Update 26 January 2012

26 January 2012
Union Hill activity

Newmont Waihi Gold is carrying out some archaeological investigations at Union Hill, the site of the battery and refinery run by Union Gold Mining Company. This is also the site of the historic cyanide tanks, listed Category A in the Hauraki District Plan and by NZ Historic Places Trust.
Newmont Waihi Gold is also installing monitoring equipment on the relics.

Ore-roasting kilns

  - The Union Gold Mining Company (later acquired by the Waihi Gold Mining Company) operated 13 kilns on Union Hill from 1889 to 1901.

Gold-bearing ore and firewood were loaded into the kilns from the top. The firewood was set alight. Later the ore was removed from the bottom of the kilns and more fresh ore and firewood added at the top. The aim was to 'roast' the gold-bearing ore by slowly burning the wood. Too hot and the gold was less accessible than before; not enough heat and the process failed to work. Roasted gold-bearing ore was more friable and so it crushed more readily. This reduced wear and tear on machinery and improved the recovery rate. In addition the heating process oxidised sulphides present in the rock which would otherwise hinder the separation and then amalgamation of gold particles.