Tellurides from Sunrise Dam gold deposit, Yilgarn Craton, Western Australia: a new occurrence of nagyágite     

Y.-H. Sung  C. L. Ciobanu  A. Pring  J. Brügger  W. Skinner  N. J. Cook  M. Nugus 《Mineralogy and Petrology》2007,90(3-4):249-270

Summary The Cu–Fe–Au–Mo (W) deposits in southeastern Hubei are an important component of the Middle–Lower Yangtze River metallogenic belt. Molybdenite from the Fengshandong Cu- (Mo), Ruanjiawan W–Cu- (Mo), Qianjiawan Cu–Au, Tongshankou Cu–Mo and Tonglüshan Cu- (Fe) deposits yielded Re–Os ages of 144.0 ± 2.1 Ma, 143.6 ± 1.7 Ma, 137.7 ± 1.7 Ma, 142.3 ± 1.8–143.7 ± 1.8 Ma and 137.8 ± 1.7–138.1 ± 1.8 Ma, respectively. Phlogopite from the Tieshan Fe- (Cu) deposit yielded an Ar–Ar age of 140.9 ± 1.2 Ma. These data and other published isotopic ages (Re–Os molybdenite and Ar–Ar mica ages) for the Cu–Fe–Au–Mo (W) deposits in the Middle–Lower Yangtze River metallogenic belt show that Cu–Fe–Au–Mo (W) mineralisation in the Tongling, Anqing, Jiurui and Edong ore districts developed in a narrow time span between 135.5 and 144.9 Ma, reflecting an important regional metallogenic event. An integrated study of available petrological and geochronological data, together with relationships to magmatism and the regional geodynamic framework, indicate that the Cu–Fe–Au–Mo (W) mineralisation in the Middle–Lower Yangtze River belt occurred during a regime of lithospheric extension. This extension is probably related to Late Mesozoic processes of lower crustal delamination and lithospheric thinning in East China.  相似文献   

Preface – Special Issue: Telluride and selenide minerals in gold deposits – how and why?     

C. L. Ciobanu  N. J. Cook  P. G. Spry 《Mineralogy and Petrology》2006,87(3-4):163-169

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Gold scavenged by bismuth melts: An example from Alpine shear-remobilizates in the Highiş Massif, Romania     

C. L. Ciobanu  N. J. Cook  F. Damian  G. Damian 《Mineralogy and Petrology》2006,87(3-4):351-384

Summary Gold mineralization occurs in the Şoimuş Ilii vein, the main Cu prospect in the Highiş Massif, Western Apuseni Mts., Romania. The Highiş Massif is part of the Highiş Biharia Shear Zone, a 320–300 Ma Variscan greenschist belt, with a 114–100 Ma Alpine overprint. In Highiş, phyllonites enclose an igneous core consisting of an Early Permian basic complex intruded by Middle Permian granitoids. The vein is hosted within basalt hornfels at its contact with the 264 Ma Jernova granite. Gold is not only present as native gold, but also as jonassonite (ideally AuBi₅S₄). The latter occurs as inclusions 1–30 μm in size in chalcopyrite; microanalysis gives the empirical formulae Au_1.02(Pb_0.47Bi_4.51)_4.98S_4. The two Au minerals are spatially associated with Bi–(Pb) sulfosalts (oversubstituted bismuthinite, cosalite) and sulfotellurides/selenides (ingodite, ikunolite and laitakarite) in blebs/patches, mainly hosted in chalcopyrite. This Au–Bi–Te association overprints an earlier, chalcopyrite-quartz assemblage, occurring as trails along discrete zones of brecciation that crosscut former mineral boundaries. Curvilinear and cuspate boundary textures within the blebs/patches suggest deposition in a molten form. Mineral associations in combination with phase relations indicate that the Au–Bi–Te association formed as a result of melting of pre-existing native Bi (and possibly sulfosalts) at 400 °C under sulfidation conditions. These melts incorporated Au, Pb, Te and S as they moved in the vein during shearing and were locked within dilational sites. Native Bi occurs as coarse aggregates along vein margins, but in the Au–Bi–Te association, it is present only as small droplets in shear gashes, never together with other Bi- and Au-minerals. The Bi-derived melts are part of an internal remobilizate which also includes chlorite and adularia. Minerals in the system Au–Bi–Te were deposited from a neutral low reducing fluid during Alpine shearing in the Early Cretaceous. The fluid also assisted solid-state mobilisation of chalcopyrite and cobaltite. This study illustrates the significant potential of Bi, a low melting-point chalcophile element (LMCE), to act as Au scavenger at temperatures as low as 400 °C.  相似文献   

Multiple current sheets in a double auroral oval observed from the MAGION-2 and MAGION-3 satellites     

M. Echim  M. Ciobanu  O. Balan  A. Blagau  O. Marghitu  E. Georgescu  Y. I. Galperin  N. V. Jorgio  T. M. Muliarchik  A. L. Kotikov  E. M. Shishkina  O. A. Troshichev 《Annales Geophysicae》1997,15(4):412-423

A case is described of multiple current sheets crossed by the MAGION-2 satellite in the near-midnight quieting auroral oval. The data were obtained by the magnetometer experiment onboard. Results show during a quieting period after a preceding substorm, or during an early growth phase of the next substorm, two double-sheet current bands, POLE and EQUB, located at respectively the polar and equatorial borders of the auroral oval separated by about 500 km in latitude. This is consistent with the double-oval structure during recovery introduced by Elphinstone et al. (1995). Within the POLE, the magnetic field data show simultaneous existence of several narrow parallel bipolar current sheets within the upward current branch (at 69.5–70.3° invariant latitude) with an adjacent downward current branch at its polar side at (70.5–71.3°). The EQUB was similarly stratified and located at 61.2–63.5° invariant latitude. The narrow current sheets were separated on average by about 35 km and 15 km, respectively, within the POLE and EQUB. A similar case of double-oval current bands with small-scale structuring of their upward current branches during a quieting period is found in the data from the MAGION-3 satellite. These observations contribute to the double-oval structure of the late recovery phase, and add a small-scale structuring of the upward currents producing the auroral arcs in the double- oval pattern, at least for the cases presented here. Other observations of multiple auroral current sheets and theories of auroral arc multiplicity are briefly discussed. It is suggested that multiple X-lines in the distant tail, and/or leakage of energetic particles and FA currents from a series of plasmoids formed during preceding magnetic activity, could be one cause of highly stratified upward FA currents at the polar edge of the quieting double auroral oval.  相似文献   

Trace and minor elements in sphalerite: A LA-ICPMS study   总被引：18，自引：0，他引：18  

Nigel J. Cook  Cristiana L. Ciobanu  Allan Pring  William Skinner  Leonid Danyushevsky  Frank Melcher 《Geochimica et cosmochimica acta》2009,73(16):4761-4791

Sphalerite is an important host mineral for a wide range of minor and trace elements. We have used laser-ablation inductively coupled mass spectroscopy (LA-ICPMS) techniques to investigate the distribution of Ag, As, Bi, Cd, Co, Cu, Fe, Ga, Ge, In, Mn, Mo, Ni, Pb, Sb, Se, Sn and Tl in samples from 26 ore deposits, including specimens with wt.% levels of Mn, Cd, In, Sn and Hg. This technique provides accurate trace element data, confirming that Cd, Co, Ga, Ge, In, Mn, Sn, As and Tl are present in solid solution. The concentrations of most elements vary over several orders of magnitude between deposits and in some cases between single samples from a given deposit. Sphalerite is characterized by a specific range of Cd (typically 0.2-1.0 wt.%) in each deposit. Higher Cd concentrations are rare; spot analyses on samples from skarn at Baisoara (Romania) show up to 13.2 wt.% (Cd²⁺ ↔ Zn²⁺ substitution). The LA-ICPMS technique also allows for identification of other elements, notably Pb, Sb and Bi, mostly as micro-inclusions of minerals carrying those elements, and not as solid solution. Silver may occur both as solid solution and as micro-inclusions. Sphalerite can also incorporate minor amounts of As and Se, and possibly Au (e.g., Magura epithermal Au, Romania). Manganese enrichment (up to ∼4 wt.%) does not appear to enhance incorporation of other elements. Sphalerite from Toyoha (Japan) features superimposed zoning. Indium-sphalerite (up to 6.7 wt.% In) coexists with Sn-sphalerite (up to 2.3 wt.%). Indium concentration correlates with Cu, corroborating coupled (Cu⁺In³⁺) ↔ 2Zn²⁺ substitution. Tin, however, correlates with Ag, suggesting (2Ag⁺Sn⁴⁺) ↔ 3Zn²⁺ coupled substitution. Germanium-bearing sphalerite from Tres Marias (Mexico) contains several hundred ppm Ge, correlating with Fe. We see no evidence of coupled substitution for incorporation of Ge. Accordingly, we postulate that Ge may be present as Ge²⁺ rather than Ge⁴⁺. Trace element concentrations in different deposit types vary because fractionation of a given element into sphalerite is influenced by crystallization temperature, metal source and the amount of sphalerite in the ore. Epithermal and some skarn deposits have higher concentrations of most elements in solid solution. The presence of discrete minerals containing In, Ga, Ge, etc. also contribute to the observed variance in measured concentrations within sphalerite.  相似文献   

Multivariate Analysis of an LA-ICP-MS Trace Element Dataset for Pyrite   总被引：2，自引：0，他引：2  

Lyron Winderbaum  Cristiana L. Ciobanu  Nigel J. Cook  Matthew Paul  Andrew Metcalfe  Sarah Gilbert 《Mathematical Geosciences》2012,44(7):823-842

Application of multivariate statistics to trace element datasets is reviewed using 164 multi-element LA-ICP-MS spot analyses of pyrite from the Moonlight epithermal gold prospect, Queensland, Australia. Multivariate analysis of variance (MANOVA) is used to demonstrate that classification of pyrite on morphological and other non-numeric factors is geochemically valid. Parallel coordinate plots and correlation cluster analysis using Spearman??s coefficients are used to discover unexpected elemental relationships without making assumptions a priori. Finally, principal component analysis and factor analysis are used to demonstrate the presence of sub-classes of pyrite. Corroborated with geological data, statistical analysis provides evidence for successive generations of hydrothermal fluids, each introducing specific metals, and for partial or complete replacement of different minerals. The data permit reinterpretation of Moonlight as a telescoped system where epithermal-Au (± base metals) is superposed onto early porphyry-Mo mineralization.  相似文献   

Accuracy and sensitivity analysis for 54 models of computing hourly diffuse solar irradiation on clear sky     

Viorel Badescu  Christian A. Gueymard  Sorin Cheval  Cristian Oprea  Madalina Baciu  Alexandru Dumitrescu  Flavius Iacobescu  Ioan Milos  Costel Rada 《Theoretical and Applied Climatology》2013,111(3-4):379-399

Fifty-four broadband models for computation of solar diffuse irradiation on horizontal surface were tested in Romania (South-Eastern Europe). The input data consist of surface meteorological data, column integrated data, and data derived from satellite measurements. The testing procedure is performed in 21 stages intended to provide information about the sensitivity of the models to various sets of input data. There is no model to be ranked “the best” for all sets of input data. However, some of the models performed better than others, in the sense that they were ranked among the best for most of the testing stages. The best models for solar diffuse radiation computation are, on equal footing, ASHRAE 2005 model (ASHRAE 2005) and King model (King and Buckius, Solar Energy 22:297–301, 1979). The second best model is MAC model (Davies, Bound Layer Meteor 9:33–52, 1975). Details about the performance of each model in the 21 testing stages are found in the Electronic Supplementary Material.  相似文献   

Minor and trace elements in bornite and associated Cu-(Fe)-sulfides: A LA-ICP-MS studyBornite mineral chemistry   总被引：1，自引：0，他引：1  

Nigel J. Cook  Cristiana L. Ciobanu  Sarah Gilbert 《Geochimica et cosmochimica acta》2011,75(21):6473-6496

In situ laser ablation inductively-coupled mass spectroscopy (LA-ICP-MS) has been used to provide a baseline dataset on the minor element contents in hypogene bornite and accompanying Cu-sulfides from 12 deposits with emphasis on syn-metamorphic Cu-vein systems in Norway, and skarn, porphyry and epithermal systems in SE Europe.Bornite contains significant concentrations of both Ag and Bi, especially in the vein and skarn deposits studied and has the potential to be a major Ag-carrier in such ores. Concentrations of up to >1 wt.% of both elements are documented. Measured concentrations appear to be independent of whether discrete Ag- and/or Bi-minerals are present within the analyzed sulfide. Where bornite and chalcocite (or mixtures of Cu-sulfides) coexist, Ag is preferentially partitioned into chalcocite over co-existing bornite and Bi is partitioned into the bornite. Bornite is a relatively poor host for Au, which mimics Ag by being typically richer in coexisting chalcocite. Most anomalous Au concentrations in bornite can be readily tracked to micron- and submicron-scale inclusions, but bornite and chalcocite containing up to 3 and 28 ppm Au in solid solution can be documented. Selenium and Te concentrations in bornite may be as high as several thousand ppm and correlate with the abundance of selenides and tellurides within the sample. Selenium distributions show some promise as a vector in exploration, offering the possibility to track a fluid source. Bornite and chalcocite are poor hosts for a range of other elements such as Co, Ni, Ga and Ge, etc. which have been reported to be commonly substituted within sulfides. Hypogene bornite and chalcocite may have significantly different trace element geochemical signatures from secondary (supergene) bornite.  相似文献   

Skarn textures and a case study: the Ocna de Fier-Dognecea orefield, Banat, Romania   总被引：5，自引：0，他引：5  

Cristiana Liana Ciobanu  Nigel John Cook 《Ore Geology Reviews》2004,24(3-4):315

We address the question of the predictability of skarn textures and their role in understanding the evolution of a skarn system. Recent models of skarn formation show that skarns are ideal for application of self-organisation theory, with self-patterning the rule in fluid-rock interaction systems rather than the exception. Zonation in skarn deposits, a consequence of infiltration-driven metasomatism, can also be treated in terms of self-organisation. Other less commonly described features, such as scalloping, fingering and mineral banding, can be understood by application of reactive infiltration and hydrodynamics at the skarn front. Devolatilisation may trigger formation of back-flow fluxes that overprint previously formed skarn. The range of textures formed from such events can be used to discriminate between prograde and retrograde stages. Refractory minerals, such as garnet, magnetite and pyrite, readily retain overprinting events. Skarns are also composed largely of minerals from solid solution series (garnet, pyroxene, pyroxenoids, etc.) and therefore skarn mineralogy helps to establish trends of zonation and evolution. The same minerals can act as ‘chemical oscillators’ and record metasomatic trends.The Ocna de Fier-Dognecea deposit was formed in a 10 km deep skarn system. Zonation and evolution trends therefore represent only the result of interaction between magmatically derived fluids emerging at the source and limestone. From the same reason, the transition from prograde to retrograde regime is not influenced by interaction with external fluids. Thirdly, the mineralisation comprises Fe, Cu and Zn-Pb ores, thus facilitating comparison with skarn deposits that commonly are formed in shallower magmatic-hydrothermal environment. Copper-iron ores (magnetite+Cu-Fe sulphides), hosted by magnesian (forsterite+diopside) skarn, occur in the deepest and central part of the orefield, at Simon Iuda. Their petrological character allows interpretation as the core of the skarn system formed from a unique source of fluids emerging from the subjacent granodiorite. It formed first as a consequence of the local setting, where a limestone indented in the granodiorite permitted strong reaction at 650 °C and focussed the up-streaming, buoyant fluids. The first sharp front of reaction is seen at the boundary between the Cu-Fe core and Fe ores hosted by calcic skarn (Di_70-90-And_70-90), where Cu-Fe sulphides disappear, and forsterite gives way to garnet in the presence of diopside (Di₉₀). Following formation of forsterite, devolatilisation and transient plume collapse is interpreted from a range of piercing clusters and trails. We presume lateral flow to have been initiated at the source, as the emerging fluids are in excess to the fluids driven into reaction by the plume. Formation of the other orebodies, up to 5 km laterally downstream in both directions, is interpreted as skarn fingering at the limestone side. The metasomatic front is perpendicular to the flow along the channel of schists placed between the limestone base and the granodiorite.A metal zonation centred onto the source is defined, based on metal distribution: Cu-Fe/Fe/Zn-Pb. The second front of reaction, at the boundary between the Fe and Zn-Pb zone, has a sulphidation/oxidation character, with diopside giving way to a Fe-Mn-rich pyroxene, (HedJoh)_>60+pyroxmangite±bustamite; garnet is minor. Johannsenite-rich pyroxene (Di_20-40Hed_20-40Joh₄₀) is found in proximal skarn at the upper part of Simon Iuda, stable with Zn_0.95Fe_0.05S, at an inferred 570 °C. In distal skarn from Dognecea and Paulus, Mn-hedenbergite (Di_<10Hed₇₀Joh_20-30) formed at 400 °C is stable with Zn_0.84Fe_0.16S. Extensive compositional fields, eutectic decomposition and lamellar intergrowths characterise pyroxene in the Zn-Pb zone, formed at the magnetite-hematite buffer in the presence of pyrite. Distal skarn has a reducing character, in comparison with the proximal. A drop in both fS₂ and O₂, with the zoned system moving closer to the pyrite-pyrrhotite buffer, is induced from the temperature gradient. Based on pyroxene mineralogy and calculated fS₂, the metal zonation is confirmed as being formed upwards and outwards from the source.The Fe and Zn-Pb zones both have a patterned side coexisting with the unpatterned one. Patterning is seen at scales from macroscopic (rhythmic banding, nodular, spotted, orbicular, mossy, mottled textures) to microscopic scales (oscillatory zonation in garnet and silica-bearing magnetite). Following plume updraft, the path of decarbonation reaction controlled the motion of the skarn front until, towards the end of the prograde stage, a multiple steady state regime developed and produced rhythmic patterns on all scales. The activation of powerful patterning operators, represented by Liesegang banding alone, or coupled with competitive particle growth, show that the skarn front had the characteristics of an unstable coarsening front of reaction.A second retrograde event, carbofracturing, triggered by erratic decarbonation after cessation of infiltration, can be interpreted from overprinting textures in the Fe and Zn-Pb zone. A major drop in fO₂ is inferred from extensive, pseudomorphous replacement of hematite by magnetite. Textures show progressive destruction of prograde assemblages, i.e., piercing clusters, shock-induced, fluid-pressure assisted brecciation and deformation, followed by healing of the disrupted assemblages. Release of trace elements accompanies both retrograde events, with a Bi-Te-Au-Ag association common to both. The importance of shock-induced textures is emphasised in the context of Au enrichment, especially when the retrograde fluids cross the main buffers in fO₂-fS₂ space.The presence of Bi-sulphosalt polysomes in the Fe zone indicates that patterning extends down to the nanoscale. The key role played by polysomatism in stabilising compositional trends that cannot otherwise be formed at equilibrium is a fertile ground yet to be adequately explored.  相似文献   

Invisible gold in arsenian pyrite and arsenopyrite from a multistage Archaean gold deposit: Sunrise Dam,Eastern Goldfields Province,Western Australia   总被引：5，自引：0，他引：5  

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, D_4a, and D_4b) 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 (D_4a 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 D_4a 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 D_4a. In contrast, Au in D_4b 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