223-1 Tectonic Controls on Porphyry Copper Formation in the Southwest USA

Session: Rock Deformation and the Dynamics of Mountain Building: A Session Honoring the Scientific Contributions of John P. Platt (Posters)

Poster Booth No.: 206

Presenting Author:

Frances Cooper

Authors:

Bain, Hero R¹, Cooper, Frances J², Bevan, Dan³, Lamont, Thomas N⁴, Elliott, Tim⁵, Roberts, Nick MW⁶, Bouvier, Audrey⁷, Gorecki, Adam⁸

(1) School of Earth Sciences, University of Bristol, Bristol, United Kingdom, (2) Department of Earth Sciences, University College London, London, United Kingdom, (3) Centre for Exploration Targeting, The University of Western Australia, Perth, Australia, (4) Department of Geoscience, University of Nevada, Las Vegas, Las Vegas, Nevada, USA, (5) School of Earth Sciences, University of Bristol, Bristol, United Kingdom, (6) Geochronology and Tracers Facility, British Geological Survey, Keyworth, United Kingdom, (7) Bayerisches Geoinstitut, University of Bayreuth, Bayreuth, Germany, (8) BHP, Tucson, USA,

Abstract:

Copper is an essential metal in the clean energy technologies that will underpin the global green energy transition. With global demand set to rise by over 40% over the next two decades [1], the heat is on to discover more high-quality mineable deposits. Most of the copper we use is sourced from porphyry copper deposits (PCDs), which are magmatic-hydrothermal systems typically formed above subduction zones. Clustering of PCDs in space and time within magmatic arcs implies the existence of overarching tectono-magmatic controls on their formation. However, these controls must be better constrained if they are to be used to guide exploration.

In the copper-rich Laramide Porphyry Province of Arizona, PCDs are thought to have formed in a single 20 Myr period during crustal relaxation following prolonged compression [2]. However, in the adjacent Northern Great Basin (Nevada-Utah-Idaho), a lower copper endowment and longer, episodic history of PCD formation (~170–25 Ma) suggests different tectonic controls were at play. We seek to determine the spatial-temporal links between crustal compression, relaxation, extension, and PCD formation in the Northern Great Basin by reconstructing the deformational and metamorphic history preserved within three exhumed metamorphic core complexes that are temporally and spatially associated with PCDs.

To constrain the timing of deformation we use in-situ Rb-Sr dating of syn-kinematic micas that grew during contractional and extensional deformation. Our data highlight two distinct tectonic contexts for PCD formation: (1) late syn-orogenic deposits formed during stress relaxation synchronous with peak metamorphism (~170–150 and 90–70 Ma), and (2) post-orogenic deposits formed during the early stages of crustal extension and core complex exhumation (~120–100 and 38–25 Ma).

New Lu-Hf and Sm-Nd garnet dating, combined with garnet trace element profiles and pseudosection modelling, provide additional constraints on how the timing and magnitude of crustal thickening may have influenced subsequent PCD formation. A preliminary garnet Lu-Hf date of ~106 Ma from the Northern Snake Range in eastern Nevada indicates burial started earlier than has been widely recognised before, which may be connected with formation of the adjacent 120–105 Ma Ely PCD cluster.

References:

[1] IEA Report (2021), https://www.iea.org/reports/the-role-of-critical-minerals-in-clean-energy-transitions

[2] Lamont et al. (2024), Nature Geoscience, doi: 10.1038/s41561-024-01575-2

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-4299

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