Standard Rocks Research Articles

High-precision Sr and Nd isotope measurements using a dynamic zoom lens-equipped thermal ionisation mass spectrometer

Techniques for the determination of radiogenic strontium (87Sr/86Sr) and neodymium (143Nd/144Nd) isotope ratios by Thermal Ionisation Mass Spectrometry (TIMS) are presented in this study. We have developed a 5 lines acquisition routine for both elements, taking advantage of the 16 Faraday cups available on the Nu Instruments TIMS in conjunction with an efficient zoom lens system. This allows increased flexibility regarding the number of lines in a multidynamic acquisition routine whilst maintaining optimal peak alignment and peak shape for every measurement line despite the fact that the detectors are not movable. The long-term reproducibility obtained for our Sr (NBS 987) and Nd (Rennes-Ames) standard solutions gives a (87Sr/86Sr)multidyn of 0.7102467 ± 0.0000043 (6.0 ppm, 2 s.d., n = 38) and a (143Nd/144Nd)multidyn of 0.5119537 ± 0.0000022 (4.2 ppm, 2 s.d., n = 31), respectively. We also report (87Sr/86Sr)multidyn and (143Nd/144Nd)multidyn for a set of terrestrial rock standards (including 5 basalts (BCR-2, BHVO-2, BIR-1, Be-N and BR-24), one rhyolite (RGM-1) and one andesite (AGV-2)) with the same, or greater, level of precision as for the pure standards solutions. This level of precision is 2 to 3 times better than the literature data for Sr isotope ratios, and comparable to the latest high precision data reported for Nd isotope ratios. This is the first paper reporting such high precisions for radiogenic Sr and Nd data generated using a TIMS from Nu Instruments. Significant statementHigh precision Sr and Nd isotopic measurements are of key importance in the field of Earth Sciences because they are powerful tools to trace sources of materials and to date them. Here, we report the first high-precision data for 87Sr/86Sr and 143Nd/144Nd (external error of 5–6 ppm for Sr and 4–5 ppm for Nd) measured using a Nu Instruments TIMS. Such precisions will open new opportunities in fields such as geochemistry, geochronology, cosmochemistry, archaeology or forensics.

Comprehensive research on the failure evolution of the floor in upper mining of deep and thick coal seam

The Group A coal seam represents one of the most important coal deposits of the Huainan coalfield. It poses a series of dynamic geohazards during mining operations due to its thickness, stratification, and depth location. One of the major issues is the susceptibility of the coal floor to failure under the combined action of mining and pressurized water. At greater depths, the stress becomes concentrated at the tip of the primary fractures under the influence of the high surrounding pressure. The exploitation of coal has caused new fissures to develop along the primary fissures, with energy regrouping occurring at the tips of the new fissures. To better understand the rock deformation and failure of the coal floor, uniaxial loading strain tests were performed on a standard rock specimen based on the Brillouin optical frequency domain analysis (BOFDA) to capture the deformation characteristics on the surface of the rock specimen with high accuracy. During loading, the strain of the fiber optic at peak strength was equal to 4281 με. To further study the evolution of the failure of the coal floor rock stratum during mining, electrodes, and distributed fiber optic were placed in the coal floor monitoring borehole of the coal seam to record the changes in the current and strain. The monitoring results indicate that during the initial stage, when the working face was close to the monitoring borehole, the abutment pressure of the surrounding rock mass gradually increased, the strain increased, and the current value steadily rose. During the middle stage of the monitoring process, the working face was located above the monitoring hole, the upper part of the hole was under compressive strain, the current value increased, the bottom of the hole was under tensile strain, and the electrode current showed fluctuating values. At the late stage of the monitoring process, the working face was located in proximity to the monitoring hole and the mudstone layer. The current value dropped below 1 mA, and the peak tensile strain reached 8589 με, which was followed by an abrupt change, showing the characteristics of rock failure. Comprehensive diagnosis indicated that the maximum floor failure depth was at the 21.0 m mark. During mining, the electrical current and the strain values had a positive correlation when the rock at the bottom was not failure. However, these values suddenly changed after the rock failed. The obtained results can serve as guidance for borehole multi-field monitoring in mining engineering.

Quantification of the dependence of the emanation of radon from water on the pH and temperature of water

Uranium- and thorium-series isotopes are able to dissolve in hot spring waters and decay into radon, which could potentially cause health risk of the public. Besides, several environmental investigations can be carried out by measuring radon concentrations in hot spring waters. Accordingly, the measurement of radon in hot spring water is a significant issue.A practical method for measuring radon in hot spring water was developed by using a silicon semiconductor detector, RAD-7. The overall effect of detection efficiency and radon leakage of the measuring system were examined to calibrate the measured concentration of radon in hot spring waters. In addition, the effect of water temperature and pH on emanation of radon from standard 226Ra solutions as well as that of the measuring time on precision of the measurement were investigated. The correlation among temperature, pH and emanation of radon was then obtained. Further, the established method was applied to in-situ measurement to investigate the concentration of radon in hot spring waters from different geological areas in Taiwan.According to the percent error of the measurement, the measuring time for environmental samples was set as 50 min. The overall effect of radon leakage and detection efficiency of the measuring system was estimated to be 99.19 ± 7.47% with a standard rock source of 222Rn from NIST. Standard sources of 222Rn were prepared from 226Ra standard solutions with different pH values. The 226Ra standard solutions were sealed and stand for 38 days in a 250 mL vial specific for the RAD-7. After measured by the WAT250 mode of the RAD-7, the data were measured as (52.5 ± 8.9)%∼(83.6 ± 11.0)% of the prepared concentration of 222Rn (from 226Ra). The emanation rate of 222Rn from standard solution under pH 1.44–9.07 was (53.2 ± 6.9)% ∼(84.3 ± 11.1)% and decreased with pH to a minimum value at 7.00. Moreover, the effect of temperature increases with pH. High correlated trend curves (r2 = 0.9829–0.9999) for 222Rn emanation rate versus pH under different temperature were obtained. A smooth curved surface fitted by the MATLAB for emanation rate of 222Rn was accordingly derived. The 222Rn concentrations in waters of the Beitou Hot Spring (acid-digestion sulfate spring on sedimentary rock strata), Wulai Hot Spring (sodium bicarbonate spring on metamorphic rock strata), Choshuitan (sodium bicarbonate spring on mudstone strata) and Zhaori Hot Spring (acid-digestion sulfate spring on andesite strata) were measured with RAD-7 by WAT250 for 50 min and then calibrated by 222Rn emanation rate estimated above, which were 215 ± 37 (Bq/m3), 6797 ± 1073 (Bq/m3), 2124 ± 577 (Bq/m3) and 26644 ± 2768 (Bq/m3).

High-precision and high-accuracy magnesium isotope analysis on multiple-collector inductively coupled plasma mass spectrometry using a critical mixture double spike technique

A new procedure has been developed for high precision and high accuracy Mg isotope analysis on multiple-collector inductively coupled plasma mass spectrometry using a critical mixture double spike technique. Errors arising from improper preparation of the critical double spike solutions are able to be corrected against the regression on a set of over- and under-spiked standards. Accuracy is ensured by correcting mass bias offset based on Monte Carlo calculations. Doping experiments indicate that the double spike method is robust to non-spectrum matrix effects. A long-term precision and accuracy of ±0.03‰ (2SD) was demonstrated for δ26Mg by replicate analyses of well-characterized in-house pure Mg solutions and synthetic samples passed through the column chemistry, provided that each sample was measured four times. The robustness of the method was further assessed by replicate analyses of fifteen geological reference materials ranging from peridotite, basalt, granodiorite, carbonatite to seawater. Rock standards yielded consistently higher δ26Mg by 0.076 ± 0.052‰ (2SD, N = 12) compared to data previously reported by standard-sample-bracketing from the same lab. This discrepancy might result from the difficulty in matching the matrices of natural samples exactly the same to the bracketing standards, even after purification, suggesting a careful evaluation on residual matrix effect for the standard-sampling-bracketing method. Our new data for geological reference materials serve as a reference for quality assessment and inter-laboratory comparison in future studies.

Rock Damage Model Coupled Stress-Seepage and Its Application in Water Inrush from Faults in Coal Mines.

Mining-induced fractures often constitute water inrush channels, which lead to mine water inrush accidents. In this paper, a coupled model of stress–seepage–damage based on micromechanics is established, which simulates the initiation and propagation of cracks in rock materials and their interaction with fluid flow. The method combines the continuous damage model with the effective stress principle, in which the elastic modulus and permeability are related to the damage variables. The model is implemented via the COMSOL code based on the finite element method, and the reliability of the model is verified by the axial compression–seepage test of standard rock samples. According to the actual geological conditions of F13 fault in Wugou Coal Mine, Anhui Province, the damage of the floor rock mass and the risk of fault water inrush in the 1033 mining face with 50, 40, 30, and 20 m waterproof coal pillars are predicted. When the coal pillar width is 30 or 20 m, the fault, the surrounding rock of the fault, and the failure zone of the floor constitute the water inrush channel. This model provides an intuitive understanding of the rock damage and water inrush evolution, which is difficult to observe, and will contribute to prevent water inrush disasters in practical engineering.

The high-efficiency methods to identify lithology with well logging plates or a program

As traditional manual method to identify lithology of cored wells is laborious and lack of efficiency, two efficient methods are used this time. One method is the identification with well logging plates while another is a program. The critical values of 5 kinds of well loggings are found to be relatively stable through many trials, and some major steps should be taken before using the logs. First is to find standard rock types and their logging values. Rock types are more reliable after the observation under microscopes. The second step is to find out the logging data ranges of each rock type. The third step is to quantitatively identify rock types with the optimal critical values. In this process, the multi-array logs (M2Rn) is found to be the most effective log to distinguish mudstone and oil reservoir. Low density (DEN) value is effective to distinguish the lightest matter or pores. The other two well logs, i.e. AC and CNL, can be used to distinguish whether there is limy content. Wave impedance (PD=DEN/AC) log can be a supplementwhen that kind of data is available, and finally all lithology is identified after that. The result that calculated from well logs with a program is similar to litholgy of drilling cores. Through many trials and errors, it is finally found and proved to be a successful approach to automatically and efficiently distinguish rock types in the software of Direct and Petrel. This method is more efficient and easier to operate with a program when there are hundreds of wells, and it is a progem made that work possible. There is more widespread use in deep carbonate buried hill with this method, simply by changing the lithology codes and critical values in the program.

Rapid unseparated rare earth element analyses by isotope dilution multicollector inductively coupled plasma mass spectrometry (ID-MC-ICP-MS)

We present a method for analyzing rare earth elements (REEs) by isotope dilution without separation of individual elements. Utilizing a Nu Plasma 2 multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS) equipped with an Aridus II desolvation nebulizer, sample introduction tuning parameters (torch position, gas flows) were investigated and used to minimize oxide formation (e.g., NdO/Nd <0.05%) and obviate the need to analyze the REEs as separated “cuts.” Ratios for spike isotopes relative to reference in mixed elemental standards containing varying amounts of Ce, Nd, Sm, Eu, Gd, Dy, Er, and Yb were measured accurately within 1% of IUPAC values. La and Lu in the standards deviated more than 2% from expected values due to more pronounced interferences reducing the efficacy of corrections. A USGS (United States Geological Survey) BCR-2 rock standard was also processed with flux fusion, iron coprecipitation and bulk REE separation by a single column pass followed by analysis. The concentrations for Ce, Nd, Sm, Eu, Dy, Er, and Yb fell within 2% of consensus values. A USGS BIR-1A rock standard was also processed in triplicate by hydrofluoric and nitric acid digestion followed by iron coprecipitation and a single ion exchange column pass, yielding rare earth concentrations within 3% of consensus values with 0.3% relative standard deviation (n = 3). This demonstrates the ability to produce high quality REE patterns of comparable quality to traditional methods which require labor and time intensive REE separation, but with sample preparation and analytical times that are comparable to isotope dilution analyses by single-collector ICP-MS.

Single-Stage Extraction Technique for Ce Stable Isotopes and Measurement by MC-ICP-MS

The separation of Ce from other rare earth elements has not been well established because of their similar geochemical properties. In this study, we report a single-stage extraction technique to purify Ce from natural samples with Eichrom DGA resin. This method separates Ce effectively from matrices and interfering elements, such as Ba, La, and Nd. The Ce elution curve would not drift with different Ce loading masses and rock types. The Ce isotope compositions were measured using a Thermo Scientific Neptune Plus multicollector (MC)-inductively coupled plasma (ICP)-mass spectrometry (MS) instrument. The instrumental mass bias of Ce isotopes was corrected with a sample-standard bracketing combined with a Sm-doping method. The δ142Ce values of standard solutions (CDUT-Ce and JMC304) relative to National Institute of Standards and Technology SRM 3110 measured were +0.128 ± 0.028‰ (2SD, N = 30) and 0.005 ± 0.038‰ (2SD, N = 30), respectively. The reproducibility for δ142Ce was better than 0.040‰. The Ce isotopic compositions of nine United States Geological Survey standard rocks, including carbonatite, basalt, andesite, quartz latite, dolerite, rhyolite, and granodiorite, were measured in this study. Our result showed that δ142Ce values of these rocks varied slightly, indicating that insignificant fractionation occurred during igneous processes. The technique proposed in this study is simple and time-efficient, which is beneficial for further studies on Ce isotope geochemistry.

Considerations Relevant to the Stability of Granite Boulders

Granite boulders are characteristic geomorphological structures formed in granitic terrains. Due to their formation process associated with typical spheroidal weathering phenomena, they tend to show more or less ellipsoidal shapes prone to instability, and they often lie on small contact surfaces. Analyzing the stability of these boulders is not a straightforward task. First, these boulders may topple or slide. Additionally, their typically irregular geometry and uneven contact with the surface where they lie makes the analysis more complex. The authors have identified some critical issues that are relevant to characterize these boulders from a rock mechanics point of view, with the aim of estimating the stability of boulders. In particular, an accurate description of the geometry of the boulder is necessary to perform accurate toppling calculations. Additionally, the contact area and the features of the contact plane need to be known in detail. The study is intended to serve as a guideline to address the stability of these granite boulders in a rigorous way, since standard rock mechanics approaches (planar failure, toppling stability, standard rock joint strength criteria, etc.) may not be directly applicable to these particular cases.

Accurate whole-rock geochemistry analysis by combined ICP-OES and LA-ICP-MS instruments

ICP-OES and LA-ICP-MS instruments routinely used to assess the geochemical properties of the various natural and synthetic materials. In this contribution, the analytical routines and method development procedures of the ICP-OES and LA-ICP-MS facilities installed at the İstanbul University-Cerrahpaşa Geological Engineering Department, Geochronology and Geochemistry Laboratory have been evaluated using well-known international rock standards. Sample preparation techniques, method development, experimental setup and measurement conditions for the both ICP-OES and LA-ICP-MS instruments were discussed and specific analyze results of NIST SRM 614, BCR-2, AGV-2, BCR-2G and AGV-2G were evaluated. Flux-free USGS glass standards were produced by in-house techniques and flux-bearing glasses were produced by fusion of sample with the mixture of ultra-pure lithium-tetraborate, lithium metaborate and lithiumbromide were evaluated and compared with the well-known reference values in the literature. Relative standard deviation (RSD) values for the major oxide measurements for standards changes between of 0.0 wt. % to 1.5 wt. %. RSD values for the trace and rare-earth-elements values were mainly lower than 10 wt. %. The results confirm that the both flux-bearing and flux-free glasses reasonably match with the world-wide inter-laboratory values for international standards samples. The combination of these two instruments can be used to conduct geochemistry of various solid earth materials.

Canonical Correlation Analysis Based on Site-Response Proxies to Predict Site-Specific Amplification Functions in Switzerland

ABSTRACTThe national seismic networks of Switzerland comprise more than 200 stations. At the station sites, the empirical amplification functions (EAFs) are routinely computed after each earthquake using a generalized inversion method based on separation of source, path, and site effects. The seismic stations are also characterized through geophysical measurements aiming to estimate shear-wave velocity profiles and horizontal-to-vertical spectral ratio of ambient vibrations (HVNR). Using this information, the correlation between the HVNR and EAF is assessed through canonical correlation. Once established, the canonical correlation is used to reconstruct the expected EAFpred at each considered station site in the dataset. The prediction is individually made for all seismic stations in the dataset, excluding every time the investigated station is from the calibration dataset; the reconstruction of the EAFpred is performed resorting to two parallel methods. The first method uses a combination of the canonical correlation parameters and Moran index, and the second one solves in a least-squares sense an overdetermined linear equation system including the canonical couples deemed as reliable. After a first round of predictions, a systematic lower EAFpred in soft sediment sites and a higher EAFpred in hard-rock sites is observed. A possible explanation for this behavior is found in the “normalization” to the Swiss standard rock profile in the computation of the EAF at the Swiss stations. Therefore, to reduce this effect, geological and geophysical parameters are considered in addition to the HVNR in the canonical correlation. We observe that the final solution improves when the least-squares solution approach is used with a combination of HVNR, VS30, and thickness of the ice cover at the last glacial maximum. Moreover, a blind test is performed using data not considered in the calibration dataset. The results highlight the ability of the method to provide an estimate of the site amplification over chosen frequency bins.

Characterization and microfabrication of natural porous rocks: From micro-CT imaging and digital rock modelling to micro-3D-printed rock analogs

Tests on standard rock specimens with controlled and identical pore structure are critical to validating the analytical and numerical models. However, it is usually difficult to acquire two natural samples with the same internal structure for the destructive laboratory tests, for the sake of the heterogeneity of natural rock which is caused by the complex diagenetic processes. Three-dimensional (3D) printing technology provides an alternative approach to produce geometry-identical, features-controllable, and lab-testable analogs of natural rock from digital data in a faster and more cost-effective way. This paper presents a customized workflow of 3D-printed rock analogs from micro-CT images combining with digital rock modelling. Three types of natural rock specimens are imaged by micro-CT and processed as inputs for two types of 3D printing techniques. Rock analogs are printed at multiple magnifications from original CT volume in five curable resin materials. Petrophysical parameters of 3D-printed rock analogs are acquired through helium pycnometry (HP) and mercury intrusion porosimetry (MIP). The accuracy of 3D-printed rock analogs is evaluated by comparing the measured results with the benchmark data derived from the digital rock modelling. Both the advantages and the current challenges to reproduce the real pore structure of natural rock by the 3D-printed analogs are discussed. The results indicate that the gypsum-based printed analogs are prior to modelling the surface roughness and wettability properties to natural rock grains, while the resin-based printed analogs owe advantages on reproducing pore structure. As the first effort in literature, this study investigates the inherent relationship between digital rock and 3D-printed rock analogs via comprehensive comparison on petrophysical properties. The results approve that the 3D printing technique is a novel, feasible, and alternative approach for laboratory test to generate rock analogs from the digital model of the natural rock. However, it is still difficult to print the pore structure of the rock at the original dimension. • A customized framework of rock analogs 3D printed from micro-CT image was established. • As the first effort in literature, the inherent relationship between digital rock and 3D-printed rock was investigated. • The effects of different printing techniques, materials, and up-scaling factors on reproducing pore structure was discussed.

Uniaxial Compression Mechanical Analysis of Cylindrical Rock Specimens Based on Space Axisymmetric Problem

The common failure forms in the uniaxial compression test of standard cylindrical rock specimens are symmetric cone failure and splitting failure. In the past, two kinds of failure forms were explained from the plane problems of elasticity theory. However, there was a lack of research based on space problems. In this paper, based on spatial axisymmetric elastic mechanics theory, three-dimensional stress function is constructed for the cylindrical rock specimen under uniform axial compression by adopting the semi-inverse method. According to the stress function, the stress components and the principal stress are deduced when considering the end effect. The failure form is speculated, which can well explain the two common types of damage in uniaxial compression. This work may enrich the basic research of rock mechanics.

A New Spectrophotometric Method for Thorium Determination Using 1,4-Dihydroxyanthraquinone

A new reagent, 1,4-dihydroxyanthraquinone (1,4-DHA), is described for the spectrophotometric determination of thorium(IV). Optimization of the formed thorium−1,4-DHA complex was performed by studying several parameters such as methanol concentration, suitable pH, dye concentration, temporal stability of the formed complex and thorium concentration (calibration curve). The optimized method was applied to different rock types bearing thorium with good accuracy results. This reagent is highly sensitive toward thorium; thorium complex has a molar absorptivity of 1.82 × 104 L/(mol cm) at 600 nm and pH 3.25. Beer’s law was obeyed in the range from 0.9 to 20 µg/mL for Th(IV). The tolerance limits for several metal ions were calculated and gave high tolerance limit especially for uranium. Details are given for the estimation of thorium in standard reference and natural rocks.

ХАРАКТЕР РАСПРЕДЕЛЕНИЯ РЕДКОЗЕМЕЛЬНЫХ ЭЛЕМЕНТОВ В МЕЗОЗОЙСКИХ ОСАДОЧНЫХ ПОРОДАХ НИЖНЕГО ПРИАМУРЬЯ

The article presents original data on the contents of rare earth elements (REE) and characterizes their distribution in Mesozoic sedimentary rocks of the Lower Amur region. The author compares various parameters of the studied rocks with similar parameters in the standards of the same rocks. The stratigraphic divisions made on the M-54-I sheet of the 1:200,000 scale State Geological Map belong to the Amur (or Chayatyn) subzone (SFPZ) of the West Sikhote-Alin Structural-Formation Zone (SFZ). Among them, the Zhorminsky (K1 zm) strata, Silasinsky (K 1-2 sl) and Utitsky (K2 ut K2) formations are distinguished. The stratons are composed of sandstones and siltstones in different ratios. They also contain conglomerates, tuffs of different composition, and andesites. The REE content in siltstones is higher than in sandstones. Higher concentrations of elements were found in the studied rocks relative to the rocks of the Caucasian Folded System (CC). Compared to the aleuropes of the Russian platform, the sandstones of Priamurye subzone have less REE content, and the siltstones have more. Compared to PAAS (post-Archean Australian shale), the REE content is less. Chondrite normalized REE contents. The trend of the charts is negative. The same behavior of elements is characteristic of the distribution spectra in the studied sandstones, siltstones, RAAS, aleuropesstones of the Russian platform, and rocks of the Caucasian SS. In most of the rocks presented, the LRSE/TRSE is higher than 8, this indicates that the sedimentation basin of detrital material has a predominantly acidic composition. There is a significant negative europium anomaly – from 0.34 to 0.71 in sandstones, and from 0.47 to 0.75 in siltstones. It also indicates the acidic rocks erosion. Consequently, a set of parameters determines the rocks acidic composition in the demolition areas.

Accuracy and reproducibility of trace and selected major element measurements in geological standard rocks using inductively coupled plasma mass spectrometry (ICP-MS)

Accuracy and reproducibility of trace and selected major element measurements in geological standard rocks using inductively coupled plasma mass spectrometry (ICP-MS)

Evaluation of load transfer mechanism under axial loads in a novel coupler of dual height rock bolts

The effective reinforcement of two or more overlying layers of mine openings in a single installation is usually done by coupling of two standard rock bolts mainly during the extraction of medium-thick coal seams. However, field observations show that the couplers of multiple bolts often degrade or break mostly at their connections. These types of failures can be avoided by strengthening the couplers of such multi-bolts assemblies. To achieve this, a novel threaded coupler system with an expansion shell was suggested in this paper. The newly designed coupler consists of a threaded tapered-plug-cum-connector with an expansion shell for connecting and tightening two standard rock bolts. An analytical model for evaluating the load distribution along the coupler subject to axial load was derived. Numerical analysis was performed to analyse the load transfer, deformation, and strains across the coupler including the factor of safety for the bolt-coupler-resin and bolt-coupler-expansion shell. The results validated the analytical model of the proposed coupler design, which provides better anchorage near the interface of the host rock mass. Thus, the developed coupler design would reduce the failures of the proposed coupler and stabilize laminated roof strata above the medium-thick coal seams in underground mines.

Comparation of Pressed Powder Pellet and Fused Glass Bead Preparation Techniques for Mayor Elements Analysis of Rock Samples using X-Ray Fluorescence (XRF)

The composition of chemical elements in rock samples can be used as a tool for classifying rock types, predicting the depositional environment, rock age, and the tectonic environment in which the rock is formed. X-Ray Fluorescence (XRF) is one of the instruments used to analyze rock samples. The advantage of using XRF analysis is that the analysis process can be done more quickly, easily, accurately, and does not damage the sample. However, before measurements are made using the XRF instrument it needs to be supported by an appropriate sample preparation process. In this study, optimal conditions in the standard (CRM) rock sample preparation of GBW 07105 and JR-1 have been studied. The parameters studied were variations in the composition ratio of Cellulose Mycro Crystalin (CMC) with standard (CRM) samples, namely 1: 4 and 1: 3. The technique of mixing the sample is done by using a mortar grinder and a shaker. Optimization of sample preparation was carried out using pressed powder pellet and fused glass bead techniques. Based on the data obtained from the analysis results the best ratio of binders to standard samples is 1: 3. The pressed powder pellet preparation technique is the best technique in analyzing samples using the X-Ray Fluorescence method. Further studies also need to be carried out to analyze minor elements and traces (REEs).

Accuracies and detection limits of major, minor, and trace element quantification in rocks by portable laser-induced breakdown spectroscopy

The recent manufacture of portable laser-induced breakdown spectroscopy (pLIBS) instruments has permitted widespread applications of an established analytical technique for in situ geochemical quantifications. This novelty has created a need for investigations comparing the default univariate pLIBS calibration accuracies to custom instrument calibrations based on geological samples and to other modeling methods. Previous research has shown that multivariate models can mitigate some of the matrix effects that cause intensity and concentration non-linearity within LIBS plasmas of rocks. This study thus makes two pLIBS calibration comparisons: one compares partial least squares (PLS) multivariate regression to univariate instrument models, while the other compares the default instrument calibration, intended for general industrial use, to a custom instrument calibration based on rock standards. Both comparisons use root mean squared errors (RMSE) between model-predicted and true standard values of the major oxides Al2O3, CaO, Fe2O3, K2O, MgO, MnO, Na2O, P2O5, SiO2, and TiO2, and minor and trace elements Ba, Cr, Cu, H2O, Li, Ni, Pb, S, and Zn to test calibration accuracies. pLIBS spectra from 2007 diverse rock standards were used for the PLS versus univariate model comparison, while 89 publicly-available geochemical standards were used to compare the default and custom instrument calibrations. PLS models give test accuracies for major elements of ±8.61 wt% for SiO2, ±3.38 for Al2O3, ±0.77 for TiO2, ±3.84 for Fe2O3, ±4.41 wt% for MgO, ±3.08 wt% for CaO, ±1.09 wt% for Na2O, and ±1.52 wt% for K2O. Quantification of trace and minor elements was more accurate with multivariate regression than with univariate instrument models, and the new custom instrument calibration had lower prediction errors for these elements than those of the default models. However, minor and trace element errors from all three calibrations were often greater than the average concentration of the test standards, which suggests that these substances are not well quantified in rocks by pLIBS instruments.

Optimized switch-over between CHNS abundance and CNS isotope ratio analyses by elemental analyzer-isotope ratio mass spectrometry: Application to six geological reference materials.

Elemental abundances and isotopic ratios of carbon, nitrogen, sulfur and hydrogen have become important tools for reconstructing the evolution of Earth and life over geologic timescales, requiring accurate and precise analytical methods with high sample throughput. However, these measurements may require separate instruments for each task, such as an elemental analyzer (EA) with a thermal conductivity detector (TCD) for elemental abundances and an EA interfaced with a mass spectrometer for isotopic ratios. To improve sample throughput and laboratory up-time, we developed a switch that allows converting an EA IsoLink™ system from a standalone mode using only a TCD to a mode for isotope ratio mass spectrometry (IRMS) within minutes. This permits accurate measurements of elemental abundances and isotopic ratios with high throughput and lower cost. We validated this method with six shale standards from the US Geological Survey (USGS) and compared our abundance data with those from another laboratory. Our results show that (a) abundance data agree well between the different laboratories and setups; (b) reproducible isotopic data can be obtained before and after the switch-over from EA standalone mode; and (c) the USGS rock standards cover a wide range in CHNS abundances and CNS isotopes, making them ideal reference materials for future geochemical studies. This ideal analytical setup has the advantage that abundance measurements can be performed to determine optimal sample amounts for later isotopic analyses, ensuring higher data quality. Our setup eliminates the need for a separate EA while freeing up the mass spectrometer for other tasks during abundance measurements.