Types of endogenous geochemical fields and their significance for prospecting

When prospecting ore deposits in Trans-Baikal region the endogenous geochemical fields (EGF) are taken as the main search element, as was proposed by L.V. Tauson (1983). Such fields are classified into: geochemical fields of dispersion (GFD), concentration (GFC) and removal (GFR). With regard to their formation conditions they are subdivided into magmatic (associated with magmatic chambers), intratelluric (associated with activity of intratelluric emanations), hydrothermal-metamorphic (vadose-thermal solutions), metamorphogenic, and sedimentary-metamorphogenic ones. Magmatic EGFs are divided into three groups: magmatic, pneumatolytic, and hydrothermal stages. This study identified their polygenetic origin and association with ore-magmatic systems. The geochemical fields of ore zones, fields, and deposits result from the late and post-magmatic processes; they also include the EGF of host rocks and those which altered at pre-ore stage of the natural system development.At ore deposits the EGFs are responsible for supply and redistribution of elements through the entire ore formation process. The fields were divided into EGF of poor concentration (contrast coefficient CC normalized after background to 10), mean (CC >10–100), and intense (CC >> 100). The EGF intensity progressively increases at the hierarchy stage: “host rock—pre-ore metasomatite—syn-ore hydrothermalite—ore body—ore pillar”.To summarize, the fields, ore districts, zones, and deposits are characterized by diverse patterns of dispersion, concentration, and removal.The specific features of composition, structure, and zonal distribution of elements in geochemical fields are exemplified by some gold-bearing zones of the Trans-Baikal region. The paper reports new approaches to investigating these natural formations. The authors promote transition from the generally accepted evaluation of a halo separation to the volumetric survey of endogenous geochemical fields (GFD, GFC, and GFR included) of ore deposits and ore-magmatic systems, in general. The acquired evidence supports the assumption that endogenous geochemical fields should be regarded as a complete system differentiated in space and time preserving specifics and pattern of the internal structure.     

甘肃西秦岭地区地球化学特征及找矿预测

利用西秦岭地区近20年来取得的数以万计的化探数据,借助计算机技术及GIS地理信息进行处理,重点选择主要成矿元素Au、Cu、Pb、Zn、W进行研究。从元素地球化学特征分析入手,研究元素在空间、时间上的迁移、富集、分散规律,通过对西秦岭地区成矿元素地球化学规律研究,提供了全面、详实、系统的地球化学成果,为区域矿床地球化学预测研究提供理论依据。提出了主要找矿远景区及找矿有利地段,为下一步矿产勘查工作提供靶区。     

Factor Analysis of Soil and Attic-dust to Separate Mining and Metallurgy Influence, Meza Valley, Slovenia

Based on the factor analysis of chemical elements determined in topsoil (0–5 cm) and attic-dust, two natural and two man-made (anthropogenic) geochemical associations were discovered in the Meza valley, an old mining and metallurgic area. The natural geochemical association (Al-Ce-Co-K-La-Li-Nb-Rb-Sc-Th-Ti-V) is influenced mainly by weathering of metamorphic rocks, while the anthropogenic association (Ca-Mg) was determined in an area of carbonate rock outcrops. The man-made associations are a result of lead production (Ag-As-Cd-Mo-Pb-S-Sb-Sn-Zn) and iron production (Co-Cr-Mo-Ni-W).     

确定地球化学异常水平分带序列方法的研究

通常利用异常规模或线金属量衬度确定地球化学异常水平分带序列,由此得出的序列,主要反映不同指示元素异常强度的大小,并非是异常中心在空间上的有序排列,因此不完全反映元素的相对活动性。应用重心法计算的水平分带序列,不仅反映成矿成晕作用下不同指示元素的异常中心相对于矿化中心的空间变化规律,而且也能够有效地刻划成矿成晕过程中元素的相对活动性。重心法的数学意义和地球化学意义明确,同时适用于垂直分带序列的计算。     

指示元素垂向分带序列计算方法述评

计算和确定矿床原生晕指示元素垂向分带序列是地球化学找矿研究特别是矿床原生晕分析和研究的重要内容之一,国内、外地学者提出了多种计算方法。这里介绍几种常用的计算方法:分带指数法、广义衬值法、浓集重心法、浓集指数法、比重指数法、含量梯度法等,并指出这些方法的优点和不足,认为计算矿床原生晕指示元素垂向分带序列时,不宜采用传统的格里戈良分带指数法,而应采用广义衬值法、浓集重心法或比重指数法。     

Neuro-fuzzy modelling in mining geochemistry: Identification of geochemical anomalies

Local and mine scale exploration models for anomaly recognition within known ore fields are discussed. Traditional geochemical exploration methods are based on multivariate statistical analysis, metallometry, vertical geochemical zonality and criteria of natural field geochemical associations, which suffer several shortcomings, including lack of a geostatistical generalised approach for separating anomalies from background. These shortcomings make the interpretation process time consuming and costly. Fuzzy set theory, fuzzy logic and neural network techniques seem very well suited for typical mining geochemistry applications. The results, obtained from applying the proposed technique to a real scenario, reveals significant improvements, comparing the results obtained from applying multivariate statistical analysis. Computationally, the introduced technique makes possible, without exploration drilling, the distinction between blind mineralisation and zone of dispersed ore mineralisation. The methodology developed in this research study has been verified by testing it on various real-world mining geochemical projects.     

Erosion level of the epithermal Rogovik deposit estimated from geochemical data,northeast Russia

The geochemical zoning of the Rogovik epithermal deposit in northeast Russia has been established on the basis of endogenic anomalous geochemical fields (AGCF) of Au–Ag zones, their qualitative and quantitative compositions, and spatial distribution of chemical element indicators of Au–Ag mineralization. The obtained geochemical data (monoelemental AGCF, associations of elements, their composition, contrast, and correlation) allowed us to estimate the erosion level of Au–Ag ore zones. It has been shown that AGCF related to Au–Ag mineralization are distinguished by simple component composition (Au, Ag, Hg, Sb, As, Cu, Pb, Zn) and regular spatial distribution of the elements. It has been established that the least eroded central part of the object is characterized by widespread and the most contrasting Au, Ag, Hg, Sb, and As AGCF closely related to the ore-bearing units of the deposit. The contrast of these fields gradually decreases with depth. Low-contrast Cu, Pb, and Zn AGCF typical of the footwall depth intervals and flanks of Au–Ag zones intervals appear at depth. The northern part of the area is eroded to the deepest level. The contrast of Ag, Hg, Sb, and As geochemical fields abruptly decreases here, and Cu, Pb, and Zn AGCF become widespread with depth. The relatively contrasting fields of anomalous Au concentrations develop here extremely locally and near the surface. It has been concluded that the as yet poorly explored southern part of the Rogovik deposit most likely is promising for further geological exploration and the discovery of new mineralized areas.     

甘肃省成县李家沟层控铅锌矿床原生地球化学异常特征及其找矿意义

本文研究了甘肃省成县李家沟层控铅锌矿床的原生地球化学异常特征及找矿标志。根据矿区各种岩石中化学元素的分布和分配,相关性和组合特征的分析,提出了一些无机和有机地球化学相结合的找矿标志。为了研究矿床剥蚀程度的判断标志,文中探讨了化学元素的含量、比值、相关性和组合特征在矿体不同部位上的变化。对成晕元素的共生组合和原生晕在空间上的分布进行了研究,并且根据分带指数的计算确定了矿床原生晕指示元素的垂向和水平分带序列,这些研究将有助于这一类型矿床的找矿和评价工作。最后,本文还探讨了层控矿床和典型热液矿床原生异常的一些差异性。     

Selective chemical extraction of heavy metals in tailings and soils contaminated by mining activity: Environmental implications

Total concentrations of chemical elements in soils may not be enough to understand the mobility and bioavailability of the elements. It is important to characterise the degree of association of chemical elements in different physical and chemical phases of soil. Another geochemical characterisation methodology is to apply sequential selective chemical extraction techniques. A seven-step sequential extraction procedure was used to investigate the mobility and retention behaviour of Al, Fe, Mn, Cu, Zn, Pb, Cr, Co, Ni, Mo, Cd, Bi, Sn, W, Ag, As and U in specific physical–chemical and mineral phases in mine tailings and soils in the surroundings of the abandoned Ervedosa mine. The soil geochemical data show anomalies associated with mineralised veins or influenced by mining. Beyond the tailings, the highest recorded concentrations for most elements are in soils situated in mineralised areas or under the influence of tailings. The application of principal components analysis allowed recognition of (a) element associations according to their geochemical behaviour and (b) distinction between samples representing local geochemical background and samples representing contamination. Some metal cations (Mn, Cd, Cu, Zn, Co, Cr, Ni) showed important enrichment in the most mobilisable and bioavailable (i.e., water-soluble and exchangeable) fractions due likely to the acidic conditions in the area. In contrast, oxy-anions such as Mo and As showed lower mobility because of adsorption to Fe oxy-hydroxides. The residual fraction comprised largest proportions of Sn and Al and to a lesser extent Zn, Pb, Ni, Cr, Bi, W, and Ag, which are also present at low concentrations in the bioavailable fractions. The elements in secondary mineral phases (mainly Fe, Mn, Cu, Zn, Cd, Pb, W, Bi, Mo, Cr, Ni, Co, As and U) as well as in organic matter and sulphides are temporarily withheld, suggesting that they may be released to the environment by changes in physico-chemical conditions.     

GIS-based prospectivity-mapping based on geochemical multivariate analysis technology: A case study of MVT Pb–Zn deposits in the Huanyuan-Fenghuang district,northwestern Hunan Province,China

This paper demonstrates a partial least-squares regression (PLS) method for geochemical modelling, and then uses the models and geological favourable features to obtain mineral potential maps. The PLS is one of multivariate analysis technologies, which can identify variations in associations and correlations among geochemical elements and mineralisation. The method is here used to calculate principal components as well as to identify correlations between Pb–Zn (mineralization) and 25 stream sediment elements for constructing geochemical models in the Huayuan-Fenghuang district of northwestern Hunan Province, China. The models showing the distribution of geochemical anomaly are useful in interpreting the distribution of faults and the Cambrian Qingxudong Formation (ore-bearing formation), and to better define the architecture on mineralisation in the study area. In addition, the models and other favourable features (proxies) are easily integrated into single possibility map by Boost Weights-of-Evidence (Boost WofE) approach for targets.     

Hybridisation of mafic microgranular enclaves in the Lavras Granite Complex,southern Brazil

Twenty-five mafic microgranular enclaves of the Lavras Granite Complex in southern Brazil were studied petrographically and geochemically to establish their origin and to investigate the processes involved in their differentiation. Mesoscopic and microscopic textures indicate that they are products of magma mingling between a basic end member of probable mildly alkaline affinity and host shoshonitic and alkaline granitic rocks. The hybridisation process involved at least the following mechanisms: (i) chemical diffusion of volatiles and very mobile elements such as K to the less polymerised liquids, leading to the crystallisation of hydrated mafic minerals; (ii) chemical diffusion of Ti and P to the less polymerised liquids, leading to titanite and apatite crystallisation; (iii) mechanical accretion in the basic magma of early crystallised host granite phases that promoted enrichment of their major constituents and of trace elements with high partition coefficients in these phases; (iv) chemical diffusion of elements such as Rb, Nb, Y, and Yb with high Kd in the major enclave phases, from host magma into the basic enclaves. These processes occurred simultaneously, probably before the dispersion of basic batch magma forming the mafic microgranular enclaves, and caused hybridisation and complex geochemical patterns. The patterns are very different from the linear trends predicted for near-equilibrium systems such as those of magma mixing or fractional crystallisation.     

横断山不同成因类型花岗岩类岩石中黑云母的标型特征

本文研究了横断山区不同成因类型花岗岩类岩石中黑云母的化学成分、微量元素、结构和物理性质等。结合花岗岩类岩石的成因类型,将黑云母分为三个亚种:富镁黑云母(MF=1.3—1.5)、镁黑云母(MF=1—1.3)和富铁黑云母(MF=0.5-1)。     

鄂西地区铅锌地球化学异常分布特征及找矿意义

地球化学元素的分布特征反映了元素矿化富集及空间变化的规律。通过对鄂西地区水系沉积物地球化学测量数据的统计分析,圈定了铅锌地球化学异常,并应用因子分析方法确定了主要成矿元素的共生组合及元素组合异常,为鄂西地区铅锌多金属矿勘查提供了有用的找矿信息。Pb、Zn两元素异常主要分布在青峰断裂带附近、神农架地区、黄陵背斜周缘、鹤峰地区和恩施地区南部。Pb、Zn、Cu、Mn四种元素关系密切,反映了该区矿化以铅锌多金属元素矿化富集为主的特征。青峰断裂带附近、神农架地区和恩施南部地区三个区域铅锌多金属元素异常强度大,可以作为鄂西地区铅锌多金属矿下一步找矿勘查重点区。     

基于MAPGIS的分形方法确定化探异常

地球化学元素的异常下限值确定是地球化学中重要的问题之一,目前还没有一个令人满意的具有科学依据的计算方法。传统的化探异常下限值计算是基于元素的地球化学分布呈正态分布或元素含量在空间上呈连续的变化这一假设为基础的,而事实上地球化学元素含量的空间分布是极其复杂的,研究表明,地球化学景观可能是一个具有低维吸引子的混沌系统,元素的地球化学背景值和异常具有各自独立的幂指数关系,由此导致了一种多重分形分布,因而可以利用元素的分形分布求出其异常下限。利用元素的分形分布求异常下限的几种常用方法均是以求取不同尺度r下,对应的N(r)数。如果用手工统计方法计算,计算过程简单但繁琐,地理信息系统((}IS)可以实现图形单元的动态查询和属性统计,这种特性很适合于统计不同尺度r下对应的N(r),因此,可以将分形方法与地理信息系统加以结合,在CIS平台上对地学图形和属性信息进行分析及统计处理,将原来比较繁杂的分形计算操作变得方便简捷,易于实现。本文以武汉中地信息公司开发的．MAPGIS地理信息系统为例,对河北某地1：5万Cu元素化探数据进行了处理,具体说明了以MAPGIS为工具,利用分形方法求取元素化探异常下限的过程,并将计算结果与传统异常下限计算方法所得的结果进行了对比,所得的异常下限值相近或一致,但由于传统的计算方法不仅要求对原始数据进行预处理,而且在下限值的确定上需要结合本地区的实际地质情况确定,因此人为干扰因素较大,而利用基于MAPGIS的分形方法计算元素异常下限值不仅操作简单,而且计算时由于不受元素特高值的影响,因而不用对原始数据进行预处理,人为干扰因素较少。通过对比得知该方法在实践工作中可行。     

The geochemical features of terrigenous host rocks at massive sulfide deposits in the eastern Caucasus

Based on a great body of factual data, geochemical peculiarities in the distribution of rare, noble, radioactive, and other trace components in the Lower-Middle Jurassic terrigenous ore-enclosing (hereafter, host) rocks at massive sulfide deposits in the Vostochnyi (eastern) segment of the Greater Caucasus are high-lighted. Study of the Filizchai base metal massive sulfide deposit made it possible to define general regularities of element distribution in the ore body and altered wall rocks that reflect the general geochemical zonality. Concentrations of most components depend on the lithology and wall-rock alteration, distribution of rocks in the section, proximity of the contacting ore, and its mineral composition. Contents of typical elements in host rocks are closely associated with their concentrations in the ore bodies.     

多重分形与地质统计学方法 用于勘查地球化学异常空间结构和奇异性分析

勘查地球化学和地球物理场的局部空间结构变化性应包括空间自相关性以及奇异性 .前者可通过地质统计学中常用的变异函数来实现 ;后者可用多重分形模型进行刻划 .具有自相似性或统计自相似性的多重分形分布 (multifractaldistributions)的奇异性 (α)可以反映地球化学元素在岩石等介质中的局部富集和贫化规律 .而多重分形插值和估计方法可以同时度量以上两种局部结构性质 (空间自相关性以及奇异性 ) ,因而 ,它不仅能够进行空间数据插值 ,同时还能保持和增强数据的局部结构信息 ,这对于地球化学和地球物理异常分析和识别是有益的 .应用该方法处理加拿大NovaScotia省西南部湖泊沉积物地球化学砷等元素数据表明 ,地球化学数据的局部奇异性在该区能够反映局部金和钨 -锡 -铀矿化蚀变带或岩相变化以及构造交汇等局部成矿有利部位 .     

黑龙江沙兰站幅森林沼泽区 基础地质调查中的区域化探新方法

森林沼泽区区域化探新方法的使用,进一步拓展了区域化探资料的应用范围,使其在基础地质调查中的应用成为可能。根据沙兰站幅区域化探扫面成果,从元素组、元素的表生富集系数、元素的含量区间、岩石地球化学资料等方面,对区域化探资料在基础地质调查中的应用进行了探讨。     

A comparison of selective extraction soil geochemistry and biogeochemistry in the Cobar area, New South Wales

In parts of the deeply weathered and semi-arid environments of the Cobar area (NSW, Australia), detection of mineralisation using conventional soil sampling and total metal analysis is impeded. This is due to the intense leaching of trace elements within the weathered profile, discontinuous coverage of transported materials and the existence of diffuse regional geochemical anomalies of ill-defined source. Selective chemical extractions, applied to various regolith components, and biogeochemistry offer a means of isolating localised geochemical patterns related to recent dispersion of trace elements through the overburden. Lag geochemical patterns across the McKinnons deposit (Au) and Mrangelli prospect (Pb–Zn–As) reflect mechanical dispersion processes and minor hydromorphic effects. Concentrations of more mobile elements tend to be higher in the non-magnetic fraction, due to higher proportions of goethite and poorly crystalline hematite than in the magnetic fraction. The subdued soil geochemical responses for metals extractable by cold 40% hydrochloric acid (CHX) and for total element concentration reflect the leached nature of the residual profile, low grade of mineralisation, dilution by aeolian components and disequilibrium of fine fractions with coarser, relict Fe-oxides. The stronger contrast for CHX for most metals, compared with total extraction, indicates surface accumulation of trace elements derived from underlying mineralisation. Enzyme leach element anomalies are intense but generally located directly over bedrock sources or major structural breaks, irrespective of the nature of the overburden. Though mechanisms for the dispersion of trace elements extracted by enzyme leaching are not well established, the lack of lateral transport suggests vertical migration of volatile metal species (atmimorphic dispersion). The strong, multi-element response to mineralisation in cypress pine needles indicates significant metal recycling during the present erosional cycle. However, a comparison of the trace element concentrations in vegetation (cypress pine needles) and selective extractions of soils indicates that recycling by the plants is not the dominant mechanism for transportation of metals through the overburden. The vegetation may be responding to hydromorphic dispersion patterns at depth. The use of selective extractions may be useful in detecting mineralisation through deeply leached profiles, but offers even greater potential when integrated with biogeochemistry to detect targets buried by significant thickness of transported cover.     

川滇黔桂76种元素地球化学图编制中分析方法与分析质量研究(二) 关于8个实验室对银元素分析的考核

国内8个实验室对川滇黔桂相同的76个泛滥平原沉积物样品的76种元素进行了分析测试,目的在于探索更有效的分析质量的评价方案,以便为编制相应的地球化学图优选不同元素的最佳分析方法。利用参考值、样本的统计学参数、相似性、密度分布函数、地球化学场的空间结构和地球化学异常的重合性等对Ag元素的分析数据作了评价,不但要求分析数据在绝对值方面有一定的精度,还强调了化探数据的空间属性,要求分析数据的空间分布方面也尽量与理想的地球化学图之间具有一致性。