Geochemical Anomalies Identified by Multifractal Modeling: Implications for Mineral Exploration in the Ziyoutun Cu-Au District, Jilin Province, China

The Ziyoutun Cu-Au district is located in the Jizhong–Yanbian Metallogenic Belt and possesses excellent prospects. However, the thick regolith and complex tectonic settings present challenges in terms of detecting and decomposition of weak geochemical anomalies. To address this challenge, we initially conducted a comprehensive analysis of 1:10,000-scale soil geochemical data. This analysis included multivariate statistical techniques, such as correlation analysis, R-mode cluster analysis, Q–Q plots and factor analysis. Subsequently, we decomposed the geochemical anomalies, identifying weak anomalies using spectrum-area modeling and local singularity analysis. The results indicate that the assemblage of Au-Cu-Bi-As-Sb represents the mineralization at Ziyoutun. In comparison to conventional methods, spectrumarea modeling and local singularity analysis outperform in terms of identification of anomalies. Ultimately, we considered four specific target areas(AP01, AP02, AP03 and AP04) for future exploration, based on geochemical anomalies and favorable geological factors. Within AP01 and AP02, the geochemical anomalies suggest potential mineralization at depth, whereas in AP03 and AP04 the surface anomalies require additional geological investigation. Consequently, we recommend conducting drilling, following more extensive surface fieldwork, at the first two targets and verifying surface anomalies in the last two targets. We anticipate these findings will significantly enhance future exploration in Ziyoutun.

Models of Spatial Structures of Regional Multi-element Geochemical Anomalies over Copper-Polymetallic Orefields

Regional stream sediment surveys at a 1:200,000 scale reveal positive andnegative regional multi-element geochemical anomalies over medium to large copper-polymetallicorefields of different genetic types in China. Regional geochemical anomalies of orefield refer tothose geochemical anomalies that are related to metallogenesis of an orefield in a certain area. Theanomaly area is typically 10 to 100 km^2. The regional multi-element anomalies related tomineralization can be divided into three groups, that is, the ore-element anomaly association,indicator element anomaly association, and metallogenic environmental element anomaly association.Their common spatial distributions over ore deposits or orefields possess unique structures. Themodel of spatial structure of regional multi-element geochemical anomalies (RAGSS) of an orefielddelineates structural feature possessed by orderly spatial distributions of different groups ofmulti-element anomaly associations related to orefield metallogenesis. It is used to outline thecommon metallogenetic anomaly visage that is composed of the orderly spatial distribution ofdifferent groups of multi-element anomaly associations. The orderly spatial distribution ofmulti-element anomalies over an orefield reflects element distributions as they are changed from adispersed 'out-of-order' state into a concentrated 'orderly' state during the mineralization of anorefield. Three different patterns of the spatial anomaly structure related to mineralization in anorefield can be concluded: (1) nested pattern; (2) eccentric pattern and; (3) peripheral pattern.There are marked differences between multi-element anomaly patterns related and not related tomineralization. RAGSS models of orefields can be used to better understand and evaluate regionalmulti-element anomalies and identify ore types.

Application of isolation forest to extract multivariate anomalies from geochemical exploration data

Constructing a statistical model that best fits the background is a key step in geochemical anomaly identification. But the model is hard to be constructed in situations where the sample population has unknown and/or complex distribution. Isolation forest is an outlier detection approach that explicitly isolates anomaly samples rather than models the population distribution. It can extract multivariate anomalies from huge-sized high-dimensional data with unknown population distribution. For this reason,we tentatively applied the method to identify multivariate anomalies from the stream sediment survey data of the Lalingzaohuo district,an area with a complex geological setting,in Qinghai Province in China. The performance of the isolation forest algorithm in anomaly identification was compared with that of a continuous restricted Boltzmann machine. The results show that the isolation forest model performs superiorly to the continuous restricted Boltzmann machine in multivariate anomaly identification in terms of receiver operating characteristic curve,area under the curve,and data-processing efficiency. The anomalies identified by the isolation forest model occupy 19% of the study area and contain 82% of the known mineral deposits,whereas the anomalies identified by the continuous restricted Boltzmann machine occupy 35% of the study area and contain 88% of the known mineral deposits. It takes 4. 07 and 279. 36 seconds respectively handling the dataset using the two models. Therefore,isolation forest is a useful anomaly detection method that can quickly extract multivariate anomalies from geochemical exploration data.

A Study of the Method for the Recognition of Anomalies in Geochemical Hydrocarbon Exploration

The greatest difficulties in recognizing geochemical hydrocarbon anomalies are: (1) how to objectively and accurately separate anomalies from background; (2) how to distinguish hydrocarbon pool related apical anomalies from lateral anomalies controlled by faults; and (3) how to eliminate interferences. These uncertainties are serious obstacles for the wide acceptance and use of geochemical techniques in hydrocarbon exploration. In this paper, the features of hydrocarbon anomalies were analyzed based on the micro migration mechanisms. In most cases, there are two anomalous populations or point groups, which are produced by two distinct mechanisms: (1) a population that directly reflects oil and gas fields, and (2) one that is related to structures such as faults. Statistical studies show that background anomalous populations and the boundaries between them can be described by the population means, prior probabilities, which are the proportions of population sizes, and covariance matrices, when background and anomalous populations have normal distributions. When this normality condition is met, a series of formulas can be derived. The method is designed on the basis of these allows: (1) univariate anomaly recognition, (2) elimination of interferences, (3) multivariate anomaly recognition, and (4) multivariate anomaly combination which depicts a more representative picture of morphology of the anomalous target than individual anomalies. The univariate and multivariate anomaly recognition can not only separate anomalies from background objectively, but also simultaneously distinguish the two types of anomalies objectively. This method was applied to the hydrocarbon data in Yangshuiwu region, Hebei Province. The interferences from regional variation of background were eliminated, and the interpretation uncertainty was reduced greatly as the anomalous populations were separated. The method was also used in Daxing region within the confines of Beijing City, and Aershan and Jiergalangtu regions in Inner Mongolia.

Mineralization-related geochemical anomalies derived from stream sediment geochemical data using multifractal analysis in Pangxidong area of Qinzhou-Hangzhou tectonic joint belt, Guangdong Province, China

Distinguishing geochemical anomalies from background is a basic task in exploratory geochemistry. The derivation of geochemical anomalies from stream sediment geochemical data and the decomposition of these anomalies into their component patterns were described. A set of stream sediment geochemical data was obtained for 1 880 km 2 of the Pangxidong area, which is in the southern part of the recently recognized Qinzhou-Hangzhou joint tectonic belt. This belt crosses southern China and tends to the northwest (NE) direction. The total number of collected samples was 7 236, and the concentrations of Ag, Au, Cu, As, Pb and Zn were measured for each sample. The spatial combination distribution law of geochemical elements and principal component analysis (PCA) were used to construct combination models for the identification of combinations of geochemical anomalies. Spectrum-area (S-A) fractal modeling was used to strengthen weak anomalies and separate them from the background. Composite anomaly modeling was combined with fractal filtering techniques to process and analyze the geochemical data. The raster maps of Au, Ag, Cu, As, Pb and Zn were obtained by the multifractal inverse distance weighted (MIDW) method. PCA was used to combine the Au, Ag, Cu, As, Pb, and Zn concentration values. The S-A fractal method was used to decompose the first component pattern achieved by the PCA. The results show that combination anomalies from a combination of variables coincide with the known mineralization of the study area. Although the combination anomalies cannot reflect local anomalies closely enough, high-anomaly areas indicate good sites for further exploration for unknown deposits. On this basis, anomaly and background separation from combination anomalies using fractal filtering techniques can provide guidance for later work.

Laboratory Simulation of the Formation Process of Surface Geochemical Anomalies Applied to Hydrocarbon Exploration

The formation mechanisms and processes of geochemical anomalies used as proxies in surface geochemistry exploration （SGE） have not been well understood. Previous studies cannot realize 3D measurement of microseeping hydrocarbons from reservoirs to the surface, which made it difficult to understand the features and pathways of deep hydrocarbon microseepages. Understanding the processes of hydrocarbon microseepages will contribute to the acceptance and effectiveness of surface geochemistry. Based on a simplified geological model of hydrocarbon microseepages, including hydrocarbon reservoir, direct caprock, overlying strata and Quaternary sediments, this work established a 3D experimental system to simulate the mechanisms and processes of deep hydrocarbon microseepes extending to the surface. The dispersive halos of microseeping hydrocarbons in the subsurface were adequately described by using this 3D experimental system. Results indicate that different migration patterns of hydrocarbons above the point gas source within the simulated caprock and overlying strata can be reflected by the ratio of i-butane to n-butane （i-C4/n-C4）, which follow diffusion and infiltration （buoyancy） mechanisms. This is not the case for vertical measurement lines far from the point gas source. A vertical gas flow in the form of a plume was found during hydrocarbon microseepage. For sampling methods, the high-density grid sampling is favorable for delineating prospecting targets. Hydrocarbon infiltration or buoyancy flow occurs in the zones of infiltration clusters, coupling with a diffusion mechanism at the top of the water table and forming surface geochemical anomalies. These results are significant in understanding hydrocarbon microseepage and interpreting SGE data.

Evaluation and extraction of weak gravity and magnetic anomalies

In this paper, I introduce what are called weak gravity and magnetic anomalies and propose standards for estimating their reliability. I also introduce new techniques for processing this kind of weak anomaly. These techniques consist of interference elimination and weak signal extraction. Practical applications have proved their effectiveness, Weak gravity and magnetic anomalies will get more attention with the development of targeted exploration.

Post-subdution evolution of the Northern Lhasa Terrane, Tibet: Constraints from geochemical anomalies, chronology and petrogeochemistry

Bangong-Nujiang collisional zone(BNCZ)is an older one in Qinghai-Tibet Plateau and resulted in the famous Bangong-Nujiang metallogenic belt,which plays an important role in evaluating the formation and uplift mechanism of plateau.The northern and central Lhasa Terrane composed the southern part of the BNCZ.Since ore deposits can be used as markers of geodynamic evolution,the authors carried 1∶50000 stream sedimental geochemical exploration in the Xiongmei area in the Northern Lhasa Terrane to manifest the mineralization,and based on this mineralization with geochemical and chronological characteristics of related magmatic rocks to constrain their geodynamics and connection with the evolution of the Lhasa Terrane.The authors find Early Cretaceous magma mainly resulted in Cu,Mo mineralization,Late Cretaceous magma mainly resulted in Cu,Mo,and W mineralization in the studying area.The results suggest a southward subduction,slab rolling back and break-off,and thickened lithosphere delamination successively occurred within the Northern Lhasa Terrane.

Evaluation of Gold Geochemical Anomalies in the Liaodong Paleorift

89 Au geochemical anomalies are delineated by using 1/200000 regional geochemical exploration data. By researching regional geochemical characteristics and the relationship with the geological background, the author points out that： the main factors causing high background of Au geochemical anomalies are Gaixian and Dashiqiao formation of Liaohe group, intrusions of Mesozoic intermediate-acid intrusive rocks. The elements combination types of typical anomalies are determined by using factorial analysis,cluster analysis and other mathematical methods with the combination of elements association in typical anomalies：the composite anomaly of Baiyun gold deposits is Au-As-Sb, Maoling gold deposit is Au-As- Bi-Mo, Wulong gold deposits is Au-As-Bi-W, Xiaotongjiapuzi gold deposit is Au-As-Bi-Mo-Sb. By using multivariate statistical analysis method,62 ore-caused anomaly are preferred in 89 Au geochemical anomalies delineated. On this basis, the 62 anomalies are divided into 4 kinds of anomaly types reference to elements combination types of typical anomalies,the classification results of ore-caused anomalies are： 4 geochemical anomalies of Baiyun type,36 geochemical anomalies of Maoling type,11 geochemical anomalies of Wulong type, 11 geochemical anomalies of Xiaotongjapuzi type. According to the results, the prospecting direction is provided for the futme of gold exploration.

Surface geochemical anomaly pattern of medium-to-high temperature geothermal systems in South China and its application

The existence of thermal storage will correspondingly increase the temperature of surrounding strata and promote the continuous expansion,volatilization,upward migration,and loss of gas in the strata.As a result,a low-concentration gas field will be formed in the strata above geothermal reservoirs.Geothermal reservoirs could in turn heat formation water and increase the solubility of soluble inorganic salts in the surrounding rocks and the total dissolved solids(TDS)content in the formation water.Since water can strongly wet and permeate strata,the dissolved inorganic salts migrate into upper strata along with water,giving rise to the formation of a high-concentration inorganic salt field in the strata above geothermal reservoirs.A higher geothermal reservoir temperature corresponds to more significant characteristics mentioned above.Therefore,a medium-to-high temperature geothermal system has a surface geochemical anomaly pattern of high inorganic salt concentrations and low gas concentrations(also referred to as the high-salt and low-gas pattern).This pattern is applied to the surface geochemical exploration of the two geothermal fields in Guangdong Province,i.e.,the Huangshadong geothermal field in Huizhou City and the Xinzhou geothermal field in Yangjiang City,revealing low-concentration gas fields above both.The application results also show that the exposed thermal spring water in both geological fields has higher concentration of dissolved inorganic salt than the surface water and nearby seawater,forming high-amplitude anomalies on the surface above geothermal reservoirs.These characteristics,as well as the measured temperature at known geothermal wells,verify the validity of the high-salt and low-gas pattern of medium-to-high temperature geothermal systems proposed in this study.Moreover,the high-salt and low-gas pattern proposed predicts three favorable medium-to-high temperature geothermal zones in the surface geochemical exploration of the Shiba Basin near the Huangshadong geothermal field.

西北地区主要锂矿资源分布特征及地球化学找矿远景预测

为圈定锂成矿远景区,采用已有1∶20万地球化学数据,选取西昆仑-阿尔金和阿尔泰两个主要锂矿带,基于锂元素地球化学空间分布及异常特征圈定锂矿远景区,为找矿突破战略行动选区服务。基于重点锂矿带以往1∶20万地球化学数据库,对元素相关性、背景及异常特征等参数进行再分析,结合已有锂矿床或锂矿(化)点,圈定找矿远景区。在昆仑-阿尔金地区圈定锂地球化学异常区15处,在阿尔泰圈定锂地球化学异常区12处。研究圈定27处异常区可为下一步锂矿找矿工作部署提供参考依据。

岩性分区异常下限衬值法圈定化探异常的优劣:以江苏金山地区为例

笔者以金山地区1∶10000土壤地球化学调查数据为例,利用岩性分区异常下限衬值法圈定异常,通过与传统方法对比,发现岩性分区异常下限衬值法可以有效避免岩性对异常的控制作用,消除背景的影响,圈定的化探异常能提供更有效的找矿信息。通过野外踏勘和异常查证,并对有找矿意义的重点异常进行槽探、钻探验证,发现具工业价值钨矿体和铅锌矿脉。研究表明,利用岩性分区异常下限衬值法在岩性较复杂区确定异常下限的有效性,该方法可以推广使用。

西非科特迪瓦某区土壤地球化学特征及找矿前景分析

研究区位于西非克拉通南部的古元古代鲍勒—莫西域(Baoulé-Mossi Domain)内,该区为西非最重要的金成矿区。本文通过对研究区内土壤Au、Ag、As、Cu、Pb、Co、Cr七种元素的含量、浓集比率、变异系数等地球化学参数的系统统计分析,得出该区Au元素具有浓集比率大,变异系数高的特征,为该区主要的成矿元素,As元素具有较高的浓集比率和变异系数,且异常范围与Au元素异常范围部分重合,为Au元素的指示元素,本次测量面积为5 km~2,采样网度800 m×200 m,共采集样品594件。并在研究区土壤地球化学测量异常、地质特征及区域成矿地质背景的基础上,圈定了Au-Ⅰ、Au-Ⅱ、Au-Ⅲ、Au-Ⅳ、Au-Ⅴ、Au-Ⅵ共6处金矿找矿靶区,经钻探工程验证,在Au-Ⅰ靶区发现了隐伏金矿体。综合对比研究区内圈定的找矿靶区的地质条件与区域内已发现金矿床的成矿地质条件,推测研究区内圈定的金矿找矿靶区有巨大的找矿潜力。

云南勐海地区1∶5万水系沉积物地球化学特征及找矿预测

勐海地区处于临沧-勐海(岩浆弧)Fe-Pb-Zn-Au-Ag-Sn-Sb-Ge-REE矿带,具有较好的找矿前景.在勐海地区1∶5万水系沉积物测量基础上,对区内29种元素分布特征、元素相关性、地球化学参数特征研究,圈定了5个组合异常和13个综合异常.其中,Ce-La-Y-Zr综合异常具有较好找矿前景;Au、As、Sb、Hg、W、P等元素离散程度较高,元素局部较富集,具有成矿的可能性.结合水系沉积物测量成果,圈定找矿远景区2处,为下一步找矿工作提供了地球化学依据.

江苏新沂高流地区土壤地球化学特征及找矿预测

在总结江苏新沂高流地区地质特征的基础上,结合区内1∶10000土壤地球化学调查工作,系统研究该区元素含量及组合特征,并进行找矿预测。异常结果显示该区Au、Ag、Cu、Mo、Pb、Zn、As、Sn等单元素地球化学异常明显,其中Au、Ag、Mo 3个元素的异常强度和分带性均好,其形态分布受NNE向构造破碎和碱长花岗岩体等因素制约。在研究区共圈定了14处综合异常,通过异常评价,位于同一断裂带附近的3处异常成矿地质条件优越;对综合异常开展地球化学剖面查证工作,结果显示其中1处Au、Cu等元素峰值均位于NNE向断裂带中心位置。结合该区成矿地质条件和土壤地球化学异常特征,初步总结了研究区金、多金属矿找矿标志,为该区进一步找矿提供间接依据。

赣南铁山垅一带水系沉积物地球化学特征及找矿方向探讨

本文基于对铁山垅一带1∶5万水系沉积物测量工作,分析测试了19种元素,并分析总结了各元素地球化学的分布特征、异常特征。结果表明,该区W、Bi、As、Sb、Bi、Co、Se等元素相对富集,Hg、Ag等元素亏损较强;根据元素组合的特征,可将元素分为四组,即W、Sn、Mo、Bi、F高温元素组合,Cu、Pb、Zn、Cd中温元素组合,Au、Ag、As、Sb、Hg低温元素组合,Mn、Cr、Co、Ni亲铁元素组合;圈定了综合异常22处,找矿远景区2处;在铁山垅—白鹅钨铜多金属找矿远景区可主攻石英脉型钨铜多金属矿,石下—胎子岽钨找矿远景区可主攻隐爆角砾岩型钨矿。

自相关滤波法提取弱异常方法在油气勘查中的应用

在论述自相关滤波法理论的基础上,通过对各种理论模型进行实验,由实验效果分析方法的优势,并以我国某区域重力资料为例,对该区域内重力资料进行了自相关滤波计算,计算结果压制了区域场的影响,提取出油气藏相关的局部弱异常,并与布格重力异常、垂向导数以及剩余异常等资料相互验证,取得了很好的应用效果。基于该地区的计算结果,证明自相关滤波法可应用于油气勘查中,可为其他油气勘查区圈定油气藏的有利局部构造提供可靠并且准确的研究方法,从而达到辅助油气勘查的效果。

湖南宜章长城岭测区地球化学异常特征及找矿前景

长城岭测区位于南岭成矿带与钦杭成矿带叠合部位的长城岭矿田内,成矿地质条件优越。该地区主要发育Li、Rb、Cs、Be、Pb、Zn、Ag、Sb、Sn等有色稀有金属矿化。1∶10000土壤地球化学测量结果显示:Li、Rb为区内主成矿元素,具明显浓集趋势,具备一定成矿潜力,测区共圈定综合异常7处。通过异常查证及探矿工程揭露,认为长城岭测区具良好的锂铷矿找矿前景,为该地区下一步综合地质找矿工作提供了科学依据。

贵州兴义普克金矿区土壤地球化学异常特征及找矿方向

贵州省普克金矿区位于著名的黔西南泥堡金矿西南方向的外围区域,与泥堡金矿处于相同的大地构造环境,地层特征、构造样式基本相同,成矿地质条件良好,且早期120万水系沉积物地球化学测量成果显示普克金矿区内Au、Sb、As异常区域呈现较好的重叠关系。为进一步缩小找矿工作范围,文章通过在普克金矿区开展11万土壤地球化学测量,在统计分析12个被测元素变化系数、富集离散程度的基础上,结合聚类分析、相关分析、因子分析揭示元素组合规律,结果表明As、Sb、Cu、Hg等元素是区内寻找金矿的重要指示元素。文章采用平均值±3倍标准差的方法确定各元素的异常下限,并据此在普克金矿区内圈定了4处找矿指示元素叠加异常区域(HS-1~HS-4),其中有利找矿靶区2处。研究结果揭示了土壤地球化学在本区找矿的有效性。

保山金厂河矿集区陡崖多金属矿物化探异常特征及找矿潜力分析

金厂河矿集区位于滇西保山地块北缘,是云南保山地区重要的矿产资源基地,主要矿床类型为矽卡岩型铁铜铅锌多金属矿。本文在对矿集区内陡崖多金属矿地球物理及地球化学特征综合研究的基础上,提出依据地球化学异常、重磁异常和矿产分布特征预测隐伏岩体产出位置,采用视电阻率异常推断隐伏岩体侵入范围和标高,类比成矿带上典型矿床特征开展找矿潜力分析,提出以钨锡作为今后深部找矿的重点方向。