|The immense Earnscleugh dredge tailings on the south bank of the swift Clutha River near Alexandra represents 100 years (1860s-1960s) of technological advancement in gold mining that led the world.
The entrance to the 2–3-hour Earnscleugh Tailings Historic Reserve walk is across the Fraser River at the end of Marshall Road, 3km from Alexandra along Earnscleugh Road. It is a 30-minute return walk to the viewing platform.
During the dredging boom from the 1890s to 1905 up to 100 dredges are said to have worked Otago rivers. The gorge near Alexandra was particularly rich. Aside from the impressive tailings there are old dredging ponds, water races, remnants of original ground surfaces, buckets and trommels (screens/sieves).
The first Central Otago gold rush of 1862-64 focused on the easily accessible alluvial gold from shallow areas. As returns dwindled, attention turned to developing mechanical dredges that would go down into the river bed. The first dredges were built in the 1860s, but it was the steam-powered bucket and ladder dredge of the 1880s, which provided the means for the boom years. It was followed by the paddock dredge that floated in its own pond and from about the 1930s, the highly effective electric dredge. The huge electric Alexandra worked the Earnscleugh plains from 1951-1963 and gained hansom returns.
During the boom years tailings were a problem. This leftover gravel from which the gold was extracted, tended to backfill into operations. The creation of a dredge elevator in 1894 was a revolutionary solution. It discarded tailings well away from the dredging operation.
This innovation opened up mining on the river flats and terraces. As the technology improved, operations moved further inland, progressively higher and spread tailings further away. This progression is clearly evident in the varying levels of tailings at the reserve.