Alluvial Mining

Gold Ore Extraction Beneficiation

Gold Ore Extraction Beneficiation

Alluvial mining deposits were discovered near Paddys Rockliole in 1887. Initially the gold was obtained by using a panning dish to wash the lighter sands from the gold. However due to water shortages the miners had to substitute water for air using two methods.

  • Standing with their back to the wind and poring the dirt from one pan to the other with the aim of separating the lighter sand from the heavier gold.
  • Using a shaker box and air blown from bellows to remove unwanted material and allowing the gold to settle on a screen below.

Reef Mining

From the mid 1890s reef mining replaced alluvial mining and the gold extraction process became centered around the Government Works area using two techniques, mercury amalgamation and cyanidation.

Mercury Amalgamation

The ore obtained from the reefs was transported by horse and cart to a rock crusher, which would reduce large rocks into 50mm pieces. Via a conveyor belt, the rock was placed in an ore bin and fed into a battery. The battery was driven by an engine using steam from a wood fired boiler. The iron stamps of the battery reduced the ore into fine grains, which were sifted through fine mesh onto mercury plates. Particles of gold would fuse to the plates and transferred into a gold retort. The retort consisted of an iron bowl and pipe coming from the top. when heated in a furnace (smelted) to purify it and poured into bullion.

Cyanidation

Cyaiiidation is an improved Technique as it allows nearly all of the gold to be extracted compared to only 70-80% with mercury amalgamation. The process is similar to that of mercury amalgamation, but when the gold is scraped off the mercury plates it is moved over Wilfrey (agitation) tables. Through gravity larger pieces of gold would settle into shallow grooves at the feed end. while the finer grains were transferred into the deeper groves at the other end. The larger gold pieces could be picked out. while the finer grains were transferred into vats of cyanide where the gold would dissolve forming a gold-cyanide solution. This solution was passed through a zinc tank, the gold separated from the cyanide and fused to zinc shavings. To seperate the gold and Zinc the shavings were dipped into sulfuric acid forming a gold sludge, which was washed with large amounts of water to remove the acid. The remaining gold was dried, smelted and poured into bullion.

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