初论新疆多元素富集区及找矿方向

以新疆区域化探数据为基础,采用地球化学块体理论和研究方法分析元素的空间分布与成矿带的关系,据元素富集特点,以新疆背景含量为参考,结合所处地质构造背景,识别出8个面积10000~70000 km²的多元素地球化学富集区带,并对各区带目标矿种和找矿方向进行探讨,期望在特定矿种或矿床类型上有所突破。     

Chemical composition of magmatic rocks in a certain region and its regional geochemical characteristics

Based on a review of the available petrological and petrochemical data on magmatic rocks in a certain region in China, the average chemical composition of them has been calculated, and the frequency distribution of elements in the rocks, the mineralization of rock bodies and the regional geochemical characteristics have been discussed. In response to temporal and spatial variations during the evolutionary process of magmatic activity, a systematic variation is obvious from this study in the chemical composition of magmatic rocks, the frequency distribution patterns of elements, the concentration levels of various elements and the calc-alkali index of the rocks as well as in the average atomic weight and average atomic valence. Particularly, different geochemical indicators have been established for mineralized and barren rock bodies, respectively. Crystallization-differentiation and post-magmatic metasomatism constitute the most important mechanism controlling mineralization.     

Fractal and Multifractal Properties of Geochemical Fields

A fractal model, introduced by De Wijs to study the distribution, redistribution, or enrichment/depletion of element concentrations in a region, has become widely accepted. This paper uses it to simulate various geochemical fields for element concentration values. The frequency distribution and spatial pattern of the simulated values or concentrations are analyzed by the method of moments and the concentration–area (C–A) model. The spatial pattern of the original De Wijs model is shown to be intrinsically characterized by -shaped and symmetrical multifractal spectrum curves, whose center and width change systematically with the enrichment factors set in the simulation. The corresponding frequency distribution pattern on the log–log plot of frequency versus concentrations is called simple continuous multifractal (SCM) by the authors. In other experiments, when a De Wijs model is locally superimposed by another De Wijs model of different enrichment factors, the symmetry of the multifractal spectrum graph is broken and a different pattern of frequency distribution is found. It is referred to as highly accumulated continuous multifractals (HACM). Concentrations of 12 elements in 1448 rock samples from Shaoguan district, North Guangdong Province, South China, and 12 oil/gas indexes in surface soils from Sangtamu region, Tarim Basin, Northwest China, have been applied. The real geochemical fields, both metallic and oil/gas, are found to be remarkably compatible to those simulated patterns of De Wijs models with backgrounds of various enrichment and different degrees of superimposition, indicating that the frequency and spatial distribution patterns revealed by the authors are most possibly universal features of geochemical fields. It is particularly interesting to note that the major geochemical indicators of oil/gas geochemical fields are closer to the results of De Wijs models with a small enrichment factor, either with or without local superimposition, whereas those of the metallic geochemical field correspond more closely to De Wijs models with a background field of larger enrichment factors. The results obtained herein potentially have important implications in mineral and oil/gas resource assessment.     

中国花岗岩类地球化学图的多元素区域分布模式研究

花岗岩类化学元素丰度研究是花岗岩类地球化学和地壳丰度研究的一项重要内容,一直为国际上所关注,并有很多学者先后发表了不同的花岗岩类化学成分和元素丰度的数据,但迄今为止世界上还没有花岗岩类地球化学图的出版。本文以中国56种元素花岗岩类地球化学图为基础,探讨了中国大陆花岗岩类各元素地球化学图所展示的多元素的区域分布特征、空间分布规律和分布模式。结果显示,花岗岩类各元素的空间分布模式与中国花岗岩类的分布和特征密切相关。花岗岩类地球化学图能够清晰地反映出花岗岩类化学成份的空间变化规律和特征。     

内蒙古白音郭勒地区地球化学异常提取方法对比研究

勘查地球化学的基础性问题是如何合理地提取地球化学异常下限,这是影响勘查地球化学在矿产勘查中效果的主要因素。利用SPSS软件,通过含量对数频率直方图,结合偏度、峰度检验法检验元素的含量分布型式,发现研究区的Cu、Ag、Pb、Zn元素不服从正态或对数正态分布,而呈现多峰态、高丛集的多重分形特征。采用传统的统计学方法、85%累计频率法、含量-总量多重分形法提取相关元素地球化学异常,并进行对比研究。研究结果表明,基于元素空间分布及含量分布规律的含量-总量多重分形方法,有效克服了传统方法的局限,比较客观地反映研究区的地球化学异常信息,是研究地球化学异常比较合理的方法。     

Kinetic tests comparison and interpretation for prediction of the Joutel tailings acid generation potential

Five sulfide mine tailings coming from the Joutel mine tailing ponds (Quebec, Canada) were tested by the humidity cell test (30 to 52 cycles duration) and the column test (11 to 12 cycles duration). The objectives of this study were twofold. First, there was the determination of the tailings acid generation potential for site reclamation. Second, there was the kinetic test comparison for understanding the tailings geochemical behavior under different test conditions. The samples used had a wide diversity in terms of acid-generation potential, particle size distribution, and parameters influencing reaction rates. Leachates produced remained at a near neutral pH for the duration of the tests. Evolution of the main elements involved in the dissolution processes demonstrated neutralization by carbonates as a response to the acid generated by sulfide oxidation. Depletion rates given by sulfates are higher for the humidity cell tests when compared to those obtained for the column tests. This is consistent with most studies to date, the humidity cell test being considered as more severe. However, by taking the ratio between cumulative elements coming from neutralization and the ones coming from oxidation, similar curves (named herein oxidation –neutralization curves) for all tests were obtained. These results show that overall geochemical behavior of the tailings is similar at near neutral pH for both types of tests. With this interpretation method, the acid-generation potential of the Joutel tailings were tested and compared to the static test results to constrain their uncertainty zone with regard to the studied tailings. The tailings geochemical behavior (carbonate dissolution response to sulfide oxidation) at near neutral pH condition appears slightly dependent of test conditions under certain hypothesis.     

Trace Elements in Coals of Eastern Donbas

Peculiarities of trace element (TE) distribution in coals of the eastern Donets Basin (Donbas) are discussed. The correlation of TE distribution with specific features of the geological setting of the region can testify to the hydrothermal introduction of trace elements or their redistribution in fluid-active zones. The geochemical regionalization of eastern Donbas is based on TE distribution. Strontium–gold–base metal, tungsten, and selenium geochemical belts and a rare metal geochemical block are outlined.     

Elemental distribution of coastal sea and stream sediments in the island-arc region of Japan and mass transfer processes from terrestrial to marine environments

A total of 49 elements have been identified in 338 coastal sea sediment samples collected from an area situated off the Ise-Tokai region of Japan for a nationwide marine geochemical mapping project. The spatial distribution patterns of the elemental concentrations in coastal seas along with the existing geochemical maps in terrestrial areas were used to define the natural geochemical background variation, mass transport, and contamination processes. The elemental concentrations of coastal sea sediments are determined primarily by particle size and regional differences. Most elemental concentrations increase with a decrease in particle size. Some elements such as Ca, Mn, and Yb are found to exist in large quantities in coarse particles containing calcareous shells, Fe–Mn oxides, and felsic volcanic sediments. Regional differences reflect the mass transfer process from terrestrial areas to coastal seas and the influence of the local marine geology. An analysis of variance (ANOVA) reveals that for many elements, the particle size effect is predominant over regional difference. The mean chemical compositions of coastal sea sediments are similar to those of stream sediments in adjacent terrestrial areas and in the upper crust of Japan. This observation supports the fact that coastal sea sediments have certainly originated from terrestrial materials. However, the spatial distributions of elemental concentrations are not always continuous between the land and coastal seas. The scale of mass movement observed in marine geochemical maps occurs at a distance of 20 km from the river mouth. A detailed examination of the spatial distribution patterns of K (K₂O) and Cr concentrations suggests that terrestrial materials supplied through rivers are deposited near the shore initially, and then gravity-driven processes shift the sediments deeper into the basin. Contamination with heavy metals such as Zn, Cd and Pb was observed in coastal bays surrounded by urban and industrial areas. It is noteworthy that the areas with the highest concentration of these elements usually do not occur near the shore (not near the contamination source) but at the center of the bay. Unexpected low concentrations of Zn, Cd and Pb near shore may either be due to a decreased anthropogenic load in the most recent sediments or to dilution by unpolluted flood sediments.     

Separation of a geochemical anomaly from background by fractal and U-statistic methods,a case study: Khooni district,Central Iran

Separation of geochemical anomalies from background are one of the important steps in mineral exploration. The Khooni mineral district (Central Iran) has complex geochemical surface expression due to a complex geological background. This region was chosen as a study area for recognition of the spatial distribution of geochemical elements and separating anomalies from background using stream sediment geochemical data. In the past decades, geochemical anomalies have been identified by means of various methods. Some of these separation methods include: statistical analysis methods, spatial statistical methods and fractal and multi-fractal methods. In this article, two efficient methods, i.e. U-statistics and the fractal concentration-area for separation and detection of anomalous areas of the background were used. The U spatial statistic method is a weighted mean, which considers sampling point positions and their spatial relation in the estimation of anomaly location. Also, fractal and multi-fractal models have also been applied to separate anomalies from background values. In this paper, the concentration–area model (C–A) was suggested to separate the anomaly of background. For this purpose, about 256 stream sediment samples were collected and analyzed. Then anomaly maps of elements were generated based on U spatial statistics and the C-A fractal methods for Au, As and Sb elements. According to obtained results, the U-statistics method performed better than C-A method. Because the comparisons of the known deposits and occurrences against the anomalous area created using thresholds from U-statistics and C-A method show that the spatial U-statistics method hits all of 3 known deposits and occurrences, the C-A fractal method hits 1 and fails 2. In addition, the results showed that these methods with regard to spatial distribution and variability within neighboring samples, in addition to concentration value frequency distributions and correlation coefficients, have more accurate results than the traditional approaches.     

The Soil Geochemical Atlas of Portugal: Overview and applications

The continental area of Portugal is now entirely covered by a soil geochemical survey (1 site/135 km²), taking as the sampling media topsoils (upper mineral horizons, A) and organic horizons (humus, O). Standard methods for sampling, sample preparation and analysis were used in order to achieve high quality and consistent data. Each sample was analyzed for 32 chemical elements, pH, electrical conductivity and organic matter content.The main purpose of the survey was to obtain baseline levels for various chemical elements. The compilation of all data (nearly 45,000 individual data) in an organised way, led to the production of the first Soil Geochemical Atlas of Portugal. In this Atlas it is possible to find for each chemical element a set of information statistics (basic statistical parameters, boxplots, cumulative frequency curves, etc.), maps of spatial distribution, among other information of geochemical and environmental interest. This paper gives an overview of the Soil Atlas and examples of application. The data were used to calculate reference values for 9 elements of environmental importance and to obtain empirical formulae allowing the estimation of elements in the coarse fraction of soils (< 2.00 mm) from known concentration in a finer fraction (< 0.18 mm).     

“关键资源地球化学勘查”专辑特邀主编寄语——关键元素分布与关键资源勘查

关键资源已经成为工业4.0和低碳能源不可替代的原材料。构成关键资源的元素有50余种, 这些元素是现代社会的先进制造、电子产品、低碳能源、国防安全、生物医药等必须的原材料, 因此也称为关键元素。地球化学勘查是研究和探测关键元素分布和超常富集, 寻找关键资源行之有效的方法。中国在关键元素的分布和深部探测地球化学领域走在了国际前列, 形成了从全球尺度、全国尺度、矿区尺度直到纳米尺度地球化学探测技术体系, 实现从二维到三维、从浅表矿到千米深度矿产探测能力的飞跃, 不仅圈定了一批全国稀土、锂、铀的超常富集区, 而且取得了多处深部金矿和铜矿勘查的重大突破。本专辑选择部分研究成果介绍了稀土元素、新能源金属(铀、锂、钴)、金、铜等关键资源地球化学勘查中取得的新进展和成果。为了响应国家号召“把论文写在祖国大地上”, 专辑作者把优质素材形成的论文发表在自己的杂志上, 作为本期特邀主编对他们的奉献精神表示衷心感谢和崇高的敬意！     

Comparison of mineralization pattern of geochemical data in spatial and position-scale domain using new DWT- PCA approach

In the current research to determine the mineralization pattern and discuss the mineralization components, the information of position - scale domain of geochemical data has been analyzed. A new method is proposed based on coupling discrete wavelet transforms (DWT) and principal component analysis (PCA) for mineralization elements forecasting applications. The results of this study indicate the potential of DWT–PCA method for geochemical data processing. Wavelet transform (WT), as a multi-spectral analysis method, can decompose the spatial and temporal signals into different frequencies. The features of mineralization can be identified using the position - scale domain of geochemical data that may not be achievable in spatial domain. The geochemical data from the Dalli region have been processed in the spatial domain using PCA. The surface geochemical data of 30 elements have been transformed to position–scale domain using two-dimensional discrete wavelet transform (2DDWT). Wavelet functions (WFs) of Haar, Coiflet2, Biorthogonal3.3 and Symlet7 have been applied separately to decompose the geochemical data to high and low frequencies in one level. To obtain more accurate and complete information of mineralization, a new index has been presented based on wavelet coefficients. Based on this new index, significant results have been obtained by using PCA of the index. The coefficients distribution map (CDM) as a new exploratory criterion has been generated based on 2DDWT to show the geochemical distribution map (GDM). Finally, the results of WT have been compared with the results of spatial domain and the best method of wavelet for interpretation of geochemical data has been introduced. The results of geochemical data analysis by DWT–PCA approach have been confirmed by the exploratory drillings in the study area.     

Incorporation of principal component analysis,geostatistical interpolation approaches and frequency-space-based models for portraying the Cu-Au geochemical prospects in the Feizabad district,NW Iran

Delineation of mineralization-related geochemical anomalies of stream sediment data is an essential stage in regional geochemical exploration. In this study, principal component analysis (PCA) was applied to 12 selected elements to acquire a multi-element geochemical signature associated with Cu-Au mineralization in Feizabad district, NE Iran. The spatial distribution of enhanced multi-element geochemical signature of the second component (PC2) was modeled by different geostatistical procedures including variogram calculation, ordinary kriging (OK) and inverse distance weighting (IDW) interpolation techniques. Concentration-area (C-A) fractal and U-spatial statistics models were then applied to the continuous-value interpolated models for delineation of geochemical anomalies. Quantitative comparison of results based on the known mineral occurrences in the study area was carried out using normalized density index and success-rate curves. All generated models represent a high positive relation with known Cu (±Au) deposits in the study area, although, comparison of the results revealed that the OK-based U-spatial statistics model was superior to the rest of models. Besides, the low, moderate and high-intensity anomalies are spatially associated with geological-structural features in the study area.     

皖南地区区域地球化学特征及成矿潜力的地球化学预测

根据皖南地区1:20万区域化探资料,计算了区内元素的背景值、区域浓集系数、总体变化系数等参数,阐明了区内元素含量空间分布与成矿元素共生组合特征。使用区域浓集系数及变化系数两个参数,对皖南地区32种元素的成矿潜力进行排序,在目前安徽省地质勘查主攻矿种中,皖南地区的成矿潜力依次为金(银)-钨-钼-铜-铀-锌-铅。同时根据地球化学块体理论和方法,预测了区内金、银资源量,分别为金474t、银16117t,显示出较大的找矿潜力。     

鄂尔多斯盆地西缘煤中稀土元素特征

煤中稀土元素是煤地质领域研究源岩和沉积环境的良好地球化学指示剂,也是一种重要的矿产资源。运用ELEMENT XR等离子体质谱分析仪对鄂尔多斯盆地西缘石炭-二叠系和侏罗系延安组煤样中稀土元素进行测试,计算了多种化学参数并绘制了稀土元素分布类型曲线。在对稀土元素（REY）的地球化学特征分析的基础上,探讨了其物质来源。结果表明,石炭-二叠系煤中REY含量明显高于中国和世界煤中的均值,也高于上地壳值,呈铕（Eu）负异常,铈（Ce）负异常,这可能因为石炭-二叠系处于海陆交互相,与其处于强的还原环境有关;而侏罗系煤中REY含量却低于中国和世界煤中的均值,也低于上地壳值,呈轻微Eu负异常,轻微Ce正异常,侏罗系延安组主要为氧化的陆相环境,所以δCe在煤中的不亏损才会普遍存在。通过煤中稀土元素的分配模式、平面展布与其构造环境的综合分析,推测石炭-二叠系的物源为研究区西北部的阿拉善地块和北部的阴山古陆,南部的秦-祁造山带为侏罗系煤中稀土元素提供了主要的物质来源。     

中国煤中有害微量元素含量的空间分布

煤中有害微量元素对生态环境和人体健康的潜在影响是地球化学和能源环境领域研究的热点之一,地球化学制图对深刻理解地球化学过程及其变化规律具有重要作用。目前,尚缺乏中国煤中有害微量元素含量的空间分布图。通过对中国煤炭样品中1 167个Be、1 315个Co、1 406个Cu、1 191个Mo、1 247个Th 和1 390个Zn含量数据进行统计分析,测算中国煤中Be、Co、Cu、Mo、Th 和 Zn 的平均含量,并利用ArcGIS技术绘制中国煤中Be、Co、Cu、Mo、Th、Zn的含量地球化学空间分布地图。结果表明:中国煤中有害微量元素含量跨度大,数据分布呈正偏性,不符合正态分布特征;中国煤中Be、Co、Cu、Mo、Th和Zn 的平均含量分别为2.10、5.53、21.36、2.19、7.35和30.02 mg/kg;各元素含量的空间分布极不均匀;煤中有害微量元素含量空间分布格局是多种因素综合作用的结果,如物源区母岩、热液作用、水运移作用等,其中热液作用是煤中有害微量元素异常富集的典型特征。研究成果可为煤中微量元素研究和环境管理提供直观有效的参考。      

Geochemical background of potentially toxic trace elements in reclaimed soils of the abandoned pyrite–uranium mine (south-central Poland)

Spatial distribution patterns of As, Ba, Cd, Cr, Cu, Mn, Ni, Pb, U and Zn were determined in topsoil samples collected after 40 years of chemical remediation conducted in the inoperative “Staszic” pyrite–uranium mine in the Holy Cross Mountains, south-central Poland. Soil samples were taken from 58 sites using a systematic random sampling design. Selected samples were subjected to an X-ray diffractometry analysis on bulk soils and separated clay fractions. Hematite, goethite and gypsum are common mineral phases in soil samples. Technogenic soils developed on reclaimed mine spoils show uniform spatial element distribution patterns and additionally a distinct enrichment in As, Pb, Mn, U and Zn. Mineral and chemical composition of soils vs. rocks points to the lithogenic source of the determined elements. The results of chemical analysis have been used for evaluation of geochemical background of trace elements in the study area with the iterative 2σ-technique. This investigation shows that using mean crustal element concentrations (Clarke values) as proxies of threshold values in soils are not useful for determination of strongly positive geochemical anomalies. A modified enrichment factor, i.e. a local enrichment factor, is proposed for identification of sites where soils are contaminated.     

Application of singularity mapping technique to identify local anomalies using stream sediment geochemical data,a case study from Gangdese,Tibet, western China

Identifying geochemical anomalies from background is a fundamental task in exploration geochemistry. The Gangdese mineral district in western China has complex geochemical surface expression due to complex geological background and was chosen as a study area for recognition of the spatial distribution of geochemical elements and separating anomalies from background using stream sediment geochemical data. The results illustrate that weak anomalies are hidden within the strong variance of background and are not well identified by means of inverse distance weighted; neither are they clearly identified by the C–A method if this method is applied to the whole study area. On the other hand, singularity values provide new information that complements use of original concentration values and can quantify the properties of enrichment and depletion caused by mineralization. In general, producing maps of singularities can help to identify relatively weak metal concentration anomalies in complex geological regions. Application of singularity mapping technique in Gangdese district shows local anomalies of Cu are not only directly associated with known deposits in the central part of the study area, but also with E–W and N–E oriented faults in the north of the study area. Both types of anomalies should be further investigated for undiscovered Cu mineral deposits.     

Geochemical baseline of trace elements in the sediment in Dexing area,South China

A baseline might be used as a point of reference to monitor change from some specific data without concern for whether the baseline determination is natural or has been changed by human activity. We selected 326 sediment samples from Dexing area, South China, and analyzed for 17 chemical elements. The geochemical baseline was predicted with the method of the normalization procedure combined with the relative cumulative frequency curve. The results indicate Al was the best reference element for the normalization procedure among four potential reference elements (Al, Fe, Ti, and Mn). The baseline value range obtained from the normalization procedure method included both the regional geochemical background of the sediment and the median value of the measured contents. The median value of baselines obtained from relative cumulative frequency method was lower than that obtained from normalization procedure method. In contrast to the geochemical patterns of heavy metals in 1987, the spatial distribution of anomalies sprawled in 2004 in study area, especially for Cu, Pb, Zn, Cd, As, Fe, and Cr.     

华南陆块铜的地球化学块体与成矿省的关系

在区域化探全国扫面计划1∶20万水系沉积物样品Cu含量的基础上,描述了华南陆块铜地球化学块体的空间分布特征,并分析了它们与地质体、已知的铜成矿省(矿集区)在空间上的对应关系。发现华南陆块的铜地球化学块体主要分布于扬子地块西南缘,长江中下游、西秦岭、三江地区和湘粤桂交界区。其中扬子地块西南缘铜地球化学块体主要与峨眉山玄武岩的铜高背景值有关,其他异常与海西期镁铁质超镁铁质岩有关的铜矿和层控型铜矿有关;长江中下游地球化学块体与长江中下游成矿带吻合;西秦岭铜地球化学块体与岩体、铜矿和以铜为伴生元素的矿床有关;三江、湘粤桂交界区的铜地球化学块体也有与之对应的铜矿床或铜为伴生元素的矿床。通过这些地球化学块体与已知的地质体、成矿省(矿集区)的对比得出如下结论,铜地球化学块体的形成可能与岩石的高背景值、铜成矿省(矿集区)或铜为伴生元素的矿床有关。巨量的成矿物质的供应只是形成大型、超大型矿床的必要条件,如长江中下游铜地球化学块体为铜成矿省提供物质来源;但每个地球化学块体并不一定都有与之对应的矿集区,如峨眉山玄武岩铜地球化学块体与玄武岩高背景值有关,并没有形成大型的铜矿床。