Story: Gold and gold mining
Page 7 – Methods of mining
When a miner found an area of payable ground he pegged out a square claim. The size of claims varied among goldfields, but were usually 24 feet square (53.5 square metres). Miners often teamed up with mates to share claims and workings.
Shovel, pan and cradle
Gold mining was rough, physical work. Where alluvial gold was very rich, it could be obtained with a shovel and pan. However, pans were used mainly for prospecting. Simple machines known as cradles (often made from wooden liquor boxes) were rocked back and forth – the heavier gold collecting on matting on the cradle base.
Riffle or sluice boxes were the main methods of recovering gold. Nicknamed Long Toms, these were long, terraced wooden boxes, over which gold-bearing gravel was washed. Each step of the box had a lip that trapped the heavier gold and allowed the lighter materials to wash away. Eventually the heavy gravel and gold caught in the terraces was washed up in a pan.
These methods all relied on water, without which recovering gold was impossible. At each of New Zealand’s goldfield’s there were small dams and water races – channels that cut across contours, bringing water from creeks to areas where gold was worked.
Sluicing was a method where water was piped into successively narrower pipes leading to hoses (with nozzles called monitors), which sprayed jets of water strong enough to kill a person. The jets were aimed at gravel faces and helped to wash gold-bearing gravels down through sluice boxes. In places like Bannockburn and St Bathans in Central Otago distinctive gravel pillars are a legacy of these giant water guns.
Hydraulic elevators were used to reach leads of alluvial gold that were covered by gravel. Most elevators worked like giant vacuum cleaners, sucking a slurry of gravel and water up from beneath large gravel terraces.
Engineering was also used to expose river beds. The Oxenbridge tunnel on the Shotover River and the dam gates across the source of the Kawarau River draining Lake Wakatipu at Frankton are the two most famous examples. Both were spectacular failures – little gold was found in the exposed bed of the Shotover once water was diverted through the tunnel. And when the Kawarau dam gates were closed they had little effect on water levels downstream.
Hard-rock mines followed quartz veins, which contained gold. Underground mining was very expensive as tunnels had to be blasted and the roofs supported. Mines such as those at Waihī on Coromandel Peninsula and Waiuta on the West Coast followed reefs until they became too deep or low grade to be mined economically. The recovered quartz was crushed by stamper batteries, and cyanide was used to reclaim the gold.