Selective chemical extraction of Cu from selected mineral and soil samples: enhancement of Cu geochemical anomalies in Southern Portugal

The study described herein concerns the application of selective chemical extractions on metal-bearing minerals and soils to geochemical exploration. Specifically, the study aims at the detection of anomalous soils in the vicinity of two mineralized zones in Southern Portugal.A kinetic study of the selectivity of partial chemical extractions applied to Cu minerals has been carried out in order to establish a systematic procedure (reagents, extraction plateau, etc.) which could be recommended for soils of the two study zones. It is shown that: (1) NH₄ acetate dissolves malachite, azurite and cuprite completely and chrysocolla, conicalcite and atacamite only partially; (2) hydroxylamine hydrochloride dissolves chrysocolla and conicalcite only partially; (3) H₂O₂ dissolves chalcopyrite only partially; (4) NH₄ oxalate (U.V.) dissolves conicalcite and atacamite only partially; (5) mixed-acid attack dissolves residual chalcopyrite, chrysocolla, atacamite and conicalcite.A total of 740 soil samples were collected from the Salgadinho and Tinoca areas. The Cu mineralization in the Salgadinho area is situated in an Upper-Devonian Volcanic-Siliceous Complex. The weathering products of the mineralization are mainly amorphous iron oxides, goethite and hematite. The Cu mineralization in Tinoca area is located in the Arronches-Campo Maior belt, where stratiform Cu mineralization is found. The weathering products of the mineralization are mainly malachite, amorphous iron oxides, goethite and hematite.In order to identify the Cu-bearing phases and the extraction plateau, the −80 mesh fraction of two soil samples was submitted to an extraction procedure using the following reagents in sequence: NH₄ acetate, hydroxylamine hydrochloride, NH₄ oxalate (dark), NH₄ oxalate (U.V.) and finally strong acids.In soils from the Salgadinho and Tinoca areas, the use of NH₄ oxalate (U.V.) in single dissolution which would incorporate those phases dissolved by NH₄ acetate and NH₄ oxalate (dark), gives the broadest anomalous surface and higher contrast for Cu than acid digestion. The analysis of NH₄ oxalate (U.V.) extractions, instead of acid digestion, can thus be recommended for both areas.     

The selective extraction of Pb and Zn in selected mineral and soil samples,application in geochemical exploration (Portugal)

The study described herein concerns the application of selective chemical extractions on metal-bearing minerals and soils to geochemical exploration. Specifically, the study addresses itself to the detection of anomalous soils in the vicinity of a mineralized zone.A kinetic study of selectivity of partial chemical extractions-applied to minerals of Pb and Zn was undertaken in order to establish a systematic procedure (reagents, time of extraction, etc.) which could be recommended for the soils of the study area in Portugal. It is shown that: (1) NH₄ acetate dissolves smithsonite, willemite, cerussite, anglesite, pyromorphite completely and coronadite, galena, sphalerite only partially; (2) hydroxylamine hydrochloride dissolves coronadite only partially; (3) H₂O₂ dissolves sphalerite and galena only partially; (4) hot mixed acids dissolve residual galena, sphalerite and coronadite.About 850 soil and gossan samples were collected from two mineralized districts in Portugal, one in a carbonate environment (Portel) and the other in an aluminosilicate zone (Sanguinheiro).For the kinetic study in soil samples from Portel and Sanguinheiro zones, the minus 80 mesh fraction (−180 μm) was submitted to an extraction procedure using the following reagents, in sequence: NH₄ acetate, hydroxylamine hydrochloride, NH₄ oxalate in darkness, NH₄ oxalate under U.V. irradiation and finally strong acids.The mineralogy of the soils from the two areas is different. In the aluminosilicate zone, the products of weathering of sulphide mineralization are mainly anglesite, plumbogummite, amorphous iron oxides, goethite and hematite rich in Pb and Zn. In the carbonate area, the Pb- and Zn-bearing phases generally found in the soil and gossan are Mn oxides, lepidocrocite and hematite. The gossan, in this case, also contains smithsonite and cerussite.In soils from the aluminosilicate zone the use of NH₄ oxalate (dark) given a better geochemical response for Pb than NH₄ acetate, NH₄ oxalate (U.V.) and conventional acid digestion. On the other hand, NH₄ oxalate (U.V.) gives better results for Pb and Zn than conventional acid digestion in samples from carbonate area. The analysis of NH₄ oxalate (U.V.) extractions, instead of conventional acid digestion, can nevertheless be recommended for both environments.     

Sorptive stabilization of organic matter in soils by hydrous iron oxides

Strong correlations between iron oxides (FeOx) and organic matter (OM) in soils have implied the importance of the former in stabilizing the latter. One mechanism thought to be important in this stabilization is sorption. We tested this possibility by reductively dissolving FeOx in a wide variety of soils and measuring the organic carbon (OC) that was solubilized. The OC dissolved from non-FeOx phases via anion exchange was corrected for by parallel control extractions. The resultant pool, reductively soluble OC, made up a minor amount of total soil OC in all but one of these soils, indicating that simple sorption reactions do not stabilize the bulk of soil OC in most mineral soils. OC:Fe ratios in the extracts from 2/3 of these soils were less than 0.22 (wt/wt), consistent with a sorbed state for this OC and showing that OC sorption by FeOx in these soils is limited by the amount of FeOx. The remaining soils had low pH and high OM concentrations; their higher OC:Fe ratios indicate inclusion of precipitated organo-Fe complexes in the extracts, which are likely only partially extracted by our method. The high volumetric ratios of OM to FeOx found in correlations between them from the literature are inconsistent with a dominant sorption control and point instead to stabilization to other mechanisms such as organo-Fe complexes or ternary associations among FeOx, OM and other minerals.     

Equilibriums between Cu,Fe, and Zn sulfides and oxides in chloride solution: A thermodynamic study

The results of thermodynamic modeling of equilibriums between Cu, Fe, and Zn sulfides and oxides pertaining to the Cu-Fe-Zn-S-O₂ system in water and aqueous chloride solution are presented. The system comprises solid phases of constant composition: pyrite, pyrrhotite, hematite, magnetite, wüstite, γ-iron, chalcocite, covellite, cuprite, native copper, chalcopyrite, and bornite, as well as more than 100 ions, complexes, and molecules in an aqueous solution. The GIBBS program with the UNITHERM thermodynamic dataset used in calculations allows numerical analysis of phase assemblages in a dry system and in equilibrium with an aqueous solution. How the temperature, pressure, and the composition of the solution in the system opened for oxygen and sulfur affects the composition of phase assemblages was considered in temperature and pressure ranges of 50–350 C and 100–1000 bar, respectively. Decrease in temperature leads to a shift in stability fields of the studied phases toward the region of elevated oxygen and sulfur partial pressures. Variation of temperature is an important factor affecting precipitation of ore minerals, primarily, Cu- and Zn-bearing. The calculation results are presented in tables and diagrams. Each point in the $ (\log m_{S_{tot} } - \log f_{O_2 } ) $ (\log m_{S_{tot} } - \log f_{O_2 } ) diagram is characterized by a single possible assemblage of phases equilibrated with a solution of the given composition within the considered temperature and pressure range. Since the composition of the mineral assemblage is controlled by physicochemical conditions at the moment of mineral formation, comparison of the calculation results with mineral assemblages at ore deposits makes it possible to estimate the parameters of ore deposition at the early stage of investigation, including oxygen and sulfur activity and, occasionally, the composition and salinity of the solution. These parameters control the formation of such assemblages.     

Relationships between heavy metals and iron oxides,fulvic acids,particle size fractions in urban roadside soils

Urban roadside soils are the “recipients” of large amounts of heavy metals from a variety of sources including vehicle emissions, coal burning waste and other activities. The behavior of heavy metals in urban roadside soils depends on the occurrence as well as the total amount. Accordingly, knowledge of the interactions between heavy metals and other constituents in the soil is required to judge their environmental impact. In this study, correlations of heavy metal concentrations (Pb, Zn, Cu, Ag, Se, Ni, Cr and Ba) to iron extracted using dithionite–citrate–bicarbonate (DCB) buffer (Fe_DCB), fulvic acids and particle size fractions were examined from the Xuzhou urban roadside soils. Heavy metals except for Cr and fulvic acids had a positive significant correlation with Fe_DCB, indicating these metals and fulvic acids are principally associated with the surfaces of iron oxides of the soils. Significant positive correlations were also found between the contents of fulvic acids and heavy metals, showing these heavy metals (especially for Cu, Ni and Cr) form stable complexes with fulvic acids. Such finding is of importance with regard to the increased mobilization of heavy metals, e.g., into freshwater ecosystems. Ag, Se and Cr are independent of particle size fractions because of their low concentrations of Ag and Se in the studied soils. Pb, Zn, Cu, Ba and Ag are mainly enriched in the finer soil particles (especially <16 μm).     

Adsorption of Co and selected actinides by Mn and Fe oxides in soils and sediments

Iron and Mn oxides and associated radionuclides in soils and sediments from the radioactive waste burial grounds at Oak Ridge National Laboratory have been selectively extracted using wet chemical techniques. Product-moment-correlation analyses have demonstrated that ⁶⁰Co and various actinides, principally ²⁴⁴Cm, ²⁴¹Am and ²³⁸Pu are dominantly associated with Mn oxides. Correlation coefficients between these radionuclides and Fe oxides and organic C are generally very low. The important role of Mn oxides in radionuclide adsorption is attributed to their unique surface and colloidal properties. The data illustrate the importance of the Mn oxide component of soils and sediments in controlling transition metal and actinide solubility.These results suggest two major implications for the disposal of radioactive waste. First, in order to minimize future ⁶⁰Co and actinide mobilization from disposal sites, a chemical environment in which Mn oxides are least soluble should be maintained. Second, the liberal use of Mn oxides in waste management operations might improve long-term retention of these radionuclides. Deep-sea Mn modules, which may in the future be mined for their trace metal contents, could serve as a ready supply of Mn oxide for waste disposal applications.     

Kinetics of lead adsorption by iron oxides formed under the influence of citrate

The presence of organic acids greatly affects the formation of Fe oxides and surface properties; however, the subsequent effect on the kinetics and mechanisms of Pb adsorption by the Fe oxides formed under the influence of organic acids remains obscure. The kinetics of Pb adsorption on the Fe oxides formed in the presence of citrate ligands at initial citrate/Fe(II) molar ratios (MRs) of 0, 0.001, 0.01, and 0.1 was studied at the initial Pb concentration of 8.33 μM and pH 5.0 at 278, 288, 298, and 313 K using macroscopic batch method. The results indicate that the Pb adsorption followed multiple first-order kinetics and the rate coefficient, activation energy, and pre-exponential factor in the Arrhenius equation of the adsorption varied greatly with the surface properties of the Fe oxides formed at various citrate/Fe(II) MRs. The alteration of surface properties of Fe oxides formed at the citrate/Fe(II) MR of 0.1 and the effect on the rate coefficient of the fast and slow reactions of Pb adsorption were especially significant. The rate-limiting step of Pb adsorption reactions on the Fe oxides was predominantly a diffusion process, except for the slow reaction of Pb adsorption on the Fe oxides formed at the initial citrate/Fe(II) MR of 0.1, where the rate-limiting process was evidently a chemical process, which may involve bond breaking between the coprecipitated citrate ligand and Fe oxide. The rate coefficients of Pb adsorption by the Fe oxides formed at various citrate/Fe(II) MRs cannot be explained by the activation energy alone. The pre-exponential factor plays an important role in influencing the rate coefficient of Pb adsorption by the Fe oxides. The role of organic acids such as citric acid in influencing the crystallization and the resultant alteration of surface properties of Fe oxides, and the impact on the dynamics of Pb in terrestrial and aquatic environments, thus merit close attention.     

Rare earth element partitioning between hydrous ferric oxides and acid mine water during iron oxidation

Ferrous iron rapidly oxidizes to Fe (III) and precipitates as hydrous Fe (III) oxides in acid mine waters. This study examines the effect of Fe precipitation on the rare earth element (REE) geochemistry of acid mine waters to determine the pH range over which REEs behave conservatively and the range over which attenuation and fractionation occur. Two field studies were designed to investigate REE attenuation during Fe oxidation in acidic, alpine surface waters. To complement these field studies, a suite of six acid mine waters with a pH range from 1.6 to 6.1 were collected and allowed to oxidize in the laboratory at ambient conditions to determine the partitioning of REEs during Fe oxidation and precipitation. Results from field experiments document that even with substantial Fe oxidation, the REEs remain dissolved in acid, sulfate waters with pH below 5.1. Between pH 5.1 and 6.6 the REEs partitioned to the solid phases in the water column, and heavy REEs were preferentially removed compared to light REEs. Laboratory experiments corroborated field data with the most solid-phase partitioning occurring in the waters with the highest pH.     

Chemistry of alkali extraction of brown coals—I. Kinetics, characterisation and implications to coalification

Three Australian brown coals have been separated into humin and humic acid fractions and studied by high resolution solid state ¹³C NMR spectroscopy and Fourier transform IR spectroscopy. The aromatic rings of the humic acids are highly substituted showing that extensive cross linking must have occurred during formation from wood lignin and tannin. However, the humins contain more aliphatic carbon and hydrogen than the corresponding humic acids. This shows that little cross linking has occurred with other components of the brown coal such as resins, waxes cutin and algal detritus, and cross linking has not rendered the aromatics alkali insoluble. The kinetics of extraction are complex and not simple first order. This is reflected in the chemical composition of the humic acid which is extraction temperature dependent. We also observed that there is a conversion of aromatic carbon to aliphatic carbon and gas during extraction, probably by alkaline oxidation, resulting in ring opening. A range of suitable model compounds have been studied to confirm this finding. Such a mechanism may account for the modification of lignin in oxidising environments such as those occurring in the initial stages of coalification (lignite or brown coal formation) and in soils.     

地质样品铜、铁、锌同位素标准物质的研制

合适的标准物质是进行同位素准确分析的基础和关键,本文介绍了基于地质样品的铜、铁、锌同位素分析标准参考物质的研制过程.所研制的标准物质为CAGSR-1,用于该标准物质研制的原始样品为玄武质组分的岩石成分分析国家标准物质GBW07105.按照国家一级标准的要求,对该标准物质进行了严格的均一性、稳定性检验和同位素定值分析.标准物质CAGSR-1的主要特性量值δ65Cu、δ56Fe、δ66Zn的推荐值及95%置信水平的不确定度为:δ65CuSRM976(‰)=0.10±0.02、δ56FeIRMM014(‰)=0.12±0.02、δ66ZnRomil(‰)=7.45±0.01.该标准物质可用于地质与环境样品铜、铁、锌同位素测定中化学流程评价和验证、质谱仪的校正及整个过程的分析质量控制.     

Inter-mineral Fe isotope variations in mantle-derived rocks and implications for the Fe geochemical cycle

Iron isotope and major- and minor-element compositions of coexisting olivine, clinopyroxene, and orthopyroxene from eight spinel peridotite mantle xenoliths; olivine, magnetite, amphibole, and biotite from four andesitic volcanic rocks; and garnet and clinopyroxene from seven garnet peridotite and eclogites have been measured to evaluate if inter-mineral Fe isotope fractionation occurs in high-temperature igneous and metamorphic minerals and if isotopic fractionation is related to equilibrium Fe isotope partitioning or a result of open-system behavior. There is no measurable fractionation between silicate minerals and magnetite in andesitic volcanic rocks, nor between olivine and orthopyroxene in spinel peridotite mantle xenoliths. There are some inter-mineral differences (up to 0.2‰ in ⁵⁶Fe/⁵⁴Fe) in the Fe isotope composition of coexisting olivine and clinopyroxene in spinel peridotites. The Fe isotope fractionation observed between clinopyroxene and olivine appears to be a result of open-system behavior based on a positive correlation between the Δ⁵⁶Fe_{clinopyroxene-olivine} fractionation and the δ⁵⁶Fe value of clinopyroxene and olivine. There is also a significant difference in the isotopic compositions of garnet and clinopyroxene in garnet peridotites and eclogites, where the average Δ⁵⁶Fe_{clinopyroxene-garnet} fractionation is +0.32 ± 0.07‰ for six of the seven samples. The one sample that has a lower Δ⁵⁶Fe_{clinopyroxene-garnet} fractionation of 0.08‰ has a low Ca content in garnet, which may reflect some crystal chemical control on Fe isotope fractionation. The Fe isotope variability in mantle-derived minerals is interpreted to reflect subduction of isotopically variable oceanic crust, followed by transport through metasomatic fluids. Isotopic variability in the mantle might also occur during crystal fractionation of basaltic magmas within the mantle if garnet is a liquidus phase. The isotopic variations in the mantle are apparently homogenized during melting processes, producing homogenous Fe isotope compositions during crust formation.     

Capillary geochemistry in non-saturated zone of soils. Water content and geochemical signatures

The unsaturated zone (UZ) retains aqueous solutions against gravity by capillary forces. This suction state corresponds to a decreasing internal pressure of the water, which modifies its thermodynamic properties. Accordingly, the speciation of solutes and the solubility of solids and gases in such capillary solutions change. The volumetric capillary water content of the soil at high suction can be calculated extrapolating the water retention curves (WRC) with the Rossi–Nimmo model. Interestingly, several tens of liters per cubic meter of soil can be thus suctioned, a sufficiently large volume to support that: (1) capillary water is not restricted to nanosized pores, which means it disobeys the Young–Laplace law and is metastable with respect to vapor (superheating); and (2) the geochemistry of capillary solutions might significantly influence the subsurface mass transfer. Two field situations are here interpreted using the capillary thermodynamic properties: (1) the trapping of sand grains during the growth of desert roses (gypsum), and (2) the development of abnormal paragenetic sequences in some saprolites.The capillary approach is extended to the soil solids, so that the micro-mineralogy can be explicitly (though sketchily) integrated in the calculations. The key conclusion is that capillarity changes the saturation indexes (and so the reaction rates) at given solution composition, in a way consistent with the field observations. This perspective amounts to geochemically distinguishing the capillary and percolating solutions, which is interestingly analogous to the immobile and mobile water distinction already often integrated in UZ flow models.     

Ancient geochemical cycling in the Earth as inferred from Fe isotope studies of banded iron formations from the Transvaal Craton

Variations in the isotopic composition of Fe in Late Archean to Early Proterozoic Banded Iron Formations (BIFs) from the Transvaal Supergroup, South Africa, span nearly the entire range yet measured on Earth, from –2.5 to +1.0‰ in ⁵⁶Fe/⁵⁴Fe ratios relative to the bulk Earth. With a current state-of-the-art precision of ±0.05‰ for the ⁵⁶Fe/⁵⁴Fe ratio, this range is 70 times analytical error, demonstrating that significant Fe isotope variations can be preserved in ancient rocks. Significant variation in Fe isotope compositions of rocks and minerals appears to be restricted to chemically precipitated sediments, and the range measured for BIFs stands in marked contrast to the isotopic homogeneity of igneous rocks, which have δ⁵⁶Fe=0.00±0.05‰, as well as the majority of modern loess, aerosols, riverine loads, marine sediments, and Proterozoic shales. The Fe isotope compositions of hematite, magnetite, Fe carbonate, and pyrite measured in BIFs appears to reflect a combination of (1) mineral-specific equilibrium isotope fractionation, (2) variations in the isotope compositions of the fluids from which they were precipitated, and (3) the effects of metabolic processing of Fe by bacteria. For minerals that may have been in isotopic equilibrium during initial precipitation or early diagenesis, the relative order of δ⁵⁶Fe values appears to decrease in the order magnetite > siderite > ankerite, similar to that estimated from spectroscopic data, although the measured isotopic differences are much smaller than those predicted at low temperature. In combination with on-going experimental determinations of equilibrium Fe isotope fractionation factors, the data for BIF minerals place additional constraints on the equilibrium Fe isotope fractionation factors for the system Fe(III)–Fe(II)–hematite–magnetite–Fe carbonate. δ⁵⁶Fe values for pyrite are the lowest yet measured for natural minerals, and stand in marked contrast to the high δ⁵⁶Fe values that are predicted from spectroscopic data. Some samples contain hematite and magnetite and have positive δ⁵⁶Fe values; these seem best explained through production of high ⁵⁶Fe/⁵⁴Fe reservoirs by photosynthetic Fe oxidation. It is not yet clear if the low δ⁵⁶Fe values measured for some oxides, as well as Fe carbonates, reflect biologic processes, or inorganic precipitation from low-δ⁵⁶Fe ferrous-Fe-rich fluids. However, the present results demonstrate the great potential for Fe isotopes in tracing the geochemical cycling of Fe, and highlight the need for an extensive experimental program for determining equilibrium Fe isotope fractionation factors for minerals and fluids that are pertinent to sedimentary environments.     

Comparative stable isotope geochemistry of Ni, Cu, Zn, and Fe in chondrites and iron meteorites

High-precision Ni isotopic variations are reported for the metal phase of equilibrated and unequilibrated ordinary chondrites, carbonaceous chondrites, iron meteorites, mesosiderites, and pallasites. We also report new Zn and Cu isotopic data for some of these samples and combine them with literature Fe, Cu, and Zn isotope data to constrain the fractionation history of metals during nebular (vapor/solid) and planetary (metal/sulfide/silicate) phase changes.The observed variations of the ⁶²Ni/⁵⁸Ni, ⁶¹Ni/⁵⁸Ni, and ⁶⁰Ni/⁵⁸Ni ratios vary linearly with mass difference and define isotope fractionation lines in common with terrestrial samples. This implies that Ni was derived from a single homogeneous reservoir. While no ⁶⁰Ni anomaly is detected within the analytical uncertainties, Ni isotopic fractionation up to 0.45‰ per mass-difference unit is observed. The isotope compositions of Ni and Zn in chondrites are positively correlated. We suggest that, in ordinary chondrites, exchange between solid phases, in particular metal and silicates, and vapor followed by mineral sorting during accretion are the main processes controlling these isotopic variations. The positive correlation between Ni and Zn isotope compositions contrasts with a negative correlation between Ni (and Zn) and Cu isotope compositions, which, when taken together, do not favor a simple kinetic interpretation. The observed transition element similarities between different groups of chondrites and iron meteorites are consistent with the genetic relationships inferred from oxygen isotopes (IIIA/pallasites and IVA/L chondrites). Copper is an exception, which we suggest may be related to separate processing of sulfides either in the vapor or during core formation.     

拉脊山东段地区Au、Cu地球化学组合异常识别与提取

为削弱拉脊山东段地区化探数据(典型的成分数据)存在的闭合效应,进一步分析该区地球化学元素空间组合分布规律,使用等距对数比变换(ilr)"打开"水系沉积物地球化学数据;采用稳健主成分分析(RPCA)构建组合模型,用于识别组合地球化学异常;通过S-A分形滤波技术强化弱异常并分离异常与背景,圈定地球化学致矿异常,进一步指导矿产勘查.研究结果表明:得到两组与矿化相关的元素组合,第一组为Au-As,与研究区的构造蚀变岩型金(砷)矿(金源东沟等)相关;第二组为Cu-Ni,与区域内铜镍硫化物矿床(拉水峡等)相关.S-A滤波技术可以进一步分解组合异常,强化弱小异常,同时能够缩小强背景下的异常面积,结合研究区地质概况和分解后的异常图可以进一步指导该地区构造蚀变岩型Au(As)矿和铜镍硫化物矿床的找矿勘查工作.     

快速测定化探样品同一溶液中的铜铅锌砷锑铋

传统方法分析化探样品中的铜铅锌砷锑铋需两次称样、溶矿,工作量大、成本高。本文作者在原有方法上进行部分改进,采用王水一次溶矿,分别用原子吸收-原子荧光测定土壤化探样品中同一体系的铜铅锌砷锑铋的含量,经国家一级标准样品的验证,此种方法快捷、简便,其检出限、准确度和精密度均符合规范要求。     

Cu and Fe chalcopyrite leach activation energies and the effect of added Fe

The leaching kinetics of chalcopyrite (CuFeS₂) concentrate in sulfuric acid leach media with and without the initial addition of Fe³⁺ under carefully controlled solution conditions (E_h 750 mV SHE, pH 1) at various temperatures from 55 to 85 °C were measured. Kinetic analyses by (i) apparent rate (not surface area normalised), and rate dependence using (ii) a shrinking core model and (iii) a shrinking core model in conjunction with Fe³⁺ activity, were performed to estimate the activation energies (E_a) for Cu and Fe dissolution.The E_a values determined for Cu and Fe leaching in the absence of added Fe³⁺ are within experimental error, 80 ± 10 kJ mol⁻¹ and 84 ± 10 kJ mol⁻¹, respectively (type iii analyses E_a are quoted unless stated otherwise), and are indicative of a chemical reaction controlled process. On addition of Fe³⁺ the initial Cu leach rate (up to 10 h) was increased and Cu was released to solution preferentially over Fe, with the E_a value of 21 ± 5 kJ mol⁻¹ (type ii analysis) suggestive of a transport controlled rate determining process. However, the rate of leaching rapidly decreased until it was consistently slower than for the equivalent leaches where Fe³⁺ was not added. The resulting E_a value for this leach regime of 83 ± 10 kJ mol⁻¹ is within experimental error of that determined in the absence of added Fe³⁺. In contrast to Cu release, Fe release to solution was consistent with a chemical reaction controlled leach rate throughout. The Fe release E_a of 76 ± 10 kJ mol⁻¹ is also within experimental error of that determined in the absence of added Fe³⁺. Where type (ii) and (iii) analyses were both successfully carried out (in all cases except for Cu leaching with added Fe³⁺, <10 h) the E_a derived are within experimental error. However, the type (iii) analyses of the leaches in the presence of added Fe³⁺ (>10 h), as compared to in the absence of added Fe³⁺, returned a considerably smaller pre-exponential factors for both Cu and Fe leach analyses commensurate with the considerably slower leach rate, suggestive of a more applicable kinetic analysis.XPS examination of leached chalcopyrite showed that the surface concentration of polysulfide and sulfate was significantly increased when Fe³⁺ was added to the leach liquor. Complementary SEM analysis revealed the surface features of chalcopyrite, most likely due to the nature of the polysulfide formed, are subtly different with greater surface roughness upon leaching in the absence of added Fe³⁺ as compared to a continuous smooth surface layer formed in the presence of added Fe³⁺. These observations suggest that the effect of Fe³⁺ addition on the rate of leaching is not due to the change in the chemical reaction controlled mechanism but due to a change in the available surface area for reaction.     

Comparison of extractability of Cd, Cu, Pb and Zn with sequential extraction in contaminated and non-contaminated soils

Various extraction procedures were employed for measuring extractable concentrations of potential toxic elements in soil. The extractability of Cd, Cu, Pb and Zn in four contaminated and four non-contaminated soils of Japan, was compared by single extraction (CaCl₂, DTPA, NH₄Cl, 0.1 M HCl and 1 M HCl ) and sequential extraction procedures [(six operationally defined chemical phases, viz. water soluble (Fl), exchangeable (F2), carbonate (F3), oxide (F4), organic (F5) and residual (F6) fractions)]. Extractability of metals from soils samples varied depending on metals and/or extradants used. Among the extradants, 1 M HCl extracted the largest proportion of Cd (79 to 96% of total), Cu (61 to 83%), Pb (51 to 99%) and Zn (23 to 52%) from soils followed by 0.1 M HCl, NH₄Cl, DTPA and CaCl₂. In all the extradants, the proportion of extractability of metals was higher in the contaminated soils than the non-contaminated soils. Regardless of soils and extradants, relative extractability was higher for Cd as compared to other three metals. The use of 1 M HCl may be recommended for first-level screening of soil contamination with heavy metals. The other four weak extradants are believed to provide a better assessment of bioavailable/mobile metals content in soils than 1 M HCl extradant. However, 0.1 M HCl mobilized all four metals irrespective of soil types, therefore, might be the best choice if only one extradant is to be used. The sequential extraction procedures showed 22 to 64% of total Cd was in the mobile fraction (sum of Fl to F3), while the corresponding values for Cu, Pb and Zn in this fractions were 2 to 23% suggesting higher mobility of Cd than other three metals. The single extraction procedures are simple and easy to perform and obtained results are comparable with sequential extraction procedure.     

Geochronological and geochemical constraints on the genesis of the Tieshan complex in the Edong district,Eastern China with implications for Fe and Cu skarn mineralization

Fe and Cu skarn deposits constitute the most important skarn type worldwide, whereas the controlling factors that lead to the difference in metal associations remain not well known. The Fe- and Cu-hosting Tieshan complex in the Edong district provides a good opportunity for comparative study on the genetic differences between Fe and Cu skarn deposits. In this study, integrated studies of geochronology, geochemistry and Sr-Nd-Hf isotope compositions were conducted on the complex. LA-ICP-MS zircon U-Pb dating results show that the Tieshan complex was emplaced in the time interval of 135 ± 3 to 144 ± 1 Ma. Multiphase rocks from the complex can be broadly subdivided into two suites. The Fe-Cu-related suite, which consists of diopside diorite, quartz diorite, quartz diorite porphyrite and porphyritic granodiorite, possesses low SiO₂ (53.5–67.1 wt.%), K₂O (2.44–3.53 wt.%) and Rb (45−83 ppm) contents, but high Sr (1132−2684 ppm), Ba (1073−1656 ppm) contents and negligible Eu anomalies, with very high Sr/Y (>90) ratios, similar to typical high Ba-Sr granitoids. The rock suite has initial ⁸⁷Sr/⁸⁶Sr values of 0.70648 to 0.70737, ε_Nd(t) values of −12.3 to −8.2 and ε_Hf(t) values of −16 to −7, comparable to values of the Early Cretaceous mafic rocks in the Edong district and adjacent areas, indicating that it might be largely derived from an enriched lithospheric mantle source, along with minor involvement of lower-crustal components. By contrast, the Fe-related suite, which is composed of quartz diorite, quartz diorite porphyrite and granodiorite porphyry, is characterized by relatively high SiO₂ (63.0–71.0 wt.%) and K₂O contents (3.36–5.53 wt.%), and a wide range of Sr (158−1135 ppm), Ba (762−1366 ppm) contents and Sr/Y (11–99) ratios. In combination with the presence of abundant inherited zircon grains, the lower ε_Nd(t) (−12.4 to −9.3) and ε_Hf(t) (−25 to −15) values indicate a greater degree of lower-crustal contribution for the Fe-related suite. In addition, the calculated zircon Ce (Ce/Ce* and Ce⁴⁺/Ce³⁺) and Eu (Eu/Eu*) anomalies suggest that the Fe-Cu-related suite has much higher oxygen fugacity (fO₂) than the Fe-related suite. This study highlights fO₂ and fractionation degree of magma as useful indicators for differentiating Fe and Cu skarn mineralization.     

土壤铁锰氧化物结合态元素提取技术在内蒙古新巴尔虎右旗头道井铜金矿地球化学勘查中的应用试验

针对常规地球化学方法在水系不发育而风成砂较发育的内蒙古丘陵草原覆盖区找矿效果均不理想的问题,以新巴尔虎右旗头道井铜金矿为试验研究区,开展土壤样品中的铁锰氧化物结合态地球化学找矿试验.采用等离子体质谱法、原子荧光光谱法和无火焰原子吸收光谱法配套测试土壤铁锰氧化物结合态的元素含量,利用面积性试验对比矿体上方和外围土壤铁锰氧化物结合态的元素异常特征,圈定并发现了新的隐伏金矿体.结果 表明,本次土壤铁锰氧化物结合态元素分析测试方法的精确度和准确度满足地球化学找矿的需求;土壤铁锰氧化物结合态可有效圈定找矿靶区,寻找隐伏金矿.本试验是一项成功的找矿案例,可为该类丘陵草原覆盖区开展地球化学找矿活动提供借鉴.