Researchers develop new cost-effective method to find copper

Porphyry-type copper deposits provide 75 percent of the world’s copper and a significant amount of molybdenum and gold. These rare deposits, which originally form at several kilometers below the Earth’s surface, above large magma chambers, are most economical to mine. However, most near-surface deposits have already been discovered.

Dr. Ben Williamson, a geologist at the University of Exeter, and Dr. Richard Herrington from the Natural History Museum of London have developed a new and cost-effective way for mining companies to identify these copper deposits, particularly those located deep underground.

The project, funded by Anglo American, 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 which can be used as one of a suite of indicators to home-in on porphyry deposits. 

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The main finding in the report, which was published in Nature Geoscience, 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.

“This new method will add to the range of tools available to exploration companies to discover new porphyry copper deposits,” said Williamson. “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.”

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