News & views. Water issues related to mining     

Kretsinger Grabert V  Kaback DS 《Ground water》2011,49(3):310

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S saturation history of Nain Plutonic Suite mafic intrusions: origin of the Voisey’s Bay Ni–Cu–Co sulfide deposit, Labrador, Canada     

Peter C. Lightfoot  Reid R. Keays  Dawn Evans-Lamswood  Robert Wheeler 《Mineralium Deposita》2012,47(1-2):23-50

The Voisey’s Bay deposit is hosted in a 1.34-Ga intrusion composed of troctolite, olivine gabbro, and ferrogabbro. The sulfide mineralization is associated with magmatic breccias that are enveloped by weakly mineralized olivine gabbros and troctolites, and also occurs as veins along structures in adjacent paragneiss. A dyke is connected to the base of the north wall of the Eastern Deeps Intrusion, and the entry point of this dyke into the chamber is the locus of the Eastern Deeps nickel sulfide deposit. A detailed exploration in the area between the Eastern Deeps and the Ovoid has shown that these intrusions and ore deposits are connected by a splayed dyke. The Eastern Deeps Deposit is surrounded by a halo of moderately to weakly mineralized variable-textured troctolite (VTT) that reaches a maximum thickness above the axis of the Eastern Deeps Deposit along the northern wall of the Eastern Deeps Intrusion. The massive sulfides and breccia sulfides are petrologically and chemically different when compared to the disseminated sulfides in the VTT, and there is a marked break in Ni tenor of sulfide between the two. Sulfides hosted in the dyke tend to have low metal tenors ([Ni]₁₀₀?=?2.5–3.5%), sulfides in Eastern Deeps massive and breccia ores have intermediate Ni tenors ([Ni]₁₀₀?=?3.5–4%), and disseminated sulfides in overlying rocks have high Ni tenors ([Ni]₁₀₀?=?4–8%). Four principal processes control the compositions of the Voisey’s Bay sulfides. Coarse-grained loop-textured ores consisting of pyrrhotite crystals separated by chalcopyrite and pentlandite exhibit a two orders of magnitude variation in the Pd/Ir ratio which is due to mineralogical variations where pentlandite is enriched in Pd and Ir is dispersed throughout the mineral assemblage. A decrease in Ir and Rh from the margin of the Ovoid toward cubanite-rich parts at the central part of the Ovoid is consistent with fractionation of the sulfide from the margins toward the center of the Ovoid. The Ovoid ores have higher Ni and Pd tenor than the Eastern Deeps massive sulfides; this is consistent with both a higher R factor and greater degree of silicate parental magma evolution in the Ovoid than the Eastern Deeps. The disseminated sulfides surrounding the Eastern Deeps deposit have some of the highest Ni and Pd tenors at Voisey’s Bay, which are indicative of not only more primitive magmas but also higher R factors than the Ovoid or the Eastern Deeps. VTT and normal-textured troctolite of the Eastern Deeps that contain trace sulfide have 0.1–3?ppb Pt and 0.1–3?ppb Pd, whereas weakly to heavily mineralized variable troctolites in the same unit have one to two orders of magnitude higher abundances of Pt and Pd. Troctolites and olivine gabbros from other parts of the Voisey’s Bay Intrusion and other Nain Plutonic Suite Intrusions, including the Kiglapait, Newark Bay, Barth Island, Mushua, and Nain Bay South Intrusion, also have low platinum group element abundances. Although it is possible that this is a signature of a widespread sulfide saturation event that pre-dated ore formation at Voisey’s Bay, it is more likely that platinum group element (PGE) depletion is a product of the source melting process where low degrees of melting resulted in the retention of PGE in the mantle source. If so, this indicates that PGE depletion should be used with caution as an exploration tool in the Nain Plutonic Suite.  相似文献   

A model to simulate special concentrically braced frames beyond brace fracture     

Po‐Chien Hsiao  Dawn E. Lehman  Charles W. Roeder 《地震工程与结构动力学》2013,42(2):183-200

Special concentrically braced frames (SCBFs) are commonly used as the lateral‐load resisting system in buildings. SCBFs primarily sustain large deformation demands through inelastic action in the brace, including compression buckling and tension yielding; secondary yielding may occur in the gusset plate and framing elements. The preferred failure mode is brace fracture. Yielding, buckling, and fracture behavior results in highly nonlinear behavior and accurate analytical modeling of these frames is required. Prior research has shown that continuum models are capable of this level of simulation. However, those models are not suitable for structural engineering practice. To enable the use of accurate yet practical nonlinear models, a research study was undertaken to investigate modeling parameters for line‐element models, which is a more practical modeling approach. This portion of the study focused on methods to predict brace fracture. A fracture modeling approach simulated the nonlinear, cyclic response of SCBFs by correlating onset of fracture to the maximum strain range in the brace. The model accounts for important brace design parameters including slenderness, compactness, and yield strength. Fracture data from over 40 tests was used to calibrate the model and included single‐brace component, single story frame, and full‐scale multistory frame specimens. The proposed fracture model is more accurate and simpler than other, previously proposed models. As a result, the proposed model is an ideal candidate for practical performance simulation of SCBFs. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Seismic analyses of conventional and improved marginal wharves     

Maurizio M. Chiaramonte  Pedro Arduino  Dawn E. Lehman  Charles W. Roeder 《地震工程与结构动力学》2013,42(10):1435-1450

Marginal wharves are key components in providing functionality of port facilities. Ports are central components of the US economy. Earthquake damage to a port can disrupt the economic stability. Therefore, port facilities must be able to quickly return to full operation shortly after a seismic event. Prior studies have shown that integrity of marginal wharves may be compromised by excessive soil movement and structural damage. The latter is often localized at pile‐to‐wharf connections and in the pile body buried within the soil. Recent research has resulted in an improved connection design that mitigates damage. This study was undertaken to evaluate the full seismic performance of marginal wharves including both conventional and damage‐resisting connections. A series of finite element models of a representative pile‐supported wharf facility were created. The models varied in their moment‐resisting pile‐to‐wharf connections. A total‐stress analysis approach was used to capture the soil response along with p–y, t–z, and Q–z soil–structure interaction springs. Validated connection interface elements were integrated with non‐linear frame elements to simulate the marginal wharf structure and substructure. Non‐linear static pushover and dynamic time history analyses, for three different hazard levels, were performed. The results of the numerical simulations were used to assess the performance of the marginal wharf including estimates of crane damage and port downtime. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Effect of iron and carbonation on the diffusion of iodine and rhenium in waste encasement concrete and soil fill material under hydraulically unsaturated conditions     

Dawn M. Wellman  Kent E. Parker  Laura Powers  Greg A. Whyatt  Libby N. Clayton  Shas V. Mattigod  Marcus I. Wood 《Applied Geochemistry》2008,23(8):2256-2271

Assessing long-term performance of Category 3 cement wasteforms and accurate prediction for radionuclide encasement requires knowledge of the radionuclide–cement interactions and mechanisms of retention (i.e. sorption or precipitation). A set of sediment-concrete half-cell diffusion experiments was conducted under unsaturated conditions (4% and 7% by weight moisture content) using carbonated and non-carbonated concrete–soil half cells. Results indicate the behavior of Re and I release was comparable within a given half-cell test. Diffusivity in soil is a function of moisture content; a 3% increase in moisture content affords a one to two order of magnitude increase in diffusivity. Release of I and Re was 1–3 orders of magnitude less from non-carbonated, relative to carbonated, concrete monoliths. Inclusion of Fe in non-carbonate monoliths resulted in the lowest concrete diffusivity values for both I and Re. This suggests that in the presence of Fe, I and Re are converted to reduced species, which are less soluble and better retained within the concrete monolith. The release of I and Re was greatest from Fe-bearing, carbonated concrete monoliths, suggesting carbonation negates the effect of Fe on the retention of I and Re within concrete monoliths. This is likely due to enhanced formation of microcracks in the presence of Fe, which provide preferential paths for contaminant migration. Although the release of I and Re were greatest from carbonated concrete monoliths containing Fe, the migration of I and Re within a given half cell is dependent on the moisture content, soil diffusivity, and diffusing species.  相似文献   

Scientific information model for deepsea mapping and sampling     

Dawn J. Wright  Christopher G. Fox  Andra M. Bobbitt 《Marine Geodesy》2013,36(4):367-379

The Vents Program of the National Oceanic and Atmospheric Administration's Pacific Marine Environmental Laboratory is an interdisciplinary research initiative that brings together scientists from a wide range of disciplines, including geophysics, geology, physical oceanography, chemistry, and biology. Each discipline collects a variety of data types of varying structures and requiring intercomparison. The challenge of scientific information management is thus approached with a view of supporting data from multiple survey, mapping, and sampling tools and subject to multiple levels of interpretation. The ultimate objective is a system that integrates the functions of data storage, selective retrieval, display, and archiving. The results of our ongoing efforts in scientific information modeling and management have produced a relational database in which marine geological, geophysical, chemical, and biological observations can be accessed by any investigator.  相似文献   

Why Web GIS May Not Be Enough: A Case Study with the Virtual Research Vessel     

Dawn J. Wright  Elizabeth O'Dea  Judith B. Cushing  Janice E. Cuny  Douglas R. Toomey 《Marine Geodesy》2003,26(1):73-86

During several decades of investigation, the East Pacific Rise seafloor-spreading center at 9°-10°N has been explored by marine geologists, geophysicists, chemists, and biologists, and has emerged as one of the best studied sections of the global midocean ridge. It is an example of a region for which there is now a great wealth of observational data, results, and data-driven theoretical studies. However, these have yet to be fully utilized, either by research scientists or educators. While the situation is improving, a large amount of data, results, and related theoretical models still exist either in an inert, noninteractive form (e.g., journal publications) or as unlinked and currently incompatible computer data or algorithms. Presented here is the prototype of a computational environment and toolset, called the Virtual Research Vessel, to improve the situation by providing marine scientists and educators with simultaneous access to data, maps, and numerical models. While infrastructure is desired and needed for ready access to data and the resulting maps via web GIS in order to link disparate data sets (data to data), it is argued that data must also be linked to models for better exploration of new relations between observables, refinement of numerical simulations, and the quantitative evaluation of scientific hypotheses. For widespread data access, web GIS is therefore only a preliminary step rather than a final solution, and the ongoing implementation of the Virtual Research Vessel (scheduled for final completion in 2004-2005) is a case study for the midocean ridge community to test the effectiveness of moving beyond the data-to-data mode towards data-to-models and data-to-interpretation.  相似文献   

Implications for Neoarchaean ocean chemistry from primary carbonate mineralogy of the Campbellrand-Malmani Platform, South Africa   总被引：2，自引：0，他引：2  

Dawn Y. Sumner  John P. Grotzinger† 《Sedimentology》2004,51(6):1273-1299

The precipitation of calcite and aragonite as encrustations directly on the seafloor was an important platform‐building process during deposition of the 2560–2520 Ma Campbellrand‐Malmani carbonate platform, South Africa. Aragonite fans and fibrous coatings are common in unrestricted, shallow subtidal to intertidal facies. They are also present in restricted facies, but are absent from deep subtidal facies. Decimetre‐thick fibrous calcite encrustations are present to abundant in all depositional environments except the deepest slope and basinal facies. The proportion of the rock composed of carbonate that precipitated as encrustations or in primary voids ranges from 0% to > 65% depending on the facies. Subtidal facies commonly contain 20–35%in situ precipitated carbonate, demonstrating that Neoarchaean sea water was supersaturated with respect to aragonite, carbonate crystal growth rates were rapid compared with sediment influx rates, and the dynamics of carbonate precipitation were different from those in younger carbonate platforms. The abundance of aragonite pseudomorphs suggests that sea‐water pH was neutral to alkaline, whereas the paucity of micrite suggests the presence of inhibitors to calcite and aragonite nucleation in the mixed zone of the oceans.  相似文献   

Cone Penetrometer Testing and Discrete-Depth Ground Water SamplingL Techniques: A Cost-Effective Method of Site Characterization in a Multiple-Aquifer Setting     

Dawn A. Zemo  Yvonne G. Pierce  John D. Gallinatti 《Ground Water Monitoring & Remediation》1994,14(4):176-182

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Final dissolved organic carbon broad community intercalibration and preliminary use of DOC reference materials   总被引：1，自引：0，他引：1  

Jonathan H. Sharp  Craig A. Carlson  Edward T. Peltzer  Dawn M. Castle-Ward  Karen B. Savidge  Katherine R. Rinker 《Marine Chemistry》2002,77(4):1819

A broad community intercalibration exercise for accurate measurement of dissolved organic carbon (DOC) in seawater has been carried out over a period of 5 years. A set of 10 natural samples with DOC content from 40 to 200 μM C were accompanied by two glucose standards and a “zero C” blank; all sealed in glass ampoules. Samples were sent to all interested analysts for “blind” analysis; 62 laboratories in 17 countries participated. A total of 59 separate analyses were determined to be acceptable by screening criteria based on standards and blank; another nine sets of analyses did not pass the screening. The majority of the analyses, both those passing and those that did not, were performed with high temperature combustion (HTC) methods, six sets of analyses were done using wet chemical oxidation methods.From the 53 sets of acceptable HTC analyses, the coefficient of variation (%CV) for analytical comparability of the samples was 10% (“community precision”). It is estimated that the individual replicate injection precision for most instruments was approximately 2% and that no additional variability was caused by differences within the ampoules of individual samples. The additional variability over 2% was likely a result of both random and systematic differences in analytical capabilities from instrument to instrument and from day to day for individual instruments. With an arbitrary selection after the fact, smaller subsets of analysts can show comparability better than 10% and duplicate or triplicate runs on different days of the full sets of samples in several laboratories showed comparability in the 2–6.5% range. Experienced oceanic analysts, with internal or shared reference materials, can now show reproducibility and comparability at a level closer to 2%.Preliminary use of DOC reference materials by 14 participants showed day-to-day reproducibilities for their laboratories in the 2–6% range in most cases; several with poorer reproducibility do not normally perform DOC analyses on samples with concentrations as low as the deep ocean reference used here. Use of these reference materials can also give a demonstration of comparability between laboratories. For credibility of DOC analyses, it is necessary for analysts to use community reference materials and report results of their analytical performance with these references.This paper does not identify individual data nor should it be considered an evaluation of individual laboratories or analysts. The purpose is to show the summary picture of the international community of DOC analysts as it existed in the mid- to late 1990s.  相似文献