Beach gold transport and aeolian concentration, southern New Zealand

Abstract

ABSTRACT Aeolian concentration of iron-titanium oxides (black sand) is a common phenomenon on coasts around the world but associated aeolian detrital gold is relatively rare. In contrast, Holocene and active dunes at Waipapa beach on the coast of the southern South Island of New Zealand host aeolian black sand layers with locally abundant finely particulate (<200 µm) gold and platinum, some of which have been mined historically. Aeolian concentration of black sand, gold and platinum is driven by strong prevailing westerly winds (gusts >100 km/h) on annual or decadal time scales. Holocene fluvial recycling of aeolian sands has been important in upgrading the black sand, gold, and platinum contents. Surf concentration of black sand on the beach is minor and merely feeds the aeolian system, and this differs from other beach gold deposits around the world, which are surf-dominated. Most of the Waipapa beach gold (>90%) has flaky morphology with abundant superficial transport-related deformation reflective of fluvial transport, probably down the nearby Mataura River (∼200 km transport) between Miocene and Holocene. Minor distinctive wind-sculpted toroidal gold, and the platinum, arrived from the west (∼300 km transport) via the Waiau River and Foveaux Strait.