Overview
In New Zealand, silver is a by-product of mining for the more valuable precious metal, gold. The two metals occur together. Both are widespread but minor elements, usually found as deposits in igneous rocks (as in the Coromandel and Waihi) and metamorphic rocks (as in Otago).
New Zealand’s first gold strike was on the Coromandel Peninsula in 1852. In those days, miners generally searched for loose gold flakes or nuggets in river sediments. This is called placer mining.
The initial Coromandel goldrush was short-lived, as only small amounts of placer gold were found. Most of the gold was trapped, along with silver, in hard volcanic rock.
The early miners had more luck in the South Island. They struck gold at Collingwood in Nelson in 1857, Gabriel’s Gully in Otago in 1861, and along the West Coast in 1864. In those areas, glaciers and flowing water had eroded the gold-bearing rock and deposited plenty of placer gold downstream.
Meanwhile, in the Coromandel, miners began working at extracting gold and silver from the hard rock. They set up riverside rock crushing plants powered by water wheels. Once the rock was broken up, the precious metals could be extracted. Most New Zealand silver came from mines near Thames. The gold-bearing ore there contained about 34% silver.
In 1889, the Crown battery at Karangahake near Waihi became the first mining operation in New Zealand to use a new chemical process whereby gold and silver were dissolved from the rock in dilute cyanide solution. By 1892 there were nine cyanide plants operating in the Coromandel.
In the fifty years between 1852 and 1912, 80.6 million pounds worth of gold and 1.535 million pounds worth of silver were recovered in this country. Today that gold would be worth about $NZ250 million and the silver about $NZ5 million.
After World War I, gold and silver mining here declined, closing the last mine in 1955. However, in the 1980s, world precious metal prices rose. New Zealand mines began attracting interest once again, and some re-opened.
Today, although Westland and Otago have small placer gold mines, most New Zealand gold is mined at the Martha Mine in Waihi and Macraes Mine in Otago, both hard rock mines. The chemical processes used to extract the gold are much more sophisticated and effective than they used to be, which is vital, as the gold particles are often so finely mixed with the rock that they’re invisible to the naked eye.
The Coromandel still yields silver, too. In the year 2000, 22,886 kg were produced. Almost all of it came from the Martha Mine, which produces about a million dollars worth of precious metals each week. Approximately 85% of that is silver and 15% gold. However, gold is worth between sixty and seventy times as much as silver, so it’s still the most profitable product.
Text originally published in Tai Awatea, Te Papa's onfloor multimedia database.