VOLCANO: 4 PhD positions at Bristol

[Jean-François Smekens <jsmekens@xxxxxxx>]

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4 PhD positions at Bristol
From: Alison.Rust@xxxxxxxxxxxxx
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Four fully-funded geology PhD studentships are available as part of a 
collaboration between the University of Bristol and the global mining 
company BHP Billiton.  The projects apply volcanology, experimental 
petrology, geochemistry, structural geology, and geochronology to the 
overall theme of understanding porphyry copper deposits.

Start date: January 2013 or earlier

Open to people of any nationality (home or overseas fees covered)

To apply follow the procedure at: http://www.bristol.ac.uk/prospectus/postgraduate/2012/apply.html

Details for each project are listed below.
For further information contact:
Steve.Sparks@xxxxxxxxxxxxx
Jon.Blundy@xxxxxxxxxxxxx
Alison.Rust@xxxxxxxxxxxxx


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.

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