Precise and Accurate Doping of Nanoporous Silica Gel for the Synthesis of Trace Element Microanalytical Reference Materials

This study presents an experimental procedure to fabricate high‐purity silica glass containing a selected element at a specified mass fraction. The procedure was used to prepare glasses doped with trace‐level mass fractions of Ti with the goal of improving analytical confidence when measuring trace elements in quartz. Systematic tests were performed to determine the ideal conditions and procedures for doping nanoporous silica gel with the highest efficiency of dopant recovery. Silica gel was cleaned in concentrated HCl, immersed in a non‐polar doping medium at a controlled pH and doped with precise quantities of ICP‐MS standard solution. Using liquids composed of longer chain molecules as the doping medium diminishes recovery, suggesting that large molecules could obstruct nanopores to inhibit capillary uptake of the dopant. A control experiment using crystalline quartz reinforced the effectiveness of nanoporous silica gel for doping with trace‐level precision. Layered aggregates of silica gel doped with different Ti mass fractions were hot‐pressed to create multi‐layered reference materials that were analysed with multiple techniques at a variety of spatial scales. Analyses at the intra‐grain scale (cathodoluminescence scanning electron microscopy, electron probe microanalysis), at the single grain scale (SIMS), at the sample layer scale (EPMA, laser ablation‐ICP‐MS) and at the bulk scale (ICP‐OES) demonstrated acceptable homogeneity at sample volumes characteristic of most microanalysis techniques and show that nanoporous silica gel holds promise as a highly retentive doping substrate for preparing reference materials for laser‐, electron‐ and ion‐beam microanalysis.     

皖南印支期石英斑岩的首次发现及其构造意义

印支时期,中国东南部地区构造运动活跃,岩浆活动较为发育。但是,皖南地区一直未发现该时期侵入岩。近期在安徽省黄山市徽州区东坑口村北约500m处x046县道旁,发现石英斑岩脉体。用LA-ICP-MS技术测得其中锆石的U-Pb年龄为245.2±2.4Ma,此年龄代表石英斑岩的结晶年龄,即形成于印支期中三叠世,而非前人一直认为的燕山期岩浆活动产物。岩石地球化学特征显示,东坑口石英斑岩富集Th、La、Ce等大离子亲石元素及轻稀土元素,亏损Ba、Sr、P、Ti等高场强元素,具有高的10000×Ga/Al值及Zr、Nb、Ce、Y含量,岩石中可见半自形的石英和斜长石,具有A型花岗岩的特征。皖南印支期A型花岗岩的发现,为区域构造-岩浆演化研究提供了新的科学依据,对理解和构建中国东南部乃至华南地区早中生代构造演化具有重要意义。     

基于非线性最小二乘法的石英水平摆倾斜仪格值标定

采用非线性最小二乘法对石英水平摆倾斜仪格值标定的秒采样数据进行拟合。通过Levenberg-Marquardt算法实现迭代计算过程,准确求解光记录位移信号参数并计算标定格值。仿真和台站标定实验结果表明,采用非线性最小二乘法计算倾斜仪秒采样数据的标定格值与倾斜仪校准格值的一致性较好。     

Temporal changes of accretion rates on an estuarine salt marsh during the late Holocene — Reflection of local sea level changes? The Wadden Sea, Denmark

The temporal variability of estuarine sedimentation has been investigated in the northernmost part of the Wadden Sea (Denmark), using an estuarine sedimentary sequence at Ho Havn. The sedimentary sequence appears to have been deposited within the last ∼ 2000 yr based on detailed luminescence dating of the estuarine mud, whose ages range between 225 ± 40 and 2050 ± 300 yr. The age-depth profile reveals that the sedimentation rate has varied considerably in the past. Estuarine sedimentation was very rapid ∼ 1400 yr ago; the ages over almost 1 m of sediment are indistinguishable. After this accretion rate of ∼ 9 mm a^− 1, the rate dropped abruptly to ∼ 0.3 mm a^− 1 some time between 1340 and 970 yr ago. This slow rate of accretion continued until ∼ 350 yr ago, when it accelerated to ∼ 1.3 mm a^− 1. These abrupt changes in the accretion rate are possibly related to local sea level fluctuations, thus the period with low accretion rate most probably reflects a situation with a stable or decreasing relative sea level. The rapid deposition of ∼ 0.9 m of sediment within about one century some 1400 yr ago shows that large amounts of fine-grained sediment were available for deposition in the region at that time, and an increasing relative sea level was most probably responsible for the creation of the accommodation space for sedimentation. Recent studies on mudflats and salt marshes in the region also tend to show high accretion rates, indicating that the coastal lagoons could be less vulnerable and threatened by a future sea level rise than generally believed.     

Properties of fluids attending variable recrystallization of quartzite during contact metamorphism in the White‐Inyo Range,California

Fluid inclusions in the metamorphic aureole of the Eureka Valley‐Joshua Flat‐Beer Creek (EJB) pluton in the White‐Inyo Range, California, reveal the compositions and origin of fluids that were present during variable recrystallization of quartzite with sedimentary grain shapes to metaquartzite with granoblastic texture. Metamorphosed sedimentary formations, including quartzites, marbles, calcsilicates and schists, became ductile and strongly attenuated in the aureole during growth of the magma chamber. The microstructures of quartzites have an unusual distribution in that within ~250 m from the pluton, where temperatures exceeded 650 °C, they exhibit relict sedimentary grain shapes, only small amount of grain boundary migration (GBM), and crystallographic preferred orientations (CPOs) dominated by <a> slip. At distances >250 m, quartzites were completely recrystallized by GBM and CPOs are indicative of prism [c] slip, characteristics that are typically associated with H₂O‐assisted, high‐T recrystallization. The lack of extensive GBM in the inner aureole can be attributed to rapid replacement of H₂O by CO₂ produced by reaction of quartz grains with calcite cement that also produced interstitial wollastonite. Fluid inclusions in the inner aureole generally occur in margins of quartz grains and are either wholly aqueous (Type 1) or also contain H₂S, CO₂ and CH₄ (Type 2). Type 2 inclusions occur only in some stratigraphic layers. In both inclusion types, NaCl and CaCl₂, in variable proportions, dominate the solutes in the aqueous phase, whereas FeCl₂ and KCl are less abundant solutes. The solutes indicate attainment of a degree of equilibrium with carbonates and schists that are interbedded with the quartzites. Some Types 1 and 2 inclusions in the inner aureole show evidence of decrepitation due to high amounts of strain and/or heating suffered by the host rocks, which suggests that they represent pore fluids that existed in the rocks prior to contact metamorphism. In addition to Type 1 inclusions, outer aureole quartzites also contain inclusions that contain CO₂ vapour bubbles in addition to aqueous phase (Type 3). These inclusions only occur in interiors of granoblastic quartz that was produced by large amounts of GBM. The aqueous phase has identical ranges of first melting and final ice melting temperatures as Type 1 inclusions, suggesting that they have the same solute compositions. These inclusions are thought to represent the interstitial pore H₂O that promoted recrystallization of quartz and reacted with graphite to produce CO₂. Absence of significant amounts of CH₄ in Type 3 inclusions is attributed to elevated fO₂ that was buffered by mineral assemblages in interbedded schists. As opposed to the large amount of CO₂ that was produced by the wollastonite‐forming reaction in the inner aureole to inhibit GBM, the amount of CO₂ produced in the outer aureole by reaction between H₂O and graphite was apparently insufficient to inhibit recrystallization of quartz.     

Opal and chalcedony speleothems on quartz sandstones in the Sydney region,southeastern Australia

Speleothems of silica are far rarer than those of calcite but occur in a range of types including stalactites, stalagmites and flowstones. This study has found a wider range and far greater number of silica speleothems on the quartz sandstones of the Sydney region than the small number of previous accounts had suggested. Speleothems on the Sydney region sandstones are composed of multiple layers of amorphous opal‐A and cryptocrystalline chalcedony. Silica slowly dissolved from detrital and diagenetic quartz and kaolinite clays of the host arenites is redeposited as opal‐A at the sandstone surface when groundwater evaporates. This amorphous silica converts over time by Ostwald‐type paragenesis to the cryptocrystalline form, but the expected intermediate opal‐CT phase has not been detected. The crystallisation of chalcedony at earth‐surface temperatures is generally believed to take an extremely long time and its presence makes these speleothems very significant, especially as it is reported in only a small number of silica speleothems elsewhere. Furthermore, a similar paragenetic silica‐‘ripening’ mechanism may also be involved in the low‐temperature earth‐surface formation of other crystalline silica deposits such as silcrete duricrusts and pedogenic quartz. Additional closely coupled laboratory and field investigations into the processes that control silica paragenesis under earth‐surface conditions are sorely needed.     

A note on the generation of periodic granular microstructures based on grain size distributions

This short communication discusses an algorithm suited for the generation of periodic microstructures of granular media. Its particular features are a user‐defined grain size distribution, a representative volume element which is intrinsically periodic ab initio and a user‐defined termination criterion, controlled by an increase of volume fraction. For low densities our particle packings resemble fluids or gases, while we aim to reach for rather dense particle packings, similar to granular solids. The generated microstructures can thus be readily incorporated into large multiscale simulations, e.g. on the integration point level of a finite element analysis of a particular sand or concrete. The individual grain size distribution of the granular medium is incorporated through the introduction of different growth rates governing the final particle size distribution. We briefly sketch the generation of the representative volume element within a serial event‐driven scheme and demonstrate how periodic boundary conditions are ensured throughout the representative volume element generation process. The potential of the suggested algorithm will be illustrated through the generation of two different periodic multi‐disperse microstructures. They are based on different given grain size distributions, one for a quartz sand with a low non‐uniformity index and one for concrete aggregates classified as A32 by the German standard norm DIN 1045 to have a rather large variation in grain size. Copyright © 2007 John Wiley & Sons, Ltd.     

山西省吕梁山秦家崖钨铜矿床地质特征及找矿前景北大核心CSCD

山西省岩浆热液型矿床主要形成于中生代,与燕山期岩浆活动关系密切,在东部灵丘地区发育多个与次火山岩有关的铜铅锌银矿,近年来在吕梁山地区离石断裂东部也发现了多处钨铜多金属矿化,其中秦家崖钨铜矿床是工作程度最高、规模最大的矿床。本文在野外工作的基础上,对矿床地质、矿物组合、物化探异常体特征与成矿规律进行分析,研究认为:(1)钨矿体主要赋存于NE走向F_(1)断层破碎带中,矿体类型以石英脉型为主,另有少量蚀变岩型,矿物组合为黑钨矿+白钨矿+黄铜矿+黄铁矿,热液蚀变以硅化与绢云母化为主;(2)断裂破碎带中发育多条与矿体关系密切的长英质岩脉,激电测深剖面指示深部(~1000 m)存在隐伏的岩体;(3)秦家崖一带已发现的钨铜矿脉仍处于浅部细脉带,物探剖面揭示矿脉走向与延深位置均有高阻、中低极化的物探异常,指示矿体延深稳定,化探剖面与钻孔岩心元素组成证实矿体附近Cu、W异常明显,同时伴有Au、Mo异常,可作为找矿指标。综合分析认为,秦家崖钨铜矿床是与花岗岩类侵入有关的中、高温热液脉型矿床,进一步进行深边部勘查工作有望在研究区实现钨、铜、钼的找矿突破。     

南秦岭安康地区高纯石英用脉石英矿特征及质量影响因素

南秦岭安康地区志留系梅子垭组千枚岩中赋存丰富的脉石英矿产资源, 但其作为高纯石英原料研究程度低, 尤其是对其中影响石英提纯的痕量杂质元素含量及其赋存状态缺乏系统认识, 很大程度制约了该区高纯石英原料的质量评价和进一步的找矿突破。本文在厘定安康地区脉石英地质发育特征的基础上, 对研究区产出的3件脉状石英样品(AK200、AK201、AK202)开展了样品杂质元素检测, 对样品矿物学特征、杂质赋存形式和可提纯性能进行了研究, 进而进行了提纯实验, 结果显示, 3件样品提纯后SiO₂含量分别为99.993 11%、99.997 66%和99.998 58%, 均达到高纯石英产品质量要求, 其中AK202样品提纯后达到4N8级。研究表明, 提纯后Al、Ti、Na、K为主要杂质元素, Al可能以杂质矿物、晶格杂质两种方式存在; Ti可能多以晶格杂质的方式存在; Na、K多以流体包裹体的方式存在; 杂质矿物、流体包裹体、晶格杂质对该区脉石英质量均产生不同程度影响, 其中流体包裹体为主要影响因素, 晶格杂质次之, 杂质矿物影响最小。这一结论对于评价该区的脉石英矿产资源质量、明确今后找矿目标体特征具有重要参考意义。