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Volatile budgets and evolution in porphyry-related magma systems, determined using apatite

Lormand, Charline; Humphreys, Madeleine C.S.; Colby, David J.; Coumans, Jason P.; Chelle-Michou, Cyril; Li, Weiran

Volatile budgets and evolution in porphyry-related magma systems, determined using apatite Thumbnail


Authors

David Colby david.j.colby@durham.ac.uk
Post Doctoral Research Associate

Jason P. Coumans

Cyril Chelle-Michou

Weiran Li



Abstract

Volatile-bearing minerals, such as apatite, Ca5(PO4)3(OH,F,Cl), can record changes in dissolved magmatic volatile species during differentiation and, unlike melt inclusions, are sensitive to the presence of an exsolved fluid phase. Populations of apatite crystals from an individual sample can therefore be used to define the progressive volatile evolution of melt ± fluid during magma differentiation. Despite the importance of fluid chemistry in mineralisation processes, this approach remains relatively underdeveloped for porphyry mineralisation scenarios. Here, we present a model, including a standalone MATLAB app, for melt + apatite ± fluid fractionation that incorporates non-ideal, temperature-dependent KDs for OH-Cl-F exchange and permits an analysis of uncertainty arising from non-unique parameter combinations. We apply the model to apatite from the Fe-Cu-Au Corrocohuayco porphyry-skarn system and analyse differences in volatile saturation state and fluid salinity between different units. We find that there is little difference in the overall fluid salinity, and thus the fluid copper loads, but that the more primitive unit (i.e. the gabbrodiorites) reached fluid saturation much later (after around 50% crystallisation) than the more evolved units, implying that the melt volatile concentration recorded by the apatites in the gabbrodiorites is not representative of the initial magma volatile budget. This work demonstrates that apatite can be a good alternative means of reconstructing the evolving magmatic fluid salinity within mineralising systems, and linking this to the trace metal content of the melt.

Journal Article Type Article
Acceptance Date Apr 26, 2024
Online Publication Date May 5, 2024
Publication Date May 5, 2024
Deposit Date Jun 19, 2024
Publicly Available Date Jun 19, 2024
Journal Lithos
Print ISSN 0024-4937
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 480-481
Article Number 107623
DOI https://doi.org/10.1016/j.lithos.2024.107623
Public URL https://durham-repository.worktribe.com/output/2486077

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