Reassessment of Hydrofluoric Acid Desilicification in the Carius Tube Digestion Technique for Re–Os Isotopic Determination in Geological Samples

In this study, Re and Os isotopes were systematically determined in six geological reference materials (RMs; covering a wide range of lithologies) using the Carius tube (CT) digestion technique with and without hydrofluoric acid desilicification. Our results show that the HF desilicification increased the Re extraction efficiency (by 9–15%) evidenced from basaltic and andesitic rocks (e.g., BHVO‐2, TDB‐1 and AGV‐2). This implies that a small proportion of Re resides in silicate phases. For mafic–ultramafic rocks (e.g., BCR‐2, WGB‐1 and WPR‐1), Re extraction efficiencies obtained by the CT digestion with and without HF desilicification were similar. This may indicate that Re in these rocks may dominantly reside in some phases (e.g., magnetite and sulfides) that could be completely dissolved in aqua regia solutions without the aid of HF desilicification. Our results also show that the HF desilicification increased Os extraction efficiency (by 13–99%) in some RMs (e.g., BHVO‐2, WGB‐1 and AGV‐2). This observation suggests that a portion of Os‐rich trace phases may occur as inclusions in the silicate phases that act as isolators at ~ 200 mesh sizes. This study demonstrates that the HF desilicification step prior to CT digestion is important for complete extraction of Re and Os in geological samples.     

SPECTROPHOTOMETRIC DETERMINATION OF FERROUS IRON IN EIGHTEEN UNITED STATES GEOCHEMICAL REFERENCE STANDARDS

Iron (II) oxide in 50 mg samples of silicate rocks, deposits, and soils is measured after digestion with HF and HCl in the presence of ICl. The iodine produced is measured spectrophotometrically. Results are presented for the eighteen available USGS geochemical reference standards including the GXR series.     

Boron Determination in Twenty One Silicate Rock Reference Materials by Isotope Dilution ICP-MS

The concentration of boron was determined in twenty one geochemical reference materials (silicate rocks) by isotope dilution inductively coupled plasma-mass spectrometry. Boron was extracted from the rocks using HF digestion, suppressing boron volatilisation through boron-mannitol complexation. Sample solutions, in a diluted HCl matrix, were analysed by ICP-MS without any separation of boron from the matrix elements. The results obtained were in agreement with the literature data and indicate that using the described procedure, trace amounts of boron can be very easily determined in complex matrices with rapidity and precision. With the instrumentation and reagents used in this study, this procedure can be used for the determination of 0.5 μg g⁻¹ boron in a 15 0 mg silicate rock sample. Replicate analyses of the twenty one geochemical reference materials (GRM), ranging in boron concentration from 1.35 to 15 7 μg g⁻¹, yielded precisions (relative standard deviation) varying between 0.9 and 9.8%.     

The Bulk Analysis of Silicate Rocks by Portable X-Ray Fluorescence: Effect of Sample Mineralogy in Relation to the Size of the Excited Volume

This paper examines the limitations arising from sample mineralogy when a portable X-ray fluorescence instrument is applied to the direct in situ analysis of silicate rocks. Estimates were made of the size of the excited volume from which the X-ray fluorescence signal originates by calculating the critical penetration depth for selected X-ray lines. Measurements were made of the variations in detected intensities over the area of the P-XRF analyser window and showed that, using radioisotope sources incorporated in the instrument used in this study (Spectrace TN9000), excitation intensities were six to ten times greater at the centre compared to the edge of the analyser window. These data indicated that the region of the sample at the centre of the window will make an enhanced contribution to detected spectra. Replicate measurements on slabs of rock selected to represent fine-to coarse-grain size textures indicated the magnitude of the sampling precision that can be achieved in the direct analysis of silicate rocks. Typical values were better than 5% relative standard deviation of the mean from an average of five determinations on fine- to medium-grained rocks and better than 10 % relative standard deviation in a single determination on these samples.     

Simple Spectrophotometric Determination of Ferrous Iron in Twelve French Geochemical Reference Standards

Iron (II) oxide in silicate rocks can readily be measured after digestion with HF and HCl by reaction with KI and KIO₃. The iodine produced during the digestion is trapped in CCl₄ and measured at 512 nm spectrophotometrically. Results for ten accepted and two new geochemical reference standards are presented.     

Petrology and genesis of Karelian shungite—high rank coal

Shungites are highly carbonaceous, highly metamorphosed rocks associated with several stratigraphic levels of the Lower Proterozoic in Karelia. Being a complex material, shungite is very important also as oldest accumulations of concentrated organic matter. The nature of shungite is still unclear despite its more than a century-long study by Russian and western scientists.A chemical coal-petrographic study of shungite has been conducted using a specially designed technique: the etching of polished surfaces. It is found that the shungite bed (near Shunga village) is a coal seam with a typical set of megascopic features rather than an accumulation of bitumen. This bed consists not only of sapropelic but of humic organic matter as well.Unlike other biogenic structures from Precambrian coal, such as the Huron Series, Michigan Lake, the structures established in shungite near Shunga village have a more complex plant composition. Organic matter from various types of shungite-bearing rocks show different petrographic and chemical properties. Thus, organic matter of sapropelic nature from silicate rocks with traces of stromatolite texture, differs from the coal matter composing the Shunga bed. Shungites are the most metamorphosed coals among all those known at present and they are assigned here to metaanthracite rank. The results obtained show a new insight into the biogenic remains composing an ancient coal bed, and in terms of the present stratigraphic scale allow the beginning of coal accumulation to be placed in the Proterozoic, although the possibility of a non-Precambrian age cannot be ruled out.     

Direct Quantitative Determination of Trace Elements in Fine‐Grained Whole Rocks by Laser Ablation‐Inductively Coupled Plasma‐Mass Spectrometry

Previous laser ablation‐ICP‐MS bulk analyses have been confined to volcanic glasses and glass disks or powder pellets similar to those used for XRF analysis. This study proposes a method to determine twenty trace elements (fourteen rare earth elements, Sc, Y, Zr, Nb, Hf and Ta) by LA‐ICP‐MS directly from polished thick sections and rock slabs of six fine‐grained crystalline and aphanitic rocks (five volcanic rocks and one pelitic tillite). Laser scanning of eight to ten 20 mm long linear tracks using a spot size of 160 μm, with a total ablated area of 26–32 mm², was performed. Quantification was carried out by (a) internal standardisation using Si and (b) without applying internal standardisation. In the latter method, external determination of one element in conventional LA‐ICP‐MS quantification is no longer needed. Although the fine‐grained rocks studied contained variable amounts of volatiles (up to 4%), this method gave results that agree within 10% relative with those obtained by internal standardisation using Si. Two USGS basalt glass reference materials (BCR‐2G and BHVO‐2G) were used for external calibration. The results and the associated trace element patterns and ratios of elemental pairs obtained from both methods of quantification showed good agreement with the results from solution nebulisation ICP‐MS within 20% (mostly within 10%) relative. Fine‐grained rocks are common and include volcanic, sedimentary and low‐grade metamorphic rocks (e.g., basalt, andesite, rhyolite, shale, mudstone, tillite, loess, pelite and slate) and their trace element contents and associated ratios are important geochemical tracers in studies focusing on the composition and evolution of the crust and mantle. Our method provides a simple and quantitative way to determine trace elements in fine‐grained rocks even with those displaying complex textures.     

Reassessment of HF/HNO3 Decomposition Capability in the High‐Pressure Digestion of Felsic Rocks for Multi‐Element Determination by ICP‐MS

Complete dissolution is essential to obtain accurate analytical results for geological samples. Felsic rocks are known to be very difficult to dissolve because of the presence of refractory minerals such as zircon. In this study, we undertook a systematic evaluation of the effect of the HF/HNO₃ ratio, digestion time, digestion temperature, digested test portion mass and the presence of insoluble fluorides on analytical results for the felsic rock GSP‐2 using high‐pressure HF and HF/HNO₃ digestion. Digestion in mixtures of HF and HNO₃ acids is a commonly used method of dissolution for geological samples. However, our results clearly indicate that adding HNO₃ inhibited the digestion capabilities of HF for refractory minerals such as zircon. It took 8–12 hr for Zr to be completely recovered in GSP‐2 at 190 °C, whereas it needed about 36 and 72 hr at 160 and 140 °C, respectively. White precipitates were observed in the final solution for test portion mass > 100 mg, irrespective of which of the five different digestion solutions was used (1 ml HF, 2 ml HF, 1 ml HF + 0.5 ml HNO₃, 1 ml HF + 1 ml HNO₃ and 1.5 ml HF + 1.5 ml HNO₃). Environmental scanning electron microscopy showed that these precipitates were mainly composed of AlF₃. Instead of further HCl, HNO₃ or HClO₄ attack, we propose that using ultra‐fine samples and a small sample size is a good way to avoid the formation of insoluble residues (e.g., fluorides). To further investigate the precision and accuracy of the proposed method (using HF alone as the digestion solution during the first acid attack step), a suite of silicate rock reference materials was analysed. Most of the results were found to be in reasonable agreement with the reference values, with a relative error of < 10%.     

Decoupling of paired elements,crossover REE patterns,and mirrored spider diagrams: Fingerprinting liquid immiscibility in the Tapira alkaline–carbonatite complex,SE Brazil

Tapira is an alkaline silicate–carbonatite complex belonging to the kamafugite-carbonatite association in the Late-Cretaceous Alto Paranaíba Igneous Province (APIP). It is dominated by coarse-grained plutonic rocks (bebedourite – a phlogopite-, apatite-, and perovskite-rich clinopyroxenite – with subordinated dunites, wehrlites, carbonatites and phoscorites). The plutonic rocks are crosscut by fine-grained ultramafic alkaline rocks (phlogopite picrites, bebedouritic dikes) and fine-grained carbonatites. Both types of dike-rocks show petrographic evidence of the coexistence of immiscible silicate and carbonatite liquids, such as carbonate ocelli present in the silicate rocks and, more rarely, silicate ocelli within carbonatites. A detailed geochemical study of the rock types in the complex, with emphasis on the fine-grained varieties, showed that whilst some rocks may be related to each other through crystal fractionation (e.g. phlogopite picrites and bebedouritic dikes), others display anomalous trace-element behaviour that cannot be readily explained by the fractionation of a particular phase or combination of phases. We interpret such anomalous geochemical signatures as produced by silicate–carbonate liquid immiscibility, on the basis of available experimental data on partition coefficients between coexisting immiscible liquids. The immiscibility signatures comprise: (a) decoupling of geochemical pairs, such as Nb–Ta and Zr–Hf; (b) rotation of REE patterns, which cross over the patterns of the primitive liquids; and (c) matching and opposite enrichment-depletion trace elements relationships in spider diagrams of conjugate immiscible liquids. We suggest that, once established, such geochemical signatures are very difficult to erase during the subsequent petrogenetic evolution processes, which may result in superimposed conflicting signatures.     

新疆磁海铁矿床成矿无机化学过程研究

磁海铁矿床位于东疆火山岩区,矿体产于基性次火山岩体内,次火山水热活动导致铁矿床的形成。次火山水热活动有一系列不同类型,并具一定空间分布和时间演化规律的蚀变岩响应,主期成矿作用发生在中高温压硅酸盐蚀变与中低温压硫化物蚀变之过渡阶段。硅酸盐蚀变岩中的“石榴子石-透辉石”组合与传统理解的“夕卡岩”内的相同组合名同实异。可把此矿床定名为次火山水热石榴子石-透辉石-磁铁矿矿床。     

Determination of Zirconium, Niobium, Hafnium and Tantalum at ng g-1 Levels in Geological Materials by Direct Nebulisation of Sample HF Solution into FI-ICP-MS

We have developed a rapid and accurate method to determine Zr, Nb, Hf and Ta (denoted as HFSE) in geological samples by inductively coupled plasma-mass spectrometry fitted with a flow injection system (FI-ICP-MS). The method involves sample decomposition by HF followed by HF dissolution of HFSE coprecipitated with insoluble M and Ca fluoride residues formed during the initial HF attack. This HF solution was directly nebulized into an ICP mass spectrometer. An external calibration curve method and an isotope dilution method (ID) were applied for the determination of Nb and Ta, and of Zr and Hf, respectively. Recovery yields of HFSE were > 96% for peridotite, basalt and andesite compositions, apart from Zr and Hf for peridotite (> 85%). No matrix effects for either signal intensities of HFSE or isotope ratios of Zr and Hf were observed in basalt, andesite and peridotite solutions down to a dilution factor of 100. Detection limits in silicate rocks were 40, 2, 1 and 0.1 ng g-1 for Zr, Nb, Hf and Ta, respectively. This technique required only 0.1 ml of sample solution, and thus is suitable for analysing small and/or precious samples such as meteorites, mantle peridotites and their mineral separates. We also present newly determined data for the Zr, Nb, Hf and Ta concentrations in USGS silicate reference materials DTS-1, PCC-1, BCR-1, BHVO-1 and AGV-1, GSJ reference materials JB-1, -2, -3, JA-1, -2 and -3, and the Smithsonian reference Allende powder.     

Experiments on thermal fatigue of non-igneous rocks

This paper is a logical sequence to a previous study on thermal fatigue and the weather-ability of some igneous rocks by means of laboratory tests.Now the techniques are applied to several non-igneous rocks, such as limestones (seve al types), sandstones, graywackes and slates. Some conclusions are also derived from the Vickers microhardness numbers and the reflectance measurements obtained on polished surfaces of the samples tested in the “climatizing apparatus”.From a great number of quantitative determinations (weight loss, chemical leaching of the main cations of the rock-minerals, Vickers microhardness and reflectance) some conclusions are obtained, regarding (1) the use of an alterability index for classification of rocks for geotechnical purposes and (2) the ageing effects of weathering on polished surfaces of ornamental stones.     

微量元素在河北阳原球状黑云辉石正长岩的球体和基体间分配的意义

河北阳原辉石岩-正长岩杂岩体的球状黑云辉石正长岩是岩浆不混熔的产物。本文研究了微量元素、REE在球状岩石的球体相—基体相间的分配。提出控制元素在不混溶的两液相间分配的三种因素,建立了分配系数D_(M/O)~i与不混溶两液相的相对聚合度(NBO/T)_(M/O)之间的函数关系。这些研究可用于区分岩浆不混溶作用与其他作用,确定岩石成因。     

碳酸岩的地质地球化学特征及其大地构造意义

从已知碳酸岩的地质产状、岩石学特征、Nd-Sr-Pb-O-C同位素及痕量元素地球化学特征数据,结合高温高压实验岩石学资料,论述了其地幔源区的物质成分、交代过程软流圈地幔部分熔融机制和碳酸岩岩浆的演化模型。碳酸岩既可以产生于拉张岩石圈构造背景,也能够产生于挤压而派生的引张岩石圈构造背景。前者以产于裂谷环境、与硅酸不饱和过碱性岩构成环状碳酸岩—碱性杂岩为特征,主要由起源于软流圈地幔的霞石质超基性—基性岩浆经液态不混溶作用而形成;后者产于碰撞造山过程中派生的引张岩石圈断裂带,以单一的透镜状、条带状和似层状碳酸岩体为标志,直接由导源岩石圈富集地幔的低程度部分熔融作用而产生的碳酸岩浆侵入或喷发所形成。     

塔里木盆地陆相烃源岩有机组分的分类及其岩石学特征

通过对塔里木盆地陆相烃源岩所作的详细有机岩石学研究，提出了适合该盆地的陆相烃源岩有机组分分类方案，并系统地阐述各有机组分的光性、成因及岩石学特性。     

m-Benzene disulfonic acid (BDS) as a superior accompanying acid for routine silicate rock analysis

We recommend that m-benzene disulfonic acid (BDS) be used with hydrofluoric acid during the dissolution of silicate rocks and minerals for purposes of routine analysis of RO and R₂O groups and trace elements. This recommendation is based on several properties that make it superior to the alternative acids. These properties include: (1) a relatively high boiling point (resulting in more effective removal of HF and silica); (2) the high solubility of virtually all salts of BDS; (3) the non-complexing characteristics of BDS salts; (4) the thermal stability of BDS (resulting in very slight degassing at elevated temperatures, thus reducing splattering); and (5) the safety of BDS compared with highly oxidizing acids such as perchloric.     

论山东莱芜岩浆杂岩的多源成因

本文通过对山东莱芜地区与铁矿有成因关系的莱芜杂岩所作的矿物学、岩石学、岩石化学及地球化学方面的分析和讨论,初步认为这套岩石虽然从早至晚是由基性至中性至中偏碱(酸)性岩石构成,但不是单一岩浆结晶分异的产物。它是由幔源岩浆先形成基性岩,然后由壳源岩浆对其作用形成中性岩,晚期富钠流体对中性岩作用形成中偏碱(酸)性岩,故它是多源岩浆形成的杂岩。     

福建省莆田忠门地区硅线石成因

本文对福建忠门地区中生代变质岩中硅线石的产状、形成阶段及成因方式作了较详细地研究。该区出现的硅线石多属交代成因,不能作为划分变质相的标志。     

Flux‐Free Fusion of Silicate Rock Preceding Acid Digestion for ICP‐MS Bulk Analysis

We present a new method for the decomposition of silicate rocks by flux‐free fusion in preparation for whole‐rock trace element determination (Sc, Rb, Sr, Y, Zr, Nb, Cs, Ba, rare earth elements and Hf) that is especially applicable to zircon‐bearing felsic rocks. The method was verified by analyses of RMs of mafic (JB‐1a, JB‐2, JGb‐1) and felsic rocks (JG‐3, JR‐3, JSd‐1, GSP‐2, G‐2). Pellets of powdered sample (up to 500 mg) without flux were weighed and placed in a clean platinum crucible. The samples were then fused in a Siliconit® tube furnace and quenched to room temperature. The optimum condition for the fusion of granitic rock was determined to be heating for 2–3 min at 1600 °C. The fused glass in the platinum crucible after heating was decomposed using HF and HClO₄ in a Teflon® beaker. Decomposed and diluted sample solutions were analysed using a quadrupole inductively coupled plasma‐mass spectrometer. Replicate analyses (n = 4 or 5) of the RMs revealed that analytical uncertainties were generally < 3% for all elements except Zr and Hf (～ 6%) in JG‐3. These higher uncertainties may be attributed to sample heterogeneity. Our analytical results for the RMs agreed well with recommended concentrations and recently published concentrations, indicating complete decomposition of our rock samples during fusion.     

外源水和外源酸对万华岩地下河系统岩溶碳汇效应的影响

流域的岩石化学风化过程是全球碳循环中的重要环节。近年来流域水化学碳汇通量估算已越来越多地关注到外源水(硅酸盐风化)及外源酸对全球碳循环的影响。文章选取万华岩地下河流域为研究区,流域硅酸盐岩和碳酸盐岩分布面积占比为64%和36%,于2017年对洞口进行为期一年的取样监测,并分别于4月和9月对万华岩地下河系统内13个水点的离子组成进行监测,利用水化学平衡法和Galy模型,对流域岩石化学风化速率和CO2消耗通量进行了计算,对万华岩地下河系统的岩石风化和碳循环过程进行了分析。结果表明,万华岩地下河系统岩石风化消耗CO2的速率为31.02 t·(km2·a)-1;以碳酸岩风化为主,其风化速率为硅酸盐溶蚀的20倍;流域内碳酸盐岩风化对CO2消耗量占到整个流域的92.16%;不同岩石风化类型对碳通量的贡献率以碳酸溶解碳酸盐岩最大,为87.06%;流域上游的外源水对岩溶碳汇具有巨大的促进作用,外源水汇入后碳酸盐岩碳汇速率可以达到无外源水汇入流域的2倍;硫酸溶解碳酸盐岩次之,为9.24%;碳酸风化硅酸盐岩最小,为3.7%,在计算流域碳汇量的时候应将硫酸参与岩石风化的影响去除。