Remanent magnetization mapping: A tool for greenfields magmatic Ni-Cu-PGE exploration undercover: Part 1

Abstract

There are many challenges for greenfields exploration, particularly in vast, sparsely populated, partially covered terrains, e.g., a paucity of prior exploration data, and difficulties in gaining access to land. However, in many cases good aeromagnetic coverage is freely available, and for some styles of mineralization (e.g., magmatic Ni-Cu-PGE), aeromagnetic data alone can provide critical insights into the age, size and depth of multiple targets, across large regions, early in the exploration life cycle. This study investigates whether an understanding of remanent magnetization from three suites of mafic intrusions exposed in the Huckitta area, NT, Australia, can be utilized to provide a first pass exploration tool for exploration under shallow cover to the east. The study demonstrates that although the measured remanent magnetization vectors present were complex in some cases, the majority are sub-parallel (oriented steep down to the south), which implies a common mode of acquisition. It was found that the magnetizations were acquired during the Alice Springs Orogeny (ca 450–300 Ma), with the dominant magnetization occurring at ca 330 Ma. Therefore the magnetizations present do not relate to cooling of the parent magmas, but rather to cooling of lower crustal rocks from temperatures above the Curie point (>580 °C) during exhumation of the host terrain. Whilst this knowledge does not allow discrimination of the three suites remotely based purely on their remanent magnetization vectors, the recognition of a common magnetization vector present in all mafic rocks does allow us to better map mafic rocks under cover, and better constrain magnetic modelling and exploration targeting, as discussed in the second paper.