云南金宝山铂钯矿床铂族元素地球化学及找矿意义

金宝山是中国目前发现的最大的独立铂钯矿床,该岩体基性程度高,主要由橄榄石、单斜辉石组成,含大量铬铁矿〔w(Cr)约为0.5%〕。铂钯矿石呈稀疏浸染状,硫化物含量少,高铂族元素、低铜镍含量。矿体与超基性围岩界线不明显,且二者具有相似的微量、稀土元素参数和微量、稀土、铂族元素标准化配分模式,表明两者的原始岩浆具有相似的性质。超基性围岩具有高的Pd/Ir、Ni/Cu比值和Pb负异常,相反,铂钯矿石显示为低的Pd/Ir、Ni/Cu比值和Pb正异常,两者具有相似的Cu/Pd、Cu/Pt比值(≤原始地幔值),表明铂钯矿石形成于地幔柱S低度饱和环境,超基性围岩可能形成于S饱和/不饱和的地球化学界面。铂族元素地球化学的差异表明含少量富铂族元素的硫化物的含矿岩浆可能注入于稍前侵入的、且未完全固结的超基性围岩中,形成似层状矿体。峨眉地幔柱早期硫低度饱和、融离出少量硫化物以及铂族元素在硫化物/硅酸盐相中极高的分配系数是导致金宝山矿石富铂钯、贫铜镍的根本原因。金宝山是极少有的全岩体Cu/Pd、Cu/Pt值均小于原始地幔值的矿床,表明该岩体的岩浆经历了硫化物富集铂族元素的过程,推测靠近峨眉地幔柱喷发中心的基性-超基性岩体是寻找铂族元素矿床最佳远景区之一。     

Conceptual models in exploration geochemistry: Norden 1975

This compilation and summary of geochemical exploration conditions in Norden is the second in a series of special issues on exploration geochemistry. The first issue dealt with the Canadian Cordillera and Canadian Shield. The conceptual models from the Canadian Shield form an integral part of the present volume. These studies are an attempt to pull together very extensive exploration geochemical information and define it in terms of a limited number of conceptual models.A total of 45 case histories are presented in this volume which cover various aspects of collection, analysis and interpretation of data from glacial till, stratified drift, organic deposits, stream sediments and water. These data are described in a relationship to the conceptual models outlined by Bradshaw (1975). An overall summary is given with respect to these models and also a summary is given of the relative importance of frost heave, transport by glaciation, transport by water and wind, multiple glacial transport, ion and molecular dispersion, groundwater transport, transport by capillary water, electrochemical transport and mixed dispersion.The final section contains 13 short articles dealing with methods of geochemical exploration which are presently used in the different countries of Norden.     

Microthermometry and geochemistry of fluid inclusions from the Tennant Creek gold-copper deposits: implications for ore deposition and exploration

Gold-copper-bismuth mineralization in the Tennant Creek goldfield of the Northern Territory occurs in pipe-like, ellipsoidal, or lensoidal lodes of magnetite ± hematite ironstones which are hosted in turbiditic sedimentary rocks of Proterozoic age. Fluid inclusion studies have revealed four major inclusion types in quartz associated with mineralized and barren ironstones at Ten nant Creek; (1) liquid-vapour inclusions with low liquid/vapour ratios (Type I), (2) liquid-vapour inclusions with high liquid/vapour ratios or high vapour/liquid ratios and characteristic dark bubbles (Type II), (3) liquid-vapour-halite inclusions (Type III), and (4) liquid-vapour inclusions with variable liquid/vapour ratios (Type V). Type I inclusions are present in the barren ironstones and the unmineralized portions of fertile ironstones, whereas Types II and III inclusions are recognized in fertile ironstones. Trails of Types II and III inclusions cut trails of Type I inclusions. Type I fluid inclusions have homogenization temperatures of 100° to 350 °C with a mode at 200° to 250 °C. Type II inclusions in mineralized ironstones (e.g. Juno, White Devil, Eldorado, TC8 and Gecko K-44 deposits) have homogenization temperatures of 250 °C to 600 °C with a mode of 350 °C. Type I fluid inclusions have a salinity range of 10 to 30 NaCl equiv. wt %. Salinity measurements on fluid inclusions in the mineralized zones gave a range of 10 to 50 NaCl equiv. wt % with a mode of 35 NaCl equiv. wt %. Fluid inclusion studies indicate that the Tennant Creek ironstones were formed from a relatively low temperature and moderately saline fluid, where as gold and copper mineralization was deposited from later hydrothermal fluids of higher temperature and salin ity. Gas analysis indicates the presence of N₂ and CO₂, with very minor CH₄ in Types II inclusions but no N₂ or CH₄ gases in Type I inclusions. Microprobe analysis of the fluid inclusion decrepitates indicates that the inclusions from Tennant Creek contain sodium and calcium as dominant cations and potassium in a subordinate amount. The high temperatures ( 350 °C), high salinities ( 35 NaCl equiv. wt. %) and cation composition of the Tennant Creek ore fluids suggest that the ore fluids were derived from upward migrating heated basinal brines, although contribution from a magmatic source cannot be ruled out. Close association of vapour-rich Type IIb and salt-rich Type III inclusions in the mineralized ironstones (e.g. Juno, White Devil, Eldorado, TC8 and Gecko K-44) indicates heterogeneous trapping of ore fluids. This heterogeneous trapping is interpreted to be due to unmixing (exsolution) of a gas-rich (e.g. N₂) fluid during the upward migration of the metal bearing brines and/or due to degassing caused by reaction of oxidized ore fluids and host ironstones. Fluid inclusion data have important implications regarding the deposition of gold in the ironstones, and may have application in discriminating fertile from barren ironstones.     

Till and bedrock geochemistry in Sn exploration: A case study

The youngest intrusive phases of the rapakivi granites are known as Sn granites. The endocontact and exocontact zones of the Viipuri rapakivi massif and its satellites have been considered on theoretical grounds as critical areas for Sn deposits. The area between the Viipuri rapakivi massif and its satellite, the Ahvenisto massif, was selected for prospecting as one Sn critical area.Heavy-mineral geochemistry was used in the reconnaissance phase. Samples (10 1) from the surficial part of the till deposits were taken from a sparse sampling grid. Heavy minerals of the samples were concentrated by washing on a riffle box and by subsequent heavy-liquid separation. The non-magnetic heavy fraction was analyzed by XRF. Quite a large and coherent glaciogenic Sn anomaly was found, the head of which terminated in the southern part of the Ahvenisto rapakivi massif.The source of the anomaly was sought by taking basal till and bedrock samples with a tractor-mounted percussion drill. The fine fraction of till was analyzed by AAS and the bedrock samples by XRF and AAS. Mainly on the basis of Sn and Cu anomalies in basal till and bedrock 10 holes were diamond drilled into bedrock. Several topaz-bearing greisen bodies with uneconomic Sn content were penetrated. The results demonstrate the soundness of the theory and the methods used.     

Determination of background and threshold in exploration geochemistry

The graphical methods of analysing bi-modal frequency distributions are reviewed. The effects of inflection point position, curvature of the sigmoid, polymodality, and graphical and analytical precision are found to be important and are discussed in detail. The optimum method is a cumulative plot on log-probability paper with the two component distributions (linear) being asymptotic to the sigmoid tails and having a symmetry with each other about the inflection point. The method is illustrated with five natural examples to emphasise its advantages and limitations.     

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.     

Correspondence cluster analysis and its application in exploration geochemistry

Correspondence cluster analysis, developed in this paper, regroups the main advantages of correspondence analysis and cluster analysis. The output of the method, correspondence cluster dendrograms, shows clearly the relationships between variables, between samples, and between variables and samples, on a single diagram. The technique has been applied successfully to distinguish geochemical anomalies from background, to recognize types of anomalies, to study the geochemical characteristics of deposits, etc. Several practical examples presented in this paper show that the method can be used to classify elements and samples into meaningful groups, and that the geochemical character of each sample group can be interpreted in terms of the corresponding element group. The results are consistent with the geological situations at hand, and are usually more elucidating than other classification methods.     

Conceptual models in exploration geochemistry: The Canadian Cordillera and Canadian Shield

This volume summarizes the exploration geochemical conditions in the secondary environment, in the Canadian Cordillera and the Canadian Shield. This is achieved by a number of conceptual models which describe the principles and mechanisms of formation of anomalies, which govern the use of exploration geochemistry. These models have been constructed by drawing together information already existing in the literature plus 38 individual case histories contained in this volume.The formation of anomalies is described for: (1) residual overburden, (2) overburden of local origin (e.g. till), and (3) transported overburden of remote origin (e.g. stratified glacial drift and alluvium). Within each of these categories the effect of element mobility, seepage zones, bogs, variation in overburden thickness, rock type change and soil type change are also described.An attempt has been made, not only to summarize both these conditions where geochemistry can be used as a reliable exploration tool, but also to identify areas where the use of geochemistry is unreliable.A summary is also given of the length of anomalous dispersion and contrast in both soil and sediments for all the case histories quoted, both in this volume and in the literature. This summary is divided according to the type of deposit, i.e. porphyry copper, massive sulphide, etc., and provides a guide for planning the optimum sampling interval.     

波流边界层水沙运动数值模拟——II.泥沙运动模拟

为解析波流边界层内泥沙运动,建立了基于水动力-泥沙-床面互馈过程的波流边界层1DV泥沙数学模型,可用于模拟不同床面形态下粉沙-沙的含沙量过程。床面形态模块提供床面形态类型和相应参数;给出了平底和沙波床面粗糙高度和泥沙扩散系数的确定方法;采用了适宜粉沙及沙的制约沉速、底部参考浓度和起动剪切应力等公式;引入含沙量层化效应和制约沉降反映水动力与泥沙之间的相互影响。水槽试验资料验证表明,建立的模型较好地模拟了不同床面不同波流组合条件下的含沙量剖面。在此基础上,讨论了不同床面含沙量剖面模拟方法的差异,指出床面形态是决定含沙量变化的重要因素之一,仅通过改变床面粗糙高度不足以反映漩涡沙波床面的含沙量剖面特征。该模型可为研究波流边界层内泥沙运动和物质输运提供工具。     

Gas flow in anisotropic claystone: modelling triaxial experiments

Selected gas pulse tests on initially saturated claystone samples under isotropic confinement pressure are simulated using a 3D thermo‐hydro‐mechanical code. The constitutive model considers the hydro‐mechanical anisotropy of argillaceous rocks. A cross‐anisotropic linear elastic law is adopted for the mechanical behaviour. Elements for a proper modelling of gas flow along preferential paths include an embedded fracture permeability model. Rock permeability and its retention curve depend on strains through a fracture aperture. The hydraulic and mechanical behaviours have a common anisotropic structure. Small‐scale heterogeneity is considered to enhance the initiation of flow through preferential paths, following the direction of the bedding planes. The numerical simulations were performed considering two different bedding orientations, parallel and normal to the imposed flow in the test. Simulations are in agreement with recorded upstream and downstream pressures in the tests. The evolution of fluid pressures, degree of saturation, element permeability and stress paths are presented for each case analysed. This information provides a good insight into the mechanisms of gas transport. Different flow patterns are obtained depending on bedding orientation, and the results provide an explanation for the results obtained in the tests. Copyright © 2012 John Wiley & Sons, Ltd.     

Zn, Pb, Cu and As distribution patterns in overbank and medium-order stream sediment samples: their use in exploration and environmental geochemistry

Overbank and medium-order stream sediment samples were collected in Belgium and Luxembourg from 66 sampling locations (area of about 33,000 km²) and analysed for major and trace elements among which Zn, Pb, Cu and As. At each sampling location large bulk samples were taken, namely in the lower (normally at ≥1.5 m depth, over an interval of about 20–40 cm) and upper (normally upper 5–25 cm) parts of the overbank profiles and from the stream sediments. Furthermore, at a number of these sites, a detailed geochemical analysis of vertical overbank sediment profiles (sampling intervals of 10–20 cm) was subsequently carried out to unravel element variations through time and to help in the overall evaluation. For most sampled sections evidences such as ¹⁴C-dating and the absence of anthropogenic particles point towards a pre-industrial and often pristine origin of the lower overbank sediment samples. From the latter bulk samples, mean background concentrations were deduced. They reveal the existence of significant differences between the northern and southern part of Belgium (incl. Luxembourg) which relate to the difference in geological substrate. In the north dominantly non-lithified Quaternary and Tertiary sands, marls and clays occur while in the south Palaeozoic sandstones, shales and carbonate rocks outcrop. Consequently separate mean background values were calculated for the two areas. In the southern study area, some anomalous metal concentrations have been recorded in pre-industrial sediments. They are derived from mineralised Palaeozoic rocks, a feature which could be of interest for base metal exploration. In the upper overbank and stream sediments, in general, higher heavy metal and As contents were recorded with highest values in areas with metal mining, metal melting and cokes treatment industries. By comparing the trace element concentrations of the upper overbank or stream sediment samples with the concentrations detected in the lower overbank samples at each of the sampling locations, and by evaluating the vertical distribution patterns where available, the degree of pollution of the alluvial plain and the present-day stream sediments can be assessed. From this exercise, it is clear that highest pollution occurs in the northern part of Belgium, which relates to its high population density and industrial development.     

地球化学探测:从纳米到全球

文中简要总结了勘查地球化学的发展历程,阐述了从纳米尺度到全球尺度地球化学探测的最新进展。勘查地球化学从诞生初期研究手标本化学成分,到研究矿床尺度原生晕,到20世纪70年代以后研究化学元素的区域分布,到90年代以后开始研究全球尺度化学元素分布。进入2000年以后,为了更深层次理解这些宏观地球化学模式是如何受元素的微观行为控制的,开始了纳米尺度地球化学探测。目前纳米尺度地球化学和全球尺度地球化学研究成为地球化学探测的两个前沿研究领域。笔者从微观、区域和全球不同尺度地球化学探测,各列举一个前缘领域进行了介绍。(1)在微观尺度上,从纳米水平研究化学元素的存在行为、分散和迁移机理,列举了有关纳米铜和纳米金晶体颗粒的发现及其对隐伏矿勘查的意义;(2)在区域尺度上,阐述了盆地砂岩型铀矿地球化学调查理论与技术进展;(3)在全球尺度上,列举了全球地球化学基准研究的最新进展,初步总结了全球尺度化学元素分布与地质背景、矿产资源、气候变化和人类活动的关系。     

Chlorine and iodine,potential pathfinder elements in exploration geochemistry

Consideration of the geochemistry of Cl and I suggests that both elements would be useful pathfinders for hydrothermal mineralization. The results of published case studies indicate that these halogens form broad dispersion patterns in rocks and soils around many types of such mineral deposits.Simple and reliable automated photometric methods for the determination of these elements have been developed and sample preparation techniques are easily adapted to the rapid throughput of the large numbers of samples required for geochemical prospecting. Cold water extractable Cl and I in soils show strong correlation with total Cl and I concentrations and provide a rapid mthod for the detection of anomalies associated with mineralization.     

Fibre reinforced sands: from experiments to modelling and beyond

Based on hypotheses derived directly from experimental observations of the triaxial behaviour, a constitutive model for fibre reinforced sands is built in this paper. Both the sand matrix and the fibres obey their own constitutive law, whereas their contributions are superimposed using a volumetric homogenization procedure. The Severn‐Trent sand model, which combines well‐known concepts such as critical state theory, Mohr‐Coulomb like strength criterion, bounding surface plasticity and kinematic hardening, is adopted for the sand matrix. Although the fibres are treated as discrete forces with defined orientation, an equivalent continuum stress for the fibre phase is derived to allow the superposition of effects of sand and fibres. The fibres are considered as purely tensile elements following a linear elastic constitutive rule. The strain in the fibres is expressed as a fraction of the strain in the reinforced sample so that imperfect bonding is assumed at the sand‐fibre interface. Only those fibres oriented within the tensile strain domain of the sample can mobilize tensile stress—the orientation of fibres is one of the key ingredients to capture the anisotropic behaviour of fibre reinforced soil that is observed for triaxial compression and extension loading. A further mechanism of partition of the volume of voids between the fibres and the sand matrix is introduced and shown to be fundamental for the simulation of the volumetric behaviour of fibre‐reinforced soils. Copyright © 2012 John Wiley & Sons, Ltd.     

Highly fractionated I-type granites in NE China (II): isotopic geochemistry and implications for crustal growth in the Phanerozoic

NE China is the easternmost part of the Central Asian Orogenic Belt (CAOB). The area is distinguished by widespread occurrence of Phanerozoic granitic rocks. In the companion paper (Part I), we established the Jurassic ages (184–137 Ma) for three granitic plutons: Xinhuatun, Lamashan and Yiershi. We also used geochemical data to argue that these rocks are highly fractionated I-type granites. In this paper, we present Sr–Nd–O isotope data of the three plutons and 32 additional samples to delineate the nature of their source, to determine the proportion of mantle to crustal components in the generation of the voluminous granitoids and to discuss crustal growth in the Phanerozoic.

Despite their difference in emplacement age, Sr–Nd isotopic analyses reveal that these Jurassic granites have common isotopic characteristics. They all have low initial ⁸⁷Sr/⁸⁶Sr ratios (0.7045±0.0015), positive _Nd(T) values (+1.3 to +2.8), and young Sm–Nd model ages (720–840 Ma). These characteristics are indicative of juvenile nature for these granites. Other Late Paleozoic to Mesozoic granites in this region also show the same features. Sr–Nd and oxygen isotopic data suggest that the magmatic evolution of the granites can be explained in terms of two-stage processes: (1) formation of parental magmas by melting of a relatively juvenile crust, which is probably a mixed lithology formed by pre-existing lower crust intruded or underplated by mantle-derived basaltic magma, and (2) extensive magmatic differentiation of the parental magmas in a slow cooling environment.

The widespread distribution of juvenile granitoids in NE China indicates a massive transfer of mantle material to the crust in a post-orogenic tectonic setting. Several recent studies have documented that juvenile granitoids of Paleozoic to Mesozoic ages are ubiquitous in the Central Asian Orogenic Belt, hence suggesting a significant growth of the continental crust in the Phanerozoic.     

Minimum velocity dispersion in stable stellar disks. Numerical simulations

N-body dynamical simulations are used to analyze the conditions for the gravitational stability of a three-dimensional stellar disk in the gravitational field of two rigid spherical components—a bulge and halo whose central concentrations and relative masses vary over wide ranges. The number of point masses N in the simulations varies from 40 to 500 000 and the evolution of the simulated systems is followed over 10–20 rotation periods of the outer edge of the disk. The initially unstable disks are heated and, as a rule, reach a quasi-stationary equilibrium with a steady-state radial-velocity dispersion c_r over five to eight turns. The radial behavior of the Toomre stability parameter Q_T(r) for the final state of the disk is estimated. Simple models are used to analyze the dependence of the gravitational stability of the disk on the relative masses of the spherical components, disk thickness, degree of differential rotation, and initial state of the disk. Formal application of existing, analytical, local criteria for marginal stability of the disk can lead to errors in c_r of more than a factor of 1.5. It is suggested that the approximate constancy of Q_T?1.2–1.5 for r?(1–2)×L (where L is the radial scale of disk surface density), valid for a wide range of models, can be used to estimate upper limits for the mass and density of a disk based on the observed distributions of the rotational velocity of the gaseous component and of the stellar velocity dispersion.     

高黎贡构造带花岗岩的年代学和地球化学及其构造意义

产于高黎贡山脉的花岗岩（简称高黎贡花岗岩）记录中生代以来高黎贡构造带形成、演化的全部过程,高黎贡花岗岩的成因研究对于查明东喜马拉雅构造结的形成和演化乃至整个冈底斯地块的演化过程具有重要意义.高黎贡花岗岩为一套由黑云母二长花岗岩、二云母二长花岗岩、花岗岩组成的花岗质杂岩体,空间上构成一条南北向分布的挟持于怒江剪切带和龙川江剪切带之间狭长透镜体.地球化学特征研究揭示,高黎贡花岗岩为高钾钙碱性、过铝-强过铝花岗岩,其岩浆来源于中、下地壳前寒武纪变质岩的深熔作用.花岗岩源区成分不均一,以变质硬砂岩为主,并含有变质玄武岩,形成于岛弧-陆陆碰撞环境.SHRIMP锆石U-Pb定年表明,高黎贡花岗岩形成于早白垩世晚期（126～118Ma）,其年龄、地球化学特征与拉萨地块北缘花岗岩一致,说明它为冈底斯构造岩浆岩带的东延部分,是中特提斯怒江洋洋壳向南俯冲和海洋闭合过程的岩浆响应,而与新特提斯雅鲁藏布江洋的演化无关.     

The development of regolith exploration geochemistry in the tropics and sub-tropics

This essay traces the development of geochemical exploration from its early beginnings in the modern era during the 1930s, concentrating especially in its application to deeply weathered terrain in the tropics and sub-tropics. Following promising results obtained in temperate regions in North America and Europe, test orientation surveys were conducted to see whether similar procedures were applicable in the tropics, where conventional geological prospecting was largely precluded due to the extensive cover of a deep lateritic regolith and consequent lack of outcrop. After initial work in Sierra Leone and Nigeria, the emphasis transferred to East Africa in the 1950s and 1960s, aimed principally at Cu exploration. Many of the basic principles for exploration in dominantly residual, free-draining terrain were quickly established in this period. Exploration in terrains with more complex weathering histories, however, raised a number of difficulties due to leaching and secondary concentrations of elements, problems in selecting and identifying appropriate sample media, and extensive transported overburden. These were encountered especially in more arid regions in Australia and Africa during exploration for Ni and Au during the 1970s and 1980s. This led to a change in approach, placing weathering and geochemical dispersion in the context of regolith and landscape evolution –a return to the early concept of landscape geochemistry. The 3D expression of mineralization in the landscape is depicted as empirical conceptual models, that account for both relict features and active processes, and portray element associations, dispersion mechanisms and host materials. They also indicate suitable sample media, sampling intervals and procedures for analysis and interpretation.