and trace element-rich sinters. GPR was conducted over the sample sites in order to test the suitability of GPR in imaging sinters with different silica phases, density and porosity values and trace element compositions. The GPR imaging revealed that despite the differences in these sinters they were capable of reflecting the emitted high-frequency electromagnetic wave to produce clear GPR profiles. We therefore conclude that GPR can be used for imaging all types of sinters. The new application of GPR to image sinters provides a technique whereby we can map the subsurface extent of a sinter and are no longer limited to outcrop examination. This provides us with new information on the volume of sinter present at any one site which can be directly related to the amount of fluid discharged in an area, as well as a tool that enables mapping buried sinters that could cap a blind geothermal resource.
