The top photo of a photo shows how the cyanide tanks looked back in the heyday of gold mining in Karangahake Gorge. The bottom is today and some of the rusty old metal from the tanks and funnels still remains.
Read on if you're interested in a little history/science taken from the display boards at the site...
The concrete arches are part of a battery built in the late 1800s. (The arches are tall enough to walk through. A little boy, visiting with his dad at the same time as me, asked me if we were in caves!) The arches supported a set of giant steel tanks. The tanks were massive at about 50 ft/15m high. They were filled with a mix of potassium cyanide solution and crushed ore, which was "stirred" using compressed air that bubbled through the mixture. Tanks like this were a local invention to maximise gold recovery from very finely crushed ore called "slimes". This Kiwi technology was exported and used around the world.
