Inversion of magnetic and gravity data reveals subsurface igneous bodies in Northland, New Zealand

Magnetic anomalies identified in the 2011 aeromagnetic survey data of Northland generally correlate with regional geology, but several anomalies have neither surface geological expression nor identifiable associations with the known geology of Northland. Inversion of magnetic data suggests that three circular positive anomalies located east of Kawakawa, east of Kaitaia and southwest of Houhora Heads are associated with buried volcanoes and/or igneous intrusions. Models suggest the magnetic anomalies are caused by subsurface bodies with magnetisation values up to 0.4 A m–1 that are c. 5 km in diameter and extend from depths of 1–3 km to within a few hundred metres of the ground surface. The shape and magnetisation of the bodies suggest that they may be buried rhyolite or andesite volcanoes and/or large granite or diorite igneous intrusions. These previously unknown igneous bodies contribute to our understanding of the volcanic history of Northland and, by analogy to known mineral deposits in Northland, may also host mineralisation that could be of interest to mineral explorers.