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Magmatic and volcanic processing of volatile and chalcophile elements https://doi.org/10.17863/CAM.115919 Hogg, Olivia R Edmonds, Marie Chalcophile elements possess significant economic and environmental value. The transition to an electric economy has led to an unprecedented rise in the demand for critical metals, including several chalcophile elements such as copper, selenium, and silver. Copper in particular is essential – it is a key component in wind and solar technologies, as well as energy storage systems, all of which are central to the energy transition. However, with existing ore grades declining and newer resources harder to find, meeting the growing global demand for metals poses a significant challenge to current supply capacity. Over 70% of global copper is derived from porphyry copper deposits (PCDs) associated with hydrous oxidised calc-alkaline arc magmas at convergent margins. It is not uncommon for these deposits to generate other critical element byproducts like selenium, tellurium, and bismuth, which in the current economic climate also face surging demands. Despite widespread recognition of the role that magmas play in the formation of hydrothermal ore deposits, there is still no consensus on the relative importance of the various magmatic processes involved. An important and undisputed step in the process is the generation of a hydrothermal saline magmatic fluid with a proclivity to carry high quantities of metals. These fluids exsolve at depth from fractionating magmas and are subsequently conveyed to sites of mineralisation. The conditions that optimise the masses and concentrations of copper and other chalcophile elements partitioning in to these fluids are not fully understood. By definition, chalcophile elements have a strong affinity for sulfur, such that in magmatic systems they fractionate into precipitating sulfide phases. Several chalcophile elements are also highly volatile, therefore will also partition into exsolving magmatic fluids. Degassing and sulfide saturation occur ubiquitously during magma evolution, yet the impact that these processes exert on the abundance and distribution of copper in magmatic systems, and more specifically in exsolving magmatic fluids, remain unclear. Exsolved magmatic fluids are not only important within the crust, but also play a critical role in surface environments: these fluids may advect to the surface and manifest as volcanic gas plumes, which emit vast quantities of chalcophile elements into the atmosphere. These elements exist primarily as aerosols or particulate matter that eventually settle out of the plume and into the surface environments. Over a narrow interval, these elements transition from serving as essential nutrients to becoming toxic pollutants, highlighting their significant environmental implications. Metal assemblages in volcanic gas plumes vary systematically with tectonic setting. Arcs tend to be more enriched in lead, thallium, and bismuth compared to hotspots. However, despite their distinct metal fingerprints, the concentrations and mass fluxes of outgassing metals can differ by several orders of magnitude even within individual arcs. What controls the distribution and abundance of volatile and chalcophile elements in magmatic and volcanic systems? I explore this fundamental question by combining natural geochemical datasets with numerical models of degassing and sulfide saturation during fractional crystallisation and decompression. The commonality that emerges across the work contributing to this thesis is the importance of magma water concentrations on the fate of volatile chalcophile elements in magmatic and volcanic environments. University of Cambridge 2024-09-01 Thesis Doctoral Doctor of Philosophy (PhD) eng Research was supported by Natural Environment Research Council grant NE/S007164/1 https://www.repository.cam.ac.uk/handle/1810/379949 https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/82586539-d5fa-4bb1-aaec-0c999bd93d3e/download c0e7c44a739d8c6a16abf30455df60dc https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/10435810-088d-4afc-a2b3-21e5e9e3edf5/download 52dbb09c51c63042854fe01087a45eea https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/6991394a-4b29-4cf6-86ff-a3cc186e5356/download bbbb21504c70a49168e90ca651bd2929 https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/cc583838-e49d-467b-a594-c92301658c6f/download 447bb95050f6ac3b09197a4f4c4e2f29 https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/a2fe2b88-eb63-4714-b028-e6900931ccfa/download 87eda9de84448d1f82354d60eee3eb5f http://purl.org/NET/rdflicense/allrightsreserved chalcophile elements magmatic water sulfide saturation trace element partitioning volcanic degassing