New hope for the industry: sniffing out copper deposits

Geologists have developed a new and inexpensive technique to find copper deposits in volcanic rocks. With so much of the earth’s copper already dug up and companies desperately needing cost-effective ways to locate more reliable resources, could this technology prove to be a saviour?


copper deposits

The mining industry has faced many cuts and diminishing profits. Weak commodity prices have put on the pressure, and companies such as Anglo American have had to decrease their workforce considerably.

The need for many types of minerals is still high though. Copper for example is used all over the world in various different industries such as in water pipelines, electrical motors, power lines, electronic appliances, healthcare equipment and computers. According to the International Copper Study Group, world copper production increased 5% in 2014 while consumption rose by 8%.

Demand is growing for many reasons, especially in China which currently utilises around 40% or the world's copper production. However, prices are continuing to fall, as the high level of production still outweighs demand.

The conflicting dilemma between high demand and low cost means that mining companies need to be able to excavate resources while staying cost effective, which has proved a challenge.

Geology holds the key

There may still be hope for a profitable industry thanks to new technology and research by geologist Dr Ben Williamson at the University of Exeter and Richard Herrington from the Natural History Museum in London who have developed a new and relatively inexpensive method to find copper deposits in magmatic rocks.

Magmatic means rocks such as granite made from lava, which are very common in the earth's crust, often near volcanoes such as Montserrat or Mount St Helens. The method explores them for porphyry-type copper deposits, which provide around 75% of the world's copper and a substantial amount of molybdenum and gold.

Funded by mining giant Anglo American which collaborates with Camborne on many projects, Williamson's new method, published in Nature Geoscience, is based on the analysis of the specific magmatic rock plagioclase - a series of silicate minerals - comparing those with and without porphyry deposits. The method was tested on a major new porphyry discovery in the fertile La Paloma and Los Sulfatos copper porphyry systems in Chile.

"The samples would be prepared and then analysed using an electron microprobe."

Electron microprobe and laser-ablation mass spectrometry systems showed that excess aluminium - which the team used as a 'chemical signature' - occurred in concentric zones in the rock-forming minerals at the site.

"[The method] is really based on the analysis of a certain mineral in samples," says Williamson, programme director and senior lecturer in applied mineralogy at Exeter University. "The samples would be prepared and then analysed using an electron microprobe."

Williamson explains that the plagioclase from magmatic rocks with porphyry deposits has a very distinctive chemical composition that contains aluminium, as opposed to the plagioclase that is barren, so the method works as a discriminator between these magmatic rocks.

Why develop a new method?

Porphyry deposits originally form several kilometres below the Earth's surface, above magma chambers. They're relatively rare, particularly the larger, most valuable deposits.

Most of the deposits near the surface have been discovered, so drills have to go deeper to find ones large enough and thus more economically viable to extract. However, to save time and money on exploratory drilling costs, mining companies are keen to locate deposits beforehand , as magmatic rocks are widely distributed all over the world.

"They're getting harder and harder to find," says Williamson. "We've found the near-surface deposits and now we're going to have to look deeper and deeper. So, industry is interested in any new method to find copper deposits."

Instead of collecting geophysical data or having lots of people on the ground, which are both expensive options, this new method is relatively low-cost. Plus, mining companies will probably have the resources readily available to conduct tests.

Williamson says this technique won't necessarily be used find new deposits, but that it will be part of a suite of methods and can also help re-examine areas that have already been exploited.

"They've got collections of core in store where they've drilled," says Williamson. "So they can go back and look to see whether they missed something."

Predicting the future

Williamson says that this method could provide important insights into why some magma formations are more likely to produce porphyry copper deposits than others, and increase understanding of how parent magmatic rocks evolve.

The idea is to take samples from surface or existing samples in storage or core samples, to see whether they might be relative to rocks around them. In other words, by examining areas which have been successful before, teams might be able to work out other potential areas for collecting resources due to their similarities.

For example, the excess aluminium that the team found in the samples can be linked to high concentrations of water in the magma. The team could conclude from this that the aluminium zones were probably a result of water being injected into the magma chamber directly below the copper deposits and so these are conditions to look out for to make further discoveries.

Mining companies sometimes plan 20 or 30 years ahead in terms of where to drill next, so they are always aware of the importance of finding new areas to mine in the future. Establishing which areas are most likely to contain viable deposits could be a much more cost-effective way to work, especially if they can locate larger ones.

"The economy of these types of deposits is such that you really need to find the big ones," says Williamson, as it is only worthwhile to drill down if there is a big reward at the end.

"The economy of these types of deposits is such that you really need to find the big ones."

What about other minerals?

Williamson is keen to look at other minerals in this way too, as it could tell researchers more about what lies deeper within the Earth's crust.

"This mineral plagioclase is telling us about the magmatic system relatively near surface," Williamson says. "Other minerals will tell us about the deeper parts of the system and why certain magmatic systems might become more fertile to produce these deposits than others."

Mining companies are keeping one "eye on the future", according to Williamson, who believes that new technologies can go a long way to exploit much of the Earth's resources in places that haven't been explored yet.

"With growing populations we're going to need more of these types of metals," he adds. "The mining industry is depressed at the moment, but medium to long-term we are going to need more copper and molybdenum." With an uncertain industry, Williamson says "any good news is welcome".

"I've had quite a lot of feedback from mining companies suggesting that they might want to use the method," he says. "So there is interest there and it's mostly about saving cost at the moment... I'm hopeful that we can keep this project moving forward."