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ABSTRACT
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.
Acknowledgements
The authors thank colleagues at GNS Science, Mark Rattenbury, Bob Brathwaite, Tony Christie and David Skinner for helpful discussions of the initial interpretation of the data. The comments of MJ Isaac and an anonymous reviewer are gratefully acknowledged and improved the paper immensely.
Associate Editor: Associate Professor Andrew Gorman.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
Funding for the aeromagnetic survey was provided by the Ministry of Economic Development (MED), Northland Regional Council and Far North District Council. MED also funded the initial interpretation of the data.
