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1.
Weathering reactions producing and consuming acid in fresh waste rock samples from the Aitik Cu mine in northern Sweden have been investigated. Batch-scale (0.15 kg) acid titrations with waste rock of different particle sizes were operated for 5 months. The pH was adjusted to a nearly constant level, similar to that in effluents from waste rock dumps at the site (pH near 3.5). The reactions were followed by analysing for all major dissolved elements (K, Na, Mg, Ca, Si, Al, SO4, Cu, Zn, Fe) in aliquots of solution from the reaction vessels. In addition, the solids were physically and chemically characterised in terms of mineralogy, chemical composition, particle size distribution, surface area and porosity. The results show that the alkalinity production is initially dominated by a rapid dissolution of small amounts of calcite and rapidly exchangeable base cations on silicate surfaces. Steady-state dissolution of primary silicate minerals also generates alkalinity. The total alkalinity is nearly balanced by input of acid from the steady-state oxidation of sulphides, such that the pH 3.1–3.4 can be maintained without external input of acid or base. There is a large difference in weathering rates between fine materials and larger waste rock particles (diameters (d) >0.25 mm) for both sulphides and silicates. As a result particles with d smaller than 0.25 mm contribute to approximately 80% of the sulphide and silicate dissolution. Calcite dissolution can initially maintain a neutral pH but with time becomes limited by intra-particle diffusion. Calcite within particles larger than 5–10 mm reacts too slowly to neutralise the acid produced from sulphides.  相似文献   

2.
The Aitik Cu–Au–Ag deposit is located in northern Sweden and is hosted by strongly deformed 1.9 Ga Svecofennian volcano-sedimentary rocks. The main copper mineralization, which occurs as disseminations and veinlets, is hosted by garnet–biotite schist. Subeconomic mineralization in the footwall to the ore is hosted by feldspar–biotite–amphibole gneiss and porphyritic quartz monzodiorite. The deposit has been affected by post-mineralization metamorphic and igneous activity. Fluid inclusions in six samples of copper-mineralized quartz veins record the presence of three different fluid populations. The main ore was deposited from an aqueous, highly saline (31–37 eq. wt% NaCl + CaCl2) fluid. This fluid was trapped in inclusions intimately associated with the main chalcopyrite mineralization. Later bornite deposition took place from a less saline (18–27 eq. wt% NaCl + CaCl2), aqueous fluid. A third fluid composed of almost pure CO2, interacted with the copper-rich system during a post-ore event. The Aitik Cu–Au–Ag deposit shares some features with both porphyry-type and Fe-oxide–Cu–Au deposits. A high calcium content of the ore fluids, similar to other Cu–Au deposits in northern Scandinavia, suggests a contribution to the salinity of the mainly magmatic-hydrothermal fluids from evaporitic rocks in stratigraphically lower units.  相似文献   

3.
The formation of iron sulphide minerals exerts significant control on the behaviour of trace elements in sediments. In this study, three short sediment cores, retrieved from the remote Antinioti lagoon (N. Kerkyra Island, NW Greece), are investigated concerning the solid phase composition, distribution, and partitioning of major (Al, Fe) and trace elements (Cd, Cu, Mn, Pb, and Zn). According to 210Pb, the sediments sampled correspond to depositions of the last 120 years. The high amounts of organic carbon (4.1–27.5%) result in the formation of Fe sulphides, predominantly pyrite, already at the surface sediment layers. Pyrite morphologies include monocrystals, polyframboids, and complex FeS–FeS2 aggregates. According to synchrotron-generated micro X-ray fluorescence and X-ray absorption near-edge structure spectra, authigenically formed, Mn-containing, Fe(III) oxyhydroxides (goethite type) co-exist with pyrite in the sediments studied. Microscopic techniques evidence the formation of galena, sphalerite and CuS, whereas sequential extractions show that carbonates are important hosts for Mn, Cd, and Zn. However, significant percentages of non-lattice held elements are bound to Fe/Mn oxyhydroxides that resist reductive dissolution (on average 60% of Pb, 46% of Cd, 43% of Zn and 9% of Cu). The partitioning pattern changes drastically in the deeper part of the core that is influenced by freshwater inputs. In these sediments, the post-depositional pyritization mechanism, illustrated by overgrowths of Fe monosulphides on pre-existing pyrite grains, results in relatively high degree of pyritization that reaches 49% for Cd, 66% for Cu, 32% for Zn and 7% for Pb.  相似文献   

4.
Chemical weathering rates and erosionrates of granitic till in northern Sweden have beenestimated. The present-day chemical weathering rate iscompared with the long-term average weathering ratesince the last deglaciation approximately 8,700 yearsago. Also, the present-day release rates of major andtrace elements due to chemical weathering are comparedwith the mobility of these elements in a spodosolprofile as shown by soil water samples from the vadozezone. The estimation of the past weathering rate isbased on elemental depletion trends in a soil profile(typic haplocryod), whereas the present weatheringrate is based on elemental input/output budgets in asmall catchment (9.4 km2). The long-term averagechemical erosion rate, expressed as the sum of majorelement oxides (SiO2, Al2O3, CaO,Fe2O3, K2O, MgO, MnO, Na2O,P2O5, TiO2), was estimated to be4.9 gm-2 yr-1. The long-term base cation(Ca2+, Mg2+, Na+, K+) depletionwas 0.325 keq ha-1 yr-1. The currentchemical erosion rate was estimated to be2.43.0 g -2 yr-1, which is at least an order ofmagnitude higher than the rate of physical erosion,and the base cation flux due to chemical weathering is0.356–0.553~keq ha-1 yr-1. However,0.074 keq ha-1 yr-1 of this flux may be related tocation exchange processes induced by atmospheric inputof acid rain. There is no evidence for any recentlyincreased weathering rate of silicates in this area.The inputs of Cd, Cu, Ni and Zn exceed the outputs,and hence, these elements are currently accumulatingin the soil.There is a distinct seasonal variation in thechemical composition of the soil water. Results fromthe soil water samples show that Na, followed by Siand S (Cl was not measured), are the most mobileelements in the spodosol profile between the E-horizonand the C-horizon, and that Al and Fe were the leastmobile elements. However, there is no simplerelationship between the mobility of an element in thespodosol profile and the current release rate due toweathering of that element. This fact may haveimplications for the validity of the comparisonbetween the past and present weathering rates asperformed in this study.  相似文献   

5.
The degree of metal contamination (Zn, Pb, Cu, Ni, Cd) has been investigated in the vicinity of an old unmonitored municipal landfill in Prague, Czech Republic, where the leachate is directly drained into a surface stream. The water chemistry was coupled with investigation of the stream sediment (aqua regia extract, sequential extraction, voltammetry of microparticles) and newly formed products (SEM/EDS, XRD). The MINTEQA2 speciation-solubility calculation showed that the metals (Zn, Pb, Cu, Ni) are mainly present as carbonate complexes in leachate-polluted surface waters. These waters were oversaturated with respect to Fe(III) oxyhydroxides, calcite (CaCO3) and other carbonate phases. Three metal attenuation mechanisms were identified in leachate-polluted surface waters: (i) spontaneous precipitation of metal-bearing calcite exhibiting significant concentrations of trace elements (Fe, Mn, Mg, Sr, Ba, Pb, Zn, Ni); (ii) binding to Fe(III) oxyhydroxides (mainly goethite, FeOOH) (Pb, Zn, Cu, Ni); and (iii) preferential bonding to sediment organic matter (Cu). These processes act as the key scavenging mechanisms and significantly decrease the metal concentrations in leachate-polluted water within 200 m from the direct leachate outflow into the stream. Under the near-neutral conditions governing the sediment/water interface in the landfill environment, metals are strongly bound in the stream sediment and remain relatively immobile.  相似文献   

6.
The Batu Hijau porphyry copper-gold deposit, Sumbawa Island, Indonesia   总被引：4，自引：0，他引：4  
The Batu Hijau porphyry Cu---Au deposit lies in southwest Sumbawa Island, Indonesia. It is a world-class porphyry Cu deposit in an island are setting, and is typical of this deposit type in most features, including igneous association, morphology, hydrothermal alteration and mineralisation style.The region was not previously recognised as a porphyry Cu province; disseminated Cu sulphides were first recognised in float samples in southwest Sumbawa in 1987. Associated stream sediment sampling identified a broad area of anomalous Au and Cu in an area of greater than 5 km2 around Batu Hijau, including 169 ppb Au in BLEG samples and 580 ppm Cu in stream silts 1 km from the deposit. Mineralisation in bedrock at surface contains > 0.1 wt % Cu and > 0.1 ppm Au over an area of 0.6 km × 1.2 km, including a zone 300 m × 900 m containing > 0.3 wt % Cu. Areas with elevated Mo (> 30 ppm) form a distinctive annulus around this Cu-rich zone.Batu Hijau mineralisation is hosted in a tonalite intrusive complex, and diorite and metavolcanic wallrocks. There are no post-mineralisation igneous intrusions or breccia pipes within the deposit. The main tonalite intrusion forms a stock in the centre of the deposit, where it generally displays intensely pervasive potassic (biotite with magnetite-quartz) alteration and hosts most of the higher grade mineralisation. Younger tonalite dykes intruding the centre of this stock are generally less altered and mineralised than the older tonalite.The core zone of potassic alteration grades outward into extensive propylitic alteration (chlorite-epidote), with both variably overprinted by widespread fracture controlled intermediate argillic alteration (sericite-chlorite), and minor phyllic (sericite-pyrite) and sodic (albite) alteration. Argillic (sericite-kaolinite) and advanced argillic (kaolinite-alunite-pyrophyllite) assemblages occur near surface.Copper and Au grades within the orebody show a positive correlation with quartz stockwork intensity, although disseminated Cu sulphides are also common. Chalcopyrite and bornite are the principle hypogenal minerals, with minor chalcocite. Oxidation extends to a depth of 5 m to 85 m below surface across the deposit, and is underlain by weak supergene mineralisation. Drill testing of the deposit down to 650 m below surface reveals a single cylindrical to conical orebody of 334 million tonnes grading 0.8 wt % Cu and 0.69 gm per tonne Au; the depth extent of mineralisation is unknown.  相似文献   

7.
《Applied Geochemistry》1994,9(5):583-595
A steady-state geochemical model has been developed to study water-rock interactions controlling metal release from waste rock heaps at the Aitik Cu mine in northern Sweden. The Cu release in drainage waters from the site is of environmental concern. The waste rock heaps are treated as single completely mixed flow-through reactors. The geochemical model includes kinetices of sulphide and primary silicate mineral weathering, heterogeneous equilibrium with secondary mineral phases and speciation equilibrium. Field monitoring of drainage water composition provides a basis for evaluation of model performance.The relative rate of oxidative weathering of sulphides and dissolution of primary silicate minerals, using published kinetic data, are consistent with net proton and base cation fluxes at the site. The overall rate of Fe2+ oxidation within the heap is three orders of magnitude faster than that which could be explained by surface-catalysed reaction kinetics. This suggests significant activity of iron-oxidizing bacteria. The absolute weathering rates of sulphides and silicate minerals, normalized to a measured BET surface area, are approximately two orders of magnitude lower at field scale than published rates from laboratory experiments. Because of the relative absence of carbonate minerals, the weathering of biotite and plagioclase feldspar are important sources of alkalinity.  相似文献   

8.
Salts produced using brines of the Mamfe Basin were analysed by XRD for their mineral composition and ICP-MS for minor element composition. Halite (NaCl) and dolomite (CaMg (CO3)2) constitute the major minerals with minor impurities from Mo and Cd in the chlorides and Sc and Cu in the carbonates. The mineral composition is evidence of dissolution of evaporites with parent brine of marine origin. Other elements analysed are suggested to be adsorbed to these salts and result from water–rock interaction. The elements partitioned based on their correlation to other elements are suggested to derive from sulphates including barite for Ba, sulphides for Pb, Zn, silicates for Zr, Mn and oxides for V, Cr. The electrical conductance of the brines is related to the salt yield by the equation; M = 9 × 10− 4E− 3.27, and it can be used to estimate salt yield throughout the year. Over 1200 tons of salt consisting dominantly of grade I halite are lost annually as brines across the basin. Purification is required for some minor elements including Ba, Pb, Hg and Cd for use as a condiment. A genetic relation between the parent brine, sulphide minerals and organic matter-rich sediments is proposed.  相似文献   

9.
《Applied Geochemistry》2001,16(7-8):759-780
A multi-medium, multi element regional geochemical survey has been carried out in an 188,000 km2 area in the Central Barents Region, Finland, Norway and Russia. Four different sample materials (terrestrial moss, O-, B- and C-horizons of podzol) were collected at the same sites throughout the area at a density of 1 site/300 km2. While moss predominantly reflects the atmospheric input of elements, the O-horizon reflects the complex interplay between atmosphere, biosphere and lithosphere. The B-horizon can be used to study the influence of soil-forming processes, while the C-horizon represents the composition of the lithosphere at each sample site and thus the geogenic background. The concentration, variation and correlation between 24 elements (Ag, Al, As, Ba, Bi, Ca, Cd, Co, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, S, Si, Sr, Th, V, Zn) analysed with similar techniques in all 4 materials are compared. Some rare trace elements (Ag, As, Bi, Cd, Pb) appear to be considerably more enriched in the O-horizon of podzols than the main pollutants in the survey area (Ni, Cu, Co from the Russian nickel industry in Monchegorsk and Nikel-Zapoljarnij). Biological processes play an underestimated role in determining regional geochemistry at the earth's surface.  相似文献   

10.
Framboidal pyrite has been prepared by precipitation of oxyhydroxides of iron, peptized by humic acids using a solution of Na-sulphate or hydrogen sulphide, spherical grains of elemental sulphur being present. By peptization of iron oxyhydroxides using humic acids, a stable negatively charged colloidal system arises. At room temperature and a pressure of 1 atm., and at pH widely ranging between 6.5–7.5, sulphidation of this colloidal system gives rise to a monodispersive sulphidic sol whose stability depends on the concentration of iron in the solution, the amount of humic acids and the presence of electrolytes. In the presence of spherical grains of sulphur, arising by rapid oxidation (acidification) of Na2S solution or a saturated solution of hydrogen sulphide, particles of the sulphidic sol precipitate on their surface and the grains become gradually replaced by sulphides of iron. At the same time, framboids of an average diameter of 14 μm are generated.  相似文献   

11.
The Rio Tinto in SW Spain drains Cu and pyrite mines which have been in operation since at least the Bronze Age. Extensive metal mining, especially from 1873 to 1954, has resulted in contamination of the Rio Tinto alluvium with As, Cu, Pb, Ag and Zn. X-ray diffraction (XRD), wavelength-dispersive X-ray mapping, scanning electron microscope petrography and X-ray energy-dispersive (EDX) analysis has revealed that 4 major groups of contaminant metal and As-bearing minerals, including sulphides, Fe-As oxides, Fe oxides/hydroxides/oxyhydroxides, and Fe oxyhydroxysulphates, occur in the alluvium. Sulphide minerals, including pyrite, chalcopyrite, arsenopyrite and sphalerite, occur in alluvium near the mining areas. Iron hydroxides and oxyhydroxides such as goethite and possibly ferrihydrite occur in cements in both the mining areas and alluvium downstream, and carry minor amounts of As, Cu and Zn. Iron oxyhydroxysulphates, including jarosite, plumbojarosite and possibly schwertmannite, are the most common minerals in alluvium downstream of the mining areas, and are major hosts of Cu, Pb, Zn and of As, next to the Fe-As minerals. This work, and other field observations, suggest that (1) the extreme acidity and elevated metal concentrations of the river water will probably be maintained for some time due to oxidation of pyrite and other sulphides in the alluvium and mine-waste tips, and from formation of secondary oxide and oxyhydroxysulphates; (2) soluble Fe oxyhydroxysulphates such as copiapite, which form on the alluvium, are a temporary store of contaminant metals, but are dissolved during periods of high rainfall or flooding, releasing contaminants to the aqueous system; (3) relatively insoluble Fe oxyhydroxysulphates and hydroxides such as jarosite and goethite may be the major long-term store of alluvial contaminant metals; and (4) raising river pH will probably cause precipitation of Fe oxyhydroxides and oxides/hydroxides/oxyhydroxides and thus have a positive effect on water quality, but this action may destabilise some of these contaminant metal-bearing minerals, releasing metals back to the aqueous system.  相似文献   

12.
The Aitik Cu–Au–Ag deposit in the Gällivare area in northern Sweden is Sweden's largest sulphide mine with an annual production of 35 Mt of ore, and the biggest open pit operation in northern Europe. It is proposed in the present study that the Aitik deposit represents a Palaeoproterozoic, strongly metamorphosed porphyry copper deposit that was affected ca. 100 Ma later by a regional IOCG-type hydrothermal event. Consequently, the Aitik deposit might represent a mixed ore system where an early copper mineralisation of porphyry type has been overprinted by later regional IOCG mineralisation.Several attempts have previously been made to genetically classify the Aitik Cu–Au–Ag deposit as a distinct ore type. New geochemical, petrographic, structural, and fluid inclusion results combined with published data have provided the opportunity to present new ideas on the genesis and evolution of the Aitik Cu–Au–Ag deposit. The emplacement of a ca. 1.9 Ga quartz monzodiorite that host the ore at Aitik was related to subduction processes and volcanic arc formation, and synchronous with quartz vein stockwork formation and porphyry copper mineralisation. Highly saline aqueous (38 wt.% NaCl) fluid inclusions in the stockwork veins suggest entrapment at 300 °C and a pressure of nearly 3 kbar, a high pressure for a typical porphyry copper ore, but consistent with conditions at associated deep root zones of intrusion-related magmatic–hydrothermal systems. The highly saline fluid formed disseminated and vein-type ore of mainly chalcopyrite and pyrite within comagmatic volcaniclastic rocks, and caused potassic alteration (biotite, microcline) of the host rocks. The early porphyry copper mineralising event was followed, and largely overprinted, by CO2 and aqueous medium- to high-salinity (16–57 wt.% salts) fluids related to a ca. 1.8 Ga tectonic and metamorphic event (peak conditions 500–600 °C and 4–5 kbar). Extensive deformation of rocks and redistribution of metals occurred. Magnetite enrichment locally found within late veins, and late amphibole–scapolite and K feldspar alterations within the deposit, are some of the features at Aitik implying that aqueous fluids responsible for IOCG-mineralisation (200–500 °C and ~ 1 kbar) and extensive Na–Ca alteration in the region during the 1.8 Ga tectonic event also affected the Aitik rocks, possibly leading to addition of copper ± gold.  相似文献   

13.
Distinct anomalies of Cu and Ni in stream alluvium and soil are associated with the Gladesville norite, but are generally not related to significant mineralization. The origin of one of the soil anomalies was investigated by determining partitioning relationships of Cu and Ni in outcrop samples, B-horizon soil samples, and a soil profile sample utilizing selective leaching techniques and electron microprobe analyses.Silicate minerals and spinel are important controls of both Cu and Ni distribution in the outcrop samples. Sulfides are a minor residence site of Ni but an important residence site of Cu. In soil, scavenging of Cu by montmorillonite has been important. Disintegration of montmorillonite in the B-horizon leaves residual minerals as an important and probably dominant control of Cu distribution in the upper part of the soil. Iron oxide particle coatings contain more Ni (46%) than any other single material in the B-horizon soil samples but contain only 21% of the Cu.Certain characteristics of the investigated Cu and Ni soil anomaly may be significant in future exploration as indicators of “false” anomalies. These include areal anomaly distribution patterns, soil/bedrock metal ratios, and the tendency of each metal to reside principally in a single soil component.  相似文献   

14.
Sulphur isotopic compositions of copper and iron sulphides (dispersed and vein mineralization) from the Polish part of the Kupferschiefer were determined and compared with data from the literature. Most of the δ34S values of sulphides range from about -40 to -25%, indicating sulphide precipitation during bacterial sulphate reduction in an open system which gradually chanes into a closed system. Sulphides from veins are usually enriched in 34S compared to finely dispersed mineralization and were probably formed in a more closed system. Copper sulphides are generally a few permil heavier than pyrite. Coupled with detailed microscopical observations the isotope data suggest that the mineralization is either syngenetic or early diagenetic.  相似文献   

15.
Fourteen stratiform, stratabound and vein-type sulphide occurrences in the Upper Allochthon of the Central–North Norwegian Caledonides have been studied for their sulphur, oxygen and hydrogen isotope composition. Depositional ages of host rocks to the stratabound and stratiform sulphide occurrences range from 590 to 640?Ma. The sulphides and their host rocks have been affected by polyphase deformation and metamorphism with a peak temperature of 650?°C dated to 432?Ma. A total of 104 sulphide and 2 barite samples were analysed for δ34S, 16 whole-rock and quartz samples for δ18O and 12 samples of muscovite for δD. The overall δ34S values range from ?14 to +31‰ with the majority of sampled sulphides lying within a range of +4 to +15‰. In most cases δ34S within each hand specimen behaves in accordance with the equilibrium fractionation sequence, δ34Sgn<δ34Scp<δ34Ssph<δ34Spy. A systematic increase in δ34S from the vein sulphides (?8‰) through schist/amphibolite-hosted (+6‰) and schist-hosted (+7 to +12‰) to dolomite-hosted (+12 to +31‰) occurrences is documented. The δ34S averages of the stratiform schist-hosted sulphides are 17 to 22‰ lower than in the penecontemporaneous seawater sulphate. The Bjørkåsen (+4 to +6‰) occurrence is a volcanogenic massive sulphide (VMS) transitional to sedimentary massive sulphide (SMS), exhalative, massive, pyritic deposit of Cu–Zn–Pb sulphides formed by fluids which obtained H2S via high-temperature reduction of seawater sulphate by oxidation of Fe2+ during the convective circulation of seawater through underlying rock sequences. The Raudvatn, volcanic-hosted, disseminated Cu sulphides (+6 to +8‰) obtained sulphur via a similar process. The Balsnes, stratiform, ‘black schist’-hosted, pyrite–pyrrhotite occurrence (?6 to ?14‰) is represented by typical diagenetic sulphides precipitated via bacteriogenic reduction of coeval (ca. 600?Ma) seawater sulphate (+25 to +35‰) in a system open to sulphate supply. The δ34S values of the Djupvik–Skårnesdalen (+7 to +12‰), Hammerfjell (+5 to 11‰), Kaldådalen (+10 to +12‰) and Njallavarre (+7 to +8‰) stratiform, schist-hosted, massive and disseminated Zn–Pb (±Cu) sulphide occurrences, as well as the stratabound, quartzite-hosted, Au-bearing arsenopyrite occurrence at Langvatnet (+7 to +11‰), suggest that thermochemically reduced connate seawater sulphate was a principal sulphur source. The Sinklien and Tårstad, stratabound, dolomite- and dolomite collapse breccia-hosted, Zn (±Cu–Pb) sulphides are marked by the highest enrichment in 34S (+20 to +31‰). The occurrences ?are?assigned to the Mississippi-Valley-type deposits.?High δ34S values require reduction/replacement of contemporaneous (ca. 590?Ma) evaporitic sulphate (+23 to +34‰) with Corg-rich fluids in a closed system. The Melkedalen (+12 to +15‰), stratabound, fault-controlled, Cu–Zn sulphide deposit is hosted by the ca. 595?Ma dolomitised Melkedalen marble. The deposit is composed of several generations of ore minerals which formed by replacement of host dolomite. Polyphase hydrothermal fluids were introduced during several reactivation episodes of the fault zone. The positive δ34S values with a very limited fractionation (<3‰) are indicative of the sulphide-sulphur generated through abiological, thermochemical reduction of seawater sulphate by organic material. The vein-type Cu (±Au–W) occurrences at Baugefjell, Bugtedalen and Baugevatn (?8 to ?4‰) are of hydrothermal origin and obtained their sulphur from igneous sources with a possible incorporation of sedimentary/diagenetic sulphides. In a broad sense, all the stratiform/stratabound, sediment-hosted, sulphide occurrences studied formed by epigenetic fluids within two probable scenarios which may be applicable separately or interactively: (1) expulsion of hot metal-bearing connate waters from deeper parts of sedimentary basins prior to nappe translation (late diagenetic/catagenetic/epigenetic fluids) or (2) tectonically driven expulsion in the course of nappe translation (early metamorphic fluids). A combination of (1) and (2) is favoured for the stratabound, fault-controlled, Melkedalen and Langvatnet occurrences, whereas the rest are considered to have formed within option (1). The sulphides and their host rocks were transported from unknown distances and thrust on to the Fennoscandian Shield during the course of the Caledonian orogeny. The displaced/allochthonous nature of the Ofoten Cu–Pb–Zn ‘metallogenetic province’ would explain the enigmatically high concentration of small-scale Cu–Pb–Zn deposits that occur only in this particular area of the Norwegian Caledonides.  相似文献   

16.
 The major aim was to increase our knowledge on the behaviour of Al, Co, Cr, Cu, Fe, Mn, Ni and V in sulphide-bearing fine-grained sediments exposed to atmospheric oxygen. Samples of this type of sediment collected in a previous investigation at eight sites in western Finland were digested in HClO4-HNO3-HCl-HF at 200  °C and in HCl:HNO3:H2O at 95  °C (aqua regia), and subjected to extractions with ammonium acetate and hydrogen peroxide. Metals and S in the leachates were determined with ICP-AES. The results of the chemical analyses are compared with previously reported experimental data. The concentrations of Al and Fe in the sulphide-bearing fine-grained sediments are about 7% and 5%, respectively. Of the trace metals studied, Mn is most abundant followed in decreasing order by V>Cr>Ni>Cu>Co. On oxidation of the sediments, high proportions of Co, Mn and Ni, intermediate proportions of Cu but low proportions of Fe, Al, Cr and V are released. The extent of the release of a metal on oxidation is controlled either by (1) the level to which the pH of the sediments drops on oxidation (Al, Cu, Cr, V), (2) the amount of the metal associated with easily reduced phases (metal sulphides) in the sediments (Ni, Co) or (3) the sum of the amount associated with reduced phases and adsorbed on soil compounds (Mn). No control of the release of Fe on oxidation of the sediments was identified. Based on the results of the study it is argued that artificial drainage and the subsequent oxidation of sulphide-bearing sediments will result in extensive leaching of Co, Mn and Ni, moderate leaching of Cu and limited leaching of Cr and V into drainages. The major elements, Fe and Al, have the potential to be mobilised and leached in large amounts, though the proportions mobilised/leached will remain low. It is suggested that the identification of sulphide-bearing sediments with a high potential of metal release should be based on determination of metals in easily mobilised reduced compounds (dissolved e.g. in H2O2) and of the level to which the pH of the sediments drops on oxidation. Received: 16 October 1997 · Accepted: 9 March 1998  相似文献   

17.
Effect of chemical fertilizers (urea, NH4Cl, Ca(NO3)2, KCl and KH2PO4) on the fractionation of Cu, Cr and Ni was studied by a 4-month incubation experiment. Using sequential extraction procedure, it was found that the application of fertilizers could change the distribution of Cu, Cr and Ni in the fractions of soil. Applying urea (CO(NH2)2) significantly decreased the concentrations of Cu, Cr and Ni in water soluble plus exchangeable (WE) fraction, but increased those in Fe–Mn oxides bound (FM) fraction (p < 0.01). However, application of NH4Cl caused an increase in the WE fraction by 27.7% for Cu, 111.5% for Cr and 20.4% for Ni. The CO(NH2)2 raised the soil pH from 4.51 to 4.96, whereas NH4Cl lowered the pH of soil by 0.44 units. The WE fraction of the three heavy metals was significantly increased, while the FM fraction was significantly decreased by adding KCl (p < 0.01). Moreover, the supply of KH2PO4 reduced the WE and carbonate bound (CB) fractions of Cu, Cr and Ni in the soil, however, it raised Cu and Ni in the residual (RS) fraction and Cr in the FM fraction. In addition, the mobility index indicated that KCl and NH4Cl increased the mobility of Cu, Cr and Ni in the soil, whereas urea and KH2PO4 decreased the mobility of the three metals in the soil. These results suggest that applying chemical fertilizers does not only provide plant nutrients, but may also change the speciation and mobility of heavy metals in the soil.  相似文献   

18.
Analytical results for Pb-concentrations and isotopic ratios from ca. 150 samples of soil A horizon and ca. 145 samples of soil C horizon collected along a 4000-km east–west transect across the USA are presented. Lead concentrations along the transect show: (1) generally higher values in the soil A-horizon than the C-horizon (median 21 vs. 16.5 mg/kg), (2) an increase in the median value of the soil A-horizon for central to eastern USA (Missouri to Maryland) when compared to the western USA (California to Kansas) (median 26 vs. 20 mg/kg) and (3) a higher A/C ratio for the central to eastern USA (1.35 vs. 1.14). Lead isotopes show a distinct trend across the USA, with the highest 206Pb/207Pb ratios occurring in the centre (Missouri, median A-horizon: 1.245; C-horizon: 1.251) and the lowest at both coasts (e.g., California, median A-horizon: 1.195; C-horizon: 1.216). The soil C-horizon samples show generally higher 206Pb/207Pb ratios than the A-horizon (median C-horizon: 1.224; A-horizon: 1.219). The 206Pb/207Pb-isotope ratios in the soil A horizon show a correlation with the total feldspar content for the same 2500-km portion of the transect from east-central Colorado to the Atlantic coast that shows steadily increasing precipitation. No such correlation exists in the soil C horizon. The data demonstrate the importance of climate and weathering on both Pb-concentration and 206Pb/207Pb-isotope ratios in soil samples and natural shifts thereof in the soil profile during soil-forming processes.  相似文献   

19.
The Lumwana Cu (± Co ± U) deposits of NW Zambia are large, tabular, disseminated ore bodies, hosted within the Mwombezhi Dome of the Lufilian Arc. The host rocks to the Lumwana deposits are two mineralogically similar but texturally distinct gneisses, a granitic to pegmatitic gneiss and a banded to augen gneiss which both comprise quartz–feldspar ± biotite ± muscovite ± haematite ± amphibole and intervening quartz–feldspar ± biotite schist. The sulphide ore horizons are typically developed within a biotite–muscovite–quartz–kyanite schist, although mineralization locally occurs within internal gneiss units. Contacts between the ore and host rocks are transitional and characterized by a loss of feldspar. Kinematic indicators, such as S-C fabrics and pressure shadows on porphyroblasts, suggest a top to the north shear sense. The sulphides are deformed by a strong shear fabric, enclosed within kyanite or concentrated into low strain zones and pressure shadows around kyanite porphyroblasts. This suggests that the copper mineralization was introduced either syn- or pre-peak metamorphism. In addition to Cu and Co, the ores are also characterized by enrichments in U, V, Ni, Ba and S and small, discrete zones of uranium mineralization, occur adjacent to the hanging wall and footwall of the copper ore bodies or in the immediate footwall to the copper mineralization. Unlike typical Copperbelt mineralization, unmineralized units show very low background copper values. Whole rock geochemical analyses of the interlayered schist and ore schist, compared to the gneiss, show depletions in Ca, Na and Sr and enrichments in Mg and K, consistent with replacement of feldspar by biotite. The mineral chemistry of muscovite, biotite and chlorite reflect changes in the bulk rock chemistry and show consistent increases in X Mg as the schists develop. δ34S for copper sulphides range from +2.3?‰ to +18.5?‰, with pyrite typically restricted to values between +3.9?‰ and +6.2?‰. These values are atypical of sulphides precipitated by bacteriogenic sulphate reduction. δ34S data for Chimiwungo (Cu + Co) show a broader range and increased δ34S values compared to the Malundwe (Cu) mineralization. The Lumwana deposits show many characteristics which distinguish them from classical Copperbelt mineralization and which suggests that they are formed by metasomatic alteration, mineralization and shearing of pre-Katangan basement. Although this style of mineralization is reported elsewhere in the Copperbelt, sometimes associated with the more widely reported stratiform ores of the Lower Roan, none of the previously reported occurrences have so far developed the tonnages of ore reported at Lumwana.  相似文献   

20.
Samples of authigenic material, sediment overlying water and oxic surface sediment (0–0.5-cm depth) from a perennially oxygenated lacustrine basin were analysed to investigate which solid phases are important for binding a suite of trace elements (Ag, As, Ca, Cd, Cu, Hg, In, methylmercury (MeHg), Mg, Mo, Pb, Sb and Zn). The authigenic material, which was collected with inert Teflon sheets deployed for several years across the sediment–water interface, contained mainly poorly crystallized Fe oxyhydroxides and natural organic matter, presumably humic substances derived from the watershed. Manganese oxyhydroxides were not present in the collected authigenic material due to the slightly acidic condition (pH = 5.6) of the lake that prevents the formation and recycling of these compounds. Conditional equilibrium constants for the adsorption of cationic (KFe–M) and anionic (KFe–A) trace elements onto the authigenic Fe oxyhydroxides were estimated from their concentrations in the authigenic material and in bottom water samples. These field-derived values of KFe–M and KFe–A were compared with those predicted by the surface complexation model, using laboratory-derived intrinsic adsorption constants and the water composition at the study site. Equilibrium constants (KPOM–M) were also calculated for the adsorption of the cationic trace elements onto the humic substances contained in the diagenetic material. The field-derived values of KPOM–M were compared to those predicted by the speciation code WHAM 6 for the complexation of the trace elements by dissolved humic substances in the lake. Combining the results of the present study with those on the distributions of trace elements in the porewater and solid-phase sediments reported in previous studies at the same site, it was determined whether the trace elements bind preferentially to Fe oxyhydroxides or natural organic matter in oxic sediments. The main inferences are that the anionic trace elements As, Mo and Sb, as well as the cationic metal Pb are preferentially bound to the authigenic Fe oxyhydroxides whereas the other trace elements, and especially Hg and MeHg, are preferentially bound to the humic substances.  相似文献   

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