No Need to Dig Too Deep to Find Gold!


A UNIGE researcher has discovered the particularities of porphyry copper and gold deposits, providing mining companies with a new tool to maximise the extraction of these two metals.

Why are some porphyry deposits – formed by magmatic fluids in volcanic arcs – rich in copper while others primarily contain gold? In an attempt to answer this question, a researcher from the University of Geneva (UNIGE) investigated how the metals are accumulated over the time duration of a mineralizing event, looking for a correlation between the amounts of copper and gold extracted from the deposits. Not only did the researcher discover that the depth of the deposits influences the quantity of metals produced but also that over 95% of the gold is lost to the atmosphere through volcanic emissions. In short, the deeper a deposit is, the more copper there will be, while gold-rich deposits are closer to the surface. These findings, which are published in the journal Nature Communications, will provide valuable assistance to companies that mine these metals.

Geological processes produce different kinds of deposits. Porphyry-type deposits are formed underneath volcanoes by an accumulation of magma that releases fluids on cooling and precipitates metals in the form of ore. “Precipitation is the extraction of metals from the magmatic fluid and their fixation in an ore”, explains Massimo Chiaradia, a researcher in the Department of Earth Sciences in UNIGE’s Science Faculty. These porphyry deposits, which are found mainly around the Pacific Ring of Fire, produce three-quarters of the natural copper and a quarter of the natural gold mined. “A copper deposit can contain from one to 150 million tonnes, while the quantity of gold varies from ten tonnes to 2,500 tonnes per deposit,” continues Chiaradia. But will a copper-rich deposit automatically be rich in gold? And how can we tell where the largest deposits are located?

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