In 1890 the Martha Company and other claims were bought by the Waihi Gold Mining Company of London, who invested a great deal of capital into the mine.
At the time, trials were being carried out to find a more efficient way to extract precious metals from the quartz rock. By 1894, the Forrest / MacArthur process had been developed and the use of cyanide in the gold extraction process was adopted world wide. This process enabled a higher percentage of gold and silver to be extracted from hard rock, making viable many operations that would otherwise have had to close.
The Martha Mine became one of the most important gold and silver mines in the world.
By 1952, when the mighty Martha Mine closed, around 5.6 million ounces (174,160kg) of gold and 38.4 million ounces (1,193,180kg) of silver had been produced from 11,932,000 tonnes of ore.
Seven vertical shafts had been sunk for the underground Martha Mine; the deepest was 600 metres from the surface. Radiating from the shafts was a network of 175 kilometres of tunnels on 15 horizontal levels. A work force averaging 600 men was employed over the seventy year lifespan of the mine. In 1909, when gold production peaked, a total of 1500 people were employed in the mine and at the Victoria Battery.
Explosives were used to loosen the rock. The ore was mined with picks and shovels and loaded into wagons. Miners pulled or pushed the wagons inside the tunnels on carriage rails. Sometimes horses were used to pull the wagons. The ore was weighed and sent to the surface in cages, similar to lifts. Ore was then loaded onto the rake train to be transported to the Victoria Battery at Waikino, where it was crushed and treated to extract the gold and silver.
Groundwater was pumped out of the workings to enable the miners to work in the tunnels. From 1904 to 1913 the dewatering pumps were powered by steam engines that were housed in the Cornish Pumphouse, a landmark that still stands beside the Martha Mine today.
Electricity was introduced in 1913. The first hydro electric powerstation on the Waikato River was built by the Waihi Gold Mining Company at Horahora. This power station was later flooded when Lake Karapiro was formed. Around 7000 litres per minute of tepid water was pumped from underground. It flowed through the deep gutters lining SeddonStreet to the Ohinemuri River and also filled Waihi's public swimming pool.
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