A new study published in Nature Geoscience (February 2016) by Dr Ben Williamson, of the Camborne School of Mines – University of Exeter, together with Prof. Richard Herrington from the Natural History Museum, London, has proposed a new method to explore for porphyry copper deposits. These deposits provide around 75 per cent of the world’s copper and a significant amount of molybdenum and gold which makes them extremely important to the world economy.

The deposits, which originally form at several kilometres depth below the Earth’s surface, above large magma chambers, are relatively rare, particularly the largest deposits which are most economic to mine. In addition, most near-surface deposits have already been discovered. Any new method to locate deeper deposits is therefore of great interest to the mining industry.

Funded by Anglo American, this project compared the chemical compositions of minerals from magmatic rocks that host porphyry deposits against those which are barren. A case study was then undertaken of a major new porphyry discovery in Chile, to test their theory. Minerals from magmatic rocks which host porphyry deposits have distinctive chemical characteristics that can be used as one of a suite of indicators to home-in on porphyry deposits.

Unravelling the causes of the distinctive chemical signatures has also brought new insights into the formation of porphyry copper deposits, and more generally the generation of the magmatic rocks from which they form, which are an important component of the Earth’s crust. The main finding in this regard is that the magma chamber below the porphyry undergoes discrete injections of water-rich melts or watery fluids which enhance the magma’s ability to transfer copper and other metals upwards to form a porphyry copper deposit.

The team are now looking for further funding to test the new method on a range of other deposits and in different geological settings, and to develop the model for the formation of porphyry copper deposits. For more information contact:

Dr Ben Williamson 
Camborne School of Mines - University of Exeter - UK
Tel: +44 (0)1326 218146

Image: Plagioclase (blue) from magmatic rocks which host a large porphyry in Chile. Click here to review full paper.