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关键词： Marcona Fe-(Cu) deposit   IOCG   Sulfide trace element   Sulfur isotopes   Peru  

摘要： The Marcona magnetite deposit, located in the iron oxide copper-gold (IOCG) province of southern Peru, is an important Fe deposit with sub-economic Cu and Zn mineralization. Three generations of sulfides were identified at the Marcona alteration/mineralization Stages IV, V and VW Magnetite, pyrrhotite, pyrite and minor chalcopyrite started to form at Stage IV. Sulfides in Stage V are dominated by chalcopyrite and pyrite, whereas only pyrite was present in Stage VII. In-situ SIMS sulfur isotope and LA-ICP-MS trace element analyses were conducted on the sulfides of these stages. Stage IV sulfides contain et largely in the range of 0 to +4.0%o, indicating a dominantly magmatic origin. In particular, delta S-34 values of Stage IV pyrite increase from core to rim, and the corresponding trace elements concentrations vary along with delta S-34. Positive delta S-34 vs. Se/S correlation of Stage IV pyrite indicates that the ore-forming system was open. The Stage V pyrite are rich in Mn, Cu, Ag, Sb, Te, Pb and Bi, and all Stage V sulfides have also elevated delta(34)5 (up to +7.8%0), indicative of possible seawater incursion during its formation. The delta S-34 values of Stage VII pyrite are highly variable from 13.4 to 5.4%0. This, together with ubiquitous disseminated voids, low Co/Ni ratios and enrichments of Mn, Se, Sb, Te, Tl and Pb, suggests that Stage VII pyrite may have formed by sulfate reduction associated with organic materials. We propose that the ore-forming fluids of Stage IV are initially magmatic with involvement of external (e.g., seawater) at late, where the fluids of Stage V are likely mainly exotic. The external fluids, together with organic matter, may have contributed to the ore-forming fluids of Stage VII, indicating a complex fluid evolution history for this giant Fe (-Cu) deposit. (C) 2017 Elsevier B.V. All rights reserved.

关键词： Numerical modeling   Extended finite element   Acidizing   Inhomogeneous materials   Enrichment functions   Crack propagation  

摘要： Acidizing and chemical solutions may change mechanical properties of rocks and facilitate rock fracturing in different mining operation and enhanced oil recovery projects in oil fields. Characterization of rock properties shows an inhomogeneous and completely anisotropic behavior while some rocks exhibit orthotropic behavior. Chemo-mechanical processes result in the development and intensification of inhomogeneity and orthotropy in rock properties which should be characterized for numerical modeling of fracture initiation and propagation in engineering rock works. An extended finite element code which is a powerful numerical tool, compared to the other numerical methods, is developed to model fracturing graded brittle rocks by chemical corrosion. The code uses enriched functions in an anisotropic and inhomogeneous environment to reproduce singularity. A numbers of rock specimens were exposed to various degrees of acidity in different time periods in the laboratory and developed numerical code is verified by laboratory results. Crack propagation is investigated by considering different corrosive solutions under various mechanical loading in three-point and four-point bending tests both numerically and experimentally. The results show that XFEM could model rock fracturing process of the eroded materials by chemical compounds very accurately. Results also show that deformability and asymmetry in the stress distribution is increased as a strong function of chemical concentration. With decreasing pH, rock fracture toughness is also decreased and crack propagation paths is more violated compared to the non eroded rocks. It is also shown that crack orientation in respect to the main axes of orthotropy can have a decisive role on failure load. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： rare earths   separation   ion exchange   complex formation   sorption   chromatography  

摘要： Sorption methods for the concentration and separation of rare earth elements are reviewed. Sorbents based on organic polymers, specifically strongly and weakly acidic cation exchangers, anion exchangers, and complexing sorbents, are successively considered. Data on the use of inorganic sorbents and solid phase extractants in the rare earth chemistry are also given. Considerable attention is paid to hybrid organomineral materials constituting a promising class of sorbents. Advantages and disadvantages of using biosorbents, molecularly imprinted sorbents, and nanosorbents for the concentration and separation of rare earths are discussed.

关键词： coprolites   laser-induced breakdown spectroscopy   hyperspectral images   principal component analysis   ICP-OES  

摘要： This study demonstrates the application of laser-induced breakdown spectroscopy (LIBS) and hyperspectral imaging to the investigation of coprolite and fossil samples. Solid samples from the Permian (seven coprolites and one fossil), Cretaceous (one coprolite) and Oligo-Miocene (two coprolites) periods were directly analysed, and emission spectra from 186 to 1042nm were obtained in several areas covering coprolite/fossil and rock material. Initial exploratory analyses were performed using principal component analysis with the data set normalised by the norm (Euclidean norm = 1). After identification and selection of emission lines of eleven elements (Al, Ca, Cr, Fe, K, Mg, Mn, Na, Ni, P and Si), the signals were normalised again by the relative intensity of the selected element. Phosphorus was identified mainly in the coprolites, while K and Na were primarily found in the rock material. In several cases, there was a positive correlation between Ca and P. A sample from the Oligo-Miocene series was also analysed using inductively coupled plasma-optical emission spectrometry (ICP-OES) (rock and coprolites were analysed separately). Based on the quantitative results from ICP-OES, it was confirmed that the tendency was the same as that observed with the results obtained from LIBS directly in the solid sample.

关键词： Calcic amphibole   chemometrics   melt compositions   multiple regression   Ongatiti ignimbrite   plutonic xenoliths   Grenada  

摘要： We have used multiple-regression methods to calibrate new, pressure-independent empirical chemometric equations to calculate the major element composition of basanitic to rhyolitic melts in equilibrium with calcic amphibole. The equations are based on amphibole stoichiometric formula components temperature from published experimental P-T-X data and avoid some problems of previous studies associated with uncertainties in pressure determination. Compared with the pressure dependent equations of Ridolfi and Renzulli (2012), tests run using an independent data set indicate that the new equations yield improved precision and accuracy, in particular for SiO2, TiO2, CaO, and K2O. The results are only marginally more precise when temperature is used as a dependent variable, demonstrating that temperature has a relatively minor role in controlling amphibole crystal chemistry compared with melt composition. This allows us to accept a small decrease in precision in excluding temperature from the analysis, which is very convenient for application of the equations to natural amphiboles where temperature is typically unknown. Using the new chemometric equations, reconstructed melt compositions in equilibrium with the rims of amphiboles in pumice clasts of the Ongatiti ignimbrite are in good agreement with coexisting matrix glass compositions, lending support for our analysis. The compositionally variable cores of the amphiboles give predicted melt compositions with large compositional variations from andesitic (63 wt% SiO2) to high-Si rhyolite. These compositional variations in the predicted melt compositions suggest that there may be a range of heterogeneous melts undergoing progressive differentiation within a major crustal magma storage region underneath the volcano. The results support the existence of genuine intermediate composition melts within the storage region. Interaction between these stored melts, disaggregating mush fragments and replenishing magmas gives rise to th

关键词： geochemical background   heavy metals   urban soils  

摘要： Analysis and calculation techniques of geochemical background concentrations of chemical elements in various systems is of paramount importance for applied geochemistry. Herein we assume the geochemical background as the average of natural variations in the concentrations of chemical elements determined at a territory that highly probable does not host any natural and/or anthropogenic sources of contaminating chemical elements. In the context of determining geochemical background, our research was focused on determining the concentrations of heavy metals in soils in the city of Yerevan with the application of an integrated approach. Comparison of the obtained background values with the mean concentrations of elements in the upper continental crust yields representative data, and the application of various statistical tests (+/- 3 sigma, +/- 2 sigma, and boxplots) is proved to equally efficient.

关键词： Elemental quantitation   Carbon   Compound-independent calibration   Mass spectrometry   Isotopic tagging  

摘要： Elemental mass spectrometry offers quantitation and isotopic analysis without the need for compound-specific standards. We have recently introduced plasma assisted reaction chemical ionization (PARCI) as an efficient elemental ionization method for halogens. Here, we report a new ionization chemistry in PARCI for facile quantitation of elemental carbon in gas chromatography eluates. We demonstrate that in-plasma reactions of organic compounds followed by afterglow ionization lead to formation of polyatomic anions (CN-, OCN-, and CO3 (-)), among which CN- offers the best analytical sensitivity with a detection limit of similar to 25 pg (21 pg/s) carbon on column. Using a mixture of pesticides with wide variations in structures and heteroatom content, we demonstrate that CN- ion response is quantitatively correlated with the carbon concentration over two orders of magnitude (r(2) = 0.985). We show that the novel GC-PARCI-MS method provides recoveries within 80-120% using a single standard for all analytes, highlighting the strength of elemental quantitation. Further, the ability of GC-PARCI-MS to identify C-13-tagged molecules without a priori knowledge of chemical formulas of analytes is demonstrated.

关键词： Post-collisional rhyolite   Zircon U-Pb geochronology   Sr-Nd-Hf-O isotopic composition   Melting of juvenile mafic lower crust   Late Triassic   NW Thailand  

摘要： Volcanic rocks are widely exposed within the Chiang Khong-Lampang-Tak igneous zone in NW Thailand. A representative rhyolite sample from the Chiang Khong area yielded a zircon U-Pb age of 230.7 +/- 1.1 Ma (n = 20, MSWD = 0.98). The Chiang Khong rhyolites are characterized by low TiO2 (0.29-0.62 wt%) and MgO (0.04-0.82 wt%) with A/CNK values of 0.95-1.06 (one outlier at 1.47), and can be classified as highly fractionated I-type rhyolites. They are enriched in LILEs and LREEs, and depleted in HFSEs. Two representative samples have Sr-87/Sr-86 (i) ratios of 0.70497 and 0.70527, and the epsilon(Nd) (t) values fall at +1.1 and +1.3, respectively. epsilon(Hf) (t) and delta O-18 in zircon are between +4.7 to +12.0 and 5.3 to 5.9 aEuro degrees, respectively. Our geochemical data suggest that the Chiang Khong rhyolites formed by partial melting of juvenile mafic lower crust in a post-collisional setting. Deep crustal anatexis was probably induced by upwelling asthenospheric mantle, shortly after slab detachment subsequent to closure of the Paleo-Tethys.

关键词： tropical karst   element concentration   N/P ratios   Ca/A1 relationship   delta C-13   delta N-15  

摘要： Forests on calcareous substrates constitute a large fraction of the vegetation in Puerto Rico. Plant growth on these substrates may be affected by nutrient deficiencies, mainly P and Fe, resulting from high pH and formation of insoluble compounds of these elements. The occurrence of these forests in humid and dry areas provides an opportunity to compare nutrient relations, water use efficiency, and N dynamics, using biogeochemical parameters. We selected sites under humid climate in the north, and dry climate in the southwest of Puerto Rico. Adult, healthy leaves of species with high importance values were collected at each site and analyzed for their elemental composition and the natural abundance of C and N isotopes. Calcium was the dominant cation in leaf tissues, explaining over 70% of the ash content variation, and Al and Ca concentration were positively correlated, excepting only two Al-accumulating species. Karst vegetation consistently showed high N/P ratios comparable to forests on P-poor soils. Dry karst sites had significantly higher delta C-13 and delta N-15 ratios. We conclude that forests on karst are mainly limited by P availability, and that mechanisms of nutrient uptake in the rhizosphere lead to linear correlations in the uptake of Ca and Al. Isotope ratios indicate higher water use efficiency, and predominant denitrification in dry karst forest sites.

关键词： Platinum-group element (PGE)   Sulfur-saturation   Heterogeneous mantle source   Cenozoic basalt   SE China  

摘要： Cenozoic basalts in SE China may be derived from a mixture of depleted MORB mantle (DMM) and enriched mantle 2 (EM2) sources, but whether these basalts share a common mantle source or magmatic history remains unknown. To investigate these unresolved issues, this study sampled basalts from Niutoushan and Mingxi (Fujian province), Xilong (Zhejiang province), and Penghu (Taiwan) for geochemical analysis. The basalt samples show OIB-like trace element patterns and have low PGE contents, with 0.02-0.7 ppb Ir and Pd, 0.05-1.4 ppb Ru, 0.01-0.2 ppb Rh, and 0.06-1.1 ppb Pt. All samples have high Cu/Pd ratios ranging from similar to 69,000 to 3,500,000, and low Cu/Zr ratios ranging from 0.1 to 0.8, suggesting sulfur-saturated fractionation. Model calculations indicate that the basalts are depleted in PGE due to the retention of 0.001% to 0.1% sulfide in the mantle and the removal of up to 0.0022% sulfide during magma ascent. The crystallization of olivine and spinet, and partial melting are insufficient to account for the observed PGE variation in these basalts. Thus, the distinct PGE patterns in basalts with different ages may reflect the heterogeneity of the mantle source beneath SE China. The source heterogeneity may be due to compositional heterogeneity, particularly variations in oxygen fugacity and PGE mineral phases, or due to variable fluid/melt metasomatic agents in the sub-continental lithospheric mantle. This heterogeneity is possibly related to the westward subduction of the Paleo-Pacific Plate. (C) 2017 Elsevier B.V. All rights reserved.