Overbank sediments as appropriate geochemical sample media in regional stream sediment surveys for gold exploration in the savannah regions of northern Ghana

Conventional stream sediment sampling in which sediments are taken from the active channels during reconnaissance regional geochemical surveys in gold exploration has over the years failed to delineate prospective target zones in northern Ghana, where the relict is flat. Whereas the technique has been successful in the south western Ghana, which is characterised by moderate to high relief, generally the savannah north is associated with low relief, commonly with flat topographies and generally decoupled stream channels. Geochemical comparison of active stream and overbank sediments in this study demonstrate that active stream channels may contain contaminated materials of recent origin, but overbank sediments, except for the uppermost horizons, represent alluvial regolith of earlier depositional cycles over time. Based on gold value repeatability, composite samples taken from the overbank sediment layers were relatively less erratic and are considered to be an appropriate geochemical medium in delineating potential regional gold targets for follow up. The results show that overbank sediment sampling can be used as a cost-effective method to define broad anomalous zones; and the technique must be considered useful during reconnaissance geochemical surveys in the savannah regions.     

The suitability of floodplain sediment as a global sampling medium: evidence from China

Research undertaken by IGCP 259 (International Geochemical Mapping) indicates that wide-spaced sampling is a fundamental concept of international geochemical mapping as it appears to provide the only practical way to obtain a relative rapid (10–20 years) overview of global geochemistry. The main aim of this study is to test the suitability of floodplain sediment as a global sampling medium.Thirteen floodplain sediment samples and 13 stream sediment samples were taken at the exit of 13 super large drainage basins (SCB). The areal extents of these basins are in the order of 1000–10,000 km². Within each SCB, 3–11 stream sediment samples each representing a component catchment basin (CCB) of 100–1000 km² were also taken. Fourty nine elements were analyzed. The results were compared with the average values derived from calculating thousands of stream sediment data available from China's National Geochemical Mapping (RGNG) program. Strong similiarities were demonstrated in distribution and trends among the three levels of data. The set of floodplain sediment data shows great coincidence with RGNR stream sediment data.     

Quantitative analysis of anomalous sources and geochemical signatures in the Walker Lake quadrangle of Nevada and California

A new quantitative transportation model for geochemical elements in stream sediment samples is proposed and used to estimate mineral sources of anomalous concentrations and to adjust both location and concentration for the transportation effect. Subsequent to transportation analysis, data on 14 geochemical elements in the Walker Lake quadrangle are analyzed for geochemical signatures for three types of mineralization environments: epithermal gold-silver deposits, porphyry-skarn copper deposits, and a mixed occurrence. Geochemical signatures are analyzed using a multidimensional scaling method referred to as the p_ijk model, which is a factor-like model generalized to include nonlinear associations, as well as linear, among triple variables (elements). A result of this analysis is that Pb is the best indicator for epithermal gold-silver mineralization, Mo and Zn for mixed mineralization, and Cu for porphyry-skarn mineralization.     

High resolution regional hydrogeochemical baseline mapping of stream water of Wales,the Welsh borders and West Midlands region

The stream water hydrogeochemical database, produced by the Geochemical Baseline Survey (GBASE) of the British Geological Survey, has recently been enhanced in the light of experimental pilot studies in North Wales, to meet a wider range of economic and environmental objectives which require modern, integrated and strategic geochemical surveys for their implementation. Hydrogeochemical data are therefore now collected, in conjunction with geochemical data for stream sediments, soil samples and mineral concentrates. The density of sampling, based on the collection of stream water at near-baseflow conditions during the late summer period each year, has been increased to one site per 1.75 km² and a broader spectrum of geochemical determinants introduced. Provisional regional datasets are being prepared for an extensive region covering Wales, the Welsh Borders, and part of the West Midlands representing over 17 000 sample sites. Bedrock geology and base metal sulphide mineralisation are particularly well reflected in the stream water chemistry at the regional scale. The influence of secondary factors, such as geomorphology, atmospheric controls, and anthropogenic contamination due to agriculture, urban, industrial and military developments, can also be readily distinguished.The data obtained by systematic high resolution sampling of first and second order streams, vary in concentration over three or four orders of magnitude for many of the analytes studied here. This compares with a range of only one or two orders of magnitude for many of the analytes in stream sediment samples. The extended range in values for stream water is an important factor in the gridding, plotting and production of relatively stable maps. They are relatively unaffected either by short temporal changes in stream water flow, which are attributable either to storm events noted during the sampling campaign, or by annual differences between wet and dry summers in different years. This has enabled a series of robust surface hydrogeochemical maps to be prepared for analytical data collected during the summer sampling campaigns conducted annually from 1989 to 1994. These maps provide a unique source of synoptic baseline information for a wide range of economic and environmental applications especially, when combined with other geoscience datasets in a GIS environment.     

A comparison of regional geochemical data from lakes and streams in northern Labrador; implications for mixed-media geochemical mapping

Labrador has been covered by reconnaissance-scale geochemical surveys under the National Geochemical Reconnaissance program. Lake sediment and water were the chief sample media, but stream sediment and water were employed in the mountainous terrain of northern Labrador. The main objective of these surveys was mineral resource assessment, but the data are also relevant to geological and environmental studies, and would be most useful to the non-specialist if the data from the two drainage types could be combined to produce unified element distribution maps for the whole region.A comparison of stream and lake data for a 5,700-km² area where both drainage types were sampled suggests that only the pH of the lake and stream waters are directly comparable, showing a common range and similar spatial distribution. Comparing the two types of sediment, most elements show obvious differences in either median content or range or both, indicating that stream and lake sediment are geochemically distinct media, and their element contents cannot be compared directly. The distribution patterns of Cu, Ni and U reflect similar bedrock features in both sediment types. In contrast, Co, F, Fe, Hg, Mn, V and Zn show little or no spatial correlation between stream and lake sediment, but are strongly intercorrelated in the stream sediment data set.The sediments collected from lakes in Labrador represent disturbed column, about 40 cm in length, of organic debris that accumulated over the past several hundred years. Metal accumulation in the sediment is largely through fixation from inflowing surface and groundwater by microorganisms, coprecipitation with hydrous Fe and Mn oxides, sorption by clay minerals and chemical and biochemical processes at and just below the sediment/water interface. The stream sediments in this study were collected from active sediment, and represent principally the mechanical-weathering products of bedrock, with variable amounts of organic matter and hydrous Fe and Mn oxides. Considering the difference in the two sediment types, it is probably not surprising that there is rather limited spatial correlation between the geochemistry of the two sediment types indicating that to a large extent each medium reflects a different facet of the bedrock geochemistry. Only for a few elements should the data sets be merged. The degree of spatial correlation for U, Ni and Cu increases as the data are generalized by averaging into larger blocks, suggesting that the combined data sets will be more successful in defining broad crustal geochemical features rather than local details. The implication of this study for international geochemical mapping is that geochemical patterns for many elements are strongly dependent on the sample medium chosen. Therefore, when it is necessary to change sample media in passing from one terrain type to another, a comparative study must be carried out to determine how the geochemistry of the different sample media compare spatially.     

Tectonic terranes, metallogeny and regional geochemical surveys: an example from northern British Columbia

This study utilizes three major data sources: distribution of geological units; density, type, age and distribution of mineral deposits; and elemental analyses from regional geochemical stream sediment surveys to define parameters that ‘characterize’ tectonic terranes in northern British Columbia. A similar approach could be applied anywhere in the Canadian Cordillera.This area, NTS map sheets 104N, 104O and 104P along the British Columbia-Yukon border, forms a transect through allochthonous terranes into North American rocks. These are: the allochthonous island-arc Stikine, oceanic Cache Creek, cataclastic Yukon/Tanana, and island-arc Quensel terranes, the pericratonic Dorsey terrane; the parautochthonous oceanic Sylvester allochthon; and the autochthonous miogeoclinal North American Cassiar terrane. Plutonic rocks of Jurassic-Cretaceous to Tertiary age intrude all terranes.Data sources used in the study are geological base maps and reports, the Ministry of Energy Mines and Petroleum Resources' mineral deposit database (MINFILE) and analytical data from the National Regional Geochemical Survey stream sediment and water sampling program.Geological maps were compiled from various sources and plotted to act as bases for geochemical and mineral deposit overlays for analysis and interpretation.Geochemical samples were separated into background and anomalous populations and compared according to their source terranes. We found that mean concentrations from background sample populations for some elements are statistically distinctive for different terranes. Unfortunately, elemental correlation coefficients for the terranes are similar so cannot be used to characterize each terrane.Data on mineral deposits and occurrences were compiled from minfile and other sources. Particular attention was paid to deposits with histories of production or significant reported reserves. Deposits were sorted by type and commodity to produce synoptic metallogenic maps.The combined data from geological, geochemical and mineral deposit databases form a strong tool for interpreting and predicting patterns of mineralization.     

云南红河州超大规模离子吸附型稀土矿的发现及其意义

围绕国家战略性产业发展对稀土资源的需求, 特别是紧缺的重稀土资源, 如何快速有效地发现富含重稀土矿床找矿靶区是勘查地球化学急需解决的问题。“化学地球”大科学计划获得全国地球化学基准数据, 圈定稀土异常超常富集区9处, 其中新发现的滇南红河州蒙自—中越边境地区稀土富集区轻重稀土比值(LREE/HREE)为3.5, 与华南富含重稀土的离子吸附型稀土矿异常LREE/HREE比值一致。结合地质背景、成矿母岩、气候和地形地貌特点等初步判断具有寻找类似华南富含重稀土的离子吸附型稀土矿资源潜力。因此, 对这一异常的核心区, 开展了1:25万、1:5万地球化学调查和风化剖面测量, 并经29个钻孔验证, 初步发现马鞍底潜在超大型富含重稀土离子吸附型稀土矿。富矿区分布于坡度较缓的坡脚处, 风化母岩为印支期和燕山期花岗岩、元古界斜长片麻岩和变粒岩。风化剖面厚度最深可达25 m左右, 富矿层位位于全风化层, 一般在2~13 m深度, 矿体平均厚度6~13 m, 最厚可达21 m, 平均品位0.14%。根据29个钻孔和84个风化壳剖面测量, 初步估算稀土潜在矿石量约9.46亿吨、稀土氧化物潜在资源约100万吨。这是我国首次在滇南地区发现潜在超大型离子吸附型稀土矿。该离子吸附型稀土矿同时富含轻稀土(镧、铈、镨、钕)和重稀土(钆、铽、镝、钇), 具有重大经济价值和科学意义。这一发现表明开展从极低密度、低密度到高密度地球化学调查, 获得全部16个稀土元素高质量数据是发现离子吸附型稀土矿的快速有效方法。     

The Forum of European Geological Surveys Geochemistry Task Group inventory 1994–1996

The Forum of European Geological Surveys (FOREGS) includes representatives from 33 European countries and is responsible for co-ordinating Geological Survey activities in Europe. The FOREGS Geochemistry Task Group was established in 1994 to develop a strategy for the preparation of European geochemical maps following the recommendations of the International Geological Correlation Programme (IGCP) Project 259 ‘International Geochemical Mapping’ (now the International Union of Geological Sciences (IUGS) /International Association of Geochemistry and Cosmochemistry (IAGC) Working Group on Global Geochemical Baselines).The FOREGS geochemistry programme is aimed at preparing a standardised European geochemical baseline to IGCP-259 standards. The principal aims of this dataset will be for environmental purposes, as a baseline for the assessment of the extent and distribution of contaminated land in the context of variations in the natural geochemical background, but it will also have applications in resource assessment and for the development of policy for the sustainable management of metalliferous mineral and other resources.The first phase of the programme was the compilation of an inventory of geochemical data based on the results of a questionnaire completed by Geological Surveys and related organisations throughout the FOREGS community. The results show that the sample types which have been used most extensively are stream sediment (26% coverage), surface water (19% coverage) and soil (11% coverage). Stream sediments have been collected using a narrow range of mesh sizes (< 150–< 200 μm), but soil samples have been collected according to two different conventions: some surveys used a similar mesh size range to that used for stream sediments while others employed the < 1000 or < 2000 μm fractions traditionally used by soil surveys. Sample densities range from 1 sample per 0.5 km² to 1 per 3500 km². Various analytical methods have been used, but most of the available data have been calibrated using international reference materials, and data for the most important of the potentially harmful elements (PHEs) are available for most datasets. Systematic radiometric data are available for only a small proportion of Europe, a situation which compares very unfavourably with that in Australia, North America, the former Soviet Union and many developing countries.Recommendations are made for increasing the compatibility of geochemical methods between national geochemical surveys as a basis for the preparation of a series of European geochemical maps. The next stage of the FOREGS Geochemistry Task Group will be the collection of the Global Reference Network of samples against which to standardise national datasets according to the methods recommended in the final report of the IGCP 259 programme.     

Using Field-Portable XRF to Assess Geochemical Variations Within and Between Dolerite Outcrops of Preseli, South Wales

Eight dolerite outcrops in Preseli, south Wales were measured in situ using field-portable XRF analysis, in order to compare two different analysis ("sampling") strategies, and to investigate geochemical variability within and between outcrops. A sampling strategy of two (neighbouring but independent) measurements at each of a maximal number of locations dispersed over an outcrop was the more effective in indicating the overall chemical variance of that outcrop. Analysis of variance indicated that much of the observed variance within individual outcrops stems from real geochemical variability rather than from sampling and analytical factors. Standard ANOVA F tests showed that several of the studied outcrops are heterogeneous at the 5% significance level for one or more elements. Geochemical distinctions between some outcrops were demonstrated using discriminant analysis. PXRF analysis offers an alternative approach to conventional characterisation of outcrops, which is often based on laboratory analysis of small numbers of samples. However, PXRF data are affected by rock weathering and may require correction for this if they are to be compared with analyses of fresh rock.     

Geochemical dispersion of gold related to copper-gold mineralization in northeastern Thailand

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.     

1:20万区域化探方法核心技术"取样粒级"的讨论

内蒙古区域化探扫面采用水系沉积物测量(或土壤测量),取粗粒级样品,取得了较好的地质找矿效果,但局部景观区找矿效果受到了一些影响.我国南北方水系沉积物中元素含量呈"U"形分布,反映了南北方不同的风化类型,以及所取不同粒级样品的物质成分也不同;取粗粒级和细粒级样品均可能有化探异常显示,采用-5～+20目(0.9 mm≤A＜4 mm)和-120目(A＜-0.125 mm)组合粒级作为采样粒级.为提高工效,取样时可以采用-5目(或-20目)全粒级物质,也能获取更多的找矿信息.这种取样粒级技术,也适宜于全国各种不同的景观区的不同尺度的水系沉积物测量和土壤测量的化探工作.     

Low-density geochemical mapping in Hungary

Guidelines for a low-density geochemical survey were described in 1990 by the Western European Geological Surveys. A low-density geochemical survey of Hungary was carried out in 1991–1995. The results are useful for future surveys and for the IGCP 360 project ‘Global Geochemical Baseline’. In regions with well-developed drainage systems in Hungary, 196 catchment basins of approx. 400 km² were delineated and flood-plain deposits sampled at their outlets. The samples were taken from 0 to 10 cm and from 50 to 60 cm depths. Samples were analysed by ICP-AES and AAS techniques in two laboratories. A Geochemical Atlas of Hungary is in preparation that will show the distribution of 25 elements in the two sampled layers. Maps for the lower layer represent regional geochemical baseline values and a geochemical subdivision of the country (maps showing the distribution of element associations) was made on the basis of factor variables. Maps constructed from the data of the upper sampling level show us the present state of contamination of the surface. The results of this survey have contributed to the establishment of guidance values for soils prepared by the Hungarian Ministry of the Environment in 1995. Safe levels were established for As, Cd, Cr, Cu, Hg, Pb and Zn and regional environmental loads plotted. Differences between the median values of the two levels are generally small. However, the concentrations of certain elements like P, Pb and S are significantly greater in the upper layer reflecting contamination from agriculture. In certain regions, the rate of sedimentation was fairly fast such that the environmental effects of ore mining in Transylvania and southern Slovakia as well as those of heavy industry in northern Hungary can be observed in samples from the lower level. The main factor controlling the geochemical pattern in Hungary is the predominance of young (Pleistocene or Miocene) clastic sediments at the surface. Approx. 90% of the surface is covered by these young sediments. This kind of survey has the disadvantage of not providing enough contrast to differentiate geologically dissimilar areas but it has the advantage to provide regional surface background geochemical data and it helps to outline areas of possible surface contamination. Based on the results of this survey we conclude that it would be much better to sample smaller, but geologically homogeneous areas in mountainous terrain to obtain data characteristic of the geochemical background of lithologic units. This approach would mean a sampling density of a few tens of km²/sample for hilly areas, and a few hundred km²/sample for lowland areas.     

Geochemical exploration in China

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.     

Comparison of U-spatial statistics and C–A fractal models for delineating anomaly patterns of porphyry-type Cu geochemical signatures in the Varzaghan district,NW Iran

The delineation of populations of stream sediment geochemical data is a crucial task in regional exploration surveys. In this contribution, uni-element stream sediment geochemical data of Cu, Au, Mo, and Bi have been subjected to two reliable anomaly-background separation methods, namely, the concentration-area (C–A) fractal and the U-spatial statistics methods to separate geochemical anomalies related to porphyry-type Cu mineralization in northwest Iran. The quantitative comparison of the delineated geochemical populations using the modified success-rate curves revealed the superiority of the U-spatial statistics method over the fractal model. Moreover, geochemical maps of investigated elements revealed strongly positive correlations between strong anomalies and Oligocene–Miocene intrusions in the study area. Therefore, follow-up exploration programs should focus on these areas.     

Interpolation for geochemical surface reconstruction incorporating topographic catchment definitions

Geochemical surfaces are reconstructed by interpolating geochemical measurements obtained from stream-water and stream-sediment samples. The geographical region that influences (and therefore is represented by) the value of a geochemial sample is its topographic catchment area. However, standard convention is to treat and to record the stream sample in the database as a point location, and to reconstruct geochemical surfaces utilizing conventional point interpolation procedures. These interpolation procedures assume, generally, that a data point exerts geographical influence away from itself in all directions, and that influence declines with distance away from that data point. Conventional interpolation procedures are poorly suited for reconstructing geochemical surfaces from stream samples; they do not take into account the true geographic area that geochemical sample points represent (topographic catchments). In this paper we propose a method of interpolation which assumes that data points are representative of their topographic catchment areas. Experimental data indicates that a surface reconstruction procedure which preserves the areal character of geochemical samples provides results more meaningful than surfaces reconstructed using more conventional interpolation techniques.     

中国花岗岩型铀矿区域地球化学指示元素特征及异常模式

我国铀矿床主要划分为四大类型,包括花岗岩型铀矿床、火山岩型铀矿床、砂岩型铀矿床和碳硅泥岩型铀矿床。花岗岩型铀矿约占我国已探明铀矿总资源储量的三分之一以上,是我国重要的铀矿化类型。地球化学勘探方法对花岗岩型铀矿床勘查具有良好的效果。根据全国铀矿资源潜力评价项目研究成果,在大量研究中国花岗岩型铀矿化水系沉积物地球化学异常特征基础上,总结了一套对花岗岩型铀矿化勘查稳定的、行之有效的指示元素及其组合,确定了花岗岩型铀矿化地球化学异常模式,并以实例说明典型花岗岩型铀矿化异常模式。水柰沉积物地球化学异常是进行铀矿产预测评价的有效手段,对铀矿资源的潜力评价发挥了重要作用。     

形态相关系数及其在地球化学数据分析中的应用

地球化学数据元素间的相关分析具有重要意义。地球化学数据是一种不遵循正态分布的成分数据,其封闭特征存在挖掘和分析的困难和障碍,因此许多传统的统计方法不适合使用。主要通过元素值的趋势分析了地球化学元素之间的相关关系,并提出了形态相关系数的概念。该方法不需要数据服从正态分布,可以忽略闭包特征的影响。实验表明,该方法简单、稳定、准确,可以显示数据元素之间的关系。此外,方法计算过程消除了回溯,因此适用于大数据的实时和动态分析。     

Comparison of vegetation and stream sediment geochemical patterns in northeastern New South Wales

This study compares the geochemical response of stream sediments and adjacent vegetation samples, with variations in drainage catchment lithology and the occurrence of mineralisation, within a 14,000-km² block of the northeastern region of New South Wales, Australia. The area contains a range of lithologies within a Devonian–Permian accretionary complex and Mesozoic sedimentary basin, as well as a wide range of mineral deposits. Sampling was designed to confine each sub-catchment to a single lithological group (mafic and ultramafic rocks, acid intrusives, volcanics, metasedimentary and sedimentary rocks or alluvium). Leaves of over 20 genera, dominated by (Allo-)Casuarina, Eucalyptus, Acacia, Callistemon and Melaleuca, and the <250-μm fraction of the stream sediments were analysed by INAA. The uptake of most trace elements varied between genera, with Callistemon displaying the highest median As and La contents and Eucalyptus the highest Co contents. The stream sediment and vegetation geochemistry reflect both hydromorphic and mechanical dispersion within sub-catchments, with regional patterns dominant over local influences. The vegetation appears to be influenced to a greater extent by hydromorphic dispersion, as indicated by differences in the ratio of leaf to sediment Cr concentrations in sub-catchments draining serpentinites and basalts. Although most known mineral deposits in the region produced anomalies in at least one medium, there was little correlation between the trace element concentrations of the vegetation and stream sediments on a site-by-site basis. A number of Au targets were only detected on the basis of the biogeochemistry and others were only reflected in the stream sediment geochemistry. In general, vegetation displayed more extensive dispersion trains away from mineralisation than did the stream sediments. Differences in the response of the two sampling media suggest their joint use in exploration or environmental surveys to maximise the probability of detecting mineralisation.     

化探数据处理的新技术

本文论述了一种新的空间点数据处理系统（ＮＡＳＳＤ）在化探数据处理扣的应用效果，以ＮＡＳＳＤ处理平均采样密度为每１５０００ｋｍ＾２一个，样品总数为５２９个泛滥平原沉积物数据，制作 的中国铜和银地球化学图，可以较清晰地指示出中国已知大型，超大型铜和银矿床的分布，以传统的数据处理方法无论是处理上述的极低密度采样数据处理还是每１ｋｍ＾２～５０ｋｍ＾２一个的区域水系沉积物测量数据，在制作（以相同含量间隔表示     

Pathfinder applications of arsenic, antimony and bismuth in geochemical exploration

The potential applications of As, Sb and Bi as pathfinder elements in geochemical exploration have been researched using a new, rapid technique for the simultaneous determination of the three elements. Following a warm hydrochloric acid sample leach, the volatile hydrides of the elements are generated and flushed into an inductively-coupled plasma linked to an emission spectrometer. The technique offers a combination of good analytical precision and detection limits of 100 ppb for each of the elements.The principal sulphide ore minerals commonly contain traces of As, Sb and Bi, and concentrations of more than 1% of any one of these have been found in some sulphide specimens. During sub-aerial oxidation of sulphides, any As, Sb and Bi present is released and forms dispersion patterns in the surficial environment. Geochemical surveys of localities in the United Kingdom have demonstrated that anomalous dispersion trains of these elements can be detected in the sediments of streams draining the mineralized localities. In a geochemical mapping programme covering 16,000 km² of central Nepal, over 3500 stream sediment samples were analyzed for As, Sb and Bi, and many known occurrences of Cu, Pb and Zn mineralization are reflected by As, Sb and Bi anomalies. However, bedrock lithology appears to be an important factor influencing Sb and Bi dispersion patterns.In the areas studied, some or all of the elements As, Sb and Bi produce stream sediment anomalies that compare favourably in terms of contrast and extent with the heavy metal expressions, even though none of the three elements have been reported as important constituents of the mineralization with which they occur.