Abstract
Detrital platinum group minerals (PGM) are rare and distinctive in Pleistocene–Holocene sedimentary systems of the southern South Island, thereby enabling tracking of their long-distance transport for ∼200 km. The first ∼100 km of transport involved Pleistocene glaciofluvial processes southwards down the Waiau River, where PGM (principally Pt–Fe and Ru–Os–Ir alloys) became hammered into flaky morphology that remained largely unchanged thereafter. When sea level was more than 40 m below the present level, PGM were discharged southwestwards toward the offshore Solander Trough. Only at times of elevated sea levels have PGM remained onshore in beach concentrates. Pleistocene sea level high-stand beaches immediately east of the Waiau River have been uplifted tectonically and have become important secondary sources of detrital PGM. Erosion by Pleistocene coastal streams recycled flaky PGM, locally sourced equant PGM particles (principally Pt–Fe alloys and sperrylite, PtAs2), and associated detrital gold. Resultant redeposited concentrates have been mined at Round Hill. At times of lowered sea level, these PGM-bearing streams flowed southeastwards across an emergent fluvial plain on what is now Foveaux Strait. Holocene winds have formed aeolian PGM-bearing concentrates in scattered small dune fields, which are the largest repositories for PGM along the Foveaux Strait coast. Longshore drift has been important for carrying PGM for ∼100 km through Foveaux Strait in a complex long-term process involving interactions between sea level changes, tectonic uplift, and coastal recycling.