Wednesday, January 5, 2011

Otago Goldfields

I stopped at Goldfields Mining Center at Gee’s Flat in Otago for a $25 tour. Gold was discovered here in the 1861 in the Lawrence River near Dunedin - 20 years after the California gold rush and 10 years after Australia’s gold rush. Many of the men who had worked claims in these rushes traveled to New Zealand to try their luck here. After the finds petered out, they were followed by Chinese miners who kept to themselves and were discriminated against. They averaged half as much income as the European miners. The first miners took up to 40 kilos a week out of the river. Nuggets are fairly common; last week a German gold-panner found a pinky-sized nugget. Gold nuggets are worth 4-5 times their weight, due to rarity. Most Cromwell gold is quite pure. Gold is very ductile - a matchbox sized piece can be hammered into a workable sheet the size of a tennis court. The source of the Cromwell gold has been traced to the hills up the river, but never found. If it hasn’t been eroded away, it’s probably a rich deposit. The mined area is an old river bank. The current river has downcut below the level of the mining field to create the Kawarau Gorge. 200-foot deep layers of flood-deposited, gold-bearing gravel alternate with clay blown in during dry glacial periods. The gravel beds are now protected, but the gravel of the riverbed still contains gold and is still panned by individual entrepreneurs. The tour guide, a nice older fellow, passed around some gold flakes and valuable nuggets. Then he took us up and ran some still-operating 1890’s machinery. The machines were simple affairs, run off head pressure created by twin dammed lakes 180’ up the hill. One unit, called a stamper battery, contained water-driven weighted stampers that crushed gold-bearing quartz to a dust, which was then run in a water stream over a mercury-plated copper ramp, which attracted the gold dust and held it. He also showed us a California sluice gun- basically a monitor gun which flowed 200-500 gpm out of variable-sized tips to hydraulically erode the hillside. Numerous hand-dug tunnels and shafts penetrate the landscape. Miners dug down to explore deeper gravel layers as the upper ones became worked out. Mining continued off and on at Gee’s Flat for 130 years, until it became a protected historical area. Now many visitors and ticket holders from the nearby jetboat operation take tours and pan for gold in gravels borught up from the river. I tried my hand at panning- filling a shallow broad dish with gravel and some small lead pellets, then rinsing it several times and swirling water through it until all the light gravel was washed out. I was very happy to find a bit of gold-bearing quartz at the bottom. Retention pond built by miners to provide reliable water pressure to operate equipment.
Huts of Chinese miners.
Inside a hut
Hydraulic sluice guns made the work of digging out gold-bearing gravel easier.
Hydraulic power for the stamper battery.
19th century stamper battery- still operating! Ore-bearing rock was crushed by the large weighted rods of the stamper. The resulting wet slurry ran down the ramp seen in front. The ramp's coated in mercury, which has an affinity for gold and picked up the gold dust out of the slurry.
Dark layers of gold-bearing gravel visible in hillside.

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