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Vadim S. Kamenetsky Alexander Belousov Victor V. Sharygin Liudmila M. Zhitova Kathy Ehrig Michael E. Zelenski Ilya Chaplygin Marina A. Yudovskaya Pavel N. Nesterenko Sergey M. Zakharov 《地学学报》2019,31(6):511-517
Subvolcanic environments in supra‐subduction zones are renowned for hosting epithermal deposits that often contain electrum and native gold, including bonanza examples. This study examined mineral assemblages and processes occurring in shallow‐crust volcanic settings using recent eruption (2012–2013) of the basaltic Tolbachik volcano in the Kamchatka arc. The Tolbachik eruptive system is characterized by an extensive system of lava tubes. After cessation of magma input, the tubes maintained the flow of hot oxidized gases that episodically interacted with the lava surfaces and sulphate‐chloride precipitates from volcanic gases on these surfaces. The gas‐rock interaction had strong pyrometamorphic effects that resulted in the formation of molten salt, oxidized (tenorite, hematite, Cu‐rich magnesioferrite) and skarn‐like silicate mineral assemblages. By analogy with experimental studies, we propose that a combination of these processes was responsible for extraction of metals from the basaltic wall rocks and deposition of Cu‐, Fe‐ and Cu‐Fe‐oxides and native gold. 相似文献
2.
A. R. Cherry V. S. Kamenetsky J. McPhie J. M. Thompson K. Ehrig S. Meffre 《Australian Journal of Earth Sciences》2018,65(5):643-659
The Olympic iron oxide–copper–gold province in South Australia contains numerous deposits and prospects, including the Olympic Dam Cu–U–Au–Ag deposit and the Acropolis prospect. The Acropolis prospect comprises massive, coarse-grained magnetite–apatite veins partly replaced by a hematite-stable assemblage. The apatite grains in the veins contain zones with abundant inclusions of other minerals (including monazite and xenotime) and low trace-element concentrations relative to the inclusion-free zones. The inclusion-rich apatite zones are interpreted to be formed from the recrystallisation of the inclusion-free apatite and remobilisation of U, Th and rare earth element (REE) from apatite into monazite and xenotime. Apatite, monazite and xenotime are all established U–Th–Pb geochronometers and offer the potential to constrain the alteration history of the Acropolis prospect. The LA-ICPMS U–Pb age of inclusion-free apatite is within error of the age of the host volcanic units (ca 1.59 Ga). Inclusion-rich apatite yields both near-concordant analyses that are within error of the inclusion-free apatite as well as highly disturbed (discordant) analyses. The most concordant analyses of monazite (Th–Pb) inclusions and xenotime (U–Pb) inclusions and rim grains indicate an alteration event occurred at ca 1.37 Ga and possibly also at ca 500 Ma. The disparity in age of the inclusion-rich apatite and the REE-phosphate inclusions (and rim grains) is suggested to be owing to the apatite being initially recrystallised at ca 1.59 Ga and modified again by a later event that also formed (or coarsened) most of the inclusions. Partial resetting of the majority of the monazite inclusions as well as the presence of significant amounts of common Pb has complicated the interpretation of the monazite results. In contrast, xenotime is a more robust geochronometer in this setting. The ages of the two post-1.59 Ga events that appear to have affected the Acropolis prospect do not correspond to any events known to have occurred in the Gawler Craton. The earlier (ca 1.37 Ga) age instead corresponds best with metamorphic–magmatic–hydrothermal activity in Laurentia, consistent with the proximity of Laurentia and the Gawler Craton inferred from palaeogeographic reconstructions. The later (ca 500 Ma) event corresponds to the Delamerian Orogeny and has been shown by prior studies to have also affected the Olympic Dam deposit. 相似文献
3.
J. McPhie K. J. Ehrig M. B. Kamenetsky J. L. Crowley V. S. Kamenetsky 《Australian Journal of Earth Sciences》2020,67(5):699-716
AbstractAcropolis is an Fe-oxide–copper–gold prospect ～20?km from Olympic Dam, South Australia, and marked by near-coincident gravity and magnetic anomalies. Prospective Fe-oxide–apatite?±?sulfide veins occur in Mesoproterozoic and Paleoproterozoic volcanic and granitoid host units beneath unmineralised sedimentary formations. We have produced a geological map and history of the prospect using data from 16 diamond drill holes, including LA-ICPMS and high-precision CA-TIMS ages. The oldest unit is megacrystic granite of the Donington Suite (ca 1850?Ma). A non-conformity spanning ca 250 My separates the Donington Suite and felsic lavas and ignimbrites of the Gawler Range Volcanics (GRV; 1594.03?±?0.68?Ma). The GRV were intruded by granite of the Hiltaba Suite (1594.88?±?0.50?Ma) and felsic dykes (1593.88?±?0.56?Ma; same age as the Roxby Downs Granite at Olympic Dam). The felsic dykes are weakly altered and lack Fe-oxide–apatite–sulfide veins, suggesting that they post-date the main hydrothermal event. If correct, this relationship implies that the main hydrothermal event at Acropolis was ca 1594?Ma and pre-dated the main hydrothermal event at Olympic Dam. The GRV at Acropolis are the same age as the GRV at Olympic Dam and ca 3–7 My older than the GRV exposed in the Gawler Ranges. The gravity and magnetic anomalies coincide with sections through the GRV, Hiltaba Suite and Donington Suite that contain abundant, wide, Fe-oxide veins. The GRV, Hiltaba Suite and Donington Suite are unconformably overlain by the Mesoproterozoic Pandurra Formation or Neoproterozoic Stuart Shelf sedimentary formations. The Pandurra Formation shows marked lateral variations in thickness related to paleotopography on the underlying units and post-Pandurra Formation pre-Neoproterozoic faults. The Stuart Shelf sedimentary formations have uniform thicknesses.
- KEY POINTS
Fe-oxide–apatite?±?sulfide veins are hosted by the Gawler Range Volcanics (1594.03?±?0.68?Ma), the Hiltaba Suite granite (1594.88?±?0.50?Ma) and Donington Suite granite (ca 1850?Ma).
The age of felsic dykes (1593.88?±?0.56?Ma) interpreted to be post-mineralisation implies that the main hydrothermal event at Acropolis was ca 1594?Ma.
The Gawler Range Volcanics at Acropolis are the same age as the Gawler Range Volcanics at Olympic Dam and ca 3 to 7 My older than the Gawler Range Volcanics exposed in the Gawler Ranges.
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Jeff B. Boisvert Mario E. Rossi Kathy Ehrig Clayton V. Deutsch 《Mathematical Geosciences》2013,45(8):901-925
Modeling of geometallurgical variables is becoming increasingly important for improved management of mineral resources. Mineral processing circuits are complex and depend on the interaction of a large number of properties of the ore feed. At the Olympic Dam mine in South Australia, plant performance variables of interest include the recovery of Cu and U3O8, acid consumption, net recovery, drop weight index, and bond mill work index. There are an insufficient number of pilot plant trials (841) to consider direct three-dimensional spatial modeling for the entire deposit. The more extensively sampled head grades, mineral associations, grain sizes, and mineralogy variables are modeled and used to predict plant performance. A two-stage linear regression model of the available data is developed and provides a predictive model with correlations to the plant performance variables ranging from 0.65–0.90. There are a total of 204 variables that have sufficient sampling to be considered in this regression model. After developing the relationships between the 204 input variables and the six performance variables, the input variables are simulated with sequential Gaussian simulation and used to generate models of recovery of Cu and U3O8, acid consumption, net recovery, drop weight index, and bond mill work index. These final models are suitable for mine and plant optimization. 相似文献
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A. J. Mauger K. Ehrig A. Kontonikas-Charos C. L. Ciobanu N. J. Cook V. S. Kamenetsky 《Australian Journal of Earth Sciences》2016,63(8):959-972
Twenty thousand metres of diamond drill core representing a 14 km cross-section from weakly to intensely altered Roxby Downs Granite through the Olympic Dam Breccia Complex, host to the Olympic Dam iron-oxide–copper–gold–uranium deposit in South Australia, was analysed using the HyLogger-3 spectral scanner. Thermal and shortwave infrared spectroscopy results from 30 drill holes provide insight into the spatial relationships between quartz, orthoclase–microcline, albite–oligoclase and progressively changing sericite and chlorite compositions. The relative proportions of quartz, feldspars and phyllosilicates were mapped with thermal infrared spectroscopy. Variations in the chemistry of sericite and chlorite were extracted by proxy from their shortwave infrared spectral response, together with their relative spatial distribution. HyLogger scanning has revealed four deposit-scale mineralogical trends, progressing from least-altered Roxby Downs Granite into mineralisation where most of the feldspar has been replaced by sericite + hematite + quartz: (1) a progressive Al–OH wavelength shift of 2205 nm to 2210 nm for sericite, followed by a spatially rapid reversal corresponding to lower phengite/muscovite abundance ratios; (2) progressive Mg/Fe–OH wavelength shift of 2248 nm to 2252 nm reflecting an increase in the Fe:Mg ratio of chlorite; (3) increasing ratio of microcline to orthoclase followed by a rapid decrease; and (4) slightly decreasing ratio of albite to oligoclase followed by plagioclase destruction prior to albite replacement by sericite. The HyLogger feldspar results support recent petrographic evidence for hydrothermal albite and K-feldspar at the Olympic Dam deposit, not previously reported. The spectral results from continuous HyLogger scans also show that the microscopic observations and proposed feldspar replacement reactions are not locally isolated phenomena, but are applicable at the deposit and regional-scale. A modified quartz–K-feldspar–plagioclase ternary diagram utilising mineralogy interpreted from HyLogger thermal infrared spectra (QAPTIR) diagram along with supporting data on the abundance ratios of orthoclase/microcline and albite/plagioclase, and the wavelength shifts in characteristic absorption features for sericite and chlorite, can be used as empirical vectors towards mineralisation within the Olympic Dam mineral system, with potential application to other IOCG ore-forming systems. Intrusion of Gairdner Dyke Swarm dolerite dykes into sericite ± hematite altered Roxby Downs Granite results in retrograde albite–chlorite–magnetite alteration envelopes (up to tens of metres thick) overprinting the original sericite ± hematite alteration zone and needs to be carefully evaluated to ensure that such areas are not falsely downgraded during exploration. 相似文献
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Liam Courtney‐Davies Sarah E. Gilbert Cristiana L. Ciobanu Simon R. Tapster Marcus W. Richardson Nigel J. Cook Benjamin P. Wade Max R. Verdugo‐Ihl Kathy Ehrig Daniel J. Condon 《Geostandards and Geoanalytical Research》2021,45(1):143-159
In both nature and synthetic experiments, the common iron oxide haematite (α‐Fe2O3) can incorporate significant amounts of U into its crystal structure and retain radiogenic Pb over geological time. Haematite is a ubiquitous component of many ore deposit types and, therefore, represents a valuable hydrothermal mineral geochronometer, allowing direct constraints to be placed on the timing of ore formation and upgrading. However, to date, no suitable natural haematite reference material has been identified. Here, a synthetic haematite U‐Pb reference material (MR‐HFO) is characterised using LA‐ICP‐MS and ID‐TIMS. Centimetre‐scale ‘chips’ of synthesised α‐Fe2O3 were randomly microsampled via laser ablation‐extraction and analysed using ID‐TIMS. Reproducible U/Pb and Pb/Pb measurements were obtained across four separate chips (n = 13). Subsequently, an evaluation of the suitability MR‐HFO in constraining U‐Pb data via LA‐ICP‐MS is presented using a selection of natural samples ranging from Cenozoic to Proterozoic in age. The MR‐HFO normalised U‐Pb ratios are more concordant and ages more accurate versus the same LA‐ICP‐MS spot analyses normalised to zircon reference material, when compared with independently acquired ID‐TIMS data from the same natural haematite grains. Results establish MR‐HFO as a suitable reference material for LA‐ICP‐MS haematite U‐Pb geochronology. 相似文献
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Kontonikas-Charos Alkis Ciobanu Cristiana L. Cook Nigel J. Ehrig Kathy Krneta Sasha Kamenetsky Vadim S. 《Mineralogy and Petrology》2018,112(2):145-172
Mineralogy and Petrology - Rare earth element (REE) fractionation trends in feldspars are reported from Olympic Dam (including Wirrda Well and Phillip’s Ridge) and Cape Donington (Port... 相似文献
8.
Rollog Mark Cook Nigel J. Guagliardo Paul Ehrig Kathy Gilbert Sarah E. Kilburn Matt 《Geochemical transactions》2019,20(1):1-12
Iron(III)-precipitates formed by the oxidation of dissolved Fe(II) are important sorbents for major and trace elements in aquatic and terrestrial systems. Their reductive dissolution in turn may result in the release of associated elements. We examined the reductive dissolution kinetics of an environmentally relevant set of Fe(II)-derived arsenate-containing Fe(III)-precipitates whose structure as function of phosphate (P) and silicate (Si) content varied between poorly-crystalline lepidocrocite, amorphous Fe(III)-phosphate, and Si-containing ferrihydrite. The experiments were performed with 0.2–0.5 mM precipitate-Fe(III) using 10 mM Na-ascorbate as reductant, 5 mM bipyridine as Fe(II)-complexing ligand, and 10 mM MOPS/5 mM NaOH as pH 7.0 buffer. Times required for the dissolution of half of the precipitate (t50%) ranged from 1.5 to 39 h; spanning a factor 25 range. At loadings up to ~ 0.2 P/Fe (molar ratio), phosphate decreased the t50% of Si-free precipitates, probably by reducing the crystallinity of lepidocrocite. The reductive dissolution of Fe(III)-phosphates formed at higher P/Fe ratios was again slower, possibly due to P-inhibited ascorbate binding to precipitate-Fe(III). The slowest reductive dissolution was observed for P-free Si-ferrihydrite with ~ 0.1 Si/Fe, suggesting that silicate binding and polymerization may reduce surface accessibility. The inhibiting effect of Si was reduced by phosphate. Dried-resuspended precipitates dissolved 1.0 to 1.8-times more slowly than precipitates that were kept wet after synthesis, most probably because drying enhanced nanoparticle aggregation. Variations in the reductive dissolution kinetics of Fe(II) oxidation products as reported from this study should be taken into account when addressing the impact of such precipitates on the environmental cycling of co-transformed nutrients and contaminants.
相似文献9.
M. R. M. Ferguson K. Ehrig S. Meffre A. R. Cherry 《Australian Journal of Earth Sciences》2020,67(2):201-220
AbstractThe Hiltaba Suite intrusive rocks and penecontemporaneous Gawler Range Volcanics (GRV) comprise the 1590?Ma Gawler silicic large igneous province in the Gawler Craton, South Australia. Zircon is principally associated with Fe–Ti oxides and clusters of touching crystals in these rocks, including in the Roxby Downs Granite (RDG), host of the Olympic Dam iron oxide–copper–gold deposit, and in other intrusive rocks that comprise the Olympic Province. There has been no explicit evaluation and explanation of potential origins published for concentrations of zircon with Fe–Ti oxides (herein zircon-rich clusters) found in these and similar rocks of western North America and elsewhere. Here we use U–Pb geochronology, mineral morphologies and compositions, and insights from surface chemistry and liquid-bound particle interaction studies to investigate zircon-rich clusters and provide a model for their formation. U–Pb geochronology does not reveal any concordant zircon populations older than ca 1590?Ma, so it is unlikely that there are significant xenocrystic zircon grains or that the zircons include significant inherited cores. The lack of pre-magmatic zircon, consistent intra-grain and inter-grain zircon compositional trends, the predominance of oscillatory zoned zircon with morphologies indicating growth from hot, evolved silicate melts, and the lack of evidence for zircon recrystallisation, indicates that zircon crystallised in the host GRV and RDG magmas. Variable zircon compositions within individual clusters does not support epitaxial nucleation of zircon on Fe–Ti oxides, but it is likely that some zircon grains grew from seed crystals formed by exsolution of Zr from Fe–Ti oxides. Aggregation of isolated, liquid-bound crystals is energetically favourable, and the grainsize discrepancy between larger crystals (Fe–Ti oxides, pyroxenes) and smaller accessory minerals (zircon, apatite) maximises the disparity in particle velocities and hence enhances the opportunities for collisions and adhesion between these crystals. We propose that zircon adheres to Fe–Ti oxides with greater ease and/or with greater bond strengths, than to other phases present in the parental magmas. It is possible that this association is related to interactions between zircon and Fe–Ti oxide surface sites with opposing charges, presuming the distance between phase surfaces is sufficiently small. The occurrence of small zircon grains within Fe–Ti oxides and both euhedral zircon and zircon with asymmetric growth zonation in contact with Fe–Ti oxides indicates that several processes are responsible for the high concentrations of zircon crystals in some Fe–Ti oxide clusters.
Zircon is principally associated with Fe--Ti oxides in 1.59 Ga Gawler Range Volcanics (GRV) and Roxby Downs Granite (RDG)
U–Pb geochronology does not reveal any concordant zircon populations older than ca 1590?Ma
Zircon compositions and morphologies indicate that zircon crystallised in the host RDG and GRV magmas and suggest recharge, reheating and mixing occurred in these magmatic systems
Seed crystals, aggregation and surface chemical affinities contributed to the strong association of zircon and Fe–Ti oxides
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