Mining Hydrothermal Vents

Chris - Earlier in the show we heard from Crispin about how hydrothermal vents provide a home and a source of food to a range of species. But researchers are also now looking at these vents as a source of minerals and metals. So here's Steve Scott from the University of Toronto. He's a professor of ore genesis and is going to tell us all about it.

Steve - The deep sea occupies a big part of our planet. The oceans are 71% of our planet and the deep sea is about 80% of that, so there are a lot of secrets of the deep ocean that we're just beginning to understand. One of these is the hot springs that are deep on the ocean floor, spewing out fluids as high as 420 degrees centigrade. In these fluids are dissolved metals such as iron, but more interesting economically is copper, zinc, lead, silver and gold, that are precipitating around these hot springs on the sea floor and building up towering chimneys as much as 40 metres high. These are of course unstable and eventually fall over and produce accumulations of chimneys that grow into mounds and produce what to all intents and purposes are ore deposits on the ocean floor.

Chris - How abundant are those ores, Steve? How much of them is down there?

Steve - There are about 350 sites that we know about now and in total thousands of these so-called hydrothermal vents. Some of them are very small and would fit in somebody's dining room. Others are quite large, for example the ones in the Bismarck Sea off the coast of Papua New Guinea. Some of those deposits are a few hundred metres in diameter.

Chris - So are they actually exploitable, because some people have suggested that these particular ore deposits are much more enriched than ore we could get out of the ground normally in mine, and so are worth pillaging to get the goodness out.

Steve - Yes I definitely think they are exploitable, at least the ones in the Mannas Basin which is actually a site that I discovered back in the 90s. Our own sampling, plus much more detailed sampling by a mining exploration group called Nautilus Minerals, has verified that this is incredibly rich. They took a 15 tonne bolt sample out of one of the deposits and it averaged at something like 5.2% copper and 6.6 grams per tonne of gold. A typical mine of this type on land of volcanic rocks, which we have around the world in various places and lots of them in Canada, they would average about 2-4% copper and maybe a gram or two per tonne of gold.

Chris - Is it actually economically viable to recover though, because whilst it may be richer, you have the added problem of lots of sea water above you?

Steve - Yes you've got a lot of sea water. The Mannas Basin site, it's in 1600-1700 metres of water. But there are mines on land that are down 3000 metres, for example in Timmons, a Kid Creek mine here in Canada, and it's a whole lot easier to go down through a couple of thousand metres of water than a couple of thousand metres of rock. All you have to do is put a pipe down there, whereas on land you have to do an awful lot of blasting and drilling, which is very expensive to do.

Chris - Can you actually do an environmental calculation to work out which is better for the planet in the long run? Is it better to go down to these pristine marine environments and exploit those, or is it better to do the drilling and blasting that you mention?

Steve - I personally think that the ocean mining would be less of an environmental problem than mining on land. And it's a not a question of out of sight, out of mind, as no-one will accept that. On land you have to drill big holes in the ground. If you have an open cast mine, you have got to remove an awful lot of barren rock to get out the ore. Maybe for every tonne of ore, you might have to move five to ten tonnes of barren rock and you have to put that rock somewhere. You also leave a big hole in the ground and when it rains it produces acids from the breakdown of the iron sulphides to make sulphuric acid, and creates acid mine drainage, which is a big problem. In fact those are the three biggest problems of mining on land. In the oceans, you won't generate acid drainage because the oceans are alkaline, so you just don't generate the acids. They'll be no big holes in the sea beds because these things are sitting like big bumps on the sea floor, and you're going to remove that bump. It's referred to as surgical mining; you take just the ore and so you're not removing any waste rock. So the three biggest problems for mining on land just don't exist in the oceans.