Report: TR 2008/01

Author: J.G. Webster-Brown and K.L Brown, GEOKEM

Abstract

Chemical characteristics of geothermal fluids provide useful information on the deep resource, as well as on the nature of heat and mass flow from source to the surface. A geothermal geochemical monitoring programme (REGEMP) for the Waikato region was first developed in 1996 (Huser and Jenkinson, 1996), but for various reasons of budget or staff availability, never implemented until now. This new version of REGEMP, REGEMP II, is adapted from the programme of Huser and Jenkinson, taking account of developments that have occurred in the intervening period in relation to policy development, understanding of the nature of the geothermal resource, and the availability of new methods of geochemical analysis.

In addition to springs in the Taupo volcanic zone, the 1996 programme sampled a limited number of small isolated springs. The 2005 programme has added significantly to the number of isolated springs sampled. These springs are increasingly being used for leisure bathing and in some cases for horticultural uses. It is necessary to sample them to establish a baseline for unused springs, and to monitor effects of several small takes on small geothermal systems. For this reason, all small geothermal systems that have springs or wells that are readily accessible are included in the current programme.

Several features stand out as having unusual geochemistry for the region, such as Te Aroha, Tokaanu and a number of high-temperature features in the middle of the region. The only features to show a distinctive temporal trend were Horohoro (decreasing contribution from groundwater sources), and Ketetahi (an apparent decreasing contribution from steam-heated fluids). Nearly all quartz geotemperatures calculated for the low-temperature hot springs in the northern Waikato area predict temperatures greater than 100°C at depth.

Interpretation of Geochemical Data (REGEMP II) and Recommendations for Further Monitoring [PDF, 589 KB]