The volatile geochemistry of precious metal-enriched open-system layered mafic-ultramafic intrusions

Abstract

Layered mafic-ultramafic intrusions provide the ideal opportunity to study magmatic processes operating at shallow-mid crustal levels. Layered intrusions may also contain substantial concentrations of sulfide-hosted precious metals, including the platinum group elements (PGE). Despite decades of study, the provenance and role of volatiles (e.g., halogens and sulfur) in the evolution of these magmatic systems and the relationship of volatiles to PGE ore formation remains a matter of significant debate. This project concerns the volatile geochemistry of two classic examples of layered intrusions; the Rum Layered Suite (NW Scotland) and the Stillwater Complex (USA), using the novel neutron-irradiated noble gas mass spectrometric technique for halogen abundance and noble gas isotope determination. In situ sulfur isotope analyses are also carried out on selected Rum samples. The intrinsic link between halogens and fluid activity, as well as their affinity for particular reservoirs in the Earth’s crust, mean that the halogens can provide information on the provenance and subsequent processing of volatile-enriched fluids in layered intrusions. Sulfur isotopes may also reveal insights into volatile sources, as well as post-magmatic effects in the crystal mushes that solidify to form layered intrusion cumulates. For the Rum intrusion, analysis of picrite dykes, considered to be proxies for Rum parental magmas, reveal an SCLM-like halogen signature for the magma source region. Noble gas isotopes as well as evidence of pervasive iodine enrichment (

Date of Award	6 Jan 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Patricia Clay (Supervisor) & Brian O'Driscoll (Supervisor)