Interpretation of Aeromagnetic Data Over the Orakeikorako Field, Central North Island, New Zealand

Abstract

The Orakeikorako geothermal fieldwas covered by two aeromagnetic surveyswhich were conducted at different altitudes (760 m and 60 m above the ground). Interpretation of the residual magnetic anomalies from both surveys has shown that hydrothermally demagnetised rocks inside the Orakeikorako reservoir to about 0.6 below sea level. The residual anomalies also indicate the presence of another concealed non-magnetic body, elongated in the SW-NEdirection, that appears to be connecting the Orakeikorako field and Te Kopia prospect in the NE. Result from topographic modelling suggests that a rhyolite dome at Trig 8571, about 5 km to the SW of Orakeikorako, is non-magnetic. The magnetic data also indicate presence of non magneticrocks at shallow level in the area to the of Trig 8571. It is possible that these non-magnetic rocks are relicts of old hydrothermal activity in the southern part of the Maroa Volcanic Centre.