Shotover Alluvial Gold: An Evaluation of the Genesis and Chronology of the Host Sediments

Several glacial episodes have been distinguished in the Shotover Valley. These produced fluvioglacial aggradational deposits downvalley from the terminii, commonly with well-preserved terrace treads, as exemplified near Skippers. Chronological links can be determined between the Shotover tills and sediments and assessed equivalent deposits in the Wakatipu Basin/Kawarau Valley region through axial valley profiling. Constructed relationships suggest older Shotover events were probably large and left little detrital deposits within the valley. In contrast, the younger advances were smaller and valley-constrained. They are modelled as being wholly of Waimea or Otira Glaciation age, advances from the latter period producing the visually distinctive flights of terraceremnants. Both the terraces and the inner gorge, now occupied by the Shotover River, have been extensively worked for alluvial gold. Enrichments in the former environment have predominantly been as bottom or intermediate lags produced during degradation phases of catchment erosion. Surface lags have been locally targeted. Placer mining in terrace areas involved both tunnelling and sluicing techniques. In the modem river the greatest concentrations were on the schist or false bottoms, although flood gold has always contributed to the returns. Placer mining techniques here were highly variable.