Platinum-group element distribution in base-metal sulfides of the Merensky Reef from the eastern and western Bushveld Complex, South Africa     

Inga Osbahr  Reiner Klemd  Thomas Oberthür  Helene Brätz  Robert Schouwstra 《Mineralium Deposita》2013,48(2):211-232

Base-metal sulfides in magmatic Ni-Cu-PGE deposits are important carriers of platinum-group elements (PGE). The distribution and concentrations of PGE in pentlandite, pyrrhotite, chalcopyrite, and pyrite were determined in samples from the mineralized portion of four Merensky Reef intersections from the eastern and western Bushveld Complex. Electron microprobe analysis was used for major elements, and in situ laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) for trace elements (PGE, Ag, and Au). Whole rock trace element analyses were performed on representative samples to obtain mineralogical balances. In Merensky Reef samples from the western Bushveld, both Pt and Pd are mainly concentrated in the upper chromitite stringer and its immediate vicinity. Samples from the eastern Bushveld reveal more complex distribution patterns. In situ LA-ICP-MS analyses of PGE in sulfides reveal that pentlandite carries distinctly elevated PGE contents, whereas pyrrhotite and chalcopyrite only contain very low PGE concentrations. Pentlandite is the principal host of Pd and Rh in the ores. Palladium and Rh concentrations in pentlandite reach up to 700 and 130 ppm, respectively, in the samples from the eastern Bushveld, and up to 1,750 ppm Pd and up to 1,000 ppm Rh in samples from the western Bushveld. Only traces of Pt are present in the base-metal sulfides (BMS). Pyrrhotite contains significant though generally low amounts of Ru, Os, and Ir, but hardly any Pd or Rh. Chalcopyrite contains most of the Ag but carries only extremely low PGE concentrations. Mass balance calculations performed on the Merensky Reef samples reveal that in general, pentlandite in the feldspathic pyroxenite and the pegmatoidal feldspathic pyroxenite hosts up to 100 % of the Pd and Rh and smaller amounts (10–40 %) of the Os, Ir, and Ru. Chalcopyrite and pyrrhotite usually contain less than 10 % of the whole rock PGE. The remaining PGE concentrations, and especially most of the Pt (up to 100 %), are present in the form of discrete platinum-group minerals such as cooperite/braggite, sperrylite, moncheite, and isoferroplatinum. Distribution patterns of whole rock Cu, Ni, and S versus whole rock Pd and Pt show commonly distinct offsets. The general sequence of “offset patterns” of PGE and BMS maxima, in the order from bottom to top, is Pd in pentlandite?→?Pd in whole rock?→?(Cu, Ni, and S). The relationship is not that straightforward in general; some of the reef sequences studied only partially show similar trends or are more complex. In general, however, the highest Pd concentrations in pentlandite appear to be related to the earliest, volumetrically rather small sulfide liquids at the base of the Merensky Reef sequence. A possible explanation for the offset patterns may be Rayleigh fractionation.  相似文献   

Regional sulfate–hematite–sulfide zoning in the auriferous Mariana anticline, Quadrilátero Ferrífero of Minas Gerais, Brazil     

Alexandre Raphael Cabral  Nikola Koglin  Harald Strauss  Helene Brätz  Rogerio Kwitko-Ribeiro 《Mineralium Deposita》2013,48(7):805-816

The distribution of mineral deposits, characterised as barite deposits, hematite-rich auriferous deposits and auriferous tourmaline–sulfide deposits, displays a regional sulfate–hematite–sulfide zoning along the thrust-delineated limbs of the Mariana anticline, in the south-eastern part of the Quadrilátero Ferrífero of Minas Gerais, Brazil. Cross-cut relationships of barite veins and sulfide lodes indicate that sulfidation occurred in a late-tectonic context, which is here attributed to the collapse of the ～0.6-Ga Brasiliano thrust front. Reconnaissance S-isotopic data from barite and pyrite (Antônio Pereira barite deposit and its adjacent gold deposit, respectively), and arsenopyrite (Passagem de Mariana gold deposit), suggest a new interpretation for the hydrothermal fluid overprint in the Mariana anticline. The Antônio Pereira barite has Δ³³S values that are near zero, constraining the sulfate source to rocks younger than 2.45 Ga. The barite-δ³⁴S values are between +19.6 and +20.8?‰. The Passagem arsenopyrite and tourmaline have Co/Ni ratios that define a positive linear trend with the Antônio Pereira pyrite. The latter has homogenous δ³⁴S values, between +8.8 and +8.9?‰, which are compatible with thermochemical reduction of aqueous sulfate with the S-isotopic composition of the Antônio Pereira barite.  相似文献   

Cu- and Mn-bearing tourmalines from Brazil and Mozambique: crystal structures, chemistry and correlations     

Andreas Ertl  Gerald Giester  Ulrich Schüssler  Helene Brätz  Martin Okrusch  Ekkehart Tillmanns  Hermann Bank 《Mineralogy and Petrology》2013,107(2):265-279

Cu- and Mn-bearing tourmalines from Brazil and Mozambique were characterised chemically (EMPA and LA-ICP-MS) and by X-ray single-crystal structure refinement. All these samples are rich in Al, Li and F (fluor-elbaite) and contain significant amounts of CuO (up to ~1.8 wt%) and MnO (up to ~3.5 wt%). Structurally investigated samples show a pronounced positive correlation between the <Y-O> distances and the (Li + Mn²⁺ + Cu + Fe²⁺) content (apfu) at this site with R ² = 0.90. An excellent negative correlation exists between the <Y-O> distances and the Al₂O₃ content (R ² = 0.94). The samples at each locality generally show a strong negative correlation between the X-site vacancies and the (MnO + FeO) content. The Mn content in these tourmalines depends on the availability of Mn, on the formation temperature, as well as on stereochemical constraints. Because of a very weak correlation between MnO and CuO we believe that the Cu content in tourmaline is essentially dependent on the availability of Cu and on stereochemical constraints.  相似文献   

Temporal variability in the life history and reproductive biology of female dugongs in Torres Strait: The likely role of sea grass dieback     

Helene Marsh  Donna Kwan 《Continental Shelf Research》2008

The extensive sea grass meadows in Torres Strait enable it to be a globally important habitat for the dugong, Dugong dugon, a marine mammal of cultural and dietary significance to Torres Strait Islanders and the basis for the substantial island-based fishery in the Torres Strait Protected Zone. Torres Strait sea grass communities are subjected to episodic diebacks which are now believed to be largely natural events. Information on dugong life history was obtained from specimens obtained from female dugongs as they were butchered for food by Indigenous hunters at two major dugong hunting communities in Torres Strait: Daru (9.04°S, 143.21°E) in 1978–1982 (a time of sea grass dieback and recovery) and Mabuiag Island (9.95°S, 142.15°E) in 1997–1999 (when sea grasses were abundant). Dugongs sampled in 1997–1999 had their first calf at younger ages (minimum of 6 cf. 10 years), and more frequently (interbirth interval based on all possible pregnancies 2.6±0.4 (S.E.) yr cf. 5.8±1.0 yr) than the dugongs sampled in 1978–1982. Pregnancy rates increased monotonically during 1978–1982, coincident with sea grass recovery. The age distribution of the female dugongs collected in 1997–1999 also suggested a low birth rate between 1973 and 1983 and/or or a high level of mortality for animals born during this period. These results add to the evidence from other regions that the life history and reproductive rate of female dugongs are adversely affected by sea grass loss, the effect of which cannot be separated from a possible density-dependent response to changes in dugong population size. Many green turtles in Torres Strait were also in poor body condition coincident with the 1970s sea grass dieback. The impacts of future sea grass diebacks need to be anticipated when management options for the traditional Torres Strait fisheries for dugongs and green turtles are evaluated.  相似文献   

Phosphorus and nitrogen inputs to Florida Bay: The importance of the everglades watershed     

D. T. Rudnick  Z. Chen  D. L. Childers  T. D. Fontaine 《Estuaries and Coasts》1999,22(2):398-416

A large environmental restoration project designed to improve the hydrological conditions of the Florida Everglades and increase freshwater flow to Florida Bay is underway. Here we explore how changing freshwater inflow to the southern Everglades is likely to change the input of nutrients to Florida Bay. We calculated annual inputs of water, total phosphorus (TP), total nitrogen (TN), and dissolved inorganic nitrogen (DIN) to Everglades National Park (ENP) since the early 1980s. We also examined changes in these nutrient concentrations along transects through the wetland to Florida Bay and the Gulf of Mexico. We found that the interannual variability of the water discharge into ENP greatly exceeded the interannual variability of flow-weighted mean nutrient concentrations in this water. Nutrient inputs to ENP were largely determined by discharge volume. These inputs were high in TN and low in TP; for two ENP watersheds TN averaged 1.5 mg l^?1 (0.11 mM) and 0.9 mg l^?1 (0.06 mM) and TP averaged 15 μg l^?1 (0.47 μM) and 9 μg l^?1 (0.28 μM). Both TP and DIN that flowed into ENP wetlands were rapidly removed from the water. Over a 3-km section of Taylor Slough, TP decreased from a flow-weighted mean of 11.6 μg l^?1 (0.37 μM) (0.20 μM) and DIN decreased from 240 μg l^?1 (17μM) to 36 μ l^?1 (2.6 μM). In contrast, TN, which was generally 95% organic N, changed little as it passed through the wetland. This resulted in molar TN:TP ratios exceeding 400 in the wetland. Decreases in TN concentrations only occurred in areas with relatively high P availability, such as the wetlands to the north of ENP and in the mangrove streams of western ENP. Increasing freshwater flow to Florida Bay in an effort to restore the Everglades and Florida Bay ecosystems is thus not likely to increase P inputs from the freshwater Everglades but is likely to increase TN inputs. Based on a nutrient budget of Florida Bay, both N and P inputs from the Gulf of Mexico greatly exceed inputs from the Everglades, as well as inputs from the atmosphere and the Florida Keys. We estimate that the freshwater Everglades contribute <3% of all P inputs and <12% of all N inputs to the bay. Evaluating the effect of ecosystem restoration efforts on Florida Bay requires greater understanding of the interactions of the bay with the Gulf of Mexico and adjacent mangrove ecosystems.  相似文献   

Statistical Analysis of Solar Events Associated with Storm Sudden Commencements over One Year of Solar Maximum During Cycle 23: Propagation from the Sun to the Earth and Effects     

K. Bocchialini  B. Grison  M. Menvielle  A. Chambodut  N. Cornilleau-Wehrlin  D. Fontaine  A. Marchaudon  M. Pick  F. Pitout  B. Schmieder  S. Régnier  I. Zouganelis 《Solar physics》2018,293(5):75

Taking the 32 storm sudden commencements (SSCs) listed by the International Service of Geomagnetic Indices (ISGI) of the Observatory de l’Ebre during 2002 (solar activity maximum in Cycle 23) as a starting point, we performed a multi-criterion analysis based on observations (propagation time, velocity comparisons, sense of the magnetic field rotation, radio waves) to associate them with solar sources, identified their effects in the interplanetary medium, and looked at the response of the terrestrial ionized and neutral environment. We find that 28 SSCs can be related to 44 coronal mass ejections (CMEs), 15 with a unique CME and 13 with a series of multiple CMEs, among which 19 (68%) involved halo CMEs. Twelve of the 19 fastest CMEs with speeds greater than 1000 km?s^?1 are halo CMEs. For the 44 CMEs, including 21 halo CMEs, the corresponding X-ray flare classes are: 3 X-class, 19 M-class, and 22 C-class flares. The probability for an SSC to occur is 75% if the CME is a halo CME. Among the 500, or even more, front-side, non-halo CMEs recorded in 2002, only 23 could be the source of an SSC, i.e. 5%. The complex interactions between two (or more) CMEs and the modification of their trajectories have been examined using joint white-light and multiple-wavelength radio observations. The detection of long-lasting type IV bursts observed at metric–hectometric wavelengths is a very useful criterion for the CME–SSC events association. The events associated with the most depressed Dst values are also associated with type IV radio bursts. The four SSCs associated with a single shock at L1 correspond to four radio events exhibiting characteristics different from type IV radio bursts. The solar-wind structures at L1 after the 32 SSCs are 12 magnetic clouds (MCs), 6 interplanetary coronal mass ejections (ICMEs) without an MC structure, 4 miscellaneous structures, which cannot unambiguously be classified as ICMEs, 5 corotating or stream interaction regions (CIRs/SIRs), one CIR caused two SSCs, and 4 shock events; note than one CIR caused two SSCs. The 11 MCs listed in 3 or more MC catalogs covering the year 2002 are associated with SSCs. For the three most intense geomagnetic storms (based on Dst minima) related to MCs, we note two sudden increases of the Dst, at the arrival of the sheath and the arrival of the MC itself. In terms of geoeffectiveness, the relation between the CME speed and the magnetic-storm intensity, as characterized using the Dst magnetic index, is very complex, but generally CMEs with velocities at the Sun larger than 1000 km?s^?1 have larger probabilities to trigger moderate or intense storms. The most geoeffective events are MCs, since 92% of them trigger moderate or intense storms, followed by ICMEs (33%). At best, CIRs/SIRs only cause weak storms. We show that these geoeffective events (ICMEs or MCs) trigger an increased and combined auroral kilometric radiation (AKR) and non-thermal continuum (NTC) wave activity in the magnetosphere, an enhanced convection in the ionosphere, and a stronger response in the thermosphere. However, this trend does not appear clearly in the coupling functions, which exhibit relatively weak correlations between the solar-wind energy input and the amplitude of various geomagnetic indices, whereas the role of the southward component of the solar-wind magnetic field is confirmed. Some saturation appears for Dst values \(< -100\) nT on the integrated values of the polar and auroral indices.  相似文献   

Simultaneous determinations of U–Pb age,Hf isotopes and trace element compositions of zircon by excimer laser-ablation quadrupole and multiple-collector ICP-MS     

Hong-Lin Yuan  Shan Gao  Meng-Ning Dai  Chun-Lei Zong  Detlef Günther  Gisela Helene Fontaine  Xiao-Ming Liu  ChunRong Diwu 《Chemical Geology》2008,247(1-2):100-118

We describe an in situ method for simultaneous measurement of U–Pb–Hf isotopes and trace element compositions of zircons using a quadrupole and multiple-collector inductively-coupled-plasma mass spectrometer (Q-ICP-MS and MC-ICP-MS, respectively) connected to a single excimer laser-ablation system. A laser-generated zircon aerosol was split behind the ablation cell into two transport tubes via a Y-shaped connector and simultaneously introduced into the two mass spectrometers. Hafnium isotopes were measured on the MC-ICP-MS instrument, while U–Pb ages and trace element compositions were determined using the Q-ICP-MS. The precision and accuracy of this method was evaluated using six well-known and widely used zircon standards (91500, Temora-2, GJ-1, Mud Tank, BR266 and Monastery). Analyses were carried out using spot sizes of 32, 44 and 60 μm. For the 44 and 60 μm spot, the resulting U–Pb ages, Hf isotopic and rare earth element (REE) compositions of these six zircons agree with recommended/reported values within 2σ error. The difference in relative standard deviations (RSD) of ²⁰⁶Pb/²³⁸U ages between split-flow measurements and those obtained separately on the Q-ICP-MS is within ～ 20% for 91500, Temora-2 and GJ-1, and ～ 60% for Mud Tank (due to its lower U and Pb concentrations). Our method provides a precise approach for determining the U–Pb age and the Hf isotopic and trace element compositions of zircon within a single ablation event. This is in particular important for analysis of zircons that are small or contain complicated zoning patterns. Finally, the REE composition of zircon BR266 is more homogeneous than other zircons and could be a suitable standard by which to benchmark new standards for microprobe analyses of zircons.  相似文献   

Influence of sample matrix on the alkaline extraction of Cr(VI) in soils and industrial materials     

Gisela Weibel  H. Niklaus Waber  Urs Eggenberger  Urs K. Mäder 《Environmental Earth Sciences》2016,75(7):548

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Digital engagement methods for earthquake and fire preparedness: a review     

Enrica Verrucci  Gabriela Perez-Fuentes  Tiziana Rossetto  Luke Bisby  Muki Haklay  David Rush  Patrick Rickles  Gretchen Fagg  Helene Joffe 《Natural Hazards》2016,83(3):1583-1604

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A pilot tagging experiment on European hake (Merluccius merluccius): methodology and preliminary results     

de Pontual  Helene; Bertignac  Michel; Battaglia  Andre; Bavouzet  Gerard; Moguedet  Philippe; Groison  Anne-Laure 《ICES Journal of Marine Science》2003,60(6):1318-1327

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