Nicholas Mortimer, Fabio Caratori Tontini, Candace Martin

The Hekeia Gabbro in the Longwood Range of Southland is prospective for platinum group element
mineralisation. Recently acquired geological and isotopic data, combined with reinterpreted aeromagnetic
data, provide new constraints on the three dimensional extent and internal structure of the gabbro. Direct
observations of in situ subvertical igneous layering give confidence that most curvilinear aeromagnetic
patterns are largely caused by macroscopic primary igneous layering. Steep magnetic gradients can be used
to reliably define the areal limits of the Hekeia Gabbro and show that it extends to depths >1 km. Nd isotope
ratios distinguish Hekeia Gabbro from younger gabbros and confirm the presence of at least two surface
outcrops of Hekeia Gabbro a few km west of the main body. Hekeia Gabbro is interpreted to be part of a 5
km thick Late Permian lopolith that was subsequently deformed and intruded by other Late Permian and
Triassic plutons.