Distribution of platinum-group elements in magmatic and altered ores in the Jinchuan intrusion, China: an example of selenium remobilization by postmagmatic fluids     

Hazel M. Prichard  Robert D. Knight  Peter C. Fisher  Iain McDonald  Mei-Fu Zhou  Christina Y. Wang 《Mineralium Deposita》2013,48(6):767-786

The division of platinum-group elements (PGE) between those hosted in platinum-group minerals (PGM) versus those in solid solution in base metal sulfides (BMS) has been determined for ores from the PGE-bearing Ni-Cu-rich Jinchuan intrusion in northwest China. All the BMS are devoid of Pt and Ir, and magmatic BMS are also barren of Rh. These PGE may have been scavenged by arsenic to form PGM during magmatic crystallization of the BMS. Pd, Os, and Ru are recorded in BMS and Pd is predominantly in solid solution in pentlandite. Unlike the fresh magmatic ores, in altered or serpentinized ores, Pd-PGM are present. Froodite is hosted in magnetite, formed during alteration of BMS, accompanied by sulfur loss and liberation of Pd. Michenerite ([Pd,Pt]BiTe), sperrylite (PtAs₂), and Au-bearing PGM are located in altered silicates. Irarsite (IrAsS) occurs mainly enclosed in BMS. Padmaite (PdBiSe), identified at the junctions of magnetite and BMS, was the last PGM to form and locally partially replaces earlier non-Se-bearing PGM. We propose that padmaite formed under oxidizing conditions during late local remobilization of Se from the BMS. Se-bearing PGM are rare and our review shows they are frequently associated with carbonate, suggesting that Pd and Se can be mobilized great distances in low pH oxidizing fluids and may be precipitated on contact with carbonate. S/Se ratios are used by researchers of magmatic Ni-Cu-PGE ores to determine sulfur loss, assuming Se is immobile and representative of magmatic sulfur content. This study shows that Se as well as S is potentially mobile and this should be considered in the use of S/Se ratios.  相似文献   

Using the social cost of carbon to value earth observing systems     

Roger Cooke  Bruce A. Wielicki  David F. Young  Martin G. Mlynczak  Rosemary R. Baize 《Climate Policy》2013,13(3):330-345

The goal of this study is to show how to quantify the benefits of accelerated learning about key parameters of the climatic system and use this knowledge to improve decision-making on climate policy. The US social cost of carbon (SCC) methodology is used in innovative ways to value new Earth observing systems (EOSs). The study departs from the strict US SCC methodology, and from previous work, in that net benefits are used instead of only damages to calculate the value of information of the enhanced systems. In other respects the US SCC methodology is followed closely. We compute the surfeit expected net benefits of learning the actionable information earlier, with the enhanced system, versus learning later with existing systems. The enhanced systems are designed to give reliable information about climate sensitivity on accelerated timescales relative to existing systems; therefore, the decision context stipulates that a global reduced emissions path would be deployed upon receiving suitable information on the rate of temperature rise with a suitable level of confidence. By placing the enhanced observing system in a decision context, the SCC enables valuing this system as a real option.

Policy relevance

Uncertainty in key parameters of the climatic system is often cited as a barrier for near-term reductions of carbon emissions. It is a truism among risk managers that uncertainty costs money, and its reduction has economic value. Advancing policy making under uncertainty requires valuing the reduction in uncertainty. Using CLARREO, a new proposed EOS,as an example, this article applies value of information/real option theory to value the reduction of uncertainty in the decadal rate of temperature rise. The US interagency social cost of carbon directive provides the decision context for the valuations. It is shown that the real option value of the uncertainty reduction, relative to existing observing systems, is a very large multiple of the new system's cost.  相似文献   

The origin and fate of mode water in the southern Pacific Ocean     

Audrey Hasson  Ariane Koch-Larrouy  Rosemary Morrow  Mélanie Juza  Thierry Penduff 《Ocean Dynamics》2012,62(3):335-354

Understanding the origin and fate of mode and intermediate waters (MW) in the subtropical Pacific Ocean is critical for climate, as MW store and export a large volume of CO₂, heat, nutrients and salinity to lower latitudes at depths isolated from the atmosphere. A realistic 4D simulation has been used to track and quantify the MW routes and their property characteristics at the last region of subduction. It also allows us to quantify the water transformation after subduction. The simulation has been compared to available observations using a collocation method that interpolated model data onto observations in time and space. The comprehensive comparisons gave us confidence in the model’s capacity to reproduce MW characteristics. A quantitative Lagrangian analysis was performed on the model output to depict the origin, the fate and the route of MW circulating in the southern Pacific Ocean, selected in the density range of 26.8–27.4 kg m⁻³. We found 18 Sv of MW were transported northward in patches through the 42° S section, mostly between 200 and 800 m depth. Of this transport, 8 Sv enters the Pacific Ocean in the upper layer south of Tasmania and subducts in the Pacific. The remainder is not ventilated in the Pacific sector: 4 Sv is advected from the Indian Ocean south of Tasmania at intermediate depth and finally 6 Sv is part of an intermediate depth recirculation within the Pacific Ocean. Particles take up to 30 years to travel northward through our domain before crossing the 42° S section. Southward transport branches also exist: 3 Sv flows southward following the eastern New Zealand coast and then exits through Drake Passage. An additional 4 Sv passes southward in the Tasman Sea, following the eastern Tasmanian coast and enters the Indian Ocean south of Tasmania, as part of the Tasman Leakage. Four different formation sites have been identified, where the MW are last ventilated. These formation sites have different water masses with specific salinity ranges. A study on the evolution of the physical characteristics of each of these water masses has been performed. All MW characteristics become more homogeneous at 42° S than they were when they left the mixed layer. This study confirms the homogenisation of mode waters at intermediate depth in the Pacific Ocean as previously revealed in the Indian Ocean using the same methodology. Transformations are shown to be mostly isopycnal in the Tasman Sea and diapycnal farther east.  相似文献   

Comment on Use of Single‐Well Tracer Dilution Tests to Evaluate LNAPL Flux at Seven Field Sites and Measurement of LNAPL Flux Using Single‐Well Intermittent Mixing Tracer Dilution Tests          下载免费PDF全文

Gabriel Paiva Lago  John H. Knight  John L. Rayner 《Ground water》2016,54(5):623-624

  相似文献   

Controlled electrochemical dissolution of hydrothermal and sedimentary pyrite     

Ran Liu  Amy L. Wolfe  David A. Dzombak  Colin P. Horwitz  Brian W. Stewart  Rosemary C. Capo 《Applied Geochemistry》2009

Electrochemically controlled pyrite dissolution was performed with three pyrite materials from different geological origins under mixed potential and high overpotential conditions. Both solid electrodes and C paste electrodes of powdered pyrite were used. The rate of pyrite dissolution increased with applied positive potential and was strongly affected by temperature. Current density measurements over the applied potential range successfully described the rate of pyrite dissolution of each pyrite electrode. Controlled dissolution performed under mixed potential conditions on the solid electrodes successfully reflected the same pyrite reactivity and dissolution rate order as in batch reactor dissolution studies with the same pyrite materials. Therefore, the relative reactivity of different pyrite materials can be determined through current density measurements on their solid electrodes under mixed potential conditions. This technique could be a useful tool to compare rapidly the relative reactivity for different pyrite materials. In contrast, electrochemically controlled dissolution studies with C paste electrodes constructed with fine-grained pyrite and paraffin/graphite mixture did not result in accurate ranking of pyrite samples by dissolution rate.  相似文献   

Silicon isotopic fractionation of CAI-like vacuum evaporation residues     

Kim B. Knight  Noriko T. Kita  Frank M. Richter  Andrew M. Davis  John W. Valley 《Geochimica et cosmochimica acta》2009,73(20):6390-5891

Calcium-, aluminum-rich inclusions (CAIs) are often enriched in the heavy isotopes of magnesium and silicon relative to bulk solar system materials. It is likely that these isotopic enrichments resulted from evaporative mass loss of magnesium and silicon from early solar system condensates while they were molten during one or more high-temperature reheating events. Quantitative interpretation of these enrichments requires laboratory determinations of the evaporation kinetics and associated isotopic fractionation effects for these elements. The experimental data for the kinetics of evaporation of magnesium and silicon and the evaporative isotopic fractionation of magnesium is reasonably complete for Type B CAI liquids (Richter F. M., Davis A. M., Ebel D. S., and Hashimoto A. (2002) Elemental and isotopic fractionation of Type B CAIs: experiments, theoretical considerations, and constraints on their thermal evolution. Geochim. Cosmochim. Acta66, 521-540; Richter F. M., Janney P. E., Mendybaev R. A., Davis A. M., and Wadhwa M. (2007a) Elemental and isotopic fractionation of Type B CAI-like liquids by evaporation. Geochim. Cosmochim. Acta71, 5544-5564.). However, the isotopic fractionation factor for silicon evaporating from such liquids has not been as extensively studied. Here we report new ion microprobe silicon isotopic measurements of residual glass from partial evaporation of Type B CAI liquids into vacuum. The silicon isotopic fractionation is reported as a kinetic fractionation factor, α_Si, corresponding to the ratio of the silicon isotopic composition of the evaporation flux to that of the residual silicate liquid. For CAI-like melts, we find that α_Si = 0.98985 ± 0.00044 (2σ) for ²⁹Si/²⁸Si with no resolvable variation with temperature over the temperature range of the experiments, 1600-1900 °C. This value is different from what has been reported for evaporation of liquid Mg₂SiO₄ (Davis A. M., Hashimoto A., Clayton R. N., and Mayeda T. K. (1990) Isotope mass fractionation during evaporation of Mg₂SiO₄. Nature347, 655-658.) and of a melt with CI chondritic proportions of the major elements (Wang J., Davis A. M., Clayton R. N., Mayeda T. K., and Hashimoto A. (2001) Chemical and isotopic fractionation during the evaporation of the FeO-MgO-SiO₂-CaO-Al₂O₃-TiO₂-REE melt system. Geochim. Cosmochim. Acta65, 479-494.). There appears to be some compositional control on α_Si, whereas no compositional effects have been reported for α_Mg. We use the values of α_Si and α_Mg, to calculate the chemical compositions of the unevaporated precursors of a number of isotopically fractionated CAIs from CV chondrites whose chemical compositions and magnesium and silicon isotopic compositions have been previously measured.  相似文献   

Mapping and detection of land use change in a coal mining area using object-based image analysis     

Wenming Pei  Suping Yao  Joseph F. Knight  Shaochun Dong  Keith Pelletier  Lian P. Rampi  Yan Wang  Jim Klassen 《Environmental Earth Sciences》2017,76(3):125

Object-based image analysis was used to map land use in the Panxie coal mining area, East China, where long-term underground coal mines have been exploited since the 1980s. A rule-based classification approach was developed for a Pleiades image to identify the desired land use classes, and the same rule-based classification strategies, after the threshold values had been modified slightly, were applied to the Landsat series images. Five land use classes were successfully captured with overall accuracies of between 80 and 94%. The classification approach was validated for its flexibility and robustness. Multitemporal classification results indicated that land use changed considerably in the Panxie coal mining area from 1989 to 2013. The urban, coal and coal gangue, and water areas increased rapidly in line with the growth in mine production. Urban areas increased from 9.38 to 20.92% and showed a tendency to increase around the coal mines. From 1989 to 2013 the coal and coal gangue area increased by 40-fold, from 0.02 to 0.58%. Similarly, the water area increased from 2.77 to 7.84% over this time period, mainly attributable to the spread of waterlogged areas. The waterlogged areas increased to about 2900 ha in 2013, which was about 80 times more than their area in 1989. In contrast, the area of cultivated land was negatively related to the increase in mine production and decreased from 73.11 to 57.25%. The results of this study provide a valuable basis for sustainable land management and environmental planning in the Panxie coal mining area.  相似文献   

Bootstrap Calibration and Uncertainty Estimation of Downhole NMR Hydraulic Conductivity Estimates in an Unconsolidated Aquifer          下载免费PDF全文

A.D. Parsekian  K. Dlubac  E. Grunewald  J.J. Butler  R. Knight  D.O. Walsh 《Ground water》2015,53(1):111-121

Characterization of hydraulic conductivity (K) in aquifers is critical for evaluation, management, and remediation of groundwater resources. While estimates of K have been traditionally obtained using hydraulic tests over discrete intervals in wells, geophysical measurements are emerging as an alternative way to estimate this parameter. Nuclear magnetic resonance (NMR) logging, a technology once largely applied to characterization of deep consolidated rock petroleum reservoirs, is beginning to see use in near‐surface unconsolidated aquifers. Using a well‐known rock physics relationship—the Schlumberger Doll Research (SDR) equation—K and porosity can be estimated from NMR water content and relaxation time. Calibration of SDR parameters is necessary for this transformation because NMR relaxation properties are, in part, a function of magnetic mineralization and pore space geometry, which are locally variable quantities. Here, we present a statistically based method for calibrating SDR parameters that establishes a range for the estimated parameters and simultaneously estimates the uncertainty of the resulting K values. We used co‐located logging NMR and direct K measurements in an unconsolidated fluvial aquifer in Lawrence, Kansas, USA to demonstrate that K can be estimated using logging NMR to a similar level of uncertainty as with traditional direct hydraulic measurements in unconsolidated sediments under field conditions. Results of this study provide a benchmark for future calibrations of NMR to obtain K in unconsolidated sediments and suggest a method for evaluating uncertainty in both K and SDR parameter values.  相似文献   

Tentative detection of the rotation of Eris     

Henry G. Roe  Rosemary E. Pike 《Icarus》2008,198(2):459-464

We report a multi-week sequence of B-band photometric measurements of the dwarf planet Eris using the Swift satellite. The use of an observatory in low-Earth orbit provides better temporal sampling than is available with a ground-based telescope. We find no compelling evidence for an unusually slow rotation period of multiple days, as has been suggested previously. A ∼1.08 day rotation period is marginally detected at a modest level of statistical confidence (∼97%). Analysis of the combination of the Swift data with the ground-based B-band measurements of Rabinowitz et al. [Rabinowitz, D.L., Schaefer, B.E., Tourtellotte, S.W., 2007. Astron. J. 133, 26-43] returns the same period (∼1.08 day) at a slightly higher statistical confidence (∼99%).  相似文献   

A general model of lateral depth-averaged velocity distributions for open channel flows     

Xiaonan Tang  Donald W. Knight 《Advances in water resources》2008

This paper reviews a model, developed by Shiono and Knight [Shiono K, Knight DW. Two-dimensional analytical solution for a compound channel. In: Proceedings of the 3rd international symposium on refined flow modelling and turbulence measurements, Tokyo, Japan, July 1988. p. 503–10; Shiono K, Knight DW. Turbulent open channel flows with variable depth across the channel. J Fluid Mech 1991;222:617–46 [231:693]], which yields analytical solutions to the depth-integrated Navier–Stokes equations, and includes the effects of bed friction, lateral turbulence and secondary flows. Some issues about the original model developed by Shiono and Knight (1988, 1991) are highlighted and discussed. Based on the experimental data concerning the secondary flow, two assumptions are proposed to describe the contribution of the streamwise vorticity to the flow. Two new analytical solutions are compared with the conventional solution for three simple channel shapes and one trapezoidal compound channel to highlight their differences and the importance of the secondary flow and planform vorticity term. Comparison of the analytical results with the experimental data shows that the general SKM predicts the lateral distributions of depth-averaged velocity well.  相似文献