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11.
Y.-H. Sung J. Brugger C. L. Ciobanu A. Pring W. Skinner L. V. Danyushevsky M. Nugus 《Mineralium Deposita》2009,44(7):765-791
The Sunrise Dam gold mine (11.1 Moz Au) is the largest deposit in the Archaean Laverton Greenstone Belt (Eastern Goldfields
Province, Yilgarn Craton, Western Australia). The deposit is characterized by multiple events of fluid flow leading to repeated
alteration and mineralization next to a major crustal-scale structure. The Au content of arsenian pyrite and arsenopyrite
from four mineralizing stages (D1, D3, D4a, and D4b) and from different structural and lithostratigraphic environments was measured using in situ laser ablation inductively
coupled plasma mass spectrometry. Pyrite contains up to 3,067 ppm Au (n = 224), whereas arsenopyrite contains up to 5,767 ppm (n = 19). Gold in arsenopyrite (D4a stage) was coprecipitated and remained as “invisible gold” (nanoparticles and/or lattice-bound) during subsequent deformation
events. In contrast, gold in pyrite is present not only as “invisible gold” but also as micrometer-size inclusions of native
gold, electrum, and Au(Ag)–tellurides. Pristine D1 and D3 arsenian pyrite contains relatively low Au concentrations (≤26 ppm). The highest Au concentrations occur in D4a arsenian-rich pyrite that has recrystallized from D3 pyrite. Textures show that this recrystallization proceeded via a coupled dissolution–reprecipitation process, and this process may have contributed to upgrading Au grades during D4a. In contrast, Au in D4b pyrite shows grain-scale redistribution of “invisible” gold resulting in the formation of micrometer-scale inclusions of
Au minerals. The speciation of Au at Sunrise Dam and the exceptional size of the deposit at province scale result from multiple
fluid flow and multiple Au-precipitating mechanisms within a single plumbing system. 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
15.
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
17.
‘Invisible gold’ in bismuth chalcogenides 总被引：1，自引：0，他引：1
Cristiana L. Ciobanu Nigel J. Cook Joël Brugger Leonid V. Danyushevsky 《Geochimica et cosmochimica acta》2009,73(7):1970-1999
Gold concentrations have been determined by LA-ICPMS in bismuth chalcogenides (tellurides and sulfosalts, minerals with modular structures; chalcogen X = Te, Se, and S) from 27 occurrences. Deposit types include epithermal, skarn, intrusion-related and orogenic gold. The samples comprised minerals of the tetradymite group, aleksite series, bismuth sulfosalts (cosalite, lillianite, hodrushite, bismuthinite, and aikinite), and accompanying altaite. Gold concentrations in phases of the tetradymite group range from <0.1 to 2527 ppm. Phases in which Bi > X tend to contain lower gold concentrations than Bi2X3 minerals (tellurobismuthite and tetradymite). Cosalite and lillianite contain Au concentrations ranging up to 574 and 3115 ppm, respectively. Bismuthinite derivatives have lower Au concentrations: <2 ppm in bismuthinite and up to 542 ppm in aikinite. In our samples, Au concentrations in altaite range from <0.2 to 1662 ppm.Smoother parts of the LA-ICPMS profiles suggest lattice-bound gold, whereas irregularities on the profiles are best explained by the presence of gold particles (?1 μm in diameter). Plotting Au vs. Ag for the entire dataset gives a wedge-shaped distribution, suggesting that Ag underpins Au uptake in both bismuth tellurides and sulfosalts. In the tellurides, correlation trends suggest statistical substitution of Ag(Au), together with Pb, into the octahedral site in the layers. In sulfosalts, Au follows coupled substitutions in which M1+ (Ag, Cu) enters the structure. In tellurides, the presence of van der Waals gaps at chalcogen-chalcogen contacts provides for p-type semi-conductive properties critical for gold scavenging from fluids. Such weak bonds may also act as sites for nucleation of Au (nano)particles. In sulfosalts, contacts between different species that replace one another are also highly predictable to act as traps for (nano)particulate gold.Invisible gold in Bi-chalcogenides is useful to (i) identify trends of orefield zonation, (ii) discriminate between ‘melt’ and ‘fluid-driven’ scavenging, and (iii) interpret replacement and remobilisation processes. Bismuth chalcogenides have the potential to be significant Au carriers in sulfide-poor Au systems, e.g., intrusion-related gold, with impact on the overall Au budget if mean Au concentrations are high enough and the minerals are sufficiently abundant. 相似文献
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Synthetic pyrite crystals doped with As, Co, or Ni, undoped pyrite, and natural arsenian pyrite from Leadville, Colorado were investigated with electrochemical techniques and solid-state measurements of semiconducting properties to determine the effect of impurity content on pyrite’s oxidation behavior. Potential step experiments, cyclic voltammetry, and AC voltammetry were performed in a standard three-electrode electrochemical cell setup. A pH 1.78 sulfuric acid solution containing 1 mM ferric iron, open to atmospheric oxygen, was chosen to approximate water affected by acid drainage. Van der Pauw/Hall effect measurements determined resistivity, carrier concentration and carrier mobility.The anodic dissolution of pyrite and the reduction of ferric iron half-reactions are taken as proxies for natural pyrite oxidation. Pyrite containing no impurities is least reactive. Pyrite with As is more reactive than pyrite with either Ni or Co despite lower dopant concentration. As, Co, and Ni impurities introduce bulk defect states at different energy levels within the band gap. Higher reactivity of impure pyrite suggests that introduced defect levels lead to higher density of occupied surface states at the solid-solution interface and increased metallic behavior. The current density generated from potential step experiments increased with increasing As concentration. The higher reactivity of As-doped pyrite may be related to p-type conductivity and corrosion by holes. The results of this study suggest that considering the impurity content of pyrite in mining waste may lead to more accurate risk assessment of acid producing potential. 相似文献
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Madalina N. Frinculeasa Alin P. Frinculeasa Cornel David 《Studia Geophysica et Geodaetica》2014,58(2):289-301
The Roman fort from Sfârleanca is one of the most representative archaeological sites dating from the Roman period (2nd century A.D.) in Northern Muntenia. The existing natural and anthropic features of the environment required the application of geophysical methods in order to outline the spatial pattern of the buried remains, to define the geometry of the anthropogenic settlements and to obtain detailed information about different archaeological materials without digging. During the survey, two different geophysical methods have been employed: total magnetic field measurements and electrical resistance mapping using Twin-probe array. The instrument consists of GSM19W Overhauser magnetometers with GPS, in base-rover system, and a twin-probe array LGM 4-Point light hp. The measurements were used to draw primary maps of the physical parameters (total magnetic field strength/intensity, electrical resistance), and also processed maps (filtering, derivative). The magnetic results obtained by interpreting the anomalies yielded information about the limits of the fort, about the internal organization of the military structure (its axial road, partially its secondary road, the localization and the shape of its constructions) and at the bath and heating installation. A previously unknown element is the possible water supply pipe made of ceramic material highlighted by the mathematical modelling of the data obtained by the magnetic investigations. Electrical resistance results provide complementary information to the magnetic survey concerning the limits of the baths and the remains of the fort structure. This paper brings to light geophysical investigations into this Roman fort and baths, extending the picture produced by previous archaeological excavations that only dealt with a small part of the site. It indicates the importance of using geophysical methods in preliminary archaeological research and the advantages of combining total magnetic field measurements and electrical resistance mapping when investigating an archaeological site characterized by a number of environmental difficulties. 相似文献
20.
Julian A. Lockington Nigel J. Cook Cristiana L. Ciobanu 《Mineralogy and Petrology》2014,108(6):873-890
Sphalerite is a common sulphide and is the dominant ore mineral in Zn-Pb sulphide deposits. Precise determination of minor and trace element concentrations in sulphides, including sphalerite, by Laser-Ablation Inductively-Coupled-Plasma Mass-Spectrometry (LA-ICP-MS) is a potentially valuable petrogenetic tool. In this study, LA-ICP-MS is used to analyse 19 sphalerite samples from metamorphosed, sphalerite-bearing volcanic-associated and sedimentary exhalative massive sulphide deposits in Norway and Australia. The distributions of Mn, Fe, Co, Cu, Ga, Se, Ag, Cd, In, Sn, Sb, Hg, Tl, Pb and Bi are addressed with emphasis on how concentrations of these elements vary with metamorphic grade of the deposit and the extent of sulphide recrystallization. Results show that the concentrations of a group of trace elements which are believed to be present in sphalerite as micro- to nano-scale inclusions (Pb, Bi, and to some degree Cu and Ag) diminish with increasing metamorphic grade. This is interpreted as due to release of these elements during sphalerite recrystallization and subsequent remobilization to form discrete minerals elsewhere. The concentrations of lattice-bound elements (Mn, Fe, Cd, In and Hg) show no correlation with metamorphic grade. Primary metal sources, physico-chemical conditions during initial deposition, and element partitioning between sphalerite and co-existing sulphides are dominant in defining the concentrations of these elements and they appear to be readily re-incorporated into recrystallized sphalerite, offering potential insights into ore genesis. Given that sphalerite accommodates a variety of trace elements that can be precisely determined by contemporary microanalytical techniques, the mineral has considerable potential as a geothermometer, providing that element partitioning between sphalerite and coexisting minerals (galena, chalcopyrite etc.) can be quantified in samples for which the crystallization temperature can be independently constrained. 相似文献