On the second rest day of our trip there was again a 20km tour from Waihi Beach to Waihi to visit the gold mine there. Actually, 90% silver and 10% gold are mined there, but marketing-wise it seems to work better with the gold mine than with the title silver mine :-)
Like real tourists we visited a two-hour guided tour. There we were shown the huge hole (700m x 600m, 200m deep) in the middle of Waihi Town, where gold is dug in open pit mining. "Unfortunately" the operating company cannot enlarge the mine, because otherwise parts of the village would have to give way, which has met with lively resistance from the population. Nevertheless, test drillings are currently taking place on the schoolhouse site. However, these are apparently for the mine approx. 2km away, which is not operated as an open pit mine.
Until the 50's, the mine in Waihi itself was dug without open pit mining, and the miners searched for gold up to 600m deep. This is below the sea surface, as Waihi is about 50-100m.above sea level.
The blasting in the open pit is relatively simple. Holes are drilled and then filled with ammonium nitrate and diesel. It seems so simple and economical. And yes, eventually about 1g of gold is extracted from a ton of rock.
The open pit is expected to reach the lowest possible point next summer. The pit will then be filled with water for 5 years, giving Waihi a new, relatively deep, lake.