Scientists have made an intriguing new discovery about the formation of mineral deposits critical to our transition to a ‘green economy’.
The new collaborative study, led by Lawrence Carter of the University of Exeter’s Camborne School of Mines, has shown that porphyry-style copper deposits form due to a rapid change in the underlying magmatic piping system that forms them.
The study describes a new 4-D model for the formation of porphyry-style copper deposits that challenges the current paradigm of a progressive, multimillion-year increase in the “fertility” or mineralization potential of radian-scale igneous systems. Instead, there may be an order of magnitude faster switch from intrusion from non-mineralizing to porphyry-depositing magmas over a period of less than 200,000 years. The proposed cause of this is a switch from mid-crust to lower-crust magma production, likely initiated by the intrusion of much hotter mantle magma.
Researchers believe these results will help exploration geologists discover the next generation of porphyry copper deposits. Porphyry-type deposits provide most of the world’s copper and molybdenum, as well as large amounts of gold and other metals that are increasingly in demand for green technologies such as electric vehicles, wind turbines and solar panels, and power transmission. As such, they are the primary target of many mining companies worldwide. The problem is that most of the large near-surface deposits have already been found, so geologists have to look deeper and under thicker layers of younger rock to find them. There is therefore a growing need to better understand where and how porphyry copper deposits form and new methods to find them.
The new study was conducted in Nevada’s Yerington batholith, where tipping of the upper crust has provided one of the world’s most exposed (~8 km deep) sections through an igneous-hydrothermal system, ranging from the volcanic to the plutonic environment, including four porphyry deposits. For this reason, previous studies in the district have underpinned much of the current understanding of how porphyry-like deposits form.
Lawrence Carter, lead author of the study and collaborator at Camborne School of Mines on the University of Exeter’s Penryn campus, said: “To improve the previously fragmented understanding of the magmatic timescales associated with the formation of porphyry deposits, we have the world’s best investigates exposed porphyry system by integrating field observations and geochemistry with state-of-the-art, highly accurate Zircon-U-Pb geochronology. We show that magmatic systems can ‘switch on’ their ability to form ore deposits due to a rapid change in their magmatic conduits and tap into a deeper, more ephemeral ‘fertile’ zone.”
Lawrence Carter said, “We also show that the distinct ‘fertile’ geochemical signatures associated with ore-forming magmas develop almost instantaneously (
The research was supported by the NERC GW4+ DTP program, a NERC Isotope Facilities Grant, SelFrag AG, the Society of Economic Geologists Foundation and the NERC Highlight topic FAMOS.
The study, entitled “A rapid change in magma plumbing taps porphyry copper deposit-forming magmas,” was published in the journal Scientific Reports and is available at https://doi.org/10.1038/s41598-022-20158-y
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