Gold Education ~ School Information ~ Australian History

Old Mogo Town, Tourism theme park near Batemans Bay, south coast NSW

Australian Gold Rush History Educational Information

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Page 4 ~ Reef Gold and Hard Rock Mining

The quartz reefs that had eroded, supplied the alluvial gold that fuelled the goldrush. The rest of the reef that remained in the ground was the ore for the hard rock miners to exploit.

The ambitious diggers who became the reef miners, panned their way up the gullies until the trace of colour disappeared. This was near the head of the old reef. They would dig large furrows across the immediate area, usually a ridge top, looking for the reef. These furrows were called costains. When they found the quartz seam, a shaft would be the next task. The shaft would follow the seam down and while digging this they would crush the ore. This, apart from yielding gold, would allow them to sample the progress to see if their endeavours were worthwhile.

Because of the steepness of Mogo terrain, the majority of mines in this area were shaft and drive mines. A drive was duly put in and this linked up with the shaft, relegating the shaft to the role of an air vent. The drives were horizontal and level with the stamp battery. Many of the smaller mines in the area did not crush their ore at the mine but took it to a communal battery. The larger mines placed their stampers in a position where water and access were easily available. In this steep and hilly country, adequate water supply was not usually a problem, with the many creeks and rivers throughout the bush. In other areas, aqueducts had to be constructed to carry the required water and could be up to 8 kilometres long. From this point mining was a simple matter of digging out the ore, crushing and chemically extracting the gold. The ore after crushing went through a screen, with the assistance of water and ran over a flat area that was treated with, firstly, copper sheet, cyanide paste and then mercury. Mercury has a chemical affinity with gold, silver and other metals. As the processed ore runs over this area, the gold attaches itself to the mercury while the rest of the ore passes through to the tailings dump. Eventually the cyanide, mercury and gold are scraped up and placed in a retort, where the mixture is heated until the cyanide and mercury evaporate off and are recycled, leaving the gold behind. The cyanide paste acts as a buffer so that scrapings of copper do not contaminate the separated gold. The extraction is a dirty process, often doing environmental damage and causing lung damage and deafness to the workers, as well as the dangers of mercury and cyanide poisoning.

The old batteries, although widely used, were only about 60% effective and therefore 40% of the gold ended up on the tailings dump. Modern ball mills claim 98% effectiveness and therefore are being used all over the world reworking old tailings.

As with alluvial gold, there is little knowledge of how much was taken. But in the Mogo area, many mines, registered and unregistered, operated from the 1870s to the 1940s and some for even longer. So we can assume that gold kept many people gainfully employed for a long time.

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