Insights into the Waiotapu geothermal field using high resolution SkyTEM data

Abstract

Airborne Transient ElectroMagnetic (ATEM) geophysical methods enable high densities of data to be collected over large areas in an efficient manner. Resistivity models derived from the ATEM data enable high-resolution geological and hydrological structures to be interpreted in the near surface (approx. 400 m). We use ATEM data to interpret geological and hydrological features in the Waiotapu and Reporoa Geothermal Fields of New Zealand.
Selected cross-sections of resistivity models derived from ATEM data collected over the Waiotapu and Reporoa study areas are interpreted in terms of geology, hydrogeology and geothermal influences. Preliminaryinterpretations from the cross-sections show:
Good correlation between the ATEM data and the direct current resistivity maps of the spatial extent of low resistivity anomalies associated with the Waiotapu and Reporoa Geothermal Fields.
Good correlation between the locations of low resistivities and geothermal surface features.
A near-vertical low resistivity boundary on the western side of the Waiotapu Geothermal Field correlating with the mapped Ngapouri Fault. This implies a constrained permeable structure, or bounding structure.
Possible eastern extension of the Waiotapu Geothermal Field under the Kaingaroa Ignimbrite.
Correlation between some mapped active faults and low resistivity anomalies, indicating that faults (and specifically, which parts of the fault) could support geothermal fluid flow.
Abrupt resistivity boundaries may indicate either possible unmapped faults and/or geological boundaries.
Potential geothermal flows to the surface can be inferred in areas where low resistivity anomalies from the deeper part of the system can be traced to the surface.