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Cluster analysis can be used to group samples and to develop ideas about the multivariate geochemistry of the data set at hand. Due to the complex nature of regional geochemical data (neither normal nor log-normal, strongly skewed, often multi-modal data distributions, data closure), cluster analysis results often strongly depend on the preparation of the data (e.g. choice of the transformation) and on the clustering algorithm selected. Different variants of cluster analysis can lead to surprisingly different cluster centroids, cluster sizes and classifications even when using exactly the same input data. Cluster analysis should not be misused as a statistical “proof” of certain relationships in the data. The use of cluster analysis as an exploratory data analysis tool requires a powerful program system to test different data preparation, processing and clustering methods, including the ability to present the results in a number of easy to grasp graphics. Such a tool has been developed as a package for the R statistical software. Two example data sets from geochemistry are used to demonstrate how the results change with different data preparation and clustering methods. A data set from S-Norway with a known number of clusters and cluster membership is used to test the performance of different clustering and data preparation techniques. For a complex data set from the Kola Peninsula, cluster analysis is applied to explore regional data structures. 相似文献
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Factor analysis method is a multivariate analysis technique that is widely used for the interpretation of stream sediment geochemical data. The purpose of factor analysis is describing the changes in a set of multi-element geochemical data by reducing the dimension of the data and variables to a number of factors that can present the hidden association between elements. Differences in mobility, physical, and chemical properties of the elements and the nature of the factor analysis method in which the matrix of all data is used cause paragenes elements not to be found on the output of factor analysis. In this research, to improve the output of factor analysis for deriving the best reagent multi-element mineralization, robust staged factor analysis method was used according to the close nature of geochemical data in order to identify the Cu-mineralization potential in Khusf 1:100,000 sheets located at the east of Iran. The robust staged factor analysis enhances the recognition of anomalous geochemical signatures and increases geochemical anomaly intensity and the percentage of the total explained variability of data. As indicated by the results of the study, few anomalous zones have been found in the study area. The observation of chalcopyrite and malachite mineralization in andesite and dacite–andesite rocks in a region during the field study confirms the effectiveness of the robust SFA technique. Such studies can be used by mine engineers and geologists for designing an optimum grid exploration on the next exploration steps. 相似文献
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Pieter-Jan van Helvoort Peter Filzmoser Pauline F.M. van Gaans 《Applied Geochemistry》2005,20(12):2233-2251
Sequential Factor Analysis (seqFA) is presented here as an enhanced alternative to multivariate factorial techniques including robust and classical Factor Analysis (FA) or Principal Component Analysis (PCA). A geochemical data set of 145 sediment samples from very heterogeneous, mainly riverine, deposits of the Rhine-Meuse delta (The Netherlands) analyzed for 27 bulk parameters was used as a test case. The innovative approach explicitly addresses the priority issues when performing PCA or FA: heterogeneity and overall integrity of the data, the number of factors to be extracted, and which optimum minimal set of key variables to be included in the model. The stepwise decision process is based on quantitative and objectively derived statistical criteria, yet also permitting arguments based on geochemical expertize. The results show that seqFA, preferably in combination with robust methods, yields a highly consistent factor model, and is favorable over classical methods when dealing with heterogeneous data sets. It optimizes rotation of the factors, and allows the extraction of less distinct factors supported by only a few variables, thus uncovering additional geochemical processes and properties that would easily be missed with other approaches. The identification of key variables simplifies the geochemical interpretation of the factors, and greatly facilitates the construction of a geochemical conceptual model. For the case of the fluvial deposits, the conceptual model effectively describes their bulk chemical variation in terms of a limited number of governing processes. 相似文献
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《Chemie der Erde / Geochemistry》2016,76(4):519-527
The spatial distribution of Cu and its pathfinder elements in quartz porphyrites along Wadi Araba was studied in order to gain an insight about the geologic framework of Cu mineralization in the area. A geochemical exploration data set of 242 samples was revisited. Multivariate statistical and geostatistical analysis were performed on the data set. The objectives of the study were to define Cu relationships with its possible pathfinder elements and to figure out whether geostatistical treatment of exploration data would help telescoping already existing Cu mineralization in Wadi Araba, SW Jordan. Factor analysis and hierarchical cluster analysis were performed on the data set. The results of which indicate that seven elements, namely, Ba, Cr, Mn, Ni, Sc, Sr and V can be considered as pathfinder elements for Cu. Significant correlations do exist between Cu and these elements. The encountered experimental semivariograms of the defined pathfinders were fit to exponential models with varying nugget effects with the exception of Mn which was fit to the spherical model. Ordinary kriging was found to be most appropriate to generate geochemical exploration maps. The applied methods succeeded in deriving valuable information and visualizing the already existing Cu mineralization in Wadi Abu Khusheiba area. 相似文献
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正态分布在区域地球化学调查样品分析质量评价中的应用探讨 总被引：2，自引：1，他引：1
区域地球化学样品长期以来一直是采用间接方法对实际样品元素分析质量进行评价,有效地提高了区域地球化学样品的整体分析质量,但是当实际样品和外部质量控制样品含量范围差别较大时,间接评价的效果会减弱。本文从区域地球化学样品大部分元素符合标准(对数)正态分布的规律出发,运用SPSS、Excel等软件对区域地球化学调查样品元素含量正态分布情况进行研究,通过计算元素含量实际正态分布图和标准正态分布图的重合度直接评价元素的分析质量。运用整套方法对实验室分析的江西某地多目标区域地球化学样品的分析数据进行了质量评价,正态分布检验表明微量元素需要通过对数转换才能进行正态分布分析,该地区钛、钨、铬等元素不适合用本方法进行质量评价;钴、汞、镓等18个元素的重合度都在0.9以上;氧化钙和氧化钠重合度小于0.9,样品实际结果分析表明需降低分析方法检出限,提高低含量氧化钙和氧化钠的分析质量。本方法对区域地球化学调查样品的分析数据质量的直接评价作了有益的尝试,可以作为现有区域地球化学调查样品质量评价办法的参考和补充。 相似文献
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Semi-hierarchical correspondence cluster analysis and regional geochemical pattern recognition 总被引：3，自引：0，他引：3
Hongjin Ji Daoming Zeng Yanxiang Shi Yangang Wu Xisheng Wu 《Journal of Geochemical Exploration》2007,93(2):109-119
Semi-hierarchical correspondence cluster analysis (SHCCA), firstly developed in this paper, extracts the main advantages of correspondence analysis, hierarchical and non-hierarchical cluster analysis, and unifies the R- and Q-mode cluster analysis of large data set. A systemic program to recognize the regional geochemical patterns is built up based on this method. With this program, the complex tasks for data interpretation can be achieved by simple processes, and important geochemical information can be displayed by a single diagram, i.e. the multivariate regional geochemical image. As one of the applied examples of this program, the regional geochemical pattern recognition for a shallow covered area around Tahe in Heilongjiang Province is introduced. The results show that many hidden geochemical patterns related to the lithologies, structures, ore-forming conditions and prospecting targets etc are revealed by the geochemical image, and that the main geochemical patterns are related with certain geological and gravitational patterns. By finding contrasts between geochemical patterns and geological or gravitational patterns, the SHCCA results assist the geological mapping in this area. Geochemical data obtained in Chinese regional geochemical exploration provides useful information regarding geology and minerals, and the method described in this paper provides a new way to examine this type of resource. 相似文献
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因子分析结果受样品数量的影响，同一件样品的因子计量也随之发生变化，使传统因子计量方法在地球化学数据处理中的应用受到一定的限制。因子计量模型法综合了因子计量的优点和利用模型找矿的思路，通过选定的某一典型地质单元计算因子计量系数矩阵，建立因子计量模型，用模型类比未知区。该方法使因子计量图的地球化学意义更加明确，并且可节省重新处理数据的工作量。因子计量模型方法和传统因子计量方法应用于某地区1：20万水系沉积物地球化学数据处理，因子计量模型法得出的地球化学异常规律性更为明显，更好地反映了区域地质构造与异常的关联性，有利于异常的解释和评价。 相似文献
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The complexity of modern geochemical data sets is increasing in several aspects (number of available samples, number of elements measured, number of matrices analysed, geological-environmental variability covered, etc), hence it is becoming increasingly necessary to apply statistical methods to elucidate their structure. This paper presents an exploratory analysis of one such complex data set, the Tellus geochemical soil survey of Northern Ireland (NI). This exploratory analysis is based on one of the most fundamental exploratory tools, principal component analysis (PCA) and its graphical representation as a biplot, albeit in several variations: the set of elements included (only major oxides vs. all observed elements), the prior transformation applied to the data (none, a standardization or a logratio transformation) and the way the covariance matrix between components is estimated (classical estimation vs. robust estimation). Results show that a log-ratio PCA (robust or classical) of all available elements is the most powerful exploratory setting, providing the following insights: the first two processes controlling the whole geochemical variation in NI soils are peat coverage and a contrast between “mafic” and “felsic” background lithologies; peat covered areas are detected as outliers by a robust analysis, and can be then filtered out if required for further modelling; and peat coverage intensity can be quantified with the %Br in the subcomposition (Br, Rb, Ni). 相似文献
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本文以敞开式四酸溶样,电感耦合等离子体质谱测定了新疆、青海区调样品中的Co、Mo、W、Pb等元素,并把ICP-MS、ICP-AES和XRF三个大型仪器对新疆卡克-色帕巴衣地区样品的测定结果进行了比较,确定了区调样品元素分析方法的配套方案,并对溶样过程进行了一系列的优化,其方法检出限和精密度均符合DZ0130.4-2006及补充说明中1﹕5万化探样品标准要求。经国家标准物质验证,结果与标准值相符。优化的分析方法快速灵敏度高,能用于地球化学填图计划中分析测试任务, 同时也用于日常大规模多元素分析。 相似文献
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区域化探样品元素测定几个问题的探讨 总被引：4，自引：0，他引：4
化探样品元素测定的要求,因任务的不同而异。区测与普查相比其要求不同。在普查(及详查)阶段,工作限定在较小的范围内,可能发现的矿种有限或可以预测,测定元素的数目也相应较少(约20种元素)．普查的测网较密,主要是圈出含量和衬度较高的异常内带,对灵敏度和准确度要求可以低些。区域化探主要是发现强度低、衬度低而范围大的区域地球化学异常,而且做为地球化学基础资料,是按分幅扫面,最后要拼缩成全国性的地球化学图。由于图幅间的对比拼接,要求较高的灵敏度和准确度。在区测中凡是能形成独立矿产的元素(包括稀有分散元素)以及有指示意义的伴生元素都要测定。区测化探不但用于找矿,目前日益为区域地质、自然区划、环境保护和农林畜牧的研究,提供重要的地球化学资料。目前测定的元素包括成岩特征元素在内已达39种。文中还探讨了在我国目前化验水平和能力的情况下,完成区测化探样品测定的方法和工作步骤。 相似文献
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竹山幅区域化探数据因子计量地球化学图的编制与效果 总被引：1，自引：0，他引：1
本文用R型因子分析方法,处理1:200000竹山幅区域化探(1911件样品,28种元素定量分析)数据,编制了斜参因子计量地球化学图、因子剩余异常图及综合异常图,构成一套综合性指标的地球化学图件。这套图件在解决本区(变质岩)地层划分、岩浆岩圈定、构造预测等基础地质问题是有效的,对区内银金多金属矿产也有一定反映;提出了震旦系郧西群应归属元古界武当群的新认识,已为地质工作者接受。从地球化学数据的地质解译出发,因子地球化学图是地球化学信息的地质推断图,还可使复杂地球化学区的多种地质—地球化学因素得到分解和解释:与单元素地球化学制图相比,能直接获得地球化学的解释信息和清晰的图象显示,使单元素地球化学图解释中的困难以及综合异常图图面负担过重的问题得到一定的解决。因子地球化学图件可作为单元素地球化学制图的一种辅助形式,它有助于区域化探资料的解释与推断。 相似文献
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Xiang Sun Jun Deng Qingjie Gong Qingfei Wang Liqiang Yang Zhongying Zhao 《Journal of Geochemical Exploration》2009
Kohonen neural network (KNN) and factor analysis are applied to regional geochemical pattern recognition for a Pb–Zn–Mo–Ag mining area around Sheduolong in Qinghai Province, China. Prior to factor analysis, the geochemical data are classified by KNN. The results demonstrate that the 4-factor model accounted for 67% of the variation in the data. Factor F1, a Pb–Zn–Mo factor and Factor F4, an Au–Ag factor, correlates with monzonitic granite intrusions and particularly with Pb–Zn–Mo–Ag mineralization within those rocks. Factor F2, an As–Co factor, correlates with metamorphic rocks of paleoproterozoic Baishahe formation. Factor F3, a Bi–Cu factor, correlates with granodiorite intrusions. The factor score maps suggest a revised location of faults and their mineralization significance in coarse geological map. The approach not only effectively interprets the geological significance of the factors, but also reduces the area of exploration targets. 相似文献
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用R型因子分析方法对阿荣旗谢永贵地区1：1万土壤化探数据进行了分析表明,10种微量元素可以分为Cu、Ag、Au、As、Mo;Pb、zn、Bi、Hg及Sb三类。第一类是反映了中低温的矿化元素组合,第二类反映了中温的指示元素组合。该地区采用因子得分趋势面分析,对剩余异常进行累加法分析成图,共圈定了Ⅰ、Ⅱ、Ⅲ、Ⅳ四个异常。石英脉或蚀变岩型Au矿是异常区内的主要找矿重点地段。 相似文献
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多目标区域地球化学编图是科学表达区域土壤地球化学分布和特征的图示方法,大区域的编图一般可能涉及到对不同的工作区、不同实验室和不同时间的测试数据,以及不同景观条件和网度的表层、深层土壤元素数据或不同分度带的网格数据分别进行拼接合并,因此区域编图对原始数据的整理和网格化处理不可避免.而不同的数据整理方法及其计算参数所形成的结果是非常不同的,数据本身的特点也对编图具有很大的影响.为了真实客观地反映区域内元素的地球化学分布特征,数据整理和处理的方法及技术参数的选择是关键技术问题.作者就化探数据处理中常用的几种插值方法进行了对比评价,并分别从网格间距及搜索半径大小等方面做比较,提出了自己在编图中采用的数据处理方法及选用的技术参数. 相似文献
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P.K. Theobald R.G. Eppinger R.L. Turner Shen Shiquan 《Journal of Geochemical Exploration》1991,40(1-3)
The purpose of geochemical surveys changes with scale. Regional surveys identify areas where mineral deposits are most likely to occur, whereas intermediate surveys identify and prioritize specific targets. At detailed scales specific deposit models may be applied and deposits delineated.The interpretation of regional geochemical surveys must take into account scale-dependent difference in the nature and objectives of this type of survey. Overinterpretation of regional data should be resisted, as should recommendations to restrict intermediate or detailed follow-up surveys to the search for specific deposit types or to a too limited suite of elements. Regional surveys identify metallogenic provinces within which a variety of deposit types and metals are most likely to be found. At intermediate scale, these regional provinces often dissipate into discrete clusters of anomalous areas. At detailed scale, individual anomalous areas reflect local conditions of mineralization and may seem unrelated to each other. Four examples from arid environments illustrate the dramatic change in patterns of anomalies between regional and more detailed surveys.On the Arabian Shield, a broad regional anomaly reflects the distribution of highly differentiated anorogenic granites. A particularly prominent part of the regional anomaly includes, in addition to the usual elements related to the granites, the assemblage of Mo, W and Sn. Initial interpretation suggested potential for granite-related, stockwork Mo deposits. Detailed work identified three separate sources for the anomaly: a metal-rich granite, a silicified and stockwork-veined area with scheelite and molybdenite, and scheelite/powellite concentrations in skarn deposits adjacent to a ring-dike complex.Regional geochemical, geophysical and remote-sensing data in the Sonoran Desert, Mexico, define a series of linear features interpreted to reflect fundamental, northeast-trending fractures in the crust that served as the prime conduits for mineralizing fluids. At a larger scale, the linear, northeast-trending anomalies can be shown to result from a series of discrete mineralized systems with different ages and mineral assemblages. The linear pattern of anomalies disintegrates.A regional geochemical survey in the Sonoran Desert in southwestern Arizona displays a cluster of samples anomalous in Pb, Mo, Bi and W. In detail, the original regional anomaly separates into four discrete anomalous areas, each with its own distinctive suite of elements, geographic distribution and age of mineralization.A prominent regional gold anomaly in the Gobi Desert, Xinjiang, Peoples Republic of China, extends southeastward for 30 km from known lode gold deposits. Because the anomaly cuts both lithologic units and the structural grain, and because it parallels the prevailing direction of high-velocity winds, it was originally attributed to eolian dispersion. In detail, the regional anomaly consists of several east-west-trending anomalies, parallel to local lithology and structure that most likely reflect independent sources of lode gold. The regional anomaly results from smoothing of an en-echelon set of local anomalies.These examples emphasize that interpretation of regional anomalies must be tempered to consider regional-sized geologic features. Attempts to overinterpret anomalies by assigning deposit-scale attributes to regional anomalies can lead to confusion and incorrect interpretations. Potential targets that can be readily resolved only at intermediate or detailed scales of study may be overlooked. 相似文献
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中国以水系沉积物测量为主的区域地球化学调查自1978年开始以来,已覆盖陆地面积约690×104 km2,积累了海量的高质量基础地球化学数据.在这些数据的开发利用中不同地区、不同范围间的数据对比是研究元素分散富集、成矿趋势、异常评价的一项重要内容.以全国1:20万水系沉积物测量数据为依据,采用全部原始数据,以X±3S为临界值一次性剔除异点后的数据集的中位数作为背景值的估计值,使用统一方法计算出了全国范围、9个大地构造单元、12个地球化学景观区、19个成矿带的39种元素水系沉积物背景值,探讨了全国范围、不同构造单元、不同景观区、不同成矿带各元素背景值的区域分布规律和特征.研究表明不同的景观区、不同的成矿带、不同的大地构造单元,由于地质背景和景观条件不同,元素的地球化学分布特征也不同,表现出不同的区域分布特点和分布模式.这些背景值为进一步深入开发利用区域化探数据和资料提供了可供对比的基础数据. 相似文献