Current Research
The formation of
gold deposits beneath volcanic vents
The El Indio Cu-Au deposit,
Chile represents the deep feeder zones beneath a fossil fumarole
field. The sulfide ore minerals from this deposit are rich in
volatile metalloids (As, Sb, Bi, Te) and coexist with
tiny quartz crystals. We have undertaken a detailed textural and
geochemical study of these ores and melt inclusions to unravel
the complex history of ore deposition from high-temperature
magmatic gases.
(right)
Volcanic vent on White Island volcano, New Zealand. It is
thought that Cu-Au deposits are actively forming beneath these
fumaroles.
The opal to quartz
transition in fossil fumaroles 
I have completed a detailed textural analysis of extremely
zoned quartz microcrystals (often less than 500 μm wide)
from high-grade Cu-Au ore from El Indio, Chile in order to
determine their origin. Raman spectroscopy of these crystals
was undertaken at Geoscience Australia and revealed patches
of residual opal within the microcrystals. The Sensitive
High Resolution Ion Microprobe (SHRIMP) II, located at the
Australian National University was
then used to analyze oxygen isotopes in situ. Our data
suggests that quartz formed in high-temperature hydrothermal
systems probably evolved from hot opal. This finding has
significant implications for interpreting stable isotopes,
trace-element thermometers and trapped fluid inclusions in
many geothermal systems.
(left)
Euhedral quartz crystals separated from high-grade sulfosalt
ore from the El Indio Cu-Au mine, Chile.
Trace element geochemistry of layered mafic intrusions
Layered mafic intrusions
are economically important as they are the world’s largest
repository of Platinum Group Elements (PGEs). I studied a 3km
drillcore through the world’s largest layered mafic
intrusion – the Bushveld Complex. I analyzed the trace element
geochemistry of plagioclase, clinopyroxene, orthopyroxene and
olivine throughout the 3km drillcore in order to
understand the evolution of these intrusions. We analysed
these minerals for >50 elements in situ using Laser Ablation Inductively
Coupled Mass Spectrometry (LA-ICP-MS). Our results are very
intriguing… stay posted for more details.
(right)
LA-ICP-MS ablation pits in pyroxene from the Bellevue
drillcore, Northern Bushveld, South Africa.
Diffusion of plagioclase under magmatic conditions
We have recently begun
diffusion experiments in gem-quality feldspars, using the
experimental petrology laboratory at the Research School of
Earth Sciences. We are testing and quantifying a range of
diffusion coefficients for plagioclase at magmatic conditions,
in order to “see through” the process of re-equilibration.
(left) LA-ICP-MS traverse across
plagioclase from the
Bellevue drillcore, Northern Bushveld, South Africa.
The formation of
symplectic Cr-bearing spinel in the Merensky Reef
High-grade PGE ore from the
Bushveld Complex revealed complex symplectic textures. However,
the symplectites constituted Cr-rich spinel – one of the most
refractory minerals known to mankind. Detailed petrologic and
chemical analyses suggest that these ‘chromites’ formed from
amagmatic processes – a theory never before suggested for the
Bushveld Complex.
(right)
Symplectic Cr-spinel from the Merensky Reef, Rustenburg Mines,
South Africa.
The origin of
heavy oxygen isotopes in Klyuchevskoy volcano, Kamchatka
Geologists agree that
the Klyuchevskoy volcano is one of the most active
volcanoes on Earth. However the origin of the ‘heavy
oxygen’ recorded by igneous minerals is highly
contentious. Published theories suggest an input of water
from the subducting slab, interaction with metasomatised
lower crust, or sediment assimilation. We use in situ oxygen
isotope analysis using SHRIMP II, in order to resolve the
origin of the ‘heavy oxygen’.
(left) LA-ICP-MS traverse
across plagioclase from the Bellevue drillcore, Northern Bushveld, South
Africa.
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