Investigating the spatial distribution of antimony geochemical anomalies located in the Yunnan-Guizhou-Guangxi region,China

The Yunnan-Guizhou-Guangxi region is well known for its abundant mineral resources, and low-temperature hydrothermal mineralization represented by the elemental association of gold, arsenic, antimony and mercury is widely developed there. Many studies on the geological-geochemical characteristics of gold have been conducted, but a comprehensive understanding of the antimony geochemical pattern is still lacking. This paper studied the Sb distribution characteristics and the cause of geochemical anomalies based on the geochemical data of stream sediments and rocks in the study area. In addition, the geochemical data of Au, As, Sb and Hg were centered and log-ratio transformed to eliminate the closure effect, and then random forest regression (RFR) with Au, As and Hg as the characteristic variables was used to investigate the ore-related geochemical anomalies of Sb. Seven geochemical provinces were delineated from the original geochemical data, and they are not entirely consistent with the known deposits. Sb moves from the rocks to the stream sediments during weathering. The variation trend in the Sb background values in stream sediments in each tectonic unit is consistent with that in the rocks themselves, implying that Sb in the stream sediments is inherited from the background rocks. The distributions of Sb predicted by RFR are similar to the distribution pattern of Sb in stream sediments. Of the three elements considered, the influence of As on the variations in the Sb geochemical background is the greatest, followed by Au and then Hg. The geochemical anomalies extracted by the residuals produced in this algorithm are consistent with where the known Sb metallogenic district is located, indicating that this method of recognizing geochemical anomalies is feasible and effective and has theoretical and practical significance.     

Single-element Anomaly Mapping from Stream Sediment Geochemical Landscapes Aided by Digital Terrain Analysis

The identification of anomalies within stream sediment geochemical data is one of the fastest developing areas in mineral exploration. The various means used to achieve this objective make use of either continuous or discrete field models of stream sediment geochemical data. To map anomalies in a discrete field model of such data, two corrections are required: background correction and downstream dilution correction. Topography and geomorphology are important factors in variations of element con...     

Adjusting stream-sediment geochemical maps in the Austrian Bohemian Massif by analysis of variance

The Austrian portion of the Bohemian Massif is a Precambrian terrane composed mostly of highly metamorphosed rocks intruded by a series of granitoids that are petrographically similar. Rocks are exposed poorly and the subtle variations in rock type are difficult to map in the field. A detailed geochemical survey of stream sediments in this region has been conducted and included as part of the Geochemischer Atlas der Republik Österreich,and the variations in stream sediment composition may help refine the geological interpretation. In an earlier study, multivariate analysis of variance (MANOVA) was applied to the stream-sediment data in order to minimize unwanted sampling variation and emphasize relationships between stream sediments and rock types in sample catchment areas. The estimated coefficients were used successfully to correct for the sampling effects throughout most of the region, but also introduced an overcorrection in some areas that seems to result from consistent but subtle differences in composition of specific rock types. By expanding the model to include an additional factor reflecting the presence of a major tectonic unit, the Rohrbach block, the overcorrection is removed. This iterative process simultaneously refines both the geochemical map by removing extraneous variation and the geological map by suggesting a more detailed classification of rock types.     

Seasonal variations of Zn, Cu, As and Mo in arsenic-rich stream at the Mokrsko gold deposit, Czech Republic

Monthly sampling of slightly alkaline arsenic-rich stream in the Mokrsko gold deposit revealed seasonal variations in dissolved Zn, Cu, As and Mo. Concentrations of trace metal cations (Zn, Cu) increased as much as 330 and 178%, respectively, from minimum mean values at autumn to maximum mean values at spring. In contrast, concentrations of trace element oxyanions (As, Mo) revealed opposite seasonal pattern with increase to 189% (As) and 123% (Mo) during summer–autumn, indicating that in-stream biogeochemical process(es) played the main role in controlling the seasonal variations of these trace elements. The trace elements were mainly scavenged by low crystalline Mn oxyhydroxide and Fe oxyhydroxide (ferrihydrite). Results are consistent with sorption and coprecipitation processes controlling seasonal variations of dissolved Zn and Cu, while As and Mo dynamics appear linked to Mn redox reactions. The sorption processes and Mn redox processes are attributed to the changes of pH and oxic/anoxic conditions on the surface of oxyhydroxides, respectively, which are themselves controlled by the balance between photosynthesis and respiration. Under the geochemical conditions of the stream, inferred Mn redox reactions can only be explained by microbial activity.     

Analysis and mapping of geochemical anomalies using logratio-transformed stream sediment data with censored values

There is lack of research and documentation of actual (as opposed to theoretical) benefits (e.g., mineral deposit discovery) of developments in compositional data analysis and imputation of censored values to mineral exploration geochemistry. In the present study, analyses of logratio- and ln-transformed stream sediment geochemical data containing ca. 30% of samples with censored values of a pathfinder element for the mineral deposit-type of interest yielded the following findings. Exclusion of those samples supports interpretation of multi-element anomalies reflecting the presence of mineralization. However, the multi-element anomaly maps obtained by exclusion of those samples are barely better than the multi-element anomaly maps derived by inclusion of those samples after replacing the censored values with 1/2 of detection limit or with imputed values. Logratio (i.e., alr, clr, or ilr) transformation, compared to ln-transformation, of stream sediment geochemical data does not improve mapping of pathfinder element anomalies reflecting the presence of mineralization. However, stream sediment geochemical data, excluding or including censored values (replaced with 1/2 of detection limit or with imputed values), should be clr- or ilr-transformed to enhance recognition of anomalous multi-element associations reflecting the presence of mineralization. The anomaly maps of multi-element associations derived from ilr-transformed data are better, albeit slightly, than the anomaly maps of multi-element associations derived from clr-transformed data. In the present study, the main benefit of either clr- or ilr-transformation, compared to either ln- or alr-transformation, of stream sediment geochemical data is the enhancement of anomalous multi-element associations reflecting the presence of mineralization. This is an important benefit because variations in trace element concentrations in regional-scale stream sediment geochemical data are mostly due to lithology and other factors (or processes) unrelated to mineralization. Further investigations of various exploration geochemical data are needed to demonstrate and document the actual (as opposed to theoretical) benefits of developments in compositional data analysis and imputation of censored values to mineral exploration.     

Geochemical Baselines of Nickel and Chromium in Various Surficial Materials in the Barents Region, NW Russia and Finland

The geochemical baselines of nickel and chromium were studied from the data produced by the Barents Ecogeochemistry project, a large international regional geochemical mapping exercise. The project surveyed major and trace element distributions in stream water, organic and mineralogically-modified soil horizons, and terrestrial moss in the northwestern part of Russia and in Finland. Other materials were collected during the pilot phase and later from thirty special sites. The results on respective materials by XRF, ICP-MS and ICP-AES showed that both geological and anthropogenic factors have an influence on the geochemical baseline concentrations of Ni and Cr in organic soil and stream water. The main explanation of the observed distribution patterns in terrestrial moss is human activity, but geological factors can also affect the baselines. The variation of geochemical baselines in the mineral-rich soil horizon depends only on variations in bedrock. The mineralogy of samples mainly controls the leachability properties of soil samples.     

地球化学场及其在隐伏矿体三维预测中的作用

本文从物理学"场论"的角度介绍了地球化学场的概念,并从场源、场作用及地球化学指标分布三个基本要素出发阐述了地球化学场的扩散、对流-扩散的动力学机制。首先,按照采样介质,将地球化学场分为原生的岩石地球化学场,以及次生的土壤、水系沉积物、水文和气体地球化学场,描述了组成各类地球化学场的要素。其次,将地球化学场的分析方法概括为静态的空间结构分析和动态的时空结构分析两种,提出要以场的动力学机制为基础,利用地球物理学中的正、反演理论来研究四维时空中地球化学场的发展和演化。最后,探讨了地球化学场时空结构分析与三维地学模拟两者之间彼此补充和相互验证的关系,三维地学模拟构建的场源及空间介质模型,为地球化学场的正、反演提供了初始条件,地球化学场反演的结果又可用来修正三维地质模型;探讨了地球化学场与大数据分析技术间的关系,即采用大数据的"数据驱动"的思路来挖掘其与多元地学数据之间的隐性联系,探索其与成矿过程的关联性。地球化学场与三维地学模拟、大数据分析技术的结合将为隐伏矿体三维预测中地下成矿物质的分布和演化提供依据。     

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.     

Geochemical behaviors of different element groups during shale weathering at the Susquehanna/Shale Hills Critical Zone Observatory

Major and trace element concentrations were measured in bedrock, regolith and stream sediments from a first-order catchment developed entirely on grey shale in central Pennsylvania, USA. These elements can be classified into five major groups based on statistical data analysis. The presence of different elemental groups is due to the mineralogical origin, cycling processes, and geochemical properties of these elements during soil formation. A better understanding of the behaviors of these elements during chemical weathering would allow for their possible use as natural tracers in Critical Zone processes.     

Spatial filtering of exploration geochemical data using EDA and robust statistics

The spatial filtering techniques that are used for the analysis and interpretation of exploration geochemical data to define regional distribution patterns or to outline anomalous areas are, in most cases, based on non-robust statistical methods. The performance of these techniques is heavily influenced by the presence of outliers that commonly exist in the data. This study describes a number of filtering techniques motivated by the development of exploratory data analysis (EDA) and robust statistical procedures. These are the median filter (MF) and the adaptive trimmed mean filter (ATM) for the smoothing of regional geochemical data to reduce spurious variations; two new filters, the fence filter (FF) and the notch filter (NF), have been developed to define geochemical anomalies.The application of the spatial filtering techniques is illustrated by Zn data from approximately 3100 stream sediment samples taken in a regional geochemical survey over 25,000 km² of the western margin of the São Francisco Basin, Brazil. Regional distribution patterns for Zn obtained by the MF and ATM filters are clearly related to known stratigraphic units. Anomaly filtering using the FF and NF has delineated most known base metal and gold occurrences, as well as a number of anomalies located in geologically favourable environments but unrelated to any known mineralization. The two anomaly filters have, for the most part, defined the same anomalies in the study area but only the NF highlights the anomaly associated with the important Morro Agudo Pb-Zn deposit, which is too subtle to be immediately apparent in the unprocessed data.     

Geochemical (process based) characterization of groundwater along the KT boundary of South India

A study has been carried out in KT (Cretaceous-Tertiary) boundary along the contact zones of hard rock, limestone and sedimentary formations to discern the geochemical processes governing the groundwater chemistry. A total of sixty-three groundwater samples were collected from the handpumps covering the entire study area and measured for hydrochemical species. Principal component analysis of the hydrochemical data inferred three major processes governing the geochemistry of the groundwater of the region as leaching, ion exchange and weathering. It was also inferred that there are few samples depicting the mixtures of these processes (what are they mention it) and few samples not representing any of these processes with adequate statistical significance. Hence, in order to know the geochemical behaviour of the samples representing each process, their combinations along with the samples which are not- representative samples of these processes were inferred using various standards plots to get an insight into their geochemical characteristics and affinity. This also inferred the samples representing different processes have a significant signature of geochemical facies. The major ions and the stable isotopes of groundwater were used to understand these processes. The carbonate and sulphate saturation states of these samples were calculated by PHREEQC and compared with major variations with the identified three geochemical processes. The state of saturation of Halite, Anhydrite, Gypsum, Aragonite, Dolomite, Calcite, Talc and Chrysolite were determined in all the samples. Inverse modeling was carried out considering the non-representative samples as initial solution and the samples representing each factor as final solution to understand the phase mole transfer in each process. An attempt was also made in this study to compare the geochemical behaviour of groundwaters from different KT boundaries. The samples representing these processes were plotted on an integrated map representing lithology, lineaments, drainage and elevation to determine their interrelationships. The study groups the samples into anthropogenic or geogenic. The leaching process is controlled by lithology and landuse, ion exchange processes is influenced by lithology and drainage patterns whereas weathering processes were controlled by lithology, drainage and lineaments. Non representation of samples (NRS) were mainly controlled by drainage and lineaments of the region.     

Application of multivariate statistical analysis and a geographic information system to trace element contamination in the Chungnam Coal Mine area,Korea

In order to examine contamination in the Chungnam Coal Mine area, rock, stream sediment and water samples were collected and analyzed for trace elements. In order to compile the drainage-based geochemical maps, catchment basins were calculated using aspects of DEM (data elevation model) and stream-line segments. The constructed DEMs with 3 types of resolution were examined, these need to be properly used for well-shaped and accurate catchment basins. The stream-line segments and sampling points were also considered as a target image for watershed segments and it was found that the stream-line segments as target images were better role at reflecting the catchment area rather than the sampling points. It is important that the geochemical databases were manipulated to present the various phenomena. Factor analysis in R-mode was used to integrate geochemical data, and the input data for factor analysis were the concentrations of 12 trace elements in stream sediment and 3 anion concentrations and pH values in stream water. Using a maximum likelihood scheme, eigenvalues that explained about 90% of total variance were established and 4 factors were selected. Factors 1 and 2 indicated relative enrichment of trace elements, factor 3 was explained by human activities of residents and factor 4 was related to the pH of stream water. The drainage-based geochemical maps with 4 kinds of factor scores were compiled.     

中国水系沉积物39种元素系列背景值

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.      

Compositional data analysis in the study of integrated geochemical anomalies associated with mineralization

Geochemical data are typical compositional data which should be opened prior to univariate and multivariate data analysis. In this study, a frequency-based method (robust principal component analysis, RPCA) and a frequency-space-based method (spectrum–area fractal model, S–A) are applied to explore the effects of the data closure problem and to study the integrated geochemical anomalies associated with polymetallic Cu mineralization using a stream sediment geochemical dataset collected from the Zhongteng district, Fujian Province (China). The results show that: (1) geochemical data should be opened prior to RPCA to avoid spurious correlation between variables; (2) geochemical pattern is a superimposition of multi-processes and should be decomposed; and (3) the S–A fractal model is a powerful tool for decomposing the mixed geochemical pattern.     

Drainage sampling for uranium in the Torrington district, New South Wales, Australia

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.     

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.     

The identification of various types of geochemical stream sediment anomalies in Northern Ireland

A regional geochemical stream sediment survey of part of Northern Ireland led to the recognition of three types of base metal anomaly of exploration interest. These were significant anomalies of both elastic and hydromorphic origin, and non-significant hydromorphic anomalies in several upland areas. The significant anomalies are derived from Pb-Zn-Cu mineralization, whereas the non-significant anomalies are due to the leaching of Zn and other metals from acidic and/or gleyed soils and subsequent concentration in stream channels by coprecipitation with manganese oxides. Significant hydromorphic anomalies can be identified on the basis of abnormal Zn/Mn ratios and significant elastic anomalies on the basis of anomalous Pb contents. It is of the utmost importance to distinguish the dispersion mechanisms. Regional variations in bedrock geochemistry may only be identified when consideration is given to local dispersion mechanisms and account taken of the effects of variations in the surface environment on stream sediment composition. Changes in vegetation and land use may lead to rapid alterations in the nature of the dominant dispersion mechanisms.     

Adjustment of geochemical background by robust multivariate statistics

Conventional analyses of exploration geochemical data assume that the background is a constant or slowly changing value, equivalent to a plane or a smoothly curved surface. However, it is better to regard the geochemical background as a rugged surface, varying with changes in geology and environment. This rugged surface can be estimated from observed geological, geochemical and environmental properties by using multivariate statistics.A method of background adjustment was developed and applied to groundwater and stream sediment reconnaissance data collected from the Hot Springs Quadrangle, South Dakota, as part of the National Uranium Resource Evaluation (NURE) program. Source-rock lithology appears to be a dominant factor controlling the chemical composition of groundwater or stream sediments. The most efficacious adjustment procedure is to regress uranium concentration on selected geochemical and environmental variables for each lithologic unit, and then to delineate anomalies by a common threshold set as a multiple of the standard deviation of the combined residuals. Robust versions of regression and RQ-mode principal components analysis techniques were used rather than ordinary techniques to guard against distortion caused by outliers Anomalies delineated by this background adjustment procedure correspond with uranium prospects much better than do anomalies delineated by conventional procedures. The procedure should be applicable to geochemical exploration at different scales for other metals.     

成矿带1∶20万水系沉积物地球化学分区的方法及地质意义:以西藏冈底斯铜多金属成矿带为例

以冈底斯铜多金属成矿带为例,阐述了利用1∶20万和1∶50万水系沉积物地球化学测量开展成矿区带地球化学分区的方法和思路,进一步对其地质意义进行了探讨。结果表明:小比例尺的水系沉积物地球化学数据具有地球化学分区示踪意义。总结出一套操作性强的地球化学分区方法,其方法具有指示找矿方向的实际意义,对区域构造单元划分具参考价值。地球化学分区为该区的找矿方向、成矿远景评价及基础地质调查奠定了基础。     

非负矩阵分解方法在水系沉积物地球化学数据处理中应用

鉴于水系沉积物地球化学数据可以表示为非负矩阵,这使得利用非负矩阵分解(NMF)方法处理该类数据成为可能.介绍了非负矩阵分解方法的基本原理和方法,讨论了基于非负矩阵分解方法处理水系沉积物地球化学数据的可能和效果.以个旧水系沉积物地球化学数据为例,运用NMF方法和主成分分析(PCA)方法对其进行异常分析,并对这两种方法的处理结果进行了比较,发现NMF方法对于处理水系沉积物地球化学数据是一种有效的方法.尽管这两种方法各自有其优越性,但就本实例数据而言,NMF方法优于PCA方法.