Amphibole Control on Copper Systematics in Arcs: Insights from the Analysis of Global Datasets

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Nicholas Dewitt Barber, Marie Edmonds, Frances Jenner, Andreas Audétat, Helen Williams


Copper, sourced from porphyry deposits formed in arc settings, is an increasingly scarce yet critical resource. The processes that shape the copper contents of magmas remain poorly understood. One theory is that magmas must be copper-rich in order to form porphyry deposits. Mature arcs have up to now played an outsized role in shaping existing models of copper systematics in magmas. Here we take a Big Data approach, compiling multiple data sets of volcanic whole rock compositions using open-source software. We show the global ubiquity of the "copper paradox," where rocks with high Sr/Y (and high ore potential) have the lowest copper concentrations. These calc-alkaline, ore-forming magmas undergo iron depletion caused by extensive amphibole and/or garnet fractionation, promoting sulphide fractionation and copper depletion. Despite their paucity in copper, these magmas are associated with porphyry deposits, implying that magma fertility depends on factors other than a magma’s bulk copper content.



Earth Sciences, Geochemistry, Geology, Volcanology


Magmas, Ore Deposits


Published: 2020-10-21 02:04

Last Updated: 2021-01-15 23:57

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CC BY Attribution 4.0 International

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Data Availability (Reason not available):
Data will be shared at a later stage! Currently the code is being compiled into more user friendly Jupyter Notebooks.

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