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1.
After the completion of a programme of regional stream sediment sampling to observe base metal distributions in drainage systems in the southwest of Western Australia, it was noted that above background Pb and Sn contents in minus 80-mesh fractions of samples from the Warren River area, were related to unusually high Nb contents in the same samples.Further investigations revealed that the anomalous samples were from streams draining eroded sand dunes containing heavy mineral sands, related to a former shore line. Assays of heavy mineral differentiates from these dune sands gave values up to 0.12% Nb in samples of altered ilmenite.  相似文献   

2.
Partitioning of Cu, Pb, Zn, U, As and Mo between the minus 70 μm and minus 200 μm fractions of stream sediments from arid and semi-arid terrains is examined in the light of published case histories supplemented by new data. The advantages of selecting a particular fraction for routine sampling in such arid environments are assessed in terms of five criteria: (1) homogeneity of background population; (2) definition of threshold; (3) absolute element abundance levels; (4) contrast between anomalous and background populations; and (5) length of dispersion train. The most homogeneous background population distributions and improved definition of the threshold between background and anomaly occur in the very fine, minus 70 μm fraction of stream sediments for the majority of elements, in particular for Zn, Cu, U and As. Data for Pb and Mo do not consistently favour either size fraction in the case histories studied. Increased abundance levels of elements which are normally close to the analytical detection limit (U, Mo, As) occur most frequently in the minus 70 μm fraction, although Cu, Pb and Zn levels are commonly higher in the coarser fraction. In addition the finer size fraction better defines the anomalous population and provides the longer dispersion trains for Cu, Pb, Zn, U and As in the majority of case histories.The data examined indicate that the minus 70 μm fraction provides more useful information, in many instances, than the minus 200 μm fraction. The evidence suggests that problems expected with the use of the fine fraction — dilution through the abundance of wind blown material, and insufficient fine sediment — do not restrict the use of this fraction in stream sediment surveys in arid terrains.  相似文献   

3.
The purpose of this study was to determine if metal concentrations are enriched in two size sediment fractions of streams that receive landfill effluent and, if so, whether there is a greater extent of metal enrichment in one of the fractions. Sediment samples were collected from three streams adjacent to a sanitary landfill. Sediments representing control for the study were also collected from a stream not influenced by the landfill. All samples were sieved and the <0.0625-mm and <0.25-mm to >0.149-mm size fractions from each sample were used in this study. The concentrations of acid-extractable Cu, Zn, Pb, and Cr for all samples were determined by atomic absorption techniques. Mean concentrations, coefficient of variation values, at test, and the variation of metal concentrations along the stream were used to analyze the data. Results indicated that Cu, Zn, Pb, and Cr concentrations were enriched in both size sediment fractions from the stream whose channel originated at the base of the landfill. Copper, Zn, and Pb concentrations were enriched in the <0.0625-mm size sediments of the stream whose channel did not intersect the landfill. Copper, Zn, Pb, and Cr concentrations appear enriched in both size sediment fractions of the third stream, which formed from the confluence of the other two streams. The extent of metal enrichment was greater in the <0.0625-mm size sediments. A decreasing trend of metal concentrations in a downstream direction was not present in the enriched sediments. This was true for each metal in both size sediment fractions.  相似文献   

4.
An anomalous Pb pattern occurs in drainage channel soils adjacent to the Elura Zn-Pb-Ag deposit and forms a fan shaped train extending at least 5 km on a mature weathering surface in semi-arid central-west New South Wales. This Pb pattern without a Zn component can be related to ferricrete fragments in the coarser fraction of the soil samples and has apparently formed as a result of mechanical dispersion of ferricrete from an earlier lateritic weathering profile. By considering residual Pb contents, after regressing for Fe content, the anomalous pattern can be extended and the contrast improved.  相似文献   

5.
Downstream dispersion curves for certain trace metals were obtained from two mineralized areas in the southeastern United States. Fe-Mn oxide coating on lithic fragments and quartz pebbles, as well as the minus 80-mesh fraction of the coexisting stream sediment were analyzed for a variety of metals. In Lincoln County, Georgia, 8 sample sets were collected along a stream draining the Magruder mine, a polymetallic sulfide deposit (Zn-Cu-Pb-Ag-Au) in metavolcanic rocks. Five sample sets were collected along Joe Mill Creek in Grainger County, Tennessee, downstream from a zone of zinc mineralization in carbonate rocks (Mississippi Valley-type). In addition, 5 sample sets were collected from an unmineralized area near Athens, Georgia.The results indicate the following: (1) the anomaly/background ratio for zinc and copper is markedly higher in the Fe-Mn oxide coatings in the mineralized drainages; (2) in drainages containing lead mineralization, the anomaly/background ratio is markedly higher in the minus 80-mesh fraction for lead which is not concentrated in the coatings; and (3) the ratios Zn/Mn and Cu/Mn, as well as Zn/Co and Cu/Co, in the Fe-Mn oxide coatings enhance downstream detectability of mineralization.There are several potential advantages of using coatings versus the conventional minus 80-mesh fraction in stream sediment geochemical surveys. Because soluble metal is brought into the stream mainly in groundwater, deeper anomaly sources may be detectable from the oxide coatings than from clastic fractions of alluvium where much of the metal is derived from surficial erosion. Variability due to sampling may also be reduced, providing better discrimination of anomalies. In areas of glacial or alluvial cover, coating surveys may be particularly applicable.  相似文献   

6.
《Applied Geochemistry》1999,14(5):621-633
Forms of Pb, Zn and Cd in the different size fractions (<2 μm, 2–53 μm and >53 μm) of waste dumps, stream sediments and surrounding soils from a former Au mine in Korea, were investigated chemically by sequential extraction analysis and mineralogically by XRD and analytical SEM, so as to clarify the relationships between chemical and mineralogical forms. Total concentrations for the waste dumps and the stream sediments range from 655 to 2920 mg/kg for Pb, 565 to 1191 mg/kg for Zn, and 24.4 to 71.4 mg/kg for Cd, while those for the surrounding soils do not exceed the natural background levels. Direct observations on the heavy mineral fractions of the waste dumps and the stream sediments indicates that the primary sphalerite is still the main pool of the Zn and Cd, while a large part of the primary galena has been changed into a carbonate-bound form. This is in a good agreement with the partitioning of chemical forms in the coarse fractions, in which most of the Zn (75.3 to 79.4% for the waste dumps) and Cd (54.8 to 60.1% for the waste dumps) are associated with the oxidizable form, while most of the Pb (68.8 to 71.0% for the waste dumps) is in the acid (NaOAc)-extractable form. On the other hand, the partitioning of metal forms in the clay fraction is characterised by the highest proportion of the reducible form for all metals (56.6 to 73.8% for Pb, 60.2 to 68.4% for Zn, and 27.1 to 36.8% for Cd in the waste dumps), suggesting precipitation of easily to moderately reducible oxides and hydroxides from the other forms during weathering. With the increase of pH, the dramatic changes of the acid-extractable Pb, the oxidizable Zn and Cd in the coarse fractions, and the exchangeable form, especially for Cd in the clay fraction indicate that pH is the prime factor controlling the partitioning of heavy metals.  相似文献   

7.
Sequential core sediments from northwestern Taihu Lake in China were analyzed for grain size, organic carbon and heavy metal content. The sediments are composed of organic-poor clayey-fine silts. The chemical speciations of Cu, Fe, Mn, Ni, Pb, and Zn were also analyzed using the BCR sequential extraction procedure. Cu, Fe, Ni, and Zn are mainly associated with the residue fraction; Mn is concentrated mainly in exchangeable/carbonate fraction and residue fraction; and Pb mainly in Fe/Mn oxide fraction and organic/sulfide fraction. The exchangeable/carbonate fractions of Cu, Fe, Ni, Zn and Pb are lower. The fractions of Ni, Pb and Zn bound to the Fe/Mn oxide have significant correlations with reducible Mn; the organic/sulfide fractions of Cu, Mn, Ni, Pb, and Zn have significant correlations with TOC. The extractable fractions of Cu, Mn, Ni, Pb, and Zn are high at the top 4 cm of the core sediments as compared to those in the deeper layers, showing the anthropogenic input of heavy metals is due to rapid industrial development. The heavy metal pollution history of the sediments has been recorded since the late 1970s, determined by the result of ^137Cs dating.  相似文献   

8.
This investigation revealed the presence of traffic-derived metals within road, stream and estuarine sediments collected from a coastal catchment, northern Australia. Studied road sediments displayed variable total metal concentrations (median Cd, Cu, Pb, Pd, Pt, Ni and Zn values: 0.19, 42.6, 67.5, 0.064, 0.104, 36.7 and 698 mg/kg, respectively). The distinctly elevated Zn values are due to abundant tyre rubber shreds (as verified by SEM-EDS and correlation analysis). By comparison to the road sediments, background stream sediments taken upstream from roads have relatively low median Pb, Pd, Pt and Zn concentrations (7.3 mg/kg Pb, 0.01 mg/kg Pd, 0.012 mg/kg Pt, 62 mg/kg Zn). Stream and estuarine sediment samples collected below roads have median values of 21.8 mg/kg Pb, 0.014 mg/kg Pd, 0.021 mg/kg Pt and 71 mg/kg Zn, and exhibit 207Pb/206Pb and 208Pb/206Pb ratios that appear on a mixing line between the isotopically distinct background stream sediments and the road sediments. Thus, mobilisation of dusts and sediments from road surfaces has resulted in relatively elevated Pb, Pd, Pt and Zn concentrations and non-radiogenic Pb isotope ratios in local coastal stream and estuarine sediments. The investigation demonstrates that traffic-derived metals enter coastal stream and estuary sediments at the fringe of the Great Barrier Reef lagoon.  相似文献   

9.
《Applied Geochemistry》2001,16(6):597-608
Most current investigations of sites contaminated with heavy metals (e.g. Pb, Zn, Cu) emphasise the importance of determining the amounts of physical and chemical forms of metals rather than just the total amounts present. Chemical extraction techniques used for this purpose are inevitably operationally defined. A more direct approach to the identification of crystalline forms can be made by mineralogical techniques such as X-ray powder diffraction (XRPD), but quantitative determination of a particular form is not often attempted. Recent advances in methods of analysis and sample preparation for XRPD mean that it is now a relatively simple matter to obtain quantitative XRPD data. Here, it is applied to the quantitative determination of the forms of Pb in different size-fractions of stream sediment samples from Leadhills/Wanlockhead, SW Scotland, an historic Pb mining area. Comparison of the XRPD analyses with determinations of Pb by atomic absorption spectrophotometry demonstrates that a large proportion of the Pb present in the stream sediments is in the form of cerussite (PbCO3). Furthermore, the cerussite tends to be concentrated in the silt fraction and is even a minor component of the clay-size fraction. However, quantitative analysis of fractions <6 μm indicates that cerussite alone cannot account for all the Pb in this size range. Indirectly, this result suggests that Pb adsorbed to clay minerals, organic matter and/or amorphous Fe and Mn oxides may be proportionally more important for the <6 μm materials. Sediment in this size range, however, typically accounts for no more than 1% by weight of the total stream bed sediment samples collected in the study area. In relation to its size distribution, the mobility of Pb within the wider environment is most likely to occur principally through physical transport of fine particles.  相似文献   

10.
为了响应国际地球化学旗图计划(ICCP259)中的全球地球化学采样子计划的实施,研制超低密度地球化学采样的最佳方法,1989～1990年在江西省开展了一项试点研究.在约15.7万平方公里的可采面积内采集了121件河漫滩沉积物样品.平均采样密度约为五个点/1300km2.采样覆盖度为24%.采样点主要布置在100-500km2的汇水盆地口上,其中有33个采样点控制的汇水盆地面积在400～2000km2之间.河漫滩沉积物样品来自深度在0.5m以下到1.2m的柱状剖面.样品定量分析了38种元素.文章从多方面讨论了超低密度河漫滩沉积物地球化学术样的代表性,并得出以下主要结论:1.在400-2000km2的汇水盆地口上采集河漫滩沉积物样品能较好地反映上游汇水盆地中的主要矿化.2.超低密度采样和以2个点/km2采集水系沉积物样品所获得的W、Sn、Cu、Pb和Zn五个元素的地球化学趋势相似.3.超低密度样品中W、Ph、Be、Rb等元素的分布特征与省内花岗岩的分布相吻合.4.超低密来样品中“3Ni+Cr+V”的分布能较好地反映扬子准地台与华南加里东精皱系在省内的分界线.  相似文献   

11.
Geochemical investigations have shown that the nickel sulphide mineralisation at Kambalda is detectable by sampling and analysing the minus 80-mesh fraction of near-surface soils. Over unmineralised mafic and ultramafic rocks the distribution of Ni in soils accurately reflects bedrock Ni distribution. In the environment of sulphide mineralisation Ni is preferentially concentrated in the coarse fractions of the soils, with a corresponding depletion in the minus 80-mesh fraction. Both Ni and Cu nevertheless display strong anomalies in minus 80-mesh fraction soils in the immediate vicinity of sub-outcropping mineralisation.  相似文献   

12.
Gold anomalies in drainage sediments are often erratic, reflecting both the nugget effect and hydraulic effects whereby gold is concentrated at favorable sites along a stream. This study investigates these factors in a stream in northeastern Thailand.Bulk sediment samples, consisting of approximately 40 kg of −12 mm material, were collected from bar and pavement sites along an 8 km study reach. Samples were wet sieved into eight size fractions. The five fractions between 425 μm and 53 μm were then processed to obtain heavy mineral concentrates (SG > 3.3). Gold content of all size and density fractions finer than 425 μm was determined by fire assay-atomic absorption.Concentrations of Au in the heavy mineral concentrates typically range from 10,000 to 50,000 ppb (maximum 198,000 ppb), whereas the corresponding light mineral fractions and the −53 μm fraction generally contain <5 ppb gold. Within the heavy mineral fractions concentrations of Au generally increase downstream away from their supposed source and are higher at pavement than at point bar sites. Variations in abundance of gold between point bar sites can be related to stream characteristics (such as width, velocity and bed roughness) that are indicative of changing energy conditions and of the ability of the stream to winnow light minerals from its bed.The estimated median number of gold particles in the heavy mineral concentrates increase from less than one in the 212–425 μm fraction to about three in the 53–106 μm size range. However, because of dilution by the light mineral and −53 μm fractions, the probability of a 30 g analytical sub-sample containing a particle of gold is so low that in thirteen out of sixteen −149 μm sediment samples no gold was detected. Insofar as this results from dilution by large quantities of −53 μm sediment, failure of conventional sieved sediment samples to reliably detect the anomaly is probably a consequence of increased erosion caused by deforestation and land usage.Heavy mineral concentrates from pavement and other high energy sites are more reliable than conventional sediment samples for detecting gold anomalies of the Huai Hin Laep type. A low sample density is adequate but, because anomaly contrast may increase downstream, careful interpretation is required.  相似文献   

13.
The nature of gold dispersion in soils and stream sediments associated with a copper-gold-mineralized system in northeastern Thailand has been investigated as a basis for identifying appropriate geochemical exploration techniques for the search for comparable deposits in similar environments.Soils were collected with varying relationships to mineralization as a basis for determining sample representativity, size distribution of gold, variation with soil horizon and possible pathfinder elements. Similarly, stream sediments were collected to estimate sample representativity, size distribution of gold, variation of gold with depth in the stream sediment profile and to compare the relative recoveries of gold in field-panned and laboratory-prepared heavy-mineral concentrates. Samples were analyzed for Au and potential indicator elements by a variety of methods but mostly by instrumental neutron activation analysis.Results indicate the consistent distribution of fine-grained gold in soils which allows Au analysis of relatively small samples from B-horizon soils to be used effectively and reliably to identify the surficial patterns of gold mineralization in the study area. Anomalous patterns of other indicator elements, Co, As, Cu, Sb, W, Pb, Zn, Ag, Fe and Mn, may contribute additional information regarding type of mineralization. This finding indicates the effectiveness of soil surveys in gold exploration, particularly in areas of deep weathering where fresh bedrock exposures are infrequent.Unlike soils, size distributions of gold in stream sediments, as a result of the local flow regime, vary both between sampling sites and at depths within a sampling site. Exploration requires Au analysis of the fine fraction (minus 63 μm) of active stream sediments to reduce the problem of sampling representativity. The presence of coarse-grained gold in the stream channel has drawn attention to the possible benefit of using the conventional field-panning method as a semiquantitative technique for providing immediate results. However, highly erratic distribution of pannable gold on a very local scale together with variable proportions of the total gold recovered in field-panned or heavy-mineral concentrates highlights a potentially serious drawback of the method. Combination of analysis of the minus 63 μm fraction and field panning appears warranted to cover the possible existence of gold of a wide size range in stream sediments.The overall results indicate the utility of geochemical exploration techniques in the search for gold mineralization. However, particular care is necessary in the design and implementation of geochemical techniques to ensure maximum reliability of exploration.  相似文献   

14.
This study assesses a simple sediment source tracing method using major- (Al, Ca, Fe, K, Mg, Mn, Na, P, Si, Ti) and trace-element (Ba, Be, Ce, Co, Cr, Mo, Nd, Pb, Sr, Th, V, Y, Zn) signatures of stream suspended particulate matter (SPM), bed sediments and soils in a small agricultural catchment in NE Scotland. Whilst most erosion studies characterise the large amounts of material mobilised at the highest flows, this study aimed to assess properties of sediments during moderate to low flow periods. These occur more frequent than intense storms and are important in linking stream sediments, near-channel sources and aquatic ecosystem impacts. Data were transformed by multivariate statistical methods to compare elemental signatures of SPM (ranging from 3 to 53 mg L−1 in the stream) and stream bed sediments with a limited number of near-channel source soils. Increased concentrations of Ce, Nd, Th and Y in subsoils contributed to the ability to discriminate between surface fieldslope and stream bank erosion sources. Stream bed sediments showed close matches with compositions of stream bank and arable surface soils, but signatures of SPM differed greatly from any of the sources. Large concentrations of Cr, Pb and Zn in SPM, particularly during summer (677, 177 and 661 mg kg−1, respectively) exceeded water quality standards and were linked to an accumulation of trace elements associated with biological material. The potential for within-stream alteration of SPM in relation to erosion sources was confirmed by changes in the nature of the SPM organic matter observed by IR spectroscopy. Thus the potential is shown for multi-element signatures to give information on catchment sediment sources to aid land management decisions, given careful consideration of the effects of in-stream alteration of eroded material. However, this combined information may be beneficial to process understanding linking land use and stream ecosystems at critical ecological periods.  相似文献   

15.
Small-scale mining and mineral processing at the Webbs Consols polymetallic PbZnAg deposit in northern New South Wales, Australia has caused a significant environmental impact on streams, soils and vegetation. Unconfined waste rock dumps and tailings dams are the source of the problems. The partly oxidised sulphidic mine wastes contain abundant sulphides (arsenopyrite, sphalerite, galena) and oxidation products (scorodite, anglesite, smectite, Fe-oxyhydroxides), and possess extreme As and Pb (wt% levels) and elevated Ag, Cd, Cu, Sb and Zn values. Contemporary sulphide oxidation, hardpan formation, crystallisation of mineral efflorescences and acid mine drainage generation occur within the waste repositories. Acid seepages (pH 1.9–6.0) from waste dumps, tailings dams and mine workings display extreme As, Pb and Zn and elevated Cd, Cu and Sb contents. Drainage from the area is by the strongly contaminated Webbs Consols Creek and although this stream joins and is diluted by the much larger Severn River, contamination of water and stream sediments in the latter is evident for 1–5 km, and 12 km respectively, downstream of the mine site. The pronounced contamination of local and regional soils and sediments, despite the relatively small scale of the former operation, is due to the high metal tenor of abandoned waste material and the scarcity of neutralising minerals. Any rehabilitation plan of the site should include the relocation of waste materials to higher ground and capping, with only partial neutralisation of the waste to pH 4–5 in order to limit potential dissolution of scorodite and mobilisation of As into seepages and stream waters.  相似文献   

16.
Levels of heavy metals are found in soils and waters of the major tributary valleys of the Jordan Valley. Heavy metal content in soils irrigated by treated waste water were measured for a 40 km reach of Zarqa River. Soil samples from eight different sites along the upper course of this river were analyzed to determine the concentration of selected heavy metals (CO, Cr, Cu, Pb, Ni, Zn). Silt forms the major component of the soils with an average of 54%. Clay fractions show an increase with depth from 17 to 41%. Trends in particle size distribution and metal contents were compared across sample sites. Samples contained moderate to considerable levels of Pb and Ni. Concentrations of Cu and Cr ranged between 33–59 and 65–90 ppm, respectively. These values represent a slight to moderate class of pollution. The concentration of Cr shows a decrease with depth and distance from the waste water plant. Cu, Zn, and Ni show increasing concentrations with depth but Pb and CO do not. The concentrations of the measured heavy metals increases near the waste water treatment plant but decreases with distance from the plant due to precipitation in the stream bed and dilution with stream water. This decline in metal content with distance from the treatment plant suggests that most metals reaching floodplain soils may derive from the same source. Although current metal concentrations are low to moderate, floodplain surface soils in this area should be regarded as a potential source for future heavy metal pollution downstream.  相似文献   

17.
Bed sediment-associated trace metals in an urban stream, Oahu, Hawaii   总被引：78，自引：0，他引：78  
 Of the 117 stream and lake systems sampled nationwide, fish from Manoa Stream on Oahu, Hawaii, have consistently shown the highest Pb concentrations. Therefore a detailed study was conducted to examine total metal contents in bed sediments from a 5.8-km stretch of Manoa Stream. A total of 123 samples (<63 μm) were examined for 18 elements and 14 samples for 21 elements. Selected samples were also examined using different leach solutions to examine metal phase associations. All trace metal data, computations of enrichment ratios and the modified index of geoaccumulation point to mineralogical control for Cr and Ni; minor anthropogenic contamination for Ba, Cd, Cu, Hg and Zn; and a very strong contamination signal for Pb. Maximum Pb contents (up to 1080 mg kg−1) were associated with anthropogenic material dumping in minor tributaries, storm sewer sediments and sediments in the “lower” section of the basin. Proportionally Pb had the highest non-residual component of elements examined; dominantly in the reducible phase associated with Mn and amorphous Fe oxyhydroxides. The contamination signal was typically lowest in the “undisturbed” headwater reach of the basin (above 5.1 km) with significant increases throughout the “residential” and “commercial-institutional” zones of the mid-basin. The spatial pattern of bed sediment contamination and evidence from storm sewer-outlet sediments strongly indicates that Pb, and to a lesser degree some other metals, is still being transported to the stream and the primary agent is soil erosion and transport of metals sorbed to sediments. The primary source of sediment-associated metals is considered to be the automobile, though other minor sources can not be ruled out. Received: 3 November 1998 · Accepted: 26 January 1999  相似文献   

18.
 A total of 121 bed sediment samples were collected from a 5.8-km stretch of Manoa Stream, Hawaii. Samples were physically partitioned into two grain-size fractions, <63 μm and 63–125 μm, acid digested and analyzed by ICP-AES and FAAS. Non-parametric matched-pair statistical testing and correlation analysis were used to assess differences and strengths of association between the two fractions for Al, Ba, Cu, Fe, Mn, Ni, Pb, Ti and Zn. Results indicated statistically significant differences between fractions for all elements except Mn. Concentrations were significantly greater in the <63 μm fraction for Al, Cu, Pb, Ti and Zn, while Ba, Fe and Ni were higher in the 63–125 μm fraction. Though some elements had statistically significant differences between fractions (Al, Ba, Fe and Zn) percentage differences were in the range of analytical precision of the instrument and thus differences were not practically significant. Correlation analysis indicated strong positive associations for all elements between the two fractions (p<0.0001). Three contamination indices indicated similar degrees of pollution for each size fraction for four elements having an anthropogenic signal (Ba, Cu, Pb and Zn). The environmental information obtained from the 63–125 μm fraction was essentially equivalent to that from the <63 μm fraction. In this system it is clear that both bed sediment fractions indicate anthropogenic enrichment of trace metals, especially Pb, and further supports previous research that has found that aquatic sediments are critical median for tracing sources of pollution. Received: 17 August 1998 · Accepted: 30 October 1998  相似文献   

19.
To test the relative effectiveness of stream water and sediment as geochemical exploration media in the Rio Tanama porphyry copper district of Puerto Rico, we collected and subsequently analyzed samples of water and sediment from 29 sites in the rivers and tributaries of the district. Copper, Mo, Pb, Zn, SO42?, and pH were determined in the waters; Cu, Mo, Pb, and Zn were determined in the sediments. In addition, copper in five partial extractions from the sediments was determined. Geochemical contrast (anomaly-to-background quotient) was the principal criterion by which the effectiveness of the two media and the five extractions were judged.Among the distribution patterns of metals in stream water, that of copper most clearly delineates the known porphyry copper deposits and yields the longest discernable dispersion train. The distribution patterns of Mo, Pb, and Zn in water show little relationship to the known mineralization. The distribution of SO42? in water delineates the copper deposits and also the more extensive pyrite alteration in the district; its recognizable downstream dispersion train is substantially longer than those of the metals, either in water or sediment. Low pH values in small tributaries delineate areas of known sulfide mineralization.The distribution patterns of copper in sediments clearly delineate the known deposits, and the dispersion trains are longer than those of copper in water.The partial determinations of copper related to secondary iron and manganese oxides yield the strongest geochemical contrasts and longest recognizable dispersion trains. Significantly high concentrations of molybdenum in sediments were found at only three sites, all within one-half km downstream of the known copper deposits. The distribution patterns of lead and zinc in sediments are clearly related to the known primary lead-zinc haloes around the copper deposits. The recognizable downstream dispersion trains of lead and zinc are shorter than those of copper.  相似文献   

20.
Heavy metal levels in surface sediments from Tamaki Estuary demonstrate significant up estuary increases in Cu, Pb, Zn, Cd and mud concentrations. Increased metal levels towards the head of the estuary are linked to local catchment sources reflecting the historical development, industrialisation and urbanisation of catchment areas surrounding the upper estuary. The relatively narrow constriction in the middle estuary (Panmure area), makes it susceptible to accumulation of upper estuary pollutants, since the constriction reduces circulation and extends the time required for fine waterborne sediments in the upper estuary to exchange with fresh coastal water. As a result fine fraction sediments trapped in the upper estuary facilitate capture and retention of pollutants at the head of the estuary. The increase in sandy mud poor sediments towards the mouth of the estuary is associated with generally low metal concentrations. The estuary’s geomorphic shape with a mid estuary constriction, sediment texture and mineralogy and catchment history are significant factors in understanding the overall spatial distribution of contaminants in the estuary. Bulk concentration values for Cu, Pb, Zn, and Cd in all the studied surface samples occur below ANZECC ISQG-H toxicity values. Cd and Cu concentrations are also below the ISQG-L toxicity levels for these elements. However, Pb and Zn concentrations do exceed the ISQG-L values in some of the surface bulk samples in the upper estuary proximal to long established sources of catchment pollution.  相似文献   

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