The University of Exeter has developed a cost-effective way to distinguish valuable metal deposits from differing types of magmatic rock.
A study published in Nature Geoscience by Dr Ben Williamson of the University’s Camborne School of Mines, in collaboration with Dr Richard Herrington from the Natural History Museum, London, now proposes a new method to explore for porphyry-type copper deposits. Such deposits account for 75% of the global copper supply and a large amount of molybdenum and gold, making them extremely important to the world economy. The deposits are rare, forming several kilometres below the Earth’s surface, meaning the larger deposits offer more incentive to mine. Since most near-surface deposits have already been discovered, this new method to locate deeper deposits is therefore of great interest to the mining industry.
The Anglo American funded project uses a system in which the chemical compositions of magmatic rock minerals that host porphyry deposits are compared, in order to see which ones contain nothing. A case study of a new porphyry discovery in Chile was used to test their theory. In which, they note that certain minerals in the magmatic rock have distinctive chemical characteristics which can be used as one indicator to home-in on porphyry deposits. The effort to distinguish the sources of such chemical signatures brought new insights into the formation of the deposits, and the generation of the magmatic rocks from which they form. The main discovery being the process in which, magma chambers below the porphyry undergo discrete injections of water-rich melts or watery fluids that enhance the magma’s ability to transfer copper and other metals upwards to form a porphyry copper deposit.
Dr Ben Williamson, of the University’s Camborne School of Mines, said: “This new method will add to the range of tools available to exploration companies to discover new porphyry copper deposits. Our findings also provide important insights into why some magmas are more likely to produce porphyry copper deposits than others, and add to our understanding of how their parent magmatic rocks evolve.”
The paper, entitled “Porphyry copper enrichment linked to excess aluminium in plagioclase”, by B.J. Williamson, R.J. Herrington and A. Morris, was published in Nature Geoscience on 1 February 2016.