Environmental externalities from Mining in New Zealand (unverified notes)

With everything happening lately regarding opening up (or not) land listed in Schedule 4 of the Crown Minerals Act to mining, and with me being someone who likes getting outdoors, I’ve been keen to find some vaguely objective information about effects of mining on the surrounding environment. On July 21st I went to a public presentation by Professor Dave Craw, of the Geology Department at Otago University, and the director of the Environmental Science programme there. It’s part of a series of winter lectures being hosted by Otago University in Auckland and Wellington. Given his background, Professor Craw seems to be in a good position to comment on the topic of mining in New Zealand with some scientific authority. He’s been cited in the news a few times on this topic (example 1, example 2).

Later in this post, I’ve reproduced the notes I took during Professor Craw’s presentation. It’s not authoritative coming from me. As interested as I am in comprehending things on a level that transcends what’s most easily available through polarised press releases, I’m not a geologist and I’ve not been involved in New Zealand’s mining industry. My note-taking skills from a one hour public lecture are nothing compared with various other people’s years or decades of working with or researching this stuff, so please use these notes as an approximate guide only.

Professor Craw’s main interest is in understanding the science of what happens in the environment around mines, what the effects are, the best ways to mitigate those effects if we need to do so, and how effective these methods actually are. He studies historic and often unregulated mining (totally unregulated mining no longer exists in New Zealand), and the clean-up processes that have followed, to better understand possible effects and what can be done about them. His line is that it’s great to debate mining New Zealand’s land, but the debate’s much more useful if those taking part on all sides have a good understanding of what they’re debating and what’s at stake. Obviously however (and this is me speaking), there’s far more information that can be injected into debates than just the environmental impact information which is Professor Craw’s main focus. As with the talk I attended, the notes below don’t cover everything relevant.

Before getting into my notes from his presentation, I’ll prefix them with a few paragraphs of introduction about why this interests me. Please skip past it if that kind of thing bores you.

Several months ago I made a submission on the government’s proposals to open Schedule 4 land to mining, along with tens of thousands of other people. My submission was thin on science. I figured I’d be better to leave that to people who could demonstrate they actually knew what they were talking about, and I commented mostly on what to me seemed like a lazily constructed discussion document that didn’t make its point very well, whatever that was, or appear to justify what it was proposing. This has been in the wake of some fierce campaigns against the proposal by several environmental and recreation groups, including Federated Mountain Clubs which I think represents my ideals most closely, though nobody will ever represent me exactly except for me.

Two days before the talk I attended, on 19th July 2010, the New Zealand government finally revealed (and confirmed the next day) that the removal of land from Schedule 4 would not take place. Since then a lot of groups have been metaphorically leaping up and down in a “we won” kind of fashion. I guess I’ve found it an anti-climax, because whether Schedule 4 land is involved or not, I’m not convinced much has changed. Following the submission process, the government is now declaring it has a mandate to increase mining activities in non Schedule 4 lands, and basically that it wants mining to increase overall. I suppose if you want something that may be controversial, one way to get it is to pretend you want something that’s just totally nutty and absurd, then slink away with what you really wanted once everyone’s distracted and happy that you’ve not gotten what you said you wanted. Whatever — it’s politics and marketing, which are two stereotypes I don’t gel with very well.

For some examples, I think:
This is not protected
under Schedule 4.

Neither is this.

Or this.

What gets to me in this is that the places I most frequently visit for recreation, nearly all the fantastic outdoor regions described in this blog, are very rarely covered by Schedule 4 anyway. They’re simply awesome back-country wilderness areas, not necessarily unique enough to be classified as Schedule 4, but very accessible and wonderful places to experience all the same, completely different from a daywalk through the local regional park. Even if it doesn’t affect me directly, I still wonder how this might affect people in other parts of New Zealand who benefit from the presence and accessibility of other non-Schedule-4 conservation land in ways similar to myself.

There’s a lot in the notes, but points from Professor Craw’s presentation that I found especially interesting were that:

  • He thinks that debating access to Schedule 4 land over the past several months has been fairly meaningless, because at present there’s little of interest for mining under National Parks and Schedule 4 land anyway. You can draw from this what you will.
  • New Zealand’s phosphorous resources on the sea floor are likely to be of great interest in a few decades time. As a nation that exports so much food, and appears to be wanting to keep doing so, we’re automatically exporting huge amounts of phosphorous from our soil which needs to be replaced. In recent history we’ve imported it from the far side of the world, lately somewhere in Africa.

The notes below are a reproduction of what I scribbled down in handwriting on the night. They’re not a perfect reproduction of his slides or what he said, and I’ve decorated the text with links to related resources as I’ve thought appropriate. These notes are prone to misunderstandings or lack of context on my part, and if I’ve recorded any of the talk incorrectly (as may be the case) then it’s my own responsibility. Please keep this in mind if you browse the notes, and comment below if you wish to correct anything. If I’ve interpreted anything radically wrong, I’ll update my post.

The notes


  • New Zealand’s had completely unregulated mining up until the late 1950s, when rudimentary regulations began to be put in place. It’s becoming more stringent over time. We can look at what’s happened with unregulated mining to learn more about consequences.
  • New Zealand’s main mining products are gold, coal and iron. All of these are geologically favourable, and will likely be what new mines go after over the next 20 years.
  • Four key factors for managing mining are:
    1. Bond deposition for rehabilitation, where a mining company sets aside money to rehabilitate land afterwards.
    2. Zero tolerance for transgressions of regulations.
    3. Offsets and net positive conservation outcomes. For example, a mining company might offer to improve something else to a greater extent than the damage they cause elsewhere.
    4. Scientific prediction of environmental issues, and scientific mitigation of environmental problems.

    The first three are legal and political factors, and should be taken into account. For his work, Professor Craw is really interested in item 4. He’s done lots of studying of old and nasty sites to learn more objective information about effects of mining and ways to mitigate problems.

  • There’s a general consensus after a dialogue with many people from different backgrounds that water quality is what most people are interested in. This is either of direct interest, or because the quality of water is typically a good indicator of what’s going on up-stream, and how much damage it’s causing. The dialogue included Mining Companies, Environmental Consultants, the Department of Conservation, Regional Councils, the Ministry for the Environment, Crown Minerals, Geologists, Environmental Scientists, Ecologists, Exotoxicologists, and Environmental Engineers.
  • Professor Craw worked on the “Mine Drainage Framework for Predicting and Managing Stream Water Quality“, which is a guide for everyone involved on both sides of mining regarding prediction and management of water quality impacts of mining on streams.


  • About 20% of the current demand is now for electronics. A typical computer includes roughly 100 milligrams of gold. (New Zealand currently produces enough gold for 100 million computers per year.)
  • Most gold comes from Otago, the West Coast, or Coromandel.
  • The North Island and South Island are geologically different. Obtaining the gold requires different approaches and has different side effects.

South Island Gold

  • South Island gold is found in schist and greywacke. The nearby water is nearly always a neutral pH=7. The process generates lots of calcium carbonate (which doesn’t dissolve in the water so doesn’t really affect the pH).
  • The number one South Island problem is Arsenic. Mining produces 2000 times as much arsenic as gold. Professor Craw showed an example photo of a truck which would have been carrying roughly 200 grams of gold and 500 kg of arsenic.
  • Cyanide is sometimes referred to as a big problem, but it’s nothing compared with Arsenic. Cyanide gets added to extract gold (typically in the North Island), but breaks down in sunlight to Carbon and Nitrogen. Arsenic is extracted from the rock, and doesn’t break down. It’s a big long term issue.
  • Arsenic was once used to kill pests in orchards and a few other things, but not since it’s been realised just how poisonous it is. It has no value for mining companies, but New Zealand imports it for timber treatment.
  • From unregulated days, there are many arsenic-contaminated sites that are still un-known. DoC has to deal with them as they’re discovered. The worst known site at present is the historic Waiutu Gold Mine, where arsenic was dumped on-site in large amounts, the mine was eventually abandoned, and the soil is now roughly 40% arsenic.
  • Arsenic is very poisonous for humans, but many plants are unaffected. Species of moss continue to grow in arsenic-contaminated streams, and can end up being 3% arsenic, dangerous to touch. Other New Zealand native shrubs will grow in arsenic-soil without issues, and don’t suck it up at all. Many stream and river invertebrates are also unaffected. It seems to be mostly humans that find arsenic very poisonous.
  • Arsenic in water sticks to Iron Oxide, which is in the mud. Over distance the mud in a stream tends to pull the arsenic from the water, resulting in cleaner water down-stream.
  • One method for cleaning water that goes through mines is by mixing iron oxide with gravel, and filtering the water through the mixture to clean it.
  • Old abandoned mines tend to become covered with re-growth and generally fit back into the surrounding environment (scenically at least) after about 50 years.


  • The old abandoned Reefton mine is now covered in Beech Forest. The new Reefton gold mine cleans water with an artificial iron oxide that’s made by adding lots of ferric chloride. The water that leaves the mine is drinkable.
  • Arsenic from Reefton is put on trains, and transported to a major arsenic dump at Macraes Mine Tailings – a major dumping site where tailings are consolidated for management.
  • At Macraes, the soil contains about 3kg arsenic/tonne. Dust storms have been a problem, as they’ve whipped up dust full of arsenic. Previously it was necessary to spray water over tailings. Lately grass has been grown to keep down the dust. Ryecorn is a species that’s very useful, being tolerant to both drought and arsenic. An overnight experiment showed 40 centimetres depth of erosion of the soil without ryecorn, compared with ryecorn-planted soil next to it.
  • There is no fully tested long term treatment for tailings, largely because nobody’s been interested in treating them until it’s become an issue in the last few decades. In Australia, arsenic dumps have been converted to artificial wet-lands. So far this seems to be working and keeping things contained, but it has to be monitored in case of future leaks, as it’s never been done before.

North Island Gold

  • North Island Gold is from volcanic activity. The water pH is often acidic.
  • The Martha Mine at Waihi yields gold at about 3kg/tonne. It’s easy to get out with cyanide, and the Coromandel’s so attractive because it’s so much easier than gold elsewhere. Professor Craw thinks the issue of mining in the Coromandel will simply keep coming up every ten years or so with changes of government.
  • The main problem in the North Island is that every tonne of rock results in about 80 kg of sulphuric acid. ie. A typical computer with 100mg of gold has resulted in 5kg of sulphuric acid being produced. A typical wedding ring will be responsible for 160 kg of sulphuric acid (or 8 kg of arsenic if it’s South Island gold).
  • The Tui Mine, considered the most contaminated site in New Zealand, has water coming out with a pH of 2 — very acidic.
  • Acidic water from mines that meets neutral pH=7 water results in iron oxide and heavy metals precipitating on the river bed. This happens naturally around acidic springs in the hillsides, but on a much larger scale where mines are involved.


  • By world standards, the coal produced in New Zealand is very good for making steel. It’s mostly exported to Asia, and cars (made from steel) tend to be imported.
  • Coal from coastal areas has lots of sulfur and boron, whereas inland coal doesn’t. From a mining exploration perspective, it’s easy to know what to expect by knowing where a rock formed.
  • Acidic soil with high amounts of boron kills many shrubs, but some plants will grow on it (such as Manuka).
  • The Mangatini Stream, which flows through the Stockton Mine, emerged with an acidic pH of 2.7. Solid Energy tries to clean it by settling the water in a “sump” before it’s released. It now emerges “relatively” clean at about pH>5. (Also see here.)

Predictions for the next 100 years

  • Commodity prices will rise.
  • Other countries are less likely to send scarce resources to New Zealand.
  • Campaigns to mine the Coromandel gold will keep coming up, probably about every ten years as the government cycles, because it’s so rich and easy to extract.
  • Some other rare elements might be mined in the next 50 years when it becomes problematic to source them from overseas, such as Nickel, Chromium, Copper, and Zinc. These kinds of elements will be needed, for instance, if New Zealand needs to produce steel.
  • National Parks are of negligible interest, because there’s not much in them.
  • Much of the recent debate about mining Schedule 4 land has been irrelevant, because Schedule 4 land does not have much of value from a mining perspective.
  • There are substantial resources off-shore of Iron, Copper, Gold and Phosphate, and there will be much interest in mining these minerals.
  • Phosphate will be particularly interesting in the future. There’s a lot of it sitting on the sea floor off the eastern coast of New Zealand. As a nation that exports food, we’re constantly exporting phosphate, and it needs to be replaced in the soil to be able to keep producing food. Presently we import phosphate from the far side of the world (lately from Africa), but doing so is very uneconomic. (Shipping costs are higher than phosphate costs!)
  • There will be an environmental outcry when someone decides they want to mine phosphate, but regardless of what happens, New Zealand needs a plan of what to do when importing phosphates from overseas to replace what’s leaving our soil becomes impractical.
  • There will not be many new mines in the next 100 years, perhaps on the order of 10 (maybe more, maybe less). This is because mines take about 10 years to simply get started. Mines are ugly for about 10 to 30 years, and mostly “invisible” after about 50 years.
  • Professor Craw thinks current discussions about “surgical” mining are strange. It’s not feasible to look at land and then decide how to mine it — the appropriate method of mining depends entirely on what’s being mined.
This entry was posted in musing and tagged , , , , . Bookmark the permalink.