Cu-Ni-PGE mineralisation at the Aurora Project and potential for a new PGE province in the Northern Bushveld Main Zone

- Mineralisation at Aurora is different to established Platreef-type mineralisation.
- Base metal sulphides are hosted by leucocratic not melanocratic rocks.
- Pigeonite and orthopyroxene co-exist in the mineralised zone.
- Mineralogy and geochemistry are consistent with the Upper Main Zone.
- Aurora-type mineralization may be traced along strike for > 20 km to north and south.

The Aurora Project is a Cu-Ni-PGE magmatic sulphide deposit in the northern limb of the Bushveld Complex of South Africa. Since 1992 mining in the northern limb has focussed on the Platreef deposit, located along the margin of the complex. Aurora has previously been suggested to represent a far-northern facies of the Platreef located along the basal margin of the complex and this study provides new data with which to test this assertion. In contrast to the Platreef, the base metal sulphide mineralisation at Aurora is both Cu-rich (Ni/Cu < 1) and Au-rich. The sulphides are hosted predominantly in leucocratic rocks (gabbronorites and leucogabbronorites) with low Cr/MgO (< 30) where pigeonite and orthopyroxene co-exist as low-Ca pyroxenes without cumulus magnetite. This mineral association is found in the Upper Main Zone and the Aurora mineral chemistry is consistent with this stratigraphic interval. Pigeonite gabbronorites above the Aurora mineralisation have high Cu/Pd ratios (> 50,000) reflecting the preferential removal of Pd over Cu in the sulphides below. Similarly high Cu/Pd ratios characterise the Upper Main Zone in the northern limb above the pigeonite + orthopyroxene interval and suggest that Aurora-style sulphide mineralisation may be developed here as well. The same mineralogy and geochemical features also appear to be present in the T Zone of the Waterberg PGE deposit, located under younger cover rocks to the north of Aurora. If these links are proved they indicate the potential for a previously unsuspected zone of Cu-Ni-PGE mineralisation extending for over 40 km along strike through the Upper Main Zone of the northern Bushveld.