@Nicspicsnz and I had a trip out to the Karangahake gorge today. Although I have ridden my bike past the old mines before in the past, I have never explored it before. If you like rusty things, its a great place to find things. This is a mill tube, something to do with gold mining.
The site was the largest quartz ore processing plant in Australasia and one of the biggest industrial sites in New Zealand in the early 1900’s. Then it was the country’s largest producer of gold -10 times more than the next largest battery.