首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
In Iran, ultramafic rocks cover substantial areas at many locations in the country. These rocks consist predominantly of peridotite which has been serpentinized to some degree. Anarak and Nain are two ultramafic areas in Central Iran comprising about 180 and 270 km2, respectively, located in a coloured melange zone. There is little information available regarding the geobotany and biogeochemistry of these areas. They have a dry climate, with low rainfall and high temperatures in summer which encourages mostly annual and perennial herbaceous types of plants. In this paper, we report a reconnaissance study of these two ultramafic areas of Iran. Soil analysis of total elements indicates that typical concentrations of Ni, Cr, Co, Mn, Fe, Mg and Ca are about 1500, 300, 75, 800, 45.000 150.000 and 2000 μg g− 1, respectively. During this study 176 plant species were collected, belonging to 29 families. The species diversity at Anarak is more than at Nain, possibly due to microclimatic differences and a greater precipitation. The number of plants endemic to ultramafic soils of these two areas is very low. The herb Cleome heratensis (Capparaceae) appears to be an indicator of ultramafics in Central Iran. Populations of this plant cover quite extensive areas during summer and autumn when there is no rainfall. Analysis of the dry matter of the leaves of all plants collected did not reveal any hyperaccumulator of nickel or any other ‘serpentine’ metals. The ultramafic endemic plant C. heratensis contained low concentrations of all metals and thus it possesses exclusion mechanisms to restrict excessive metal uptake. The Mg/Ca ratio for some plants collected is high—up to 4.9. This initial survey suggests that a more complete investigation of the ultramafic areas of Iran would be valuable.  相似文献   

2.
A soil geochemical survey was conducted in a 27,000-km2 study area of northern California that includes the Sierra Nevada Mountains, the Sacramento Valley, and the northern Coast Range. The results show that soil geochemistry in the Sacramento Valley is controlled primarily by the transport and weathering of parent material from the Coast Range to the west and the Sierra Nevada to the east. Chemically and mineralogically distinctive ultramafic (UM) rocks (e.g. serpentinite) outcrop extensively in the Coast Range and Sierra Nevada. These rocks and the soils derived from them have elevated concentrations of Cr and Ni. Surface soil samples derived from UM rocks of the Sierra Nevada and Coast Range contain 1700–10,000 mg/kg Cr and 1300–3900 mg/kg Ni. Valley soils west of the Sacramento River contain 80–1420 mg/kg Cr and 65–224 mg/kg Ni, reflecting significant contributions from UM sources in the Coast Range. Valley soils on the east side contain 30–370 mg/kg Cr and 16–110 mg/kg Ni. Lower Cr and Ni concentrations on the east side of the valley are the result of greater dilution by granitic sources of the Sierra Nevada.Chromium occurs naturally in the Cr(III) and Cr(VI) oxidation states. Trivalent Cr is a non-toxic micronutrient, but Cr(VI) is a highly soluble toxin and carcinogen. X-ray diffraction and scanning electron microscopy of soils with an UM parent show Cr primarily occurs within chromite and other mixed-composition spinels (Al, Mg, Fe, Cr). Chromite contains Cr(III) and is highly refractory with respect to weathering. Comparison of a 4-acid digestion (HNO3, HCl, HF, HClO4), which only partially dissolves chromite, and total digestion by lithium metaborate (LiBO3) fusion, indicates a lower proportion of chromite-bound Cr in valley soils relative to UM source soils. Groundwater on the west side of the Sacramento Valley has particularly high concentrations of dissolved Cr ranging up to 50 μg L−1 and averaging 16.4 μg L−1. This suggests redistribution of Cr during weathering and oxidation of Cr(III)-bearing minerals. It is concluded that regional-scale transport and weathering of ultramafic-derived constituents have resulted in enrichment of Cr and Ni in the Sacramento Valley and a partial change in the residence of Cr.  相似文献   

3.
  相似文献   

4.
Serpentine soils derived from the weathering of ultramafic rocks and their metamorphic derivatives (serpentinites) are chemically prohibitive for vegetative growth. Evaluating how serpentine vegetation is able to persist under these chemical conditions is difficult to ascertain due to the numerous factors (climate, relief, time, water availability, etc.) controlling and affecting plant growth. Here, the uptake, incorporation, and distribution of a wide variety of elements into the biomass of serpentine vegetation has been investigated relative to vegetation growing on an adjacent chert-derived soil. Soil pH, electrical conductivity, organic C, total N, soil extractable elements, total soil elemental compositions and plant digestions in conjunction with spider diagrams are utilized to determine the chemical relationships of these soil and plant systems. Plant available Mg and Ca in serpentine soils exceed values assessed in chert soils. Magnesium is nearly 3 times more abundant than Ca in the serpentine soils; however, the serpentine soils are not Ca deficient with Ca concentrations as high as 2235 mg kg−1. Calcium to Mg ratios (Ca:Mg) in both serpentine and chert vegetation are greater than one in both below and above ground tissues. Soil and plant chemistry analyses support that Ca is not a limiting factor for plant growth and that serpentine vegetation is actively moderating Mg uptake as well as tolerating elevated concentrations of bioavailable Mg. Additionally, results demonstrate that serpentine vegetation suppresses the uptake of Fe, Cr, Ni, Mn and Co into its biomass. The suppressed uptake of these metals mainly occurs in the plants’ roots as evident by the comparatively lower metal concentrations present in above ground tissues (twigs, leaves and shoots). This research supports earlier studies that have suggested that ion uptake discrimination and ion suppression in the roots are major mechanisms for serpentine vegetation to tolerate the chemistry of serpentine soils.  相似文献   

5.
Geochemical mapping of Shikoku in the SW Japan Arc was conducted using stream sediments (<0.18 mm fraction) with sample densities of 1 site per 106 km2. Concentrations of 51 elements in 173 stream sediments were determined. Areas with especially high Cr, Ni, Mg and Co concentrations run intermittently and linearly through Shikoku, and coincide with exposures of the Mikabu greenstone complex composed of oceanic basaltic and gabbroic rocks with minor ultramafic bodies. Areas with higher concentrations of Fe, V, Sc, Ti, Mn, Cr, Ni, Mg, Co and Eu are distributed widely along the Shikoku Island axis; they mainly overlap with the zones of the high-pressure type metamorphic rocks (Sanbagawa Belt) and of the Jurassic accretionary complexes with sedimentary rocks (Chichibu Belt): in contrast, areas with lower concentrations spread over the northern coastal zone of Cretaceous granitoids (Ryoke Belt) and in the southern coastal zone of Cretaceous-Paleogene accretionary complexes (Shimanto Belt). Distribution patterns of these elements reflect that various amounts of mafic and ultramafic materials, possibly of oceanic origin, are associated with the rocks in the Sanbagawa and Chichibu Belts, although such components occur sparsely in the Shimanto and Ryoke Belts. Calcium, Sr, Na, Nb, Sm and Gd contents are lower along the southern coastal zone. High values of Th, U, La, Ce and Ba are associated with granitic rocks. The positive anomalies of Cu and Cd coincide with the distribution of stratabound Cu deposits in the Sanbagawa Belt. Positive anomalies of Sb in the northern area are associated with Sb deposits near the large Median Tectonic Line fault zone. A high-Hg zone is present in the southern fore-arc area. The median concentrations for stream sediments in Shikoku are higher in Hg, Cu, Ni, Cr, Rb, Li, Cs, K, slightly higher in Nb, Ta, La, Ce, Sn and lower in Ca than those for average Japanese stream sediments. The median concentrations for the four geologic zones show systematic wide variations of mafic associated elements, and narrow variations of lithophile elements generally more abundant in felsic rocks. The chemical compositions of the stream sediments in Shikoku largely reflect the concentrations in the pre-Neogene accretionary complexes and in the high-P metamorphic rocks mainly formed from clastic materials derived from continental margins, and ratios of mafic and ultramafic materials within surface rocks; they are partly influenced by sulfide mineralization and fluid migration.  相似文献   

6.
Serpentinized ultramafic rocks and associated soils in northern California are characterized by high concentrations of Cr and Ni, low levels of radioelements (K, Th, and U) and high amounts of ferrimagnetic minerals (primarily magnetite). Geophysical attributes over ultramafic rocks, which include airborne gamma-ray and magnetic anomaly data, are quantified and provide indirect measurements on the relative abundance of radioelements and magnetic minerals, respectively. Attributes are defined through a statistical modeling approach and the results are portrayed as probabilities in chart and map form. Two predictive models are presented, including one derived from the aeromagnetic anomaly data and one from a combination of the airborne K, Th and U gamma-ray data. Both models distinguish preferential values within the aerogeophysical data that coincide with mapped and potentially unmapped ultramafic rocks. The magnetic predictive model shows positive probabilities associated with magnetic anomaly highs and, to a lesser degree, anomaly lows, which accurately locate many known ultramafic outcrops, but more interestingly, locate potentially unmapped ultramafic rocks, possible extensions of ultramafic bodies that dip into the shallow subsurface, as well as prospective buried ultramafic rocks. The airborne radiometric model shows positive probabilities in association with anomalously low gamma radiation measurements over ultramafic rock, which is similar to that produced by gabbro, metavolcanic rock, and water bodies. All of these features share the characteristic of being depleted in K, Th and U. Gabbro is the only rock type in the study area that shares similar magnetic properties with the ultramafic rock. The aerogeophysical model results are compared to the distribution of ultramafic outcrops and to Cr, Ni, K, Th and U concentrations and magnetic susceptibility measurements from soil samples. Analysis of the soil data indicates high positive correlation between magnetic susceptibilities and concentration of Cr and Ni. Although the study focused on characterizing the geophysical properties of ultramafic rocks and associated soils, it has also yielded information on other rock types in addition to ultramafic rocks, which can also locally host naturally-occurring asbestos; specifically, gabbro and metavolcanic rocks.  相似文献   

7.
A national-scale survey of the environment in and around mines was conducted to evaluate the status of total As contamination in agricultural soils surrounding numerous abandoned metal mines in Korea. This survey aimed to compare As concentrations in soils in relation to geology and mineralization types of mines. A total of 16,386 surface soil (0–15 cm in depth) samples were taken from agricultural lands near 343 abandoned mines (within 2 km of each mine). These samples were decomposed by aqua regia and analyzed for As by AAS with a hydride-generation (HG) device. To compare As levels in soils meaningfully with geology and mineralization types, three sub-classification criteria were adapted: (1) five mineralization types, (2) four valuable ore mineral types, and (3) four parent rock types. The average concentration of As in all the soils was 11.6 mg kg−1 with a range of 0.01–4230 mg kg−1. Based on the mineralization types, average As concentrations (mg kg−1) in the soils decreased in the order of pegmatite (18.2) > hydrothermal replacement (14.5) > sedimentary deposits (12.4) > hydrothermal vein (10.7) > skarn (4.08). In terms of the valuable ore mineral types, the concentrations decreased in the order of Sn, W, Mo, Fe and Mn mines > Au, Ag, and base metal mines > Au and Ag mines ≈ base metal mines. For parent rock types, soils from metamorphic rocks and heterogeneous rocks exhibited enhanced As levels related to both igneous and sedimentary rocks. Therefore, it can be concluded that soils from highly altered rocks subject to metamorphic and igneous activities contained relatively high concentrations of As in the surface environment.  相似文献   

8.
The Sb speciation in soil samples from Swiss shooting ranges was determined using Sb K-edge X-ray absorption spectroscopy (XAS) and advanced statistical data analysis methods (iterative transformation factor analysis, ITFA). The XAS analysis was supported by a spectral data set of 13 Sb minerals and 4 sorption complexes. In spite of a high variability in geology, soil pH (3.1-7.5), Sb concentrations (1000-17,000 mg/kg) and shooting-range history, only two Sb species were identified. In the first species, Sb is surrounded solely by other Sb atoms at radial distances of 2.90, 3.35, 4.30 and 4.51 Å, indicative of metallic Sb(0). While part of this Sb(0) may be hosted by unweathered bullet fragments consisting of PbSb alloy, Pb LIII-edge XAS of the soil with the highest fraction (0.75) of Sb(0) showed no metallic Pb, but only Pb2+ bound to soil organic matter. This suggests a preferential oxidation of Pb in the alloy, driven by the higher standard reduction potential of Sb. In the second species, Sb is coordinated to 6 O-atoms at a distance of 1.98 Å, indicative of Sb(V). This oxidation state is further supported by an edge energy of 30,496-30,497 eV for the soil samples with <10% Sb(0). Iron atoms at radial distances of 3.10 and 3.56 Å from Sb atoms are in line with edge-sharing and bidentate corner-sharing linkages between Sb(O,OH)6 and Fe(O,OH)6 octahedra. While similar structural units exist in tripuhyite, the absence of Sb neighbors contradicts formation of this Fe antimonate. Hence the second species most likely consists of inner-sphere sorption complexes on Fe oxides, with edge and corner-sharing configuration occurring simultaneously. This pentavalent Sb species was present in all samples, suggesting that it is the prevailing species after weathering of metallic Sb(0) in oxic soils. No indication of Sb(III) was found.  相似文献   

9.
The Idrija mine was the second largest Hg mine in the world surpassed only by the Almaden mine in Spain. It has been estimated that almost 145,000 tons of Hg was produced during operation (1490-1995) of the mine. In the first decade of Hg mining in Idrija the ore was roasted in piles; after that it was roasted for 150 years, until 1652, in earthen vessels at various sites in the woods around Idrija. Pšenk is one out of 21 localities of ancient roasting sites established on the hills surrounding Idrija and one of the largest localities of roasting vessel fragments. The unique way of roasting very rich Hg ore at this site has resulted in soil contamination and considerable amounts of waste material that potentially leach Hg into the surrounding environment. The main aim of this study was to determine the distribution and the forms of Hg in contaminated soils in order to evaluate potential environmental risk. Detailed soil sampling was performed on 37,800 m2 area to establish the extent of Hg pollution and to investigate Hg transformations and transport characteristics through the 400 a-long period. A total of 156 soil (0-15 cm and 15-30 cm) and SOM (soil organic matter) samples were collected from 73 sampling points. Three soil profiles were sampled to determine vertical distribution of Hg. The main Hg phases were determined by the Hg-thermo-desorption technique. The measured Hg contents in soil samples in the study area vary from 5.5 to almost 9000 mg/kg with a median of 200 mg/kg. In SOM, Hg contents range from 1.4 to 4200 mg/kg with a median of 20 mg/kg. Extremely high Hg contents were found in soil profiles where the metal reaches 37,020 mg/kg. In general, Hg concentrations in all three profiles show a gradual decrease with depth with the minimum values between 140 mg/kg and 1080 mg/kg. The Hg-thermo-desorption curves indicate the presence of Hg in the form of cinnabar and that of Hg bound to organic or mineral soil matter. The distribution of Hg species in soil and SOM samples show almost equal distribution of cinnabar and non-cinnabar Hg compounds. The non-cinnabar fraction shows a little increase with depth, but cinnabar represents a high portion of total Hg (about 40%). Large amounts of potentially mobile and transformable non-cinnabar Hg compounds exist at the roasting site, which are potentially bioavailable.  相似文献   

10.
  相似文献   

11.
Anthropogenic Pb affects the environment worldwide. To understand its effect on forest ecosystem, Pb isotope ratios were determined in precipitation, various components of vegetation, the forest floor, soil and parent material in a Japanese cedar (Cryptomeria japonica D. Don) forest stand. The average 206Pb/207Pb ratio in bulk precipitation was 1.14 ± 0.01 (mean ± SD), whereas that in the subsoil (20–130 cm) was 1.18 ± 0.01. Intermediate ratios ranging from 1.15 to 1.16 were observed in the vegetation, the forest floor, and the surface soil (0–10 cm). Using the 206Pb/207Pb ratios, the contribution of anthropogenic sources to Pb accumulated in the forest were estimated by the simple binary mixing model. Sixty-two percent of the Pb in the forest floor, 71% in the vegetation, and 55% in the surface soil (0–10 cm) originated from anthropogenic sources, but only 16% in the sub-surface soil (10–20 cm) was anthropogenic. These results suggest that internal Pb cycling occurs mainly between surface soil and vegetation in a Japanese cedar ecosystem, and that anthropogenic Pb strongly influences Pb cycling. Although the Japanese cedar ecosystem has a shallow forest floor, very little atmospherically derived Pb migrated downward over 10 cm in depth.  相似文献   

12.
The abandoned Hg mine in Podljubelj was in operation with interceptions from 1557 to 1902. The entire operating period yielded about 110 000 tons of ore, from which 360 tons of Hg was produced. The objective of the research project was to establish the contents and spatial distribution of Hg in soils and stream sediments in the vicinity of the mine. On an area of 88 ha the soil was sampled in a 100 × 100 m grid. Two soil horizons (0–5 cm and 20–30 cm) were sampled in order to distinguish between geogenic and anthropogenic Hg sources. It was established that on an area of about 9 ha Hg content in soil exceeds The New Dutchlist action value for Hg (10 mg/kg). Total Hg concentrations in soil samples vary between 0.17 and 719 mg/kg, with a mean of 3.0 mg/kg. Mercury contents in stream sediments range from 0.065 to 1.4 mg/kg, with a mean of 0.64 mg/kg. The highest determined value in soils was found in the area around the former roasting furnace, where the ore was processed. Increased Hg concentrations were also found on the mine waste dump (108 mg/kg). Mercury contents in soils generally decrease with soil profile depth and with the distance from the mine and from the roasting furnace location. Mercury also appears in higher concentrations along the road that runs through the valley, which results from the use of Hg-bearing ore residues in road construction. The average enrichment factor (EF) of Hg in topsoil with respect to subsoil is 3.3. Calculated enrichment factors show higher values also for Cd (3.2), Pb (2.7), Ca (2.4) and P (1.9). The average enrichment factor of Hg in topsoil with regard to the established Slovenian soil averages (EFslo) is 19. EFslo of other determined chemical elements do not exceed 3.0.  相似文献   

13.
Slag from the former Hegeler Zn-smelting facility in Illinois (USA) is mainly composed of spinifex Ca-rich plagioclase, fine-grained dendritic or coarse-grained subhedral to anhedral clinopyroxenes, euhedral to subhedral spinels, spherical blebs of Fe sulfides, silicate glass, and less commonly fayalitic olivine. Mullite and quartz were also identified in one sample as representing remnants of the furnace lining. Secondary phases such as goethite, hematite and gypsum are significant in some samples and reflect surficial weathering of the dump piles or represent byproducts of roasting. A relatively rare Zn-rich material contains anhedral willemite, subhedral gahnite, massive zincite, hardystonite and a Zn sulfate (brianyoungite), among other phases, and likely represents the molten content of the smelting furnace before Zn extraction. The bulk major-element chemistry of most slag samples is dominated by SiO2, Al2O3, Fe2O3 and CaO. The bulk composition of the slag suggests a high viscosity of the melt and the mineralogy suggests a high silica content of the melt. Bulk slag trace-element chemistry shows that the dominant metal is Zn with >28.4 wt.% in the Zn-rich material and between 212 and 14,900 mg/kg in the other slags. The concentrations of other trace elements reach the following: 45 mg/kg As, 1170 mg/kg Ba, 191 mg/kg Cd, 242 mg/kg Co, 103 mg/kg Cr, 6360 mg/kg Cu, 107 mg/kg Ni, and 711 mg/kg Pb.  相似文献   

14.
A regional soil and sediment geochemical study in northern California   总被引：7，自引：7，他引：0  
Regional-scale variations in soil geochemistry were investigated in a 20,000-km2 study area in northern California that includes the western slope of the Sierra Nevada, the southern Sacramento Valley and the northern Coast Ranges. Over 1300 archival soil samples collected from the late 1970s to 1980 in El Dorado, Placer, Sutter, Sacramento, Yolo and Solano counties were analyzed for 42 elements by inductively coupled plasma-atomic emission spectrometry and inductively coupled plasma-mass spectrometry following a near-total dissolution. These data were supplemented by analysis of more than 500 stream-sediment samples from higher elevations in the Sierra Nevada from the same study site. The relatively high-density data (1 sample per 15 km2 for much of the study area) allows the delineation of regional geochemical patterns and the identification of processes that produced these patterns. The geochemical results segregate broadly into distinct element groupings whose distribution reflects the interplay of geologic, hydrologic, geomorphic and anthropogenic factors. One such group includes elements associated with mafic and ultramafic rocks including Cr, Ni, V, Co, Cu and Mg. Using Cr as an example, elevated concentrations occur in soils overlying ultramafic rocks in the foothills of the Sierra Nevada (median Cr = 160 mg/kg) as well as in the northern Coast Ranges. Low concentrations of these elements occur in soils located further upslope in the Sierra Nevada overlying Tertiary volcanic, metasedimentary and plutonic rocks (granodiorite and diorite). Eastern Sacramento Valley soil samples, defined as those located east of the Sacramento River, are lower in Cr (median Cr = 84 mg/kg), and are systematically lower in this suite compared to soils from the west side of the Sacramento Valley (median Cr = 130 mg/kg). A second group of elements showing a coherent pattern, including Ca, K, Sr and REE, is derived from relatively silicic rocks types. This group occurs at elevated concentrations in soils overlying volcanic and plutonic rocks at higher elevations in the Sierras (e.g. median La = 28 mg/kg) and the east side of the Sacramento Valley (median 20 mg/kg) compared to soils overlying ultramafic rocks in the Sierra Nevada foothills (median 15 mg/kg) and the western Sacramento Valley (median 14 mg/kg). The segregation of soil geochemistry into distinctive groupings across the Sacramento River arises from the former presence of a natural levee (now replaced by an artificial one) along the banks of the river. This levee has been a barrier to sediment transport. Sediment transport to the Valley by glacial outwash from higher elevations in the Sierra Nevada and, more recently, debris from placer Au mining has dominated sediment transport to the eastern Valley. High content of mafic elements (and low content of silicic elements) in surface soil in the west side of the valley is due to a combination of lack of silicic source rocks, transport of ultramafic rock material from the Coast Ranges, and input of sediment from the late Mesozoic Great Valley Group, which is itself enriched in mafic elements. A third group of elements (Zn, Cd, As and Cu) reflect the impact of mining activity. Soil with elevated content of these elements occurs along the Sacramento River in both levee and adjacent flood basin settings. It is interpreted that transport of sediment down the Sacramento River from massive sulfide mines in the Klamath Mountains to the north has caused this pattern. The Pb, and to some extent Zn, distribution patterns are strongly impacted by anthropogenic inputs. Elevated Pb content is localized in major cites and along major highways due to inputs from leaded gasoline. Zinc has a similar distribution pattern but the source is tire wear.  相似文献   

15.
Lead concentrations were determined in samples of soil B-horizon (N = 258), forest-floor humus (O-horizon, N = 259), grass (Avenella flexuosa, N = 251) and spruce (Picea abies, N = 253) needles (2nd year) collected at the same locations evenly spread over the territory of the Czech Republic at an average density of 1 site/300 km2. Median Pb concentrations differ widely in the four materials: soil B-horizon: 27 mg/kg (3.3-220 mg/kg), humus: 78 mg/kg (19-1863 mg/kg), grass: 0.37 mg/kg (0.08-8 mg/kg) and spruce needles: 0.23 mg/kg (0.07-3 mg/kg). In the Pb distribution maps for humus, grass and spruce a number of well-known Pb-contamination sources are indicated by unusually high concentrations (e.g., the Pb smelter at Pribram, the metallurgical industry in the NE of the Czech Republic and along the Polish border, as well as the metallurgical industry in Upper Silesia and Europe’s largest coal-fired power plant at Bogatynia, Poland). The ratio 206Pb/207Pb was determined in all four materials. The median value of the 206Pb/207Pb isotope ratio in the soil B-horizon is 1.184 (variation: 1.145-1.337). In both humus and grass the median value for the 206Pb/207Pb isotope ratio is 1.162 (variation: 1.130-1.182), in spruce needles the median ratio is 1.159 (variation: 1.116-1.186). In humus, grass and spruce needles the known contamination sources are all marked by higher 206Pb/207Pb isotope ratios in the maps. Furthermore, the soil B-horizon, humus, grass and spruce needles show distinctly different spatial distribution patterns of the 206Pb/207Pb isotope ratios. The B-horizon does not provide a viable background value for metal concentrations in the O-horizon or plant materials. None of the maps provides evidence for the importance of traffic-related emissions for the observed isotope ratios at the scale of the Czech Republic.  相似文献   

16.
The Totalp-Platta-Malenco ophiolites in the Eastern Central Alps offer a unique opportunity to study the behaviour of Li, Be and B in ultramafic rocks in response to serpentinization and to progressive Alpine metamorphism. These units represent the remnants of a former ocean-continent transition that was intensely serpentinized during exposure on the Jurassic seafloor of the Ligurian Tethys. From north to the south, three isograd reactions (lizardite⇒antigorite+brucite;lizardite+talc⇒antigorite;lizardite+tremolite⇒antigorite+diopside) have been used to quantify the evolution of the light element content of metamorphic minerals. We determined the Li, Be and B concentrations in major silicate minerals from the ultramafic bodies of Totalp, Platta and Malenco by secondary ion mass spectrometry. Mantle minerals have Be concentrations (e.g. <0.001-0.009 μg/g in olivine) similar to the metamorphic minerals that replace them (e.g. <0.001-0.016 μg/g in serpentine). The mantle signature of Be is thus neither erased during seafloor alteration nor by progressive metamorphism from prehnite-pumpellyite to epidote-amphibolite facies. In contrast, the Li and B inventories of metamorphic minerals are related to the lizardite-to-antigorite transition. Both elements display higher concentrations in the low-temperature serpentine polymorph lizardite (max. 156 μg/g Li, max. 318 μg/g B) than in antigorite (max. 0.11 μg/g Li, max. 12 μg/g B). Calculated average B/Li ratios for lizardite (∼1395) and antigorite (∼115) indicate that Li fractionates from B during the lizardite-to-antigorite transition during prograde metamorphism in ultramafic rocks. In subduction zones, this signature is likely to be recorded in the B-rich nature of forearc fluids.Relative to oceanic mantle the Be content of mantle clinopyroxene is much higher, but similar to Be values from mantle xenoliths and subduction-related peridotite massifs. These data support previous hypothesis that the mantle rocks from the Eastern Central Alps have a subcontinental origin. We conclude that Be behaves conservatively during subduction metamorphism of ultramafic rocks, at least at low-temperature, and thus retains the fingerprint of ancient subduction-related igneous events in mantle peridotites.  相似文献   

17.
Antimony in the environment: Lessons from geochemical mapping   总被引：2，自引：0，他引：2  
The distribution of Sb in a variety of sample materials, including soils, plants and surface water, was studied at different scales, from continental to local, combining published data sets with the aim of delineating the impact and relative importance of geogenic vs. anthropogenic Sb sources. Geochemical mapping demonstrates that variation is high at all scales – from the detailed scale with sample densities of many sites per km2 to the continental-scale with densities of 1 site per 5000 km2. Different processes govern the Sb distribution at different scales. A high sample density of several samples per km2 is needed to reliably detect mineralisation or contamination in soil samples. Median concentrations are so low for Sb in most sample materials (below 1 mg/kg in rocks and soils, below 0.1 mg/kg in plants, below 0.1 μg/L in surface water) that contamination is easier to detect than for many other elements. Distribution patterns on the sub-continental to continental-scale are, however, still dominated by natural variation. Given that the geochemical background is characterised by a high variation at all scales, it appears impossible to establish a reliable single value for “good soil quality” or a “natural background concentration” for Sb for any sizeable area, e.g., for Europe. For such a differentiation, geochemical maps at a variety of scales are needed.  相似文献   

18.
The Santa Elena peninsula in the northwest of Costa Rica protrudes about 30 km westwards into the Pacific Ocean, and measures about 8–16 km in a north–south direction. Several geological studies have been carried out since 1953, showing that much of the peninsula is made up of peridotite, cut by mafic dykes. Only one previous brief examination appears to have been made of the vegetation in relation to the composition of the soils. We present here the results of a survey of some soils and plants of the eastern part of the peridotite massif, in which 73 plant specimens representing 51 identified species were collected and analyzed. The soils sampled all showed extreme ultramafic characteristics: Fe 10–16%, Mg 4–16%, Ca 0.5–1.4%; Ni 3000–7500 mg/kg, Cr 1400–3650 mg/kg, Co 150–325 mg/kg. The plants collected include several from genera such as Arrabidaea, Chamaesyce, Helicteres, Hyptis, Lippia, Oxalis, Polygala, Turnera and Waltheria that are also represented on ultramafics elsewhere in the Americas (e.g. Cuba, Puerto Rico, Brazil). Few of the species appear to be endemic to Costa Rica or to the ultramafics of Santa Elena. None of the specimens collected exhibited hyperaccumulation of nickel, the highest Ni concentration being 275 mg/kg in Buchnera pusilla.  相似文献   

19.
This paper presents the results of a study on the geochemistry of waters circulating in the mineralised area of the south-eastern sector of Mt. Peloritani (north-eastern Sicily, Italy), aimed at basic understanding of the geochemical processes influencing their chemical composition. Chemico-physical parameters and data on 26 major and minor chemical elements are reported for 103 water samples. Water chemistry is mainly dominated by dissolution of carbonates and hydrolysis of aluminosilicate minerals. Total dissolved salts (TDS) range from 80 to 1398 mg/L. All the waters exhibit EH characteristic of an oxygenated environment. Excluding two samples, which show very high H+ activity (pH = 3.0 and 2.7), all the waters have pH values in the range 6.2–8.6. Cluster analysis based on major ion contents defined three main chemical water types, reflecting different hydrochemical processes. The first, group I, has low salinity (average TDS = 118 ± 30 mg/L) and abundance orders (meq/L) Na > Ca ≈ Mg > K and Cl ≈ HCO3 > SO4. With increased water–rock interaction, waters in groups II and III become more saline, changing composition towards SO4–Cl-alkaline earth and HCO3-alkaline earth types. Weathering of carbonate minerals causes waters to become saturated with respect to calcite and dolomite, whereas the incongruent dissolution of aluminosilicate minerals causes the solution to reach equilibrium with kaolinite and to form smectites. Trace element geochemistry in the analysed waters reflects interactions between waters and existing mineralisation, with elemental concentrations showing highly variable values, and higher concentrations of As, Pb, Sb and Zn near known mineralisation. Lead–Zn and As–Sb statistical associations, probably distinguishing interactions with different mineralogical phase paragenesis, were revealed by factor analysis. The main aqueous chemical forms of trace elements predicted by chemical speciation calculations are also reported. As most of the analysed spring waters provide the main source of freshwater for domestic purposes, attention should be given to As and Sb, whose concentrations exceed the recommended limits.  相似文献   

20.
The chemical status of ∼40 major and trace elements (TE) and organic carbon (OC) in pristine boreal rivers draining the basaltic plateau of Central Siberia (Putorana) and interstitial solutions of permafrost soils was investigated. Water samples were filtered in the field through progressively decreasing pore size (5 μm → 0.22 μm → 0.025 μm → 10 kDa → 1 kDa) using cascade frontal filtration technique. Most rivers and soil porewaters exhibit 2-5 times higher than the world average concentration of dissolved (i.e., <0.22 μm) iron (0.03-0.4 mg/L), aluminum (0.03-0.4 mg/L), OC (10-20 mg/L) and various trace elements that are usually considered as immobile in weathering processes (Ti, Zr, Ga, Y, REEs). Ultrafiltration revealed strong relationships between concentration of TE and that of colloidal Fe and Al. According to their partition during filtration and association with colloids, two groups of elements can be distinguished: (i) those weakly dependent on ultrafiltration and that are likely to be present as truly dissolved inorganic species (Li, Na, K, Si, Mn, Mo, Rb, Cs, As, Sb) or, partially (20-30%) associated with small size Fe- and Al-colloids (Ca, Mg, Sr, Ba) and to small (<1-10 kDa) organic complexes (Co, Ni, Cu, Zn), and (ii) elements strongly associated with colloidal iron and aluminum in all ultrafiltrates largely present in 1-100 kDa fraction (Ga, Y, REEs, Pb, V, Cr, Ti, Ge, Zr, Th, U). TE concentrations and partition coefficients did not show any detectable variations between different colloidal fractions for soil porewaters, suprapermafrost flow and surface streams. TE concentration measurements in river suspended particles demonstrated significant contribution (i.e., ?30%) of conventionally dissolved (<0.22 μm) forms for usually “immobile” elements such as divalent transition metals, Cd, Pb, V, Sn, Y, REEs, Zr, Hf, Th. The Al-normalized accumulation coefficients of TE in vegetation litter compared to basalts achieve 10-100 for B, Mn, Zn, As, Sr, Sn, Sb, and the larch litter degradation is able to provide the major contribution to the annual dissolved flux of most trace elements. It is hypothesized that the decomposition of plant litter in the topsoil horizon leads to Fe(III)-, Al-organic colloids formation and serves as an important source of elements in downward percolating fluids.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号