Every day, specks of gold which have been highly flattened or are too small to see pass through the screens of alluvial gold mines, uncaptured. NZIMMR is working on improving the recovery of this gold. With around 25,000-30,000 ounces of gold mined every year on the West Coast, the size of the prize is significant.
Alluvial gold is the perfect commodity; once mined, it is easily sold, refined and exported to global markets. Many of the richer deposits have been worked out, and much of the coarse gold is gone but there are still substantial amounts of gold on the West Coast. Today miners are screening alluvium in lower-grade deposits in Westland’s river valleys and sea beaches, and are recovering higher proportions of fine gold.
Processing methods continue to improve, however, NZIMMR research into gold recovery (and losses, as much as 30%) from Westland’s beaches shows that the finest gold size fractions and the more highly flattened gold grains continue to elude the miners’ grasp. Led by Geologist Dr John Youngson, the enhancing gold recovery project started with sampling West Coast mineral sands, and comparing the size and shape of gold grains in beach leads to those lost to tailings from recovery plants.
Having identified the characteristics of gold lost by current recovery methods, NZIMMR is now investigating ways of minimising gold losses and plans to test these at its Waimatuku minerals processing laboratory.