内蒙古沙章土锡铜多金属矿床成矿年代学及成因探讨

沙章土锡铜多金属矿位于内蒙古中部,近年来区内锡矿找矿工作的新发现,锡矿体为呈脉状、浸染状分布的电气石脉、电英岩及电英岩化蚀变岩,含锡矿物主要为锡石;铜矿体为浸染状分布的黄铜矿化电英岩化蚀变岩、方铅矿-闪锌矿-黄铜矿化蚀变岩,含铜矿物主要为黄铜矿,同时,经由钻探工程在矿床深部发现有闪长玢岩岩体。为了查清锡铜矿体成矿年龄及成矿物质来源,明确矿床成因类型,进一步指导找矿工作,文章在野外调查和室内综合研究基础上,对锡石开展了LA-MC-ICP-MS U-Pb定年及电子探针分析工作,并对共生的硫化物进行了硫同位素测试。测试结果显示,锡石成矿年龄为(316.3±8.9)Ma,为海西期晚石炭世阶段的产物;探针数据显示其成因为热液型锡石;硫同位素测试结果,δ³⁴S值为0.43‰～7.34‰,平均值4.39‰,具混合硫源特征。综上所述,笔者初步认为沙章土锡铜矿床的成因类型是与闪长玢岩有关的岩浆热液型。     

基于复杂网络的岩土颗粒材料分散性失稳先兆研究

岩土颗粒材料在达到Mohr-Coulomb塑性极限之前可能已经发生了没有明显局部损伤的全域准均匀破坏,即分散性失稳。近年来,网络科学工具在颗粒材料环境中的应用为研究其失稳破坏现象提供了有趣新颖的洞见。采用离散单元法对不同初始密实度的颗粒体系进行等体积应变加载路径的数值试验,发现初始状态越松散的颗粒体系越有可能发生分散性失稳;采用网络科学的理论和方法分析颗粒接触网络的拓扑结构特性和演化规律,发现颗粒材料分散性失稳的结构根源是颗粒接触网络完全崩塌。将颗粒体系划分为强、弱接触系统以构建强接触子网络、弱接触子网络和强−弱接触子网络,研究颗粒接触网络及其3个子网络的特征量演化,结果表明：当颗粒材料开始处于不稳定状态时,易受扰动的弱接触系统的部分接触先失效,导致强接触系统失去其稳定支撑作用而降低承载能力。随着加载的继续,系统通过非局部的自组织过程导致接触结构的全面崩塌,最终触发整体分散性失稳。因此,先于整体失稳的部分弱接触的失效,可视为颗粒材料分散性失稳的关键性临界征兆。     

滇东北松梁铅锌矿床成矿物质来源：来自S、Pb、Zn同位素的证据

川滇黔铅锌多金属成矿域内,碳酸盐岩容矿的热液铅锌矿床多达400个。松梁铅锌矿床地处滇东北与川东南的交接处,位于川滇黔铅锌多金属成矿域的核心部位;铅锌矿体赋存于震旦系灯影组白云岩内,矿体产出明显受断裂控制;矿石矿物组成简单,主要由闪锌矿、方铅矿和黄铁矿组成。文章重点研究了松梁铅锌矿床硫化物的S、Pb、Zn同位素组成,进而探讨了其成矿物质来源及矿床成因。研究表明,松梁铅锌矿床的硫化物δ³⁴S_CDT值在+4.6‰~+13.7‰之间,平均值为+10.5‰,显示硫来源于赋矿围岩,为震旦系灯影组硫酸盐经TSR的产物;硫化物的Pb同位素比值为²⁰⁶Pb/²⁰⁴Pb=18.158~18.513、²⁰⁷Pb/²⁰⁴Pb=15.633~15.895、²⁰⁸Pb/²⁰⁴Pb=38.096~38.786,反映成矿物质为壳源铅,源自震旦系灯影组白云岩与结晶基底的混合;闪锌矿的δ⁶⁶Zn为-0.126‰~+0.082‰,揭示成矿物质可能源自震旦系灯影组碳酸盐岩和结晶基底的混合。松梁铅锌矿床为后生碳酸盐岩容矿型铅锌矿床。     

激光剥蚀电感耦合等离子体质谱元素微区分析标准物质研究进展

激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)是目前地球科学分析领域的重要技术手段,元素微区分析标准物质研制是该分析技术发展的重要方向。本文对当前LA-ICP-MS元素微区分析标准物质的种类、元素分布以及应用上的优缺点和标准物质的制备方法进行了评述。现有的有证标准物质数量不多、种类不齐全,部分元素浓度较低,定值不确定度较大,应用上受到较大的局限性;研制标准也不成熟,均匀性检验方面尚未有统一的方法。本文参照岩石粉末标准物质均匀性检验方法提出了两步均匀性检验法,同时指出在标准物质种类方面,铂族元素及Au元素浓度适当、Pb-S等不同硫化物基体标准物质,以及化学成分不同的碳酸岩和磷酸岩基体标准物质是当前的迫切需求;在标准物质研制技术方面,纳米岩石粉末压片技术的研发、原位微区分析标准物质(固体)均匀性检验判别标准研究是亟待解决的问题。     

陕西蓝田地区三趾马化石新材料

刘东生等60多年前描述的在陕西蓝田灞河组下部的Hipparion sp.,材料较少,但形态特殊,此后一直未见相关报道.近年来在这一地区又发现了类似三趾马化石的新材料.新发现的Hipparion sp.个体小,原尖短、圆,次尖明显偏向舌侧,次尖颈收缩,DP4的次尖几乎完全孤立;原小尖褶长大复杂,次附尖粗大、分叉,向外伸出;端附尖长大,根部收缩,内侧收缩沟内伸,并呈复杂的褶沟.这些组合特征与包括Hipparion chiai在内的灞河组上部3种三趾马扁长的原尖截然不同,也区别于九老坡的Hipparion plocodus(Hipparion fossatum),而接近于大庙沟的Hipparion sp..新材料的发现表明灞河早期的这种形态比较特殊的三趾马可能延续到了灞河晚期,甚至更晚的时代,同时在白鹿塬西侧蓝田汤峪河道一带有新近系地层出露.     

Evaluation of stress strain non-uniformities in the laboratory direct simple shear test specimens using 3D discrete element analysis

The direct simple shear (DSS) device is one of the commonly used laboratory element testing tools to characterize the shear behaviour of soil. The interpretation of results from an element test requires understanding of the degree of stress and strain non-uniformities in a given test specimen. So far, studies on stress and strain non-uniformities in the DSS test have been conducted using direct boundary measurements of stresses in laboratory specimens supported by a continuum based analytical approach. Discrete element modelling now provides a means of modelling the soil behaviour in a realistic manner using a particulate approach. Accordingly, the performance of a DSS specimen was modelled using discrete element modelling with emphasis on assessing stress and strain non-uniformities in the specimen during shearing. The approach allowed for the numerical determination of stresses not only at the boundaries, but also within the DSS specimen. It was shown that mobilised stress ratio distribution throughout the shearing phase for the majority of specimen volume at locations near the central planes parallel and perpendicular to the direction of shearing is fairly uniform. Finally, it was noted that the potential for particle slippage at locations near the specimen centre can result in non-uniform shear strain distributions.     

Polygonal deformation bands

We report for the first time the occurrence of polygonal faults in sandstone, which is compelling given that layer-bound polygonal fault systems have been observed so far only in fine-grained sediments such as clay and chalk. The polygonal faults are shear deformation bands that developed under shallow burial conditions via strain hardening in dm-wide zones. The edges of the polygons are 1–5 m long. The shear deformation bands are organized as conjugate faults along each edge of the polygon and form characteristic horst-like structures. The individual deformation bands have slip magnitudes ranging from a few mm to 1.5 cm; the cumulative average slip magnitude in a zone is up to 10 cm. The deformation bands heaves, in aggregate form, accommodate a small isotropic horizontal extension (strain <0.005). The individual shear deformation bands show abutting T-junctions, veering, curving, and merging where they mechanically interact. Crosscutting relationships are rare. The interactions of the deformation bands are similar to those of mode I opening fractures. The documented fault networks have important implications for evaluating the geometry of km-scale polygonal fault systems in the subsurface, top seal integrity, as well as constraining paleo-tectonic stress regimes.     

Mass Fractions of S,Cu, Se,Mo, Ag,Cd, In,Te, Ba,Sm, W,Tl and Bi in Geological Reference Materials and Selected Carbonaceous Chondrites Determined by Isotope Dilution ICP‐MS

Mass fractions of S, Cu, Se, Mo, Ag, Cd, In, Te, Ba, Sm, W and Tl were determined by isotope dilution sector field ICP‐MS in the same sample aliquot of reference materials using HF‐HNO₃ digestion in PFA beakers in pressure bombs and glassy carbon vessels in a high‐pressure asher (HPA‐S) for comparison. Additionally, Bi was determined by internal standardisation relative to Tl. Because isobaric and oxide interferences pose problems for many of these elements, efficient chromatographic separation methods in combination with an Aridus desolvator were employed to minimise interference effects. Repeated digestion and measurement of geological reference materials (BHVO‐1, BHVO‐2, SCo‐1, MAG‐1, MRG‐1 and UB‐N) gave results with < 5% relative intermediate precision (1s) for most elements, except Bi. Replicates of NIST SRM 612 glass digested on a hot plate were analysed by the same methods, and the results agree with reference values mostly within 2% relative deviation. Data for the carbonaceous chondrites Allende, Murchison, Orgueil and Ivuna are also reported. Digestion in a HPA‐S was as efficient as in pressure bombs, but some elements displayed higher blank levels following HPA‐S treatment. Pressure bomb digestion yielded precise data for volatile S, Se and Te, but may result in high blanks for W.     

An elastoplastic model based on the shakedown concept for flexible pavements unbound granular materials

Nowadays, the problem of rutting of flexible pavements linked to permanent deformations occurring in the unbound layers is taken into account only by mechanistic empirical formulas. Finite element modelling of realistic boundary value problems with incremental rheological models will lead to unrealistic calculation time for large cycle numbers. The objective of the authors is to present a simplified model which can be used to model the flexible pavements rutting with the finite elements framework. This method is based on the shakedown theory developed by Zarka which is usually associated to materials like steels. It has been adapted for granular materials by introducing a yield surface taking into account the mean stress influence on the mechanical behaviour and a dependency of the hardening modulus with the stress state. The Drucker–Prager yield surface has been used with a non‐associated flow rule. Comparisons with repeated load triaxial tests carried out on a subgrade soil have been done. These comparisons underline the capabilities of the model to take into account the cyclic behaviour of unbound materials for roads. Finally, a discussion, dealing with the use of the simplified method within a finite element modelling of a full‐scale experiment, is presented. Copyright © 2005 John Wiley & Sons, Ltd.     

Stress–dilatancy based modelling of granular materials and extensions to soils with crushable grains

Stress–dilatancy relations have played a crucial role in the understanding of the mechanical behaviour of soils and in the development of realistic constitutive models for their response. Recent investigations on the mechanical behaviour of materials with crushable grains have called into question the validity of classical relations such as those used in critical state soil mechanics. In this paper, a method to construct thermodynamically consistent (isotropic, three‐invariant) elasto‐plastic models based on a given stress–dilatancy relation is discussed. Extensions to cover the case of granular materials with crushable grains are also presented, based on the interpretation of some classical model parameters (e.g. the stress ratio at critical state) as internal variables that evolve according to suitable hardening laws. Copyright © 2004 John Wiley & Sons, Ltd.