Spatial analysis and systematics of discrete extensional structures in the vicinity of the Kanmantoo Cu-Au mineral deposit, South Australia

Abstract

The Kanmantoo Cu-Au deposit, situated 55 km south-east of Adelaide, is hosted in the Tapanappa Formation of the Kanmantoo Trough. Recent evidence supports an epigenetic mineralising model for the deposit with respect to the Delamerian Orogeny of ~514 to 490 ±3 Ma. The Delamerian deformation event is the oldest portion of the Tasmanides, a 20 000 km orogenic belt along the eastern palaeo-pacific margin of Gondwana. Mineralisation of the Kanmantoo deposit has been linked with post-Delamerian multi-phase extension in east dipping normal faults. The final stages of extension resulted in non-mineralised north dipping normal faults and proximal discrete fracturing. Structural analysis of geology centred on the Kanmantoo deposit has classified a systematic set of extensional fracturing, developed in- the Kanmantoo deposit and in the region surrounding the deposit for >5 km radius. The fracture set trends east-west and dips steeply to the north with a recorded mean orientation of 75/359°. Fractures are characteristically not offset by shearing, strike for tens of metres, have variable frequency, and alterations influenced by fluid migration. Petrographic and geochemical analysis (SEM)in this study has defined a regionally distributed fracture-hosted albitic alteration, which is relatively enriched in Na, Ca, Al and depleted in Fe, Mg and K. A late stage extensional setting is supported for the development of the discrete sub-vertical fracturing.