共查询到20条相似文献，搜索用时 718 毫秒
1.
In Scandinavia, most fluvial erosion takes place in the Quaternary glacial overburden at a restricted number of small source areas along individual drainage channels. As a consequence, a sample of active stream sediment is representative of only a very limited portion of the drainage area. This restriction makes stream sediment less reliable for regional exploration than generally expected. Overbank (levee or river-plain) sediment produced during large floods is an alternate more representative sampling medium. The sediment suspended during a flood has a much more widespread origin, and when the load is deposited upon the flood plain, nearly horizontal strata are formed and preserved at levels above the ordinary stream channel. A composite sample through a vertical section of such strata represents a great number of sediment sources that have been active at different times and forms an integrated sample of the entire catchment area. Because young sediments overlay older, the uppermost layers will be contaminated by pollutants in industrialized regions, but those at depth may remain pristine and will to a greater extent reflect the natural pre-industrial environment. In regional geochemical mapping, overbank sediment can be sampled at widely spaced sites, keeping costs per unit area low. Examples from Norway (1 sample station per 500 km2) show that overbank sediment produces broad geochemical patterns with high contrasts reflecting the bedrock geochemistry. Some patterns agree with known geological units and metallogenic provinces, but hitherto unknown major structures have also been indicated. A large Mo-deposit missed by a traditional stream survey is readily detected in the overbank sediment. It is concluded that overbank sediment is a promising alternate sample medium that should be tested in other physiographic regions. 相似文献
2.
Overbank and medium-order stream sediment samples were collected in Belgium and Luxembourg from 66 sampling locations (area of about 33,000 km2) and analysed for major and trace elements among which Zn, Pb, Cu and As. At each sampling location large bulk samples were taken, namely in the lower (normally at ≥1.5 m depth, over an interval of about 20–40 cm) and upper (normally upper 5–25 cm) parts of the overbank profiles and from the stream sediments. Furthermore, at a number of these sites, a detailed geochemical analysis of vertical overbank sediment profiles (sampling intervals of 10–20 cm) was subsequently carried out to unravel element variations through time and to help in the overall evaluation. For most sampled sections evidences such as 14C-dating and the absence of anthropogenic particles point towards a pre-industrial and often pristine origin of the lower overbank sediment samples. From the latter bulk samples, mean background concentrations were deduced. They reveal the existence of significant differences between the northern and southern part of Belgium (incl. Luxembourg) which relate to the difference in geological substrate. In the north dominantly non-lithified Quaternary and Tertiary sands, marls and clays occur while in the south Palaeozoic sandstones, shales and carbonate rocks outcrop. Consequently separate mean background values were calculated for the two areas. In the southern study area, some anomalous metal concentrations have been recorded in pre-industrial sediments. They are derived from mineralised Palaeozoic rocks, a feature which could be of interest for base metal exploration. In the upper overbank and stream sediments, in general, higher heavy metal and As contents were recorded with highest values in areas with metal mining, metal melting and cokes treatment industries. By comparing the trace element concentrations of the upper overbank or stream sediment samples with the concentrations detected in the lower overbank samples at each of the sampling locations, and by evaluating the vertical distribution patterns where available, the degree of pollution of the alluvial plain and the present-day stream sediments can be assessed. From this exercise, it is clear that highest pollution occurs in the northern part of Belgium, which relates to its high population density and industrial development. 相似文献
3.
4.
通过对刷马地区地质构造、矿床时空演化以及水系沉积物、土壤、岩石地球化学特征的综合研究,结合地质背景和区域地质环境,认为刷马地区金矿床赋存于上三叠统侏倭组变质石英砂岩中,严格受北西向的韧-脆性剪切带控制,与金矿化有关的蚀变主要有黄铁矿化、硅化、碳酸盐化、毒砂化和黄铜矿化,1∶20万、1∶5万水系沉积物和1∶1万土壤均显示有Au、As、Sb、Hg的地球化学组合异常,1∶20万水系沉积物异常显示Au矿矿田范围,1∶5万水系沉积物异常显示矿区位置,而1∶1万土壤异常与矿体展布基本一致,异常带稳定连续、规模大,异常展布受控于韧-脆性剪切带,是有利的Au成矿区,具有巨大的找矿潜力,其矿床类型初步判定为微细浸染型金矿床(卡林型金矿)。 相似文献
5.
Reproducibility of overbank sediment sampling was tested in twenty-nine floodplains in Europe, ten in Greece and nineteen in Norway, by the collection of duplicate pairs of samples. Distances between duplicate sites in Greece were 60 to 100 m, and in Norway 100 to 200 m. In Norway the same nineteen floodplains were sampled by a second team for the purpose of investigating differences in sampling variability and technique. Total element contents were determined in all samples. Paired samples were compared by calculating Spearman's rank correlation coefficient on the raw analytical data, and one-way analysis of variance on the log-transformed data. Pairs of overbank sediment samples collected from different floodplains by the Hellenic team and the first Norwegian team showed high rank correlations and low within-basin variability (sampling and analytical variance). Statistical results of the second Norwegian team were comparatively poorer; both Spearman's rank correlation coefficient and one-way analysis of variance, showed very low positive to negative correlations and high within-basin variation, suggesting a non-uniform distribution of elements in the Norwegian overbank sediment sequences and differences in the sampling technique of the two teams. Nevertheless, careful location of sample sites, as has been done by the Hellenic and the first Norwegian teams, reduces considerably the sampling variability, and the overall sampling reproducibility for most elements is very good for distances up to 100 m in Greece and 200 m in Norway, provided correlated overbank sediment sequences are sampled. The implication of this study for multinational regional geochemical mapping is that overbank sediment sampling must be carried out by well-trained professional teams of exploration geochemists, and where possible by one sampling team for the whole country. 相似文献
6.
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
7.
Geochemical exploration in China was commenced in the early 1950's. In 1951, the first experimental work was carried out in Yeshan, and a geochemical exploration section was set up in the Ministry of Geology in 1953.Regional geochemical reconnaissance (metallometric surveying) was initiated in 1956 on a nation-wide scale. Soil samples have been collected, and analyzed by semiquantitative spectrography. The results were heavily biased and were not adequately processed and utilized. Renewed efforts have been made to reprocess the vast amount of data accumulated and to utilize them more fully in mineral exploration.Meanwhile, another nation-wide project of regional geochemistry using more refined techniques is in its preparatory stage. It is the Regional Geochemistry-National Reconnaissance Project. In this project stream sediment sampling with a density of one per km2 will be used in China Proper, and low-density sampling of various kinds of media in different environments will be used in remote areas. Pilot surveys covering areas of several thousand square kilometers are being undertaken in several provinces.Beside regional reconnaissance, geochemical prospecting has been carried out at virtually all phases of mineral prospecting in China.A brief summary of current research in exploration geochemistry taken by research institutes and universities is given, including studies on the methodology of regional geochemical surveys, primary halos around various types of ore deposits, mercury vapor survey techniques, refinement of analytical methods and instrumentation, and computerized data processing and plotting techniques.Several case histories are described where geochemical exploration techniques have led to successful ore discoveries in China. 相似文献
8.
总结了内蒙古大石寨地区1∶25万区域地球化学调查获得的1点/4km2的水系沉积物组合样品中的La、Ce、Pr、Nd、Sm、Eu、Gd、Tb、Dy、Ho、Er、Tm、Yb、Lu、Y等15种稀土元素的区域地球化学分布特征。稀土元素分布与研究区中部的黑云母花岗岩密切相关,轻稀土主要分布在该岩体外围的二叠系地层中,重稀土主要分布在该岩体上方。该岩体上方和外围地层的稀土元素分布、稀土元素总量、轻重稀土比及δCe、δEu、(La/Sm)N、(La/Tb)N、(La/Lu)N、(Ce/Yb)N、(Gd/Lu)N等稀土元素分馏特征的差异明显。利用区域地球化学调查水系沉积物样品中的稀土元素含量,可获得研究区可靠的稀土元素区域地球化学分布特征,也可反映研究区地质特点,并为区域地球化学异常解译提供参考资料。 相似文献
9.
R. Swennen J. van der Sluys R. Hindel A. Brusselmans 《Journal of Geochemical Exploration》1998,62(1-3)
A geochemical survey of Belgium and Luxembourg was carried out as part of an international research project entitled ‘Regional geochemical mapping of Western Europe towards the year 2000'. The aim of this research was to map regional background geochemical patterns based on pristine or at least pre-industrial overbank samples and to deduce regional information on the degree of environmental pollution of floodplain and present-day river sediments. Over the entire study area (about 33,000 km2), 66 overbank sites have been sampled. Catchment areas range between 60 and 600 km2. At each site an overbank profile has been dug out in the immediate vicinity of the river and described in detail. A first composite sample was taken 5–25 cm below the surface. This sample is supposed to represent deposition over the last centuries. Human interferences in this interval are often inferable based on changed sedimentary characteristics and the presence of anthropogenic particles such as charcoal, slags and brick fragments. A second composite sample was taken at depth, usually >1.5 m below the surface over an interval of about 20 cm. In most sites, the profile characteristics allowed to assume pre-industrial or even pristine conditions for this lower overbank sample. In some profiles this was confirmed by 14C-dating and/or by the absence of anthropogenic particles. Finally, a present-day stream sediment was sampled on the site to infer the actual pollution status. After drying at 80°C, disaggregation and sieving, the <125 μm fractions of the three sediment samples were analysed by XRF for major elements and several trace elements. Lower overbank samples generally show a direct link with the geological substrate and allow to assess natural background concentrations. Results from the mapping exercise as well as from the statistical analyses display a clear contrast between the northern part of Belgium where Cenozoic unconsolidated sandy and silty formations dominate which are especially vulnerable for erosion, and the southern part of Belgium and Luxembourg where Paleozoic and Mesozoic sandstones, carbonates, marls and shales are the prevalent lithologies. Here the shales are the most intensively eroded lithologies. This is especially reflected in the element patterns of Al2O3, MgO, K2O, Ga, Ni, Rb, Sc and V which negatively correlate with SiO2. Despite the human related pollution, the geological contrast between north and south Belgium is still recognisable in the geochemical pattern of the upper overbank and present-day stream sediment samples for the above-mentioned elements. Furthermore there is a clear increase in heavy metal contents (Zn, Cd, Pb, Cu), As and in certain locations in Ba from the lower to the upper overbank sediment, as well as to the present-day stream sediment. The relative increase in element content allows to assess the degree of pollution and helps to define those drainage areas where more detailed research is needed. 相似文献
10.
Drainage sampling for uranium in the Torrington district, New South Wales, Australia 总被引：1，自引：0，他引：1
A brief orientation study has been conducted to evaluate the use of drainage geochemical sampling for U in the granitic and forested terrain of the Torrington district of northeastern New South Wales. Anomalous U levels are present in both stream sediments and waters draining a known W prospect containing accessory U. The U dispersion is affected by interrelated environmental factors such as catchment physiography and the organic content of the stream sediments. The influence of organic content on U level in stream sediments is most significant. Variation in sediment organic content is related to accumulation of vegetal organic debris and charcoal in stream channels by sheetwashing of sparsely covered forest floors particularly in catchments of high topographic relief. The U is apparently absorbed onto the organic material from ephemerally flowing stream waters. Temporal variations in U content of stream sediment are indicated which necessitate careful consideration in planning and interpreting the results of a survey in this environment. 相似文献
11.
陕南某微细浸染型金矿床地球化学异常模式 总被引：1，自引：0，他引：1
陕南某微细浸染型金矿床是从发现金矿田（床）水系沉积物异常开始，运用地质，地球化学综合方法对异常反复踏勘检查，系统开展大比例尺化探详查找矿程序后找到一处有望成特大型的金矿床。 相似文献
12.
运用扫描电镜和压汞法研究江汉盆地古新统—白垩系砂岩储层孔喉结构及定量参数特征 总被引：4，自引：2，他引：2
通过储集层的孔喉结构来评价储层已广泛运用于油气开发,但目前尚未运用于钾盐储层的评价。本文利用扫描电镜和压汞法获得的大量储层孔隙、孔喉实验数据,研究了江汉盆地古新统—白垩系富钾卤水砂岩储层的孔喉类型和结构、毛细管压力曲线,以及孔喉定量特征参数。研究表明,古新统沙市组砂岩储层以Ⅱ类孔隙结构为主,排驱压力平均值为2.72 MPa,孔隙度平均值为6.32%。而白垩系红花套组砂岩储层以Ⅰ、Ⅱ类孔隙结构为主,Ⅰ类排驱压力平均值为0.28 MPa,孔隙度平均值为16.99%,渗透率为87.79×10~(-3)μm~2;Ⅱ类排驱压力平均值为1.103 MPa,孔隙度平均值为10.02%,渗透率为18.83×10~(-3)μm~2。通过综合分析孔喉定量特征参数(如最大汞饱和度、最大孔喉半径、中值半径、退汞效率等)来评价储层质量,认为古新统沙市组砂岩类型以粉砂岩为主,储层质量较差,属于特低孔低渗储层;白垩系红花套组砂岩类型以细砂岩为主,储层质量较好,属于低孔低渗储层。本研究为该区富钾卤水储层评价以及进一步勘探开发提供了可靠的地质依据。 相似文献
13.
This paper summarizes advances since 1987 in the application of glacial sediment sampling to mineral exploration (drift prospecting) in areas affected by continental or alpine glaciation. In these exploration programs, clastic glacial sediments are tested by geochemical or mineralogical methods to detect dispersal trains of mineral deposit indicators that have been glacially transported from source by mechanical processes. In glaciated terrain the key sampling medium, till, is produced by abrasion, crushing and blending of rock debris and recycled sediment followed by down-ice dispersal ranging from a few metres to many kilometres. As a consequence of the mid-1980s boom in gold exploration, the majority of case studies and regional till geochemical surveys published in the past decade deal with this commodity. Approximately 30% of Canada and virtually all of Fennoscandia have been covered by regional till geochemical surveys that aid mineral exploration and provide baseline data for environmental, agricultural, and landuse planning. The most profound event in drift prospecting in the last decade, however, has been the early-1990s explosion in diamond exploration which has dramatically increased the profile of glacial geology and glacial sediment sampling and stimulated changes in sampling and analytical methods. 相似文献
14.
礼县上坝低缓金异常的特殊查证方法 总被引：1，自引：1，他引：0
介绍了礼县上坝化探低缓金异常特征、地质背景、地球化学景观及工作方法,金区域化探异常呈低缓式样出现的主要原因,是由于本区第四系厚度大、地表径流发育等微景观特征所致。遵循常规的工作程序是实现低缓异常找矿突破的有效途径,Ⅲ级查证中加大水系沉积物采样密度、Ⅱ级查证中加大土壤样采样深度至50 cm以上及加大探槽开挖深度,是实现低缓金异常找矿突破的有效方法。 相似文献
15.
F. Felder 《Journal of Geochemical Exploration》1974,3(1):1-23
Study of an area in the southern Grenville of Quebec, by a stream sediment reconnaissance survey, outlined a previously unknown nickel-copper occurrence. Both reconnaissance and detail soil surveys were employed to define the sources of the stream sediment anomalies. A rock geochemical survey was carried out along with the detail soil survey. Some of the soil and rock geochemical anomalies were drilled and in all cases low-grade nickel-copper mineralization was encountered. 相似文献
16.
Geochemical data of altered wall rocks are important for the metallogenic prognosis of hydrothermal gold deposits. Indicator elements of altered wall rocks such as K, Al, As, Sb, and Hg have been successfully used to assess gold anomalies in lithogeochemical survey. However, such researches have rarely been done in stream sediment survey for the exploration of gold from various landscapes. On the basis of the geochemical analysis of altered wall rocks of gold deposits in the cold desert areas of Gansu (甘肃) Province in Northwest China, it is found that the combination of Al, K, and Sn could serve as an important indicator of hydrothermal gold deposits and can be used to evaluate the metallogenic prospective of gold anomalies in stream sediments. More studies performed in the cold grassland areas and the moderate-low relief mountainous areas showed that, both weak and strong geochemical anomalies can be extracted, if strictly abiding by the ways of calculation and addition of the binary values of the indicator elements with equal weight, and this provides the sound delineation of metallogenic perspective areas. 相似文献
17.
南秦岭中段中、上志留统金矿化特征及控制因素分析 总被引：2，自引：0，他引：2
区域地球化学测量和金矿勘查工作显示,中、上志留统是南秦岭中段继泥盆系之后的又一套赋金地层,这套地层的分布区存在一条近EW向展布的金矿化带,宏观上,金矿化带的展布受青泥河-留坝复背斜和大河店-长坪-留坝区域性断裂带的控制.金矿（化）点和金矿（化）体的产出受层位、岩性、煌斑岩脉、火山活动、褶皱、层间构造破碎蚀变带、标高及氧化作用等因素的联合控制.矿体呈似层状产出,由多个呈串珠状展布的透镜体组成,金矿石类型以微细浸染型为主,属金-毒砂-黄铁矿建造.通过对已有矿（化）点和区域水系沉积物异常区进一步工作,有望找到中-大型金矿产地1～2处. 相似文献
18.
本文讨论了金、银矿产普查中应用化探的找矿效果和方法使用中的一些问题。文章主要简介了1980～1985年期间化探方法找金、银矿产所取得的找矿成果,新发现59处矿床和矿产地。指出了在中国的地理一地质条件下,寻找金、银矿必须首先开展小比例尺的区域化探,以便尽快缩小找矿靶区,圈出成矿远景区,然后进行普、详查工作,才能很快取得重大找矿成果,同时也会缩短找矿周期和节约经费。还讨论了开展区域、普查和详查化探各阶段的工作任务,在1:20万区域化探和1:5万普查化探阶段主要应选用水系沉积物测量。在大比例尺详查中主要选用土壤测量或岩石测量。讨论了在普、详查中进行组合样品的问题。同时也指出承担金、银矿化探普查的野外队必须掌握痕量金分析方法和技术及形成生产能力的重要性。 相似文献
19.
To develop a technique of implementing global ultra-low density geochemical sampling and as a contribution to the International Geochemical Mapping Program (IGCP Project No. 259), an orientation study in the use of deep (lower-layer) overbank sediments was conducted in Jiangxi Province of Southeast China in 1989–1990. Ninety-four samples were collected at depths of 50 to 120 cm from overbank terraces at an average density of 1 site per 1800 km2. The total area of sampled catchment basins is approximately equivalent to 18% of Jiangxi Province. Most of the samples were collected at outflow sites of catchment basins with areas of 100 to 800 km2. The samples were analyzed for 39 elements.The representativity of wide-spaced lower-layer overbank sediment sampling is discussed from various perspectives; the following features have been observed: (1) Widespaced lower-layer overbank sediment data and the data from China's national geochemical mapping (RGNR) project show similar geochemical patterns for W, Sn, Pb, Cu and Zn. (2) The results of wide-spaced lower-layer overbank sediment sampling demonstrate that catchment basins with areas of 100 to 800 km2 are suitable sample site locations for the global geochemical reference network. (3) Wide-spaced lower-layer overbank sediment sampling is a fast and cost-effective way to identify geochemical provinces and has strategic significance in mineral exploration. (4) There is a significant correlation between the W content of wide-spaced lower-layer overbank sediment samples and the presence of W mineralizations within the catchment basins. (5) The distributions of Ni, Cr and V in wide-spaced lower-layer overbank sediment samples distinctly reveals the boundary between the Yangtze sedimentary platform and the South China Caledonian fold system in Jiangxi Province. (6) Distributions of Rb and Be coincide with the Yanshan granites, which are closely related to the major ore-forming episodes in Jiangxi Province. 相似文献
20.
Investigation on the Distribution of Gold Across the Ahar Area (NW Iran) Using Stream‐Sediment and BLEG Methods 
下载免费PDF全文
下载免费PDF全文 Vartan Simmonds Fatemeh Jahangiryar Mohssen Moazzen Ahmad Ravaghi 《Resource Geology》2016,66(2):213-225
The Ahar area is located in NW Iran. The main part of the area is covered by Eocene andesitic and andesi‐basaltic rocks within which several granitoid intrusives of Oligocene age are emplaced. This caused vast hydrothermal alterations and Cu and Au mineralization. In this regard, this contribution aims to explore the distribution of gold across the region based on systematic sampling of stream sediments and using the secondary geochemical halos, as well as the bulk leach extractable gold (BLEG) method. Meanwhile, the results obtained from these two methods will be compared in order to find out if the anomalous zones match with each other. For this, 620 stream sediment samples of ?80 mesh grain size and 422 BLEG samples were collected and analyzed by Fire Assay and atomic absorption spectroscopy (AAS) methods, respectively. For BLEG samples, gold was first dissolved using KCN before being analyzed by the AAS method. Furthermore, 84 rock samples were also collected during the field control surveys and were analyzed by Fire Assay and ICP‐OES methods for gold and other elements, respectively. After determining the distribution characteristics and statistical parameters of gold in each group of samples, anomaly maps of gold for each method were prepared, revealing almost similar anomalous zones across the region. Based on these maps, most of the discovered anomalies correlate well with granitoid intrusives of Oligocene age and the related hydrothermal alterations, which have occurred within the intrusives and the host andesitic‐basaltic rocks of Eocene age, especially at the NE and central parts of the area and east of Ahar. Some silicic veins and veinlets have been observed during field surveys in these parts, within which high concentrations of Au and sometimes Cu are determined. Another anomalous zone is located over the hydrothermal alterations within trachy‐andesitic and andesitic volcanics of Pliocene age at the SE part of the quadrangle, where vast alterations caused by volcanic fumaroles and epithermal mineralization of gold and Pb–Zn is discovered. In this regard, the SE and NE parts of the area and the east Ahar area are proposed, in order of importance, for further detailed investigations. 相似文献