How crustal exhumation rates determine the fate of porphyry copper deposits

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• Frances Cooper, University College London
• Tuesday 03 June 2025, 12:00-13:00
• Department of Earth Sciences, Tilley Lecture Theatre.

If you have a question about this talk, please contact Dr Rachael Rhodes.

Mineralogical Society Distinguished Lecturer 2024–25

Copper is an essential component in most clean energy technologies and fundamental to the success of the global green energy transition. It is mainly sourced from porphyry copper deposits (PCDs), which are metal-rich magmatic-hydrothermal systems typically associated with subduction zones. However, PCDs are rare and proving increasingly difficult to find. They are also high tonnage (_{100–1,000 Mt) and low concentration (average production grade is} 0.53% Cu), so enormous volumes of rock must be extracted to retrieve tiny amounts of metal. As the global demand for copper surges to meet ambitious green energy targets, society is confronted with the dual challenge of locating increasingly elusive PCDs while prioritising those with the lowest potential environmental impact. This means finding the most copper-rich (highest-grade) deposits, which require the smallest amount of extraction and processing, and thus create the least damage to the environment.

The exhumation history of a PCD plays an important role in determining its copper grade. During the initial “hypogene” stage of mineralisation, rapid exhumation is required to advect heat towards the surface, allowing metal-carrying magmas and fluids to transport their cargo into the shallow crust. To maximise ore grades, exhumation must then slow considerably so the deposit can linger close to the surface where secondary “supergene” enrichment by oxygenated groundwater water takes place. In this talk, I will present an example from the Eocene-Oligocene copper belt in northern Chile, which is the world’s premier PCD province, but disappears to the north as it approaches the Peruvian border. By combining U-Pb zircon geochronology, Al-in-hornblende geobarometry, low-temperature (U-Th-Sm)/He thermochronology, and thermal-kinematic modelling to track exhumation histories, I will show that (1) both the rate and timing of exhumation are critical in determining the potential of an area to host high-grade PCDs; and (2) northward disappearance of the copper belt close to Peru is due to higher exhumation rates in that area, which prevented supergene enrichment and potentially led to loss of deposits via surface erosion.

This talk is part of the Department of Earth Sciences Seminars (downtown) series.

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• Department of Earth Sciences Seminars (downtown)
• Department of Earth Sciences seminars
• Department of Earth Sciences, Tilley Lecture Theatre
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