Mines into depths

 By Eniday Staff

Rewinding the film of images from at least half a century, or even more, up to the Roman Empire, the examples that most easily come to mind, at least as far as Italy is concerned, are those of Elba, Iglesiente and Amiata. We are talking about the mines. Iron, silver and copper. In Tuscany, the unique cinnabar, the mineral from which mercury is extracted. Cogne’s iron mines, in the Aosta Valley, have been over the years running out…

The deposits in the Iglesiente region of Sardinia have gone the same way. The mercury mines might have held on for a few more decades; in the 1970s, half of the mercury in the world was extracted on Amiata. Yet the dangers of that odd but very useful mineral, the only one that takes liquid form at room temperature, spelt the end for the pits. Today Tuscany, Sardinia and the Aosta valley have wonderful mining museums, but no mines. They have undergone a total transformation, in other words, much like most of the mining areas of Europe. Copper and gold are now brought over from Chile, Australia and Indonesia, as diamonds are from South Africa. Lithium, essential in batteries for smart phones and electric cars, comes from Bolivia. Nickel is mined in Russia and the Philippines, and cobalt in the Democratic Republic of the Congo. This is because fields in developing countries, full of the minerals and precious metals most useful to world industry, have so far not been exploited much. It is also because nature is eccentric. In some places, it has left large, concentrated amounts of elements that are easy to get to, in others not. The most striking cases are lithium in Bolivia and mercury in Italy. Even the great reserves are destined to shrink, though. Take nickel, for instance. The global special steel industry consumes about 2 million tonnes of it a year, and the basic steel and battery industries also use up huge amounts. It is estimated that demand will double by 2030. Since proven reserves hold around 76 million tonnes, nickel could run out in a quarter of a century. Another example is cobalt, which is used in countless industrial processes, from metal alloys to batteries. Reserves hold around 7 million tonnes, around 100,000 tonnes of which is consumed every year, with demand rising constantly. The cobalt mines may also dry up in a quarter of a century. So, are there any solutions? Very, very few. In fact there is perhaps just one, and it lies on the ocean floor.

The Munali nickel mine in southern Zambia (Consolidated Nickel Mines)

Pros and cons of marine mineral reserves

The great flat abyss that stretches from California to the Hawaiian islands may hide more than 100 million tonnes of nickel and at least 10 million tonnes of cobalt. It might sound like science fiction, but this is the road a lot of big mining companies are going down, despite the technical, legal and environmental difficulties. Before addressing these difficulties, however, let us see what form the most sought-after minerals take on the seabed. There are essentially three kinds of field. The first is made up of sulphide clusters, where metals containing sulphur build up after volcanic activity under the water. These clusters contain significant amounts of zinc, lead and gold. The second kind of field is made up of cobalt crust. Over the slopes of under-water mountains run currents that remove salt from the metals and carry it away, forming mineral crusts that can contain a lot of precious metal. It is the third kind of field, however, that is of most interest to industry, and it consists of polymetallic nodules, or mineral concretions: these are made up mostly of manganese, with a small proportion, usually 3%, of nickel, copper and cobalt. The advantage of nodules is simple: they are easy to harvest, because they lie just a few centimetres under the mud on the ocean floor.

Main genetic types of polymetallic nodules: H – hydrogenetic, HD – hydrogenetic-diagenetic and D – diagenetic (

Turning to the problems, first of all there are technical issues. Collecting sulphide clusters is not always easy, as the beds they lie on are tortuous and full of hollows, often resulting in demanding work. As for the cobalt crust, the difficulty is managing to dislodge large amounts of it, often from unreachable depths. Nodules are, then, the best option. The concentration of precious metals in them may be low, but it is relatively easy work. Simple existing machinery can be used to dredge mostly flat seabeds. As for the legal difficulties, the fields observed so far fall within international waters, so exploiting them requires authorisation from the International Seabed Authority (ISA), set up under the auspices of the UN as part of its Convention on the Law of the Sea (UNCLOS). ISA has so far granted 28 use permits, in 20 countries spread over the world. But they are really permits for prospecting rather than actual mining. Even if they were, a research permit usually covers an area of seabed between 50,000 and 150,000 square kilometres, of which a tenth at most can be used commercially, and even then, the financial results are not always good. Finally we come to the environmental difficulties. This is a more delicate question. Gathering cobalt means dredging floors up to a depth of at least 10–15 cm, greatly upsetting the marine ecosystem. The polymetallic nodules must then be processed with and separated from other materials in coarse grains, stirring up clouds of mud at great depths that do not take long to settle back on the bottom. Once they come to the surface, the nodules are washed and put to work, leaving considerable amounts of sludge. In short, no one is saying it is the solution of the future, but we should remember that mining inland presents almost all the same environmental problems, if not more, to mining in the open sea.

READ MORE: Mining under the sea by Michelle Leslie

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Eniday Staff