ORCID Profile
0000-0002-7362-1786
Current Organisation
Curtin University
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Publisher: Mineralogical Society
Date: 02-11-2021
DOI: 10.1180/MGM.2021.81
Abstract: Ancient metamorphic processes are recorded by the formation of metallic-Pb nanospheres in zircon, a product of internal Pb mobilisation and thermally driven concentration. Here, metallic-Pb nanospheres formed within an ore deposit are characterised for the first time using high-angle annular dark field scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy element-distribution mapping. Exceptional ex les from the migmatite-hosted Archean–Paleoproterozoic Challenger Au deposit (Central Gawler Craton, South Australia) support widespread metallic-Pb nanosphere formation in zircon from rocks experiencing granulite-facies metamorphism. We also report new trace-element associations found with metallic-Pb nanospheres and a new mode of occurrence, in which Sc ‘haloes’ form adjacent to metallic-Pb nanospheres within the crystalline zircon lattice. This differs to previously characterised ex les of metallic-Pb nanospheres associated with amorphous Si-rich glasses and unidentified Al–Ti, or Fe-bearing phases. Multiple modes of metallic-Pb nanosphere occurrences and trace-element associations suggests multiple modes of formation, probably dependant on zircon composition and metamorphic conditions. Identification of metallic-Pb nanospheres in a growing range of geological settings further highlights the mobility of Pb in zircon and the importance of detailed, nanoscale mineral characterisation, in order to constrain accurate geochronological histories for rocks within high-temperature geological environments.
Publisher: MDPI AG
Date: 27-06-2019
DOI: 10.3390/MIN9070388
Abstract: Metal nanoparticles (NP) in minerals are an emerging field of research. Development of advanced analytical techniques such as Z-contrast imaging and mapping using high-angle annular dark field scanning transmission electron microscopy (HAADF STEM) allows unparalleled insights at the nanoscale. Moreover, the technique provides a link between micron-scale textures and chemical patterns if the s le is extracted in situ from a location of petrogenetic interest. Here we use HAADF STEM imaging and energy-dispersive X-ray spectrometry (EDX) mapping/spot analysis on focused ion beam prepared foils to characterise atypical Cu-As-zoned and weave-twinned hematite from the Olympic Dam deposit, South Australia. We aim to determine the role of solid-solution versus the presence of discrete included NPs in the observed zoning and to understand Cu-As-enrichment processes. Relative to the grain surface, the Cu-As bands extend in depth as (sub)vertical trails of opposite orientation, with Si-bearing hematite NP inclusions on one side and coarser cavities (up to hundreds of nm) on the other. The latter host Cu and Cu-As NPs, contain mappable K, Cl, and C, and display internal voids with rounded morphologies. Aside from STEM-EDX mapping, the agglomeration of native copper NPs was also assessed by high-resolution imaging. Collectively, such characteristics, corroborated with the geometrical outlines and negative crystal shapes of the cavities, infer that these are opened fluid inclusions with NPs attached to inclusion walls. Hematite along the trails features distinct nanoscale domains with lattice defects (twins, 2-fold superstructuring) relative to hematite outside the trails, indicating this is a nanoprecipitate formed during replacement processes, i.e., coupled dissolution and reprecipitation reactions (CDRR). Transient porosity intrinsically developed during CDRR can trap fluids and metals. Needle-shaped and platelet Cu-As NPs are also observed along (sub)horizontal bands along which Si, Al and K is traceable along the margins. The same signature is depicted along nm-wide planes crosscutting at 60° and offsetting (012)-twins in weave-twinned hematite. High-resolution imaging shows linear and planar defects, kink deformation along the twin planes, misorientation and lattice dilation around duplexes of Si-Al-K-planes. Such defects are evidence of strain, induced during fluid percolation along channels that become wider and host sericite platelets, as well as Cl-K-bearing inclusions, comparable with those from the Cu-As-zoned hematite, although without metal NPs. The Cu-As-bands mapped in hematite correspond to discrete NPs formed during interaction with fluids that changed in composition from alkali-silicic to Cl- and metal-bearing brines, and to fluid rates that evolved from slow infiltration to erratic inflow controlled by fault-valve mechanism pumping. This explains the presence of Cu-As NPs hosted either along Si-Al-K-planes (fluid supersaturation), or in fluid inclusions (phase separation during depressurisation) as well as the common signatures observed in hematite with variable degrees of fluid-mineral interaction. The invoked fluids are typical of hydrolytic alteration and the fluid pumping mechanism is feasible via fault (re)activation. Using a nanoscale approach, we show that fluid-mineral interaction can be fingerprinted at the (atomic) scale at which element exchange occurs.
Publisher: MDPI AG
Date: 23-08-2016
DOI: 10.3390/MIN6030085
Publisher: Elsevier BV
Date: 05-2019
Publisher: Elsevier BV
Date: 05-2019
Publisher: MDPI AG
Date: 20-05-2019
DOI: 10.3390/MIN9050311
Abstract: A comprehensive nanoscale study on magnetite from s les from the outer, weakly mineralized shell at Olympic Dam, South Australia, has been undertaken using atom-scale resolution High Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF STEM) imaging and STEM energy-dispersive X-ray spectrometry mapping and spot analysis, supported by STEM simulations. Silician magnetite within these s les is characterized and the significance of nanoscale inclusions in hydrothermal and magmatic magnetite addressed. Silician magnetite, here containing Si–Fe-nanoprecipitates and a erse range of nanomineral inclusions [(ferro)actinolite, diopside and epidote but also U-, W-(Mo), Y-As- and As-S-nanoparticles] appears typical for these s les. We observe both silician magnetite nanoprecipitates with spinel-type structures and a γ-Fe1.5SiO4 phase with maghemite structure. These are distinct from one another and occur as bleb-like and nm-wide strips along d111 in magnetite, respectively. Overprinting of silician magnetite during transition from K-feldspar to sericite is also expressed as abundant lattice-scale defects (twinning, faults) associated with the transformation of nanoprecipitates with spinel structure into maghemite via Fe-vacancy ordering. Such mineral associations are characteristic of early, alkali-calcic alteration in the iron-oxide copper gold (IOCG) system at Olympic Dam. Magmatic magnetite from granite hosting the deposit is quite distinct from silician magnetite and features nanomineral associations of hercynite-ulvöspinel-ilmenite. Silician magnetite has petrogenetic value in defining stages of ore deposit evolution at Olympic Dam and for IOCG systems elsewhere. The new data also add new perspectives into the definition of silician magnetite and its occurrence in ore deposits.
Publisher: Informa UK Limited
Date: 03-04-2017
Publisher: MDPI AG
Date: 24-11-2017
DOI: 10.3390/MIN7120233
Publisher: Society of Economic Geologists
Date: 27-08-2020
DOI: 10.5382/ECONGEO.4772
Abstract: Establishing timescales for iron oxide copper-gold (IOCG) deposit formation and the temporal relationships between ores and the magmatic rocks from which hydrothermal, metal-rich fluids are sourced is often dependent on low-precision data, particularly for deposits that formed during the Proterozoic. Unlike accessory minerals routinely used to track hydrothermal mineralization, iron oxides are dominant components of IOCG systems and are therefore pivotal to understanding deposit evolution. The presence of ubiquitous, magmatic-hydrothermal U-(Pb)-W-Sn-Mo–bearing zoned hematite resolves a range of geochronological issues concerning formation of the ~1.6 Ga Olympic Dam IOCG deposit, South Australia, at up to ~0.05% precision (207Pb/206Pb weighted mean 2σ) using isotope dilution-thermal ionization mass spectrometry (ID-TIMS). Coupled with chemical abrasion-ID-TIMS zircon dates from host granite and volcanic rocks within and enclosing the ore-body, a confident magmatic-hydrothermal chronology is defined. The youngest zircon date from the granite intrusion hosting Olympic Dam indicates magmatism was occurring up until 1593.28 ± 0.26 Ma. The orebody was principally formed during a major mineralizing event following granite uplift and during cupola collapse, whereby the hematite with the oldest age is recorded in the outer shell of the deposit at 1591.27 ± 0.89 Ma, ~2 m.y. later than the youngest documented magmatic zircon. Hematite dates captured throughout major lithologies, different ore zones, and the ~2-km vertical extent of the deposit support ~2 m.y. of hydrothermal activity. New age constraints on the spatial-temporal evolution of the formation of Olympic Dam are considered with respect to a mantle to crustal continuum model. Cyclical tapping of magma reservoirs to maintain crystal mushes for extended time periods and incremental building of batholiths on the million-year scale prior to main mineralization pulses can explain the ~2-m.y. temporal window temporal window inferred from the data. Despite the challenge of reconciling such an extended window with contemporary models for porphyry deposits (≤1 m.y.), formation of Proterozoic ore deposits has been addressed at high-precision and supports the case that giant IOCG deposits may form over millions of years.
Publisher: MDPI AG
Date: 20-02-2020
DOI: 10.3390/MIN10020191
Abstract: The Blackbush uranium prospect (~12,580 tonnes U at 85 ppm cut-off) is located on the Eyre Peninsula of South Australia. Blackbush was discovered in 2007 and is currently the single ex le of sediment-hosted uranium mineralisation investigated in any detail in the Gawler Craton. Uranium is hosted within Eocene sandstones of the Kanaka Beds and, subordinately, within a massive saprolite derived from the subjacent Hiltaba-aged (~1585 Ma) granites, affiliated with the S hire Pluton. Uranium is mainly present as coffinite in different lithologies, mineralisation styles and mineral associations. In the sandstone and saprolite, coffinite occurs intergrown with framboidal Fe-sulphides and lignite, as well as coatings around, and filling fractures within, grains of quartz. Microprobe U–Pb dating of coffinite hosted in sedimentary units yielded a narrow age range, with a weighted average of 16.98 ± 0.16 Ma (343 in idual analyses), strongly indicating a single coffinite-forming event at that time. Coffinite in subjacent saprolite generated a broader age range from 28 Ma to 20 Ma. Vein-hosted coffinite yielded similar ages (from 12 to 25 Ma), albeit with a greater range. Uraninite in the vein is distinctly older (42 to 38 Ma). The 17 ± 0.16 Ma age for sandstone-hosted mineralisation roughly coincides with tectonic movement as indicated by the presence of horst and graben structures in the Eocene sedimentary rocks hosting uranium mineralisation but not in stratigraphically younger sedimentary rocks. The new ages for hydrothermal minerals support a conceptual genetic model in which uranium was initially sourced from granite bedrock, then pre-concentrated into veins within that granite, and is subsequently dissolved and reprecipitated as coffinite in younger sediments as a result of low-temperature hydrothermal activity associated with tectonic events during the Tertiary. The ages obtained here for uranium minerals within the different lithologies in the Blackbush prospect support a conceptual genetic model in which tectonic movement along the reactivated Roopena Fault, which triggered the flow of U-rich fluids into the cover sequence. The timing of mineralisation provides information that can help optimise exploration programs for analogous uranium resources within shallow buried sediments across the region. The model presented here can be predicted to apply to sediment-hosted U-mineralisation in cratons elsewhere.
Publisher: Mineralogical Society
Date: 16-06-2020
DOI: 10.1180/MGM.2020.49
Abstract: Preferential removal of W relative to other trace elements from zoned, W–Sn–U–Pb-bearing hematite coupled with disturbance of U–Pb isotope systematics is attributed to pseudomorphic replacement via coupled dissolution reprecipitation reaction (CDRR). This hematite has been studied down to the nanoscale to understand the mechanisms leading to compositional and U/Pb isotope heterogeneity at the grain scale. High-Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF STEM) imaging of foils extracted in situ from three locations across the W-rich to W-depleted domains show lattice-scale defects and crystal structure modifications adjacent to twin planes. Secondary sets of twins and associated splays are common, but wider (up to ~100 nm) inclusion trails occur only at the boundary between the W-rich and W-depleted domains. STEM energy-dispersive X-ray mapping reveals W- and Pb-enrichment along 2–3 nm-wide features defining the twin planes W-bearing nanoparticles occur along the splays. Tungsten and Pb are both present, albeit at low concentrations, within Na–K–Cl-bearing inclusions along the trails. HAADF STEM imaging of hematite reveals modifications relative to ideal crystal structure. A two-fold hematite superstructure ( a = b = c = 10.85 Å α = β = γ = 55.28°) involving oxygen vacancies was constructed and assessed by STEM simulations with a good match to data. This model can account for significant W release during interaction with fluids percolating through twin planes and secondary structures as CDRR progresses from the zoned domain, otherwise apparently undisturbed at the micrometre scale. Lead remobilisation is confirmed here at the nanoscale and is responsible for a disturbance of U/Pb ratios in hematite affected by CDRR. Twin planes can provide pathways for fluid percolation and metal entrapment during post-crystallisation overprinting. The presence of complex twinning can therefore predict potential disturbances of isotope systems in hematite that will affect its performance as a robust geochronometer.
Publisher: Oxford University Press (OUP)
Date: 08-2019
Publisher: Springer Science and Business Media LLC
Date: 12-06-2019
Publisher: Elsevier BV
Date: 03-2020
Publisher: Wiley
Date: 05-12-2021
DOI: 10.1111/GGR.12365
Publisher: Elsevier BV
Date: 12-2017
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Liam Courtney-Davies.