An acid trip for NZ rivers
Blogger: Mike Joy, Senior Lecturer in Environmental Science at Massey University
Much of the rhetoric coming from the government around mining in National Parks has centred on so called “surgical mining” – the idea is that you can make a small hole and that this hole is the total impact. This is just classic greenwash.
The real issue is what happens to the stuff that comes out of the mine not the size of its opening*.
In reality what does come out of the mine is acid-leaching crushed rock that must be sealed up for eternity after the precious metals have been removed because if they ever come in contact with water they form sulphuric acid.
The tailings of martha mine, photo: Kim Westerskov
The huge tailings dam at Waihi is a good example, they have the “surgical” Favona mine nearby, a small hole but all the rock and all the associated toxic material that comes out must go into the tailings dam.
Before being mined the acid-bearing rock was sitting safely in the ground with a very small surface area in relation to its volume so very little acid was produced. The mining process takes that rock and pulverises it into talcum powder consistency which increases the surface area by many, many orders of magnitude so then if water gets to it acid is formed immediately.
To stop acid forming the tailings dam is sealed top; bottom and sides with clay liners similar to modern landfills and as long as this seal remains intact the acid forming mine tailings are “safe”. But if anything from an earthquake to a tree root were to breach this liner then the results would be disastrous for anyone downstream.
For example if a tree were to grow on the dam and the roots penetrate that liner then water would get in and then have no way out so would build-up until it blew out the liner at the weakest point, the an acidic torrent would flow downstream. So these tailings dams are forever a toxic legacy long after the mining companies have walked away with bulging wallets.
We have already had incidents with streams contaminated below tailings dams at the Tui mine in Te Aroha and the Golden Cross mine near Waihi. Now taxpayers are paying millions to clean up long after the miners walked away .
The rivers that drain the mining sites around the West coast have fared even worse – and many of them have been rendered completely lifeless because of the high levels of acidity.
Quick remedial ‘fixes’ include dosing these rivers with lime to neutralise the acid – but that just means a great big lime hole elsewhere.
The mining industry has obviously found it easy to convince some of our politicians that it is safe and surgical. I hope the rest of us I hope are not so gullible and will fight this proposal.
We should be putting money and effort into clean, new sustainable technologies to take us into the future – not selling the family silver (literally) to keep the economy afloat.
*Not to mention roads infrastructure and all the associated development to get to and make the hole!
