The projects apply volcanology, experimental petrology, geochemistry, structural geology, and geochronology to the overall theme of understanding porphyry copper deposits. Details for each project are listed below.
Open to people of any nationality (home or overseas fees covered). To apply, follow the instructions at http://www.bristol.ac.uk/prospectus/postgraduate/ 2012/apply.html
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Studentship 1 – Relationship between porphyry copper deposits (PCDs) and volcanoes
This project will assess the extent to which PCDs are consistent with modern volcanological views of how magma systems are constructed and evolve with time. Of particular interest are the depths at which magmas stall within the shallow crust, the composition of these magmas and their relationships to each other, the evidence for loss of magmatic volatiles from ascending and crystallising magma at different levels within the plumbing system, the prevalence of blind intrusions versus volcanic feeders, and the effects of volcanic eruptions on the development of economic PCDs.
The relationship between PCDs and the magmatic plumbing systems beneath arc volcanoes will be investigated via a combination of literature reviews of existing PCDs, visits to PCDs owned by BHP, and targeted fieldwork. Fieldwork will include studies of one or two deeply eroded hydrothermally altered Quaternary volcanic edifices. Magma types will be characterised using whole rock geochemistry and petrography. Magma storage conditions will be assessed by electron microprobe, applying a range of mineral and melt geothermometers and barometers. Analysis of dissolved volatiles in melt inclusions and phase equilibria in fluid inclusions will also provide valuable thermobarometric constraints. These measurements will be performed using ion-microprobe and heating-stage microscopy, respectively.
The student will work closely with a postdoc who will use diffusion chronometry to evaluate timescales of magma recharge and degassing, which will be a valuable adjunct to the petrological and geochemical work by the student.
Studentship 2 - Experimental investigation of the controls of fluid distribution and metal enrichment in porphyry copper deposits
The composition of fluids released from ascending and crystallising magmas at sub-volcanic depths is controlled by the thermodynamics of fluid-melt equilibria. Partitioning of base metals is influenced by the composition of the melt and fluid phases and intensive variables, such as pressure, temperature and redox state. This studentship focuses on partitioning experiments, with a view to generating models of how fluid chemistry evolves as magmas degas and cool. The temporal evolution of these fluids will provide important information on the sequential development of alteration haloes and base metal precipitation.
The student will conduct fluid-melt partitioning experiments over a range of pressures and temperatures using cold-seal hydrothermal pressure apparatus. Fluids will be trapped and quenched either in the pore space of diamond traps enclosed within the experimental capsule or as synthetic fluids inclusions within cracked quartz grains loaded into the capsules. Run products will be analysed by EPMA and laser ablation ICP-MS.
Studentship 3 - Chronostratigraphic evolution of volcanosedimentary rocks on a regional scale
The aim of this project is to understand how and when volcanic sequences became buried in a portion of the Andes and how this has influenced the extent of supergene activity. The chronostratigraphic evolution of the volcanic rocks and their cover sequences will be achieved through detailed analysis of a set of samples of the cover lithologies. Cores will be logged to identify sedimentary and volcanic facies and their temporal evolution. Core logging will be supplemented by study of polished thin sections for their petrography, mineral chemistry, grain size and sorting, and whole-rock chemical analyses.
A variety of geochronological techniques will be used to tie down the timing of key eruptive and sedimentary events and the provenance of detrital grains. Ar-Ar dating will provide the principal tool for the volcanic sequences. Exposure ages (and hence burial ages) will be constrained, where possible, using cosmogenic nuclides, (U-Th)/He dating of volcanic zircon and apatite, and optically stimulated luminescence (OSL) dating of detrital quartz and feldspar. It is anticipated that, in combination, these approaches will yield unprecedented images of the evolving volcanic landscape relevant to exploration for new porphyry copper deposits.
Studentship 4 - Structural controls on magma emplacement and porphyry copper deposit (PCD) formation
The relationship between regional and local tectonic stresses and PCD localisation may provide a valuable exploration tool. The relative timing of different structural elements (folds, faults, shears etc) and different magmatic and hydrothermal events will be investigated via fieldwork around two BHP mines in South America. The student will document structural events and link their orientation to the evolving local stress field. Different generations of magmatic/hydrothermal events (veins, dykes etc) will be placed in this stress framework. Results will be integrated with larger scale geophysical surveys (gravity, magnetic), where available.
The structural context of other PCDs will be reviewed in the course of the project, to identify and similarities to the field area. Of particular interest will be the relative importance of regional stresses and local stresses generated by the magma systems themselves.
This is primarily a field-oriented project, augmented by optical petrography, SEM, microprobe, and whole-rock geochemistry. Dating of some discrete magmatic events, by Ar-Ar methods, will provide useful benchmarks for the relative chronology and refinement of spatial and temporal clustering of PCDs.