共查询到20条相似文献，搜索用时 31 毫秒
1.
The problem of using surface geochemical exploration techniques in areas of very thick and electrically conductive weathering residuum is common to much of Australia. At the Elura deposit (New South Wales) a distinct electrogeochemical H+ anomaly can be detected in the top few cm of residual soil above about 100 m of conductive residual overburden. In the present paper the results of an investigation of the much more difficult problem of detecting sulfide mineralization beneath thick conductive transported overburden are described.The objective of the study was to demonstrate that sulfide mineralization beneath thick transported overburden can be detected by geochemical patterns in surface soils in the context of an electrogeochemical model of dispersion.The Thalanga massive sulfide deposit in northeast Queensland has at least 4 million tonnes of 15% combined Zn, Pb and Cu. The mineralized horizon lies at the contact between rhyolitic and dacitic rocks of the Cambro-Ordovician Mt. Windsor Volcanics. The deposit is covered by transported cemented Tertiary terrigenous clayey sandstones and grits; these are electrically conductive and vary in thickness from 0 to 70 m.Near-surface soil samples were collected along five traverses normal to the strike of mineralization. The traverses were located to give 0 m, 1 m, 30 m, 50 m, and 70 m overburden thicknesses; there is no known significant mineralization along the last traverse which is assumed to be background, and there is a small gossan where the overburden is absent.Dispersion patterns influenced by electrogeochemical processes should result in relatively low values for ions over massive sulfides with lateral peaks; this has been termed a “rabbit-ear” anomaly. “Rabbit-ear” anomalies in surface soils for H+, Cu, and Zn occur over the sulfide zone. The H+ pattern is better defined where there is a significant depth of overburden (where the anomaly is about 500 m wide). The Cu anomaly is 300–600 m wide, and the Zn anomaly is 450–675 m wide.Even where the overburden is 50 m thick, anomalous “rabbit-ear” anomalies for H+ and Zn are clearly identifiable, but the anomaly for Cu is a single peak of 20 ppm over the hanging wall. It is suggested that the results of this work convincingly demonstrate that at Thalanga surface soil samples may reliably be used to detect massive sulfide deposits - even where they are effectively blind beneath a considerable thickness of transported and conductive overburden. The processes of dispersion are speculated to be diffusion, and it is argued that the pattern-controlling mechanism is electrochemical. 相似文献
2.
In order to determine the metal-bearing phases with special emphasis on Cu, a sequential extraction has been carried out on seven soil samples from a sulphide-bearing spodosol profile in Liikavaara Östra, close to the Aitik Copper Mine in northern Sweden. A reference spodosol profile with very low abundances of sulphides located far from anthropogenic emissions was also studied. Five fractions were selected for the extraction: (I) CH3COONa-extractable (exchangeable/adsorbed/carbonate); (II) Na4P2O7-extractable (labile organics); (III) 0.25 M NH2OH·HCl-extractable (amorphous Fe oxyhydroxides/Mn oxides); (IV) 1 M NH2OH·HCl-extractable (crystalline Fe oxides); and (V) KClO3/HCl-extractable (organics and sulphides). The distribution of trace elements (Co, Cr, Cu, Ni, Pb and Zn) in the profile in Liikavaara Östra is different from that in the reference profile. Possible explanations for these differences are (i) the presence of sulphides in the soil, (ii) atmospheric deposition of dust derived from mining activities at the Aitik Copper Mine, and (iii) mineralogical heterogeneities inherited from the deposition of the till. There is no straightforward correlation between the amount of the extracted phases and the metal extractability in the soils. This fact indicates that other factors are important for the retention of trace metals as well. The data presented in this study suggest that Co, Cr and Ni, to a fairly large extent, are associated with the organic matter in the B-horizon in both profiles, while in the C-horizon in Liikavaara Östra, sulphides are probably the more important carriers of these elements. For Co and Ni, Fe oxyhydroxides seem to be important. Most of the Cr occurred in the residual remaining after the leaching procedure. Copper and Zn seem to be associated with the organic matter to some extent in the B-horizon. The concentration of Cu in the C-horizon in Liikavaara Östra is high (2310 ppm), but only a very small fraction is likely to be hosted by sulphides. It is concluded that the major part of Cu in the C-horizon and a prominent fraction in the B-horizon in Liikavaara Östra are associated with some secondary phase that is extractable during extractions III and IV. Possible candidates for this phase are goethite and inclusions of native Cu in weathered biotite. 相似文献
3.
Chunying Chang Fangbai Li Chengshuai Liu Jianfeng Gao Hui Tong Manjia Chen 《中国地球化学学报》2016,35(4):329-339
Soil secondary minerals are important scavengers of rare earth elements (REEs) in soils and thus affect geochemical behavior and occurrence of REEs. The fractionation of REEs is a common geochemical phenomenon in soils but has received little attention, especially fractionation induced by secondary minerals. In this study, REEs (La to Lu and Y) associated with soil-abundant secondary minerals Fe-, Al-, and Mn-oxides in 196 soil samples were investigated to explore the fractionation and anomalies of REEs related to the minerals. The results show right-inclined chondrite-normalized REE patterns for La–Lu in soils subjected to total soil digestion and partial soil extraction. Light REEs (LREEs) enrichment features were negatively correlated with a Eu anomaly and positively correlated with a Ce anomaly. The fractionation between LREEs and heavy REEs (HREEs) was attributed to the high adsorption affinity of LREEs to secondary minerals and the preferred activation/leaching of HREEs. The substantial fractions of REEs in soils extracted by oxalate and Dithionite-Citrate-Bicarbonate buffer solutions were labile (10 %–30 %), which were similar to the mass fraction of Fe (10 %–20 %). Furthermore, Eu was found to be more mobile than the other REEs in the soils, whereas Ce was less mobile. These results add to our understanding of the distribution and geochemical behavior of REEs in soils, and also help to deduce the conditions of soil formation from REE fractionation. 相似文献
4.
黄河下游山东段沿岸土壤中重金属元素异常的成因 总被引：9，自引：1，他引：8
山东省多目标区域地球化学调查发现,沿黄河两岸分布有As、Cd、Cr、Cu、Pb、Zn、Ni等重金属元素异常,这类异常衬度不大,并多沿河呈不连续分布。研究结果表明,异常区土壤重金属元素的含量与SiO2、Al2O3Fe2O3等常量组分间具有显著的相关性,多数微量重金属元素随SiO2含量的增加而降低,随Al2O3Fe2O3含量的增加而增加。根据常量组分与土壤质地的密切关系可以推断。土壤质地对重金属元素异常的形成具明显的控制作用。 相似文献
5.
Comparison of stream sediment and soil sampling for regional exploration in the eastern Alps,Austria
《Journal of Geochemical Exploration》1988,31(1):75-85
Tests in three different areas of the Austrian Alps showed that in mountainous areas, soil samples taken at the break of slope are an alternative sampling medium to stream sediments for regional geochemical exploration even if taken at the unusually low density of 1 sample/km2. B-horizon soil samples from the nearest break of slope were collected in conjunction with stream sediment orientation studies. The minus 0.2 mm fraction of all samples was routinely analyzed for the total contents of 36 elements. The results for the indicator elements in the three test areas (Area 1: Cu; Area 2: Ag, As, Cu, Pb, Sb, Sn, Zn; Area 3: As, Cu) showed that break-of-slope soil samples more clearly indicate known mineralization than drainage geochemistry. In the soils, almost all elements showed a higher natural variability of the data with considerably higher metal contents. In mountaineous regions, each soil sample will have a clearly defined area of influence. The break of slope represents a site where clastically and hydromorphically dispersed elements are concentrated. It is concluded that soil samples can be used for regional exploration using low sampling densities in mountaineous areas. At the same time they will provide valuable information for other fields of science (e.g. agriculture, forestry, environmental sciences) and are thus superior to stream sediments. 相似文献
6.
Source and distribution of metals in urban soil of Bombay,India, using multivariate statistical techniques 总被引：7，自引：0，他引：7
Simplification of a complex system of geochemical variables obtained from the soils of an industrialized area of Bombay is attempted by means of R-mode factor analysis. Prior to factor analysis, discriminant analysis was carried out taking rock and soil chemical data to establish the anthropogenic contribution of metals in soil. Trace elements (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) are expressed in terms of three rotated factors. The factors mostly indicate anthropogenic sources of metals such as atmospheric fallout, emission from different industrial chimneys, crushing operations in quarries, and sewage sludges. Major elements (Na, Mg, Al, Si, P, K, Ca, Ti, Mn, and Fe) are also expressed in terms of three rotated factors indicating natural processes such as chemical weathering, presence of clay minerals, and contribution from sewage sludges and municipal refuse. Summary statistics (mean, standard deviation, skewness, and kurtosis) for the particle size distribution were interpreted as moderate dominance of fine particles. Mineralogical studies revealed the presence of montmorillonite, kaolinite, and illite types of clay minerals. Thus the present study provides information about the metal content entering into the soil and their level, sources, and distribution in the area. 相似文献
7.
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. 相似文献
8.
山东省济阳县土壤重金属元素异常成因研究 总被引：1，自引：1，他引：0
基于山东省济阳县土壤地球化学调查数据,发现济阳县城北部农田区有As、Bi、Cd、Cu、F、Ni、Sb、Hg、Zn等重金属为主的元素异常,各元素异常套合较好,异常衬度相差较大,呈弱富集状态。异常查证结果表明,重金属元素含量与SiO2、Al2O3、Fe2O3等常量组分之间具有显著的相关性,随SiO2含量的增加而降低,随Al2O3、Fe2O3含量的增加而增加,说明土壤常量组分及其所决定的土壤质地是导致异常形成的主要因素,而人类活动的后期叠加作用是异常形成的次要因素。在异常区所抽检的小麦、黄瓜样品中,Hg、F等元素有不同程度超标现象,说明异常区土壤中有毒、有害元素已对农产品质量产生影响,应引起重视。科学合理施肥,加强各类污染源的控制,继续保持土壤碱性环境,是防止异常区危害人类健康的有效措施。 相似文献
9.
利用1∶25万土地质量地球化学调查数据分析和研究了安徽省宣城市南部地区土壤中As、Cd、Cr、Cu、Hg、Ni、Pb、Zn 8种重金属元素的地球化学特征以及重金属异常来源。调查发现地质背景是土壤元素含量的主控因素,调查区表、深层土壤重金属元素含量空间分布特征与地质背景、沉积环境表现出显著的空间一致性,重金属高含量成土母岩(荷塘组、皮园村组、蓝田组等地层)是土壤重金属元素高异常的主要影响因素,此外矿山开采、大气干湿沉降也是土壤重金属高异常的影响因素之一,土壤中Pb、Hg、Cd、Cr元素具有大气干湿沉降的输入来源。调查区土壤重金属污染风险主要影响指标为Cd,土壤Cd超过农用地土壤污染风险管制值的样品比例为2.56%,形态分析结果显示土壤Cd以离子交换态为主,结合农作物调查发现在土壤Cd高异常区存在一定的生态风险。 相似文献
10.
11.
红石砬铂矿地球化学异常组分简单,仅发育Ｐｔ和Ｐｄ的强异常,部分伴生Ａｕ异常,不伴生Ｃｒ、Ｃｏ、Ｃｕ、Ｎｉ、Ｖ、Ａｓ、Ｓｂ、Ａｇ、Ｐｂ等元素异常。岩石、土壤、水系沉积物中Ｐｔ、Ｐｄ的分布和异常模式与铂族矿化特征、矿体剥蚀程度及其表生地球化学行为等有关。矿体出露地表时,Ｐｔ、Ｐｄ呈强异常分布,异常的ｗ（Ｐｔ）／ｗ（Ｐｄ）比值与矿石中ｗ（Ｐｔ）／ｗ（Ｐｄ）比率基本一致;隐伏矿体上方,Ｐｄ有明显的浓集,ｗ（Ｐｔ）／ｗ（Ｐｄ）比值小于地表矿体。表生环境中,Ｐｔ、Ｐｄ可以呈矿物碎屑、可溶态等多种形式迁移,在疏松沉积物中形成异常。因此,以Ｐｔ、Ｐｄ作为直接指示元素,进行地球化学勘查,可以发现这种类型的铂族矿床。 相似文献
12.
O. A. Korotkina L. N. Kogarko E. S. Bazilevskaya I. V. Kurbakova 《Geochemistry International》2010,48(12):1166-1176
Fe-Mn deposits for this research were sampled at the floor of the Atlantic Ocean in the Cape Verde Quadrangle, Elena Seamount,
and Strakhov Basin. The samples were analyzed for major components and for Ni, Co, Cu, P, S, and other trace elements by ICP-AES.
Common features in the distribution of REE (high positive Ce anomalies) were discovered, and trends in the distribution of
elements with depths are revealed. As, Pb, Sr, Co, and Pt are prone to accumulate in shallower water areas, whereas Cu and
Li are enriched at deeper water territories. The samples are analyzed in compliance with Andreev’s classification, and their
noble metal composition is determined. 相似文献
13.
Some 3400 drill core samples of the Athabasca Group and underlying regolith have been obtained by sampling 8-m sections from 55 diamond drill holes in the McClean Lake Area, Saskatchewan. Forty eight holes are from sections over six areas known to contain uranium mineralization and 7 are from unmineralized areas. The uranium zones are covered by 30 to 180 m of Athabasca sandstones and conglomerates.The uranium mineralization of the McClean deposits can be described as belonging to two different facies; a more reduced sulphide-arsenide facies and a more oxidized hematite-“bleached” facies, superimposed on any one of three host rocks.The sulphide-arsenide facies is probably older and, except in one deposit, it forms a patchy distribution of relicts. The principal pattern is an upwards increase in sulphur/arsenic ratio. The hematite-“bleached” facies appears to be younger and may represent a reworking of the earlier sulphide-arsenide facies mineralization under more oxidizing conditions.The trace metals can be grouped according to their redox behaviour. Vanadium, Mo and U, occurring as oxides, form one group while Ni, Co, Zn, Cu and As, occurring as sulphides and/or arsenides, form intermediate and most reduced groups, respectively. Iron is concentrated in the most oxidized facies as hematite or goethite and in the most reduced facies as pyritebravoite, siderite and chlorite. Manganese follows the distribution of siderite.The ratio of oxidized to reduced minerals can be represented by the ratio of U/Ni. This ratio can be used to estimate the variation of redox potential in the deposit at the time of deposition or alteration. The principal pattern is one of systematic increase in U/Ni ratio or oxidation potential both upward and to the northeast in each of the hematite and bleached facies.A generalized Eh-pH diagram is used to qualitatively describe the significance of each mineral facies.The U/Ni ratio of the transition between the hematite and “bleached” facies increases upwards. The phase diagram suggests that a possible cause is an upward decrease in pH and increase in Eh.The overall distribution is compatible with the origin of the deposits due to reduction at the interface between a plume of reductant emanating from fractures in the sub-Athabasca basement and an oxidizing aquifer moving southwestward in the sandstone. This model does not accurately predict the distribution of elements among the seven McClean Lake pods. However, it explains the overall pattern. Local variations in metal ratios in solution either in time or reflecting local provenance could be adduced to explain local deviations from the overall pattern.Clay alteration, apparently largely contemporaneous with the earliest mineralization, is largely illitic but with sporadic occurrences of xenotime and goyazite. Thus K and to some extent P, Y and light REE's are also enriched to some degree in the deposits.Uranium analysis of the drill core shows that there is little movement of U into the overlying sandstones from basement rocks and regolith that contain no uranium deposits. Uranium in the Athabasca sandstone from these areas averages less than 1 ppm. However, where uranium zones have been found in the basement rocks, regolith and lower Athabasca sandstone, U values greater than 2–3 ppm consistently occur in the overlying sandstones at or near surface.There appear to be two types of U anomalies, those that flank the deposits and those that directly overlie them. Both types exhibit vertical and lateral continuity. They are associated with vertical to steeply dipping fracture systems that traverse the Athabasca sandstone from basement to surface. The fractures are thought to be related to diagenetic processes from compaction of the sedimentary rocks over basement irregularities as well as tectonic processes (i.e. re-adjustment along old basement structures).These results suggest that target areas containing deeply buried uranium deposits could be defined by U analyses of the Athabasca sandstone from quite widely spaced holes of limited depth. This conclusion can be compared to XRD and chemical studies of clay mineral distribution within the Athabasca sandstone about the deposits. 相似文献
14.
Partitioning,bioavailability and origin of heavy metals from the Nador Lagoon sediments (Morocco) as a basis for their management 总被引：2，自引：0，他引：2
Nador Lagoon sediments show low trace element concentrations, and, in relation to the lagoon geochemical baseline, only some
anomalies for As, Cd, Cu and Pb in the NW of the lagoon deserve to be outstanding. The distribution of major, minor and trace
elements in the lagoon allows a breakdown in four zones. Between “Beni Ensar” and “Atelouane” (zone A), a quite confined zone
rich in organic matter and S, the most important trace-element anomalies (As, Cd, Co, Cu, Mn, Pb, Zn) were found, mainly around
industry and old mining activities. In the surrounding of the city of Nador (zone B), the anomalies correspond to Mn, Cu and
Zn. The coastal barrier and Kebdana channel (zone C) show moderately concentrations of Cd, Cr and Ni at specific sites. The
less polluted area is the SE of the lagoon (zone D), with no outstanding anomaly. In lagoon sediments, metal bioavailability
is very low. The metal partitioning patterns show that Cu, Pb and Zn present a low availability because they are bounded to
the residual, non-mobile phases of the sediments. Only in some sites, the fraction was associated with organic matter, which
could be liberated easily. Arsenic is concentrated in both the residual phases and the organic matter, the latter being more
available. Cadmium is mainly concentrated in some samples in the interchangeable fraction, which could be considered as a
potentially toxic element because it is easily released. Concerning the origin of these trace elements, those found in zone A
correspond mostly to a natural source by weathering of mount Gourougou volcanic rocks (As, Co, Cu, Pb and Zn), and to an anthropogenic
origin (Cd) owing to the presence of industry and old mines. In zone B, contributions of Cu and Zn enter the lagoon through
soil weathering and river-borne, and as anthropogenic pollution from urban wastes. In zone C the most important pollutant
is Cd deduced to be of anthropogenic origin from the close industry and intensive agriculture area. In spite of the intense
socio-economic activities developed in the Nador Lagoon (agriculture, industry, fishing, tourism) trace element concentrations
in the sediments are low and with scarce bioavailability. Only the NW sector is relativity polluted because of geogenic features. 相似文献
15.
笔者以湖南大根垄钨多金属矿为试验研究区,以20 m点距在已知矿体上方取土壤样,并按照24 h提取时间、1 000 mL HNO3提取液、50 cm电极间距等工作条件进行了地电提取试验。结果表明,地电提取前后土壤中的元素含量变化不大,被提取到的金属元素应属土壤金属总量的一部分。次生晕与地电提取的异常形态对比发现:Co、Ni较清晰,W次之,Cr无异常;元素的异常特征主要取决于土壤中该元素的活性形式所占比例。综合分析认为地电提取异常与矿体的相对位置有关:矿体的下坡位置以及控矿断裂附近容易形成异常,距离原生矿体太近则会对异常有明显干扰。在本矿区,矿体风化程度越高对Co、Ni的地电提取异常越有利;其异常宽度一般比次生晕窄。 相似文献
16.
Assessment of trace element contamination in soils around Chinnaeru River Basin, Nalgonda District, India 总被引：1，自引：1，他引：0
G. Machender Ratnakar Dhakate G. Tamma Rao G. Loukya M. N. Reddy 《Environmental Earth Sciences》2013,70(3):1021-1037
Concentrations of trace elements such as As, Ba, Co, Cr, Cu, Ni, Pb, Rb, Sr, V, Y, Zn and Zr were studied in soils to understand metal contamination due to agriculture and geogenic activities in Chinnaeru River Basin, Nalgonda District, India. This area is affected by the geogenic fluoride contamination. The contamination of the soils was assessed on the basis of geoaccumulation index, enrichment factor (EF), contamination factor and degree of contamination. Forty-four soil samples were collected from the agricultural field from the study area from top 10–50 cm layer of soil. Soil samples were analyzed for trace elements using X-ray fluorescence spectrometer. Data revealed that soils in the study area are significantly contaminated, showing high level of toxic elements than normal distribution. The ranges of concentration of Ba (370–1,710 mg/kg), Cr (8.7–543 mg/kg), Cu (7.7–96.6 mg/kg), Ni (5.4–168 mg/kg), Rb (29.6–223 mg/kg), Sr (134–438 mg/kg), Zr (141.2–8,232 mg/kg) and Zn (29–478 mg/kg). The concentration of other elements was similar to the levels in the earth’s crust or pointed to metal depletion in the soil (EF < 1). The high EFs for some trace elements obtained in soil samples show that there is a considerable heavy metal pollution, which could be due to excessive use of fertilizers and pesticides used for agricultural or may be due to natural geogenic processes in the area. Comparative study has been made with other soil-polluted heavy metal areas and its mobility in soil and groundwater has been discussed. A contamination site poses significant environmental hazards for terrestrial and aquatic ecosystems. They are important sources of pollution and may result in ecotoxicological effects on terrestrial, groundwater and aquatic ecosystems. 相似文献
17.
甘肃嘉峪关市表层土壤重金属空间分布与评价 总被引：1，自引：0，他引：1
为研究嘉峪关市重金属分布对环境的影响,分析了嘉峪关市表层土壤重金属分布和含量变化,并评价其富集程度,判断其来源和影响因素。采用电感耦合等离子体质谱仪（ICP-MS）测量嘉峪关市134个表层土壤样品中六种重金属元素（Cr、Cd、Cu、Pb、Ni、Zn）的含量,其平均含量分别为281.6 mg/kg、0.35 mg/kg、60.68 mg/kg、51.39 mg/kg、108.65 mg/kg、161.0 mg/kg。在土壤重金属含量空间分布的基础上,用内梅罗指数法和地累积指数法对研究区土壤重金属富集程度进行了评价,六种元素地累积指数排序依次为: Cr > Cd > Pb > Cu > Zn > Ni,各功能区重金属元素整体富集程度依次为工业区 > 戈壁 > 生活区 > 农业区。戈壁采样点重金属元素含量（除Ni外）高于农业区,除工业因素外,地表植被的缺失加剧了戈壁地区重金属元素的富集。结合主成分分析,重金属元素空间展布,及内梅罗指数评价和地累积指数评价,分析了各元素可能的来源,认为Cr、Zn主要来自以钢铁生产加工为主的工业源,Cd、Cu、Pb来自于交通源,Ni可能与钢铁生产或当地背景值有关。通过分析嘉峪关市土壤重金属分布情况,以期为改善当地土壤质量提供科学依据,为我国西北地区土壤重金属的研究提供参考。 相似文献
18.
R.N. Carver L.M. Chenoweth R.H. Mazzucchelli C.J. Oates T.W. Robbins 《Journal of Geochemical Exploration》1987,28(1-3)
Desert land surfaces are commonly characterized by a veneer or pavement of siliceous and/or ferruginous stony material. This material can be shown in most cases to be predominantly bedrock-derived, despite often severe modification by prolonged weathering, and can therefore be selectively sampled and analyzed as an indicator of bedrock geochemistry in geochemical surveys.Most pavements probably owe their existence to the interaction of several dispersion mechanisms. However, a common factor in all cases is the concentration of coarse particles at the surface as a result of the selective removal by erosion of fine dilutant material. Hence, the preferred name when used in the geochemical context is “lag”.In lag sampling, particles in the range 2.0–6.0 mm are screened on site from the unconsolidated surface material. Material in this size range has been found to be quite uniformly distributed over a wide range of arid region environments, including areas where residual soils are severely diluted by transported alluvial and aeolian materials.Data from exploration programmes for Au, Cu-Pb-Zn-Ba, and Ni allow comparison of results for lag sampling with those for alternative sample media in a variety of arid region environments. Analysis of lag samples for Au, Cu and As clearly indicates the presence of bedrock Au mineralization in the Paterson and Eastern Goldfields Provinces of Western Australia. In these areas both lags and soils exhibit good anomaly contrast, but lags show more extensive lateral dispersion, leading to advantages in reconnaissance exploration.Strong anomalies for Ni and Cu are developed in lags, compared with subdued response in fine-fraction soils over a Ni sulphide occurrence in the Eastern Goldfields which has been subjected to deep lateritic weathering.Lag geochemistry also clearly reflects sub-economic base metal and barite occurrences in the McArthur Basin, N.T., in spite of the dilution of surface soils by sands probably related to a Mesozoic marine incursion. Orientation sampling over a Pb-Zn prospect in the Pine Creek Geosyncline has demonstrated optimum response in lag samples compared with various size fractions of the associated lithosols.Variable dilution of lag samples by coarse quartz sand can be a problem in areas with substantial transported overburden. A simple procedure to ‘correct’ trace-element values using regression analysis based on the Fe content of samples is described as a means of reducing ‘noise’ resulting from such matrix variations. 相似文献
19.
B.L. Farrell 《Journal of Geochemical Exploration》1984,22(1-3)
This paper reviews some aspects of the use of “loam” (soil) concentrates in geochemical surveys in arid, deeply weathered environments.An orientation survey at a small Ni-Cu-Co prospect in Western Australia has shown that discrimination between mineralized and unmineralized samples could be achieved using Ni, Cu, Co, Cr, Zn, As, Sn, Sc, Ti, Yb and Y in the coarse fraction of heavy concentrates. However, at the same prospect the best contrast for Ni, Cu and Co in surface samples was provided by analysis of the same fraction following a cold ammonium citrate/hydroxylamine hydrochloride digestion.At a nearby, larger prospect, some 54 km2 in area, concentrates were separated, by jigging, from bulk soil samples, themselves composites of representative subsamples. Sampling at a density of 4 samples per km2 revealed 1–2 km2 size anomalies of Cu, Ni, Co, Cr, As and Au which could be related, variously, to known Ni-Cu and Au mineralization.In Botswana, analysis of concentrates, separated by tabling from samples collected at a density of 1 sample per 7.5 km2 over an area of 5400 km2, identified distinctive geochemical districts. Enhanced values of Au and of Cu-Ni in the concentrates were relatable to known mineralization and the results suggested that there were also Sn-W-Mo-Bi (granitoid) and Au-Pb-Zn-Bi-Sn (volcanogenic) associations which could lead to new prospecting targets. Anomalies of certain elements (for example, Cu in an ultramafic environment) may be more readily detected in surface material by “enrichment indexing” the concentrate data. 相似文献
20.
三峡库区重庆段土壤某些重金属污染的矿物学方法评价 总被引：1，自引：0，他引：1
分析了三峡库区重庆段51件土壤样品的矿物组成,结果表明,石英、斜长石和钾长石是土壤中主要矿物,大部分样品中石英的含量高,主要粘土矿物是伊利石,其次是蒙脱石,其他矿物含量较低。同时,参比国家水质标准,根据土壤对金属离子的临界吸附量公式计算了样品重金属污染的阈值,对样品进行了Cd、Hg、Pb、Cu的污染状况评价。结果表明,土壤中污染元素的含量与生态效应评价值并不一致;Cd和Hg的污染尚未达到临界值,危险性较小,但不能因此忽视地球化学定时炸弹的风险;Pb和Cu的污染严重。由于包括母岩在内的样品的评价结果显示污染,可能反映研究区的地球化学背景,需要采取有效措施改善和预防目前和将来的污染危害。 相似文献