A history of the ‘Zambian copper flower', Becium centraliafricanum (B. homblei)

This contribution is a short history of the Zambian copper flower, Becium homblei (recently renamed B. centraliafricanum that has attracted attention as a plant associated with Cu-rich soils. It has a peculiar discontinuous distribution in Central Africa which has been explained in terms of biotype depletion. A field investigation into the ecology of the species shows that it is able to tolerate soil Cu concentrations of up to 15,000 μg/g (ppm), and soil nickel concentrations of nearly 5000 μg/g. B. homblei is also found on areas where soil metals are in trace quantities, and where soil bases, particularly Ca, are low. In spite of its tolerance to a wide range of edaphic conditions, the distribution of the species is very restricted in Zimbabwe, and this is almost certainly due to severe interspecific competition with a closely related species, B. obovatum, which is common on soils not unusually enriched in heavy metals. Pioneering work on geobotanical prospecting by use of Becium homblei was carried out by the late G. Woodward and others in the 1950s and 1960s. This species was used successfully for geobotanical prospecting for Cu. This present report is a brief history of these pioneering studies     

European species of Thlaspi L. (Cruciferae) as indicators of nickel and zinc

The analysis of herbarium specimens has shown that unusual metal uptake by European species of Thlaspi (Cruciferae, mustard family) is not confined to the well-known accumulation of zinc from calaminiferous soils. At least twelve species show unusual accumulation of nickel, to levels of 1000–30,000 μg/g (dry-mass basis), from serpentine or other nickel-rich substrates. In addition, accumulation of zinc to levels above 1000 μg/g in the dry mass of the plant is widespread; about three-quarters of the European species, from a wide variety of soil types, have been found to exhibit this behaviour in the natural state. These observations are significant in many fields, including taxonomy, plant physiology and phytochemistry, but are particularly important in extending the potential of biogeochemical methods of mineral exploration.     

The use of plants in prospecting for gold: A brief overview with a selected bibliography and topic index

The focal point of this report is a bibliography of 133 references and an associated topic index — both of which could be useful to geochemists attempting to locate new Au deposits. Fifty of these references originated in the Soviet Union, where most of the initial work on biogeochemical exploration for Au had been done. The 15 topics in the index range from agriculture (Au in crop plants) to silver.As an introduction to the bibliography, we have briefly described some examples of applications and difficulties in using plants. These examples are drawn from the literature and from field experience. Because of the generally low Au concentrations found in plants, the analysis of plant tissue is critical to the successful application of the biogeochemical method of prospecting. Neuron activation analysis is the most widely used method to detect Au in plants, due largely to its sensitivity; levels in the parts per billion range are easily attained. Two general types of sampling media are used in prospecting for Au: humus and living plants. Humus has been widely used in Canada, but the sampling of plants has increased there and elsewhere in recent years. Our use of douglas-fir (Pseudotsuga menziesii) at a Au-bearing stockwork in Idaho is a prime example. A maximum Au concentration of 14 μg/g (ppm) was detected in the wood ash of this coniferous tree, well above the normal concentration of ≈ 0.15 μg/g. Among shrubs that might be useful in Au prospecting, we recommend sagebrush or wormwood (genus Artemisia), because it is extremely responsive to concealed mineralization. It has been used extensively in the Soviet Union and could be used in areas of the western United States where disseminated Au occurrences might be located.Among the problems one may encounter in using plants for Au prospecting are: (1) physiological barriers, by which many plant species simply do not absorb Au at detectable levels; (2) misconceptions of soil-plant correlations; (3) localization of Au in plant tissue; and (4) the variation of Au concentrations due to season. Despite these limitations, biogeochemical techniques can complement or replace other geochemical methods currently used.     

A biogeochemical orientation survey in the Moisan gold-mineralized area, Haenam district in Korea

A biogeochemical orientation survey was carried out in the vicinity of an epithermal Au deposit in the Moisan Au–Ag mineralized area, Haenam district in Korea. The Au–Ag bearing quartz veins of the mine occur as narrow open-space fillings within Cretaceous silicic pyroclastics. The vein minerals consist mainly of quartz, sericite, pyrite, chalcopyrite, and galena, with some electrum and argentite. The main objectives of this study were to study the geochemical characteristics of rocks, soils and plants in this area, to investigate the spatial relationship between Au and associated elements in rock–soil–plant system, and to evaluate the applicability of biogeochemical prospecting for Au vein occurrences in Korea. Samples of rocks and soils, and leaves of three plant species (Japanese red pine — P. densiflora, oriental white oak — Q. aliena, Japanese mallotus — M. japonicus) were collected from the target mineralized area and control barren locations, and analyzed for trace elements by instrumental neutron activation analysis. Sampling lines were composed of one slope line which is almost parallel to the mineralized quartz-veins, and four transect lines spaced 100 m apart across the veins at 20 m sampling intervals. From the multi-element data of rock samples (n = 9), high values of Au (maximum 2030 ppb) are spatially related to Au–quartz veins. Soil samples (n = 61) collected from five sampling lines show higher values of Au (24–825 ppb) whereas soil samples from the control locations have lower values of Au (below 25 ppb). Many plant species collected from the vicinity of the veins have high Au contents compared with those at the control locations, but the ranges of Au values are variable among plant species. In a total of 128 samples of plant leaves, Q. aliena yielded Au values of 0.4 to 6.9 ppb, and M. japonicus 0.9 to 4.1 ppb. Gold contents in P. densiflora ranged from 0.1 to 5.6 ppb. Plant leaves from control areas show less than 1.6 ppb Au. The biological absorption coefficient (BAC) of Au in plants decreases in the order of Q. aliena > M. japonicus > P. densiflora. Based on the results of the study, Q. aliena appeared to be the best sampling media for biogeochemical prospecting of Au in the study area.     

Biogeochemistry, a prospecting tool in the search for mercury mineralization

Summary of biogeochemical prospecting for mercury mineralization in the Pinchi Fault is given. One thousand two hundred and eight plant samples were collected and analyzed for mercury. In mineralized areas the typical mercury content of dried plants was not less than 0.2 and 0.4 μg/g and even concentrations between 0.6 and 1.6 μg/g were observed. In nonmineralized zones at least 90% of the plants contained no more than 0.15 μg/g of mercury. Analytical and sampling procedures are described.     

Free and bound lipids in recent (1835–1987) sediments from Santa Barbara Basin

In order to study the first steps of incorporation of lipids in recent organic-rich sediments into free and bound fractions, we have selected the Santa Barbara Basin, off California. This basin with a maximum of 590 m water depth is characterized by high phytoplankton production in surface waters and a low oxygen content in bottom waters. Sediments show the following features: high sedimentation rate ≈ 4 mm/yr, no bioturbation, and development of a bacterial mat community at the surface with predominance of sulphur-oxidizing bacteria trapping particles, thus preventing re-distribution of sediment, which permit a unique observations of organic sedimentation on a new few years basis.A sediment core has been divided into 2 cm thick slices corresponding to a time resolution of ≈5 years, from 1835 up to 1987. Samples have been analyzed using a multi-parameter approach, such as for plankton species identification, carbon stable isotope ratios and, as reported here, for lipid organic tracers. Organic tracers have been analyzed in the sterol and fatty series for both free and bound compounds by gas chromatography and gas chromatography/mass spectrometry.The incorporation processes of sterols with depth appear different for free and bound compounds. Total free sterol concentrations show high values in surface sediments (≈ 100 μg/g dry sediment), rapidly decrease up to ≈ 10 cm depth and remain at a constant value of 30–40 μg/g. Total bound sterol concentrations show low values in surface sediment (13.6 μg/g), and vary irregularly with depth up to a value of 55 μg/g at 7.3 m, and then remain constant at 25–26 μg/g.Profiles of evolution with depth of free C₂₇, C₂₈ sterols show a regular decrease, whereas C₂₉ sterols show an irregular decrease with anomalies at 7.3 cm (approximately age: 1977–1978) and at 14.1 cm (1962–1964). Profiles of bound compounds are rather different, very regular for C₂₈ sterols, irregular with oscillations for C₂₇ and C₂₉ sterols at 7.3, 12.2 and 18.0 cm (1954–1956), suggesting a different mode of incorporation and probably different inputs for C₂₇, C₂₉ and C₂₈ sterols.The study of the kinetics of degradation of sterols between surface (1987) and 10.5 cm (1968–1972) shows that C₂₇ compounds are degraded at a slight higher rate (0.53 μg/μg of initial C₂₇ concentration/ year) than are C₂₈ and C₂₉ compounds (0.047 μg/μg of initial concentration/year). An intermediate value is found for brassicasterol: 0.049 μg/μg/year.     

Salix acmophylla,Tamarix smyrnensis and Phragmites australis as biogeochemical indicators for copper deposits in Elazıǧ, Turkey

The flora of Maden Çayı valley grows in a soil medium which is heavily contaminated with Cu, Fe, Mn, Zn and other metals derived from waste discharges to the Maden Çayı (stream) from the Maden Cu Mining works. Soil, water and plant samples were collected from 47 sites (mostly along the Maden Çayı valley) and analysed for copper. In all the plant species, Cu was concentrated more in the twigs of the plants than in their leaves and flowers. Correlation coefficients (r) were calculated for the correlation between the concentrations of Cu in the twigs of plants and those of the corresponding soil. Statistics of correlation were as follows: Salix acmophylla r=0.93 (n=19, P<0.01), Tamarix smyrnensis r=0.93 (n=20, P<0.01) and Phragmites australis r=0.72 (n=18, P<0.01). Salix acmophylla, Tamarix smyrnensis and Phragmites australis are therefore good indicators of the copper concentrations in the soil and these species could be successfully used for biogeochemical prospecting. These species are typical and common species of the semi-arid Anatolian climate.     

Monitoring and modelling of the solid-solution partitioning of metals and As in a river floodplain redox sequence

For a period of 2 a, pore water composition in a heavily contaminated river floodplain soil was monitored in situ. Pore water samples were collected 12 times over all seasons in a profile ranging from aerobic to sulphidic redox conditions, and As, Cd, Cr, Cu, Pb, Zn, Mn, Fe, Ca, Cl, SO₄, DOC, IOC and pH were determined. The variability of pH, IOC, DOC and Ca was found to be rather small during the year and within the profile (rsd < 0.04, 0.16, 0.24 and 0.22, respectively). The temporal variability of the metal and As concentrations was small, too, whereas changes with depth were distinct. Under sulphidic conditions, concentrations were below 1 μg L⁻¹ (Cd, Cu, Pb) or 10 μg L⁻¹ (Zn, As). The data set was compared with results from a geochemical model that was fully parameterised from literature data and included equilibrium speciation, sorption and mineral dissolution. The general pattern of the solid–solution partitioning of Cd, Cu, Zn and As in the profile was predicted well by mechanistic geochemical modelling on the basis of solid phase composition. Metals strongly bound to organic matter such as Cd and Cu were predicted better than metals mainly present within a mineral. Detailed information regarding the presence of colloidal Fe and Mn in pore water might improve the prediction of the solid–solution partitioning of a number of metals. The study also indicates that the chemical behaviour of Pb is still not understood sufficiently.     

A preliminary investigation into the use of ochre as a remedial amendment in arsenic-contaminated soils

Ochre is an unwanted waste product that accumulates in wetlands and streams draining abandoned coal and metal mines. A potential commercial use for ochre is to remediate As contaminated soil. Arsenic contaminated soil (605 mg kg⁻¹) was mixed with different ochres (A, B and C) in a mass ratio of 1:1 and shaken in 20 mL of deionised water. After 72 h As concentration in solution was ca. 500 μg kg⁻¹ in the control and 1–2.5 μg kg⁻¹ in the ochre treated experiments. In a second experiment soil:ochre mixtures of 0.05–1:1 were shaken in 20 mL of deionised water for 24 h. For Ochres A and C, as solution concentration was reduced to ca. 1 μg kg⁻¹ by 0.2–1:1 ochre:soil mixtures. For Ochre B, as concentration only reached ca. 1 μg kg⁻¹ in the 1:1 ochre:soil mix. Sorption of As was best modelled by a Freundlich isotherm using As sorption per mass of goethite in the ochre (log K = 1.64, n = 0.79, R² = 0.76, p 0.001). Efficiency of ochre in removing As from solution increased with increasing total Fe, goethite, citrate dithionite extractable Fe and surface area.     

Anthropogenic noble-metal enrichment of topsoil in the Monchegorsk area, Kola Peninsula, northwest Russia

Eight catchments, an area of 15 to 35 km², have been studied within an ecogeochemical mapping programme in the western Kola Peninsula and contiguous parts of Finland and Norway. Three catchments, one northeast of Zapolyarniy (1) and two, 5 and 25 km south of Monchegorsk (2 and 4) show high levels of deposition of heavy metals, especially nickel (Ni) and copper (Cu), related to the metallurgical industry in these cities. Twenty-five topsoil samples, from sites evenly distributed over catchment 2, have mean contents of Ni and Cu 1 to 2 orders of magnitude higher than both C-horizon samples from the same sites and topsoil samples from catchment 4, providing strong evidence for the anthropogenic origin of the heavy metals. The same samples show geometric mean total contents for the noble metals analysed of: 1.4 μg/kg rhodium (Rh), 49.6 μg/kg platinum (Pt), 187.6 μg/kg palladium (Pd) and 9.5 μg/kg gold (Au). The pattern of concentration of the noble metals mirrors that found in published averages for ore from the Talnakh mineralizations in the Noril'sk province, though 1–2 orders of magnitude lower. This also clearly shows that the noble-metal contents of the topsoil are anthropogenic, and suggests that they emanate from the plants in Monchegorsk at an early stage in treatment of the ore, probably as a minor component of Ni-Cu rich particles. The noble-metal geochemistry of the topsoil in the other catchments also reflects the nature of the ore being processed at the plants nearby.     

Gold, silver and other elements in aquatic bryophytes from a mineralised area of North Wales, U.K.

Concentrations of Au, Ag, As, Cd and Sb in aquatic bryophytes collected from the Dolgellau Mineral Belt, North Wales, U.K. are reported. One aquatic liverwort, Scapania undulata (L) Dum. and two mosses, Fontinalis squamosa Hedw. and Racomitrium aciculare (Hedw.) Brid. were collected from sites upstream and downstream of the recently reopened Gwynfyndd Au mine. There was little inter-species variation in metal contents for these three bryophytes, but Scapania undulata appeared the most sensitive to changes in water concentrations of Ag, As and Sb. Gold concentrations varied little between the contaminated and control sites. Concentrations in the range < 4–18 ng Aug g⁻¹ D.W. were typical background levels, while bryophytes collected immediately below the mine contained 6–45 ng Au g⁻¹. Silver and Sb both showed more pronounced ( 5–10 fold) elevations above control concentrations in samples collected downstream of the mine. Background concentrations for these elements were 5–85 ng Ag g⁻¹ and 0.15–1.3 μg Sb g⁻¹.Arsenic concentrations downstream of the mine (160–1080 μg g⁻¹) greatly exceeded the background range of 9–32 μg g⁻¹. It is suggested, therefore, that As may be an ideal ‘pathfinder’ element when prospecting for auriferous deposits using aquatic bryophytes.     

Equation of state,structural behaviour and phase diagram of synthetic MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript>, as a function of pressure and temperature

The behaviour of synthetic Mg-ferrite (MgFe₂O₄) has been investigated at high pressure (in situ high-pressure synchrotron radiation powder diffraction at ESRF) and at high temperature (in situ high-temperature X-ray powder diffraction) conditions. The elastic properties determined by the third-order Birch–Murnaghan equation of state result in K₀=181.5(± 1.3) GPa, K=6.32(± 0.14) and K= –0.0638 GPa^–1. The symmetry-independent coordinate of oxygen does not show significant sensitivity to pressure, and the structure shrinking is mainly attributable to the shortening of the cell edge (homogeneous strain). The lattice parameter thermal expansion is described by _a0+_a1*(T–298)+_a2/(T–298)², where _a0=9.1(1) 10^–6 K^–1, _a1=4.9(2) 10^–9 K^–2 and _a2= 5.1(5) 10^–2 K. The high-temperature cation-ordering reaction which MgFe-spinel undergoes has been interpreted by the ONeill model, whose parameters are = 22.2(± 1.8) kJ mol^–1 and =–17.6(± 1.2) kJ mol^–1. The elastic and thermal properties measured have then been used to model the phase diagram of MgFe₂O₄, which shows that the high-pressure transition from spinel to orthorombic CaMn₂O₄-like structure at T < 1700 K is preceded by a decomposition into MgO and Fe₂O₃.     

Accumulation patterns of Cu and Ni for Indigofera melanadenia and Tephrosia longipes plant species growing in Cu–Ni mining area in Botswana

Indigofera melanadenia and Tephrosia longipes plant species, collected from Cu–Ni mining area, were evaluated for accumulation of Cu and Ni. The total and bioavailable concentrations of Cu and Ni in the host soils were also determined. Flame Atomic Absorption Spectrometry was used for all metal determinations. The total and bioavailable concentrations of Cu in the soils were in the range 900–9000 μg/g and 200–2000 μg/g respectively. For Ni, the total and bioavailable concentrations were in the range 900–2000 μg/g and ∼ 40–100 μg/g respectively. The concentrations of Cu and Ni in the leaves of I. melanadenia were higher than in the roots with a range 80–130 μg/g in the leaves and 20–80 μg/g in the roots for Cu and a range of 150–200 μg/g in the leaves and 20–60 μg/g in the roots for Ni. Concentration of Cu in T. longipes was in the range of 37–240 μg/g and 150–200 μg/g in the leaves and roots respectively while the concentration of Ni was 80–140 μg/g in the leaves and 25–100 μg/g in the roots. Results indicate that both species have a potential for accumulating Cu and Ni. Translocation factor, a ratio of shoots to roots metal concentration, was used to evaluate the translocation properties of the plants from roots to shoots. Translocation factors of the plants were ≥ 1 suggesting efficient translocation of metals from roots to shoots.     

Evaluation of biogeochemical prospecting methods in the search for sulfide deposits in the Appalachian piedmont, Virginia, U.S.A.

Soil and stream sediment sampling have been the primary geochemical exploration tools in the Appalachian piedmont to date. However, the great thicknesses of soil and saprolite found in the region coupled with the dense vegetation frequently encountered favor biogeochemistry as an alternative or supplemental method since deep-rooted plants sample closer to bedrock. To evaluate this method, an orientation survey was performed in which soils and vegetation at 17 sites north of Mineral, Virginia, were sampled and analyzed for Ag, Cd, Cu, Pb and Zn. The traverse included stations over the host rocks of massive sulfide mineralization, as well as over apparent “barren” country rock. Samples were analyzed by atomic absorption spectrophotometry using standard digestion and analytical techniques.Both A- and B-horizon soil metals generally appear to be reliable indicators of mineralization, with soils developed over sulfides showing up to three-fold enrichment in metal content relative to the average soils developed on the country rock. Correlation of metal concentrations in vegetation to soil metal concentrations reveal plant concentrations expressed on a dry-weight basis correlate stronger and more frequently to soil metals than do ash-weight concentrations. Copper shows some promise in selected organs and species, Ag appears fair but data are limited to one organ of one species, and plant Pb seems totally unresponsive to soil metal concentrations perhaps because foliar absorption is an important plant uptake mechanism here. However, Zn and Cd in organs of the oak group, especially mature leaves and twigs of the current year's growth show the greatest promise as prospecting tools. They correlate well with soil metals and when compared directly to the geology they reliably reflect mineralization. Although results using White oak were slightly less profound than those obtained from the Black-Red oak group, White oak may be preferred as it is a single, more widespread, easily-identifiable species. Copper and especially Zn although essential elements to plants, do not appear to be “difficult” elements for biogeochemical prospecting in the Appalachian piedmont.     

Copper accumulation by Polygonum microcephalum D. Don and Rumex hastatus D. Don from copper mining spoils in Yunnan Province, P.R. China

A survey was made of copper mining spoils in Yunnan Province, southwest China. Polygonum microcephalum and Rumex hastatus were found to grow extensively on copper mining spoils in Yunnan Province as representatives of typical high-elevation copper flowers. Plants and their associated soil samples collected from several copper mines in the Province were analyzed for copper. It is found that both plant species can grow well on mining spoils rich in copper but with medium nutrient supply. P. microcephalum accumulated more copper in its organs than R. hastatus. The copper concentration in the roots of both species tended to increase with copper increase in the substrates. However, the tendency for the levels of copper in the leaves of both species to increase linearly with soil copper increase is not clear. This study suggests that both species may have some potential for phytostabilization of metal-contaminated soils and for biogeochemical prospecting.     

Calcite dissolution kinetics in saline waters

The effect of ionic strength (I), pCO₂, and temperature on the dissolution rate of calcite was investigated in magnesium-free, phosphate-free, low calcium (m_Ca2+ ≈ 0.01 m) simple KCl and NaCl solutions over the undersaturation range of 0.4 ≤ Ω_calcite ≤ 0.8. First-order kinetics were found sufficient to describe the rate data where the rate constant (k) is dependent on the solution composition. Rates decreased with increasing I and were faster in KCl than NaCl solutions at the same I indicating that Na⁺ interacts more strongly with the calcite surface than K⁺ or that water is less available in NaCl solutions. Rates increased with increasing pCO₂ and temperature, and their influences diminished at high I. Arrhenius plots yielded a relatively high activation energy (E_a ≈ 20 ± 2 kJ mol^− 1) which indicated that dissolution was dominated by surface-controlled processes. The multiple regression model (MR) of Gledhill and Morse (2006a) was found to adequately describe the results at high I in NaCl solutions, but caution must be used when extrapolating to low I or pCO₂ values. These results are consistent with the hypothesis that the mole fraction of “free” solvent (X_{“free”H2O}) plays a significant role in the dissolution kinetics of calcite with a minimum value of  45–55% required for dissolution to proceed in undersaturated solutions at 25–55 °C and pCO₂ = 0.1–1 atm. This hypothesis has been incorporated into a modified version of the MR model of Gledhill and Morse (2006a) where X_{“free”H2O} has replaced I and the Ca²⁺ and Mg²⁺ terms have been dropped:

     

Distribution of copper, zinc, lead and cadmium concentrations in stream sediments from the Mapocho River in Santiago, Chile

The Mapocho river, which crosses downtown Santiago, is one of the most important rivers in contact with a population of about six million inhabitants. Anthropogenic activities, industrialization, farming activities, transport, urbanization, animal and human excretions, domestic wastes and copper mining have affected the river, contaminating it and its sediments with heavy metals. Concentration and distribution of Cu, Zn, Pb and Cd were studied with the purpose of determining their bioavailability and their relation with the characteristics of the sediments. Freshly deposited seasonal sediments were collected from 0–8 cm depths from 6 locations (S₁ to S₆) along the 30-km long channel length, in the four seasons of year on the following dates: May 2001 (D₁, autumn); August 2001 (D₂, winter); October 2001 (D₃, spring) and January 2002 (D₄, summer). The dried samples were sifted to obtain the < 63-μm sediment fraction, since it has been shown that large amounts of heavy metals are bound in the fine-grained fraction of the sediment. Cu and Zn were analyzed by atomic absorption spectrophotometry and Pb and Cd by square wave anodic stripping voltammetry. The highest concentrations of Cu (2850 μg g^− 1) were found in the northern part of the river (S₁, average D₁–D₄), near the mountains and a copper mine, and then decreased downstream to 209 μg g^− 1 (S₆). Total Zn showed an irregular variation, with higher values at S₁ (1290 μg g^− 1) and high values in some winter sampling (1384 μg g^− 1 S₄, S₅–D₂). Pb showed different trends, increasing from S₁ to S₆ (17 to 61 μg g^− 1), with the highest values in the summer samples (83 μg g^− 1, S₄–S₆, D₄), and total Cd increased slightly from mean values of 0.2 and 0.5 μg g^− 1. Partition into five fractions was made using Tessier's analytical sequential extraction technique; the residue was treated with aqua regia for recovery studies, although this step is not part of the Tessier procedure. The results show that Cu, Zn and Pb in the sediments were dependent on the sampling places along the river, and variation in two years was low (D₁–D₄). The highest values of total organic matter, carbonate and conductivity were found in S₆, which has the smallest size particles, while at S₁ the sediments were predominantly sand and contain larger amounts of silica. Cu associated with carbonate decreased gradually from 58% (1771 μg g^− 1, S₁) to 16% (32 μg g^− 1, S₆); Cu bonded to reducible fraction was almost constant (33% to 37%), and Cu associated with oxidizable fraction increased from 7% (S₁) to 34% (S₆), but copper content was lower (214 to 68 μg g^− 1). Zn had a similar fractionation profile. However, Pb bound to oxidizable fraction did not show significant percent variation along the river (20% to 19%), but the amount bounded was 4 to 12 μg g^− 1. The residual fraction increased from 24% to 41% (5 to 25 μg g^− 1, S₁ to S₆). The distribution of Cd in the sediment was almost independent of the sampling stations and was bound to carbonate, reducible and residual fraction in similar proportion. Cu and Zn at S₁ were mainly bound to carbonates and reducible phases with 91% and 73% (2779 and 965 μg g^− 1, respectively), and with a change in the pH and/or the redox potential of the sediment–water system, these contaminants could easily enter the food chain. In S₆ the amount of Cu and Zn in these phases was 50% and 53% (100 to 313 μg g^− 1, respectively).     

Migration and dispersion of trace elements in the rock–soil–plant system in areas underlain by black shales and slates of the Okchon Zone, Korea

The Okchon black shale in Korea provides a typical example of natural geological materials enriched with potentially toxic elements. The Chung-Joo, Duk-Pyung, Geum-Kwan, I-Won, Bo-Eun and Chu-Bu areas are underlain by these black shales and slates of the Guryongsan Formation or the Changri Formation, which are parts of the Okchon Group in the central part of the southern Korean Peninsula. In order to investigate the enrichment levels and dispersion patterns of potentially toxic elements in the rock–soil–plant system, environmental geochemical surveys were undertaken in the above six study areas in the Okchon Zone. After appropriate preparation, rock and soil samples were analyzed for potentially toxic elements by instrumental neutron activation analysis (INAA) and inductively coupled plasma atomic emission spectrometry (ICP-AES), and plant samples by atomic absorption spectrometry (AAS). In particular, Ba, Cd, Mo, V and U in Okchon black shales are highly enriched, and their mean concentrations are significantly higher than those in black slates. These elements are geochemically associated, and might be enriched simultaneously. The highest mean concentrations of 42.0 μg g⁻¹ As, 2100 μg g⁻¹ Ba, 10.9 μg g⁻¹ Cd, 213 μg g⁻¹ Mo, 83 μg g⁻¹ U, 938 μg g⁻¹ V and 394 μg g⁻¹ Zn are found in black shales from the Duk-Pyung area. Mean concentrations of As, Mo and U in soils overlying black shales occurring in the Duk-Pyung area (30 μg g⁻¹ As, 24 μg g⁻¹ Mo and 50 μg g⁻¹ U) and Chu-Bu area (39 μg g⁻¹ As, 15 μg g⁻¹ Mo and 27 μg g⁻¹ U) are higher than the permissible level. Enrichment index values of the six study areas decrease in the order of Duk-Pyung > Chu-Bu > Bo-Eun > Chung-Joo > Geum-Kwan = I-Won areas. Relationships between trace element concentrations in soils and plants are significantly correlated, and the biological absorption coefficients (BAC) in plants are in the order of Cd > Zn = Cu > Pb, which suggests that Cd is more bioavailable to plants than the other elements. Cadmium concentrations in plant species decrease in the order of chinese cabbage > red pepper > soybean = sesame > rice stalk > corn > rice grain. From the result of sequential extraction analysis of soils, relatively high proportions of Cu, Pb and Zn are present as residual fractions, and that of Cd as non-residual fractions. Cadmium occurs predominantly as exchangeable/water-acid soluble phase in soils, and this is in agreement with the findings of high Cd concentrations in plants.     

A new simple approach to evaluate pedogenic clay transformation in a Vertic Calcisol

The aim of this study is to characterize the pedogenic clay minerals by using simple approach: mixing mineralogical and geochemical findings.The fine clay fractions (< 0.1 μm) of a Vertic Cambisol profile were studied by means of X-ray diffraction (XRD), infrared spectroscopy (FTIR) and cation exchange capacity (CEC).Qualitative and quantitative mineralogical compositions of the clay mixture were determined.Moreover, chemical equilibria and thermodynamic stabilities of minerals (calcite, gypsum, kaolinite, smectites and illites) were studied using results of ionic activities obtained from total concentration of various aqueous species in water extracts from soil-saturated pastes.XRD analysis shows a good homogeneity in the mineralogical composition of the soil material, with depth of soil profiles. The identified clay minerals are mainly illite–smectite mixed layers (I/S) and kaolinite. The chemical analysis of saturated paste extracts with clay minerals shows a slight undersaturation of the illitic phase while smectites and also calcite and gypsum reach the thermodynamic equilibrium along the soil profile.     

屏障效应对生物地球化学异常形成的影响及找矿有效指示植物的选择

采用光谱仪及透射电子显微镜对广西几个金属矿床的生物地球化学异常和植物细胞微观特征进行了研究,结果发现:生物地球化学异常对土壤地球化学异常有明显的物质性继承关系;生物地球化学异常的物质以金属聚集体(电子致高密度体物质)的形式沉淀在植物液胞中或细胞壁及膜边缘,其对植物的伤害可能只达到细胞或组织的水平.生物地球化学异常的形成...