Bias in the Determination of Zr,Y and Rare Earth Element Concentrations in Selected Silicate Rocks by ICP‐MS when Using Some Routine Acid Dissolution Procedures: Evidence from the GeoPT Proficiency Testing Programme

The analytical results for the modified river sediment, SdAR‐1 circulated in Round 31 of the GeoPT proficiency testing programme, revealed unexpected discrepancies for Zr, Y and most higher atomic number rare earth elements, in determinations made by ICP‐MS using acid attack digestion methods. This investigation compares these ICP‐MS results with those obtained for SdAR‐1 by three other methods: (a) ICP‐MS using fusion/sintering for sample digestion, (b) XRF analysis and (c) INAA. The distribution of results for the elements Rb, Sr, Ce, Y, Yb and Zr is examined and compared with those of the test material for Round 25 of GeoPT, Paraná basalt, HTB‐1. A substantial proportion (though not all) of Y, Yb and Zr determinations in SdAR‐1 by ICP‐MS/acid attack was variably low (sometimes very low) compared with other methods. A detailed evaluation of the procedures used to determine these results indicated that successful determinations by ICP‐MS/acid attack could be made if digestions were made at 180 °C for 48 hr using at least 2 ml HF per 100 mg of sample. We suggest that the more benign conditions (used by many laboratories) resulted in incomplete digestion of resistant minerals, such as zircon.     

Assessment of Dissolution of Silicate Rock Reference Materials with Ammonium Bifluoride and Nitric Acid in a Microwave Oven

The complete dissolution of representative test portions of powdered rock samples for the determination of the mass fractions of trace elements by ICP‐MS relies either on aggressive and time‐consuming acid digestions or fusion/sintering with appropriate fluxes. Here, we evaluate a microwave oven dissolution method that employs a solution of NH₄HF₂ and HNO₃. The entire procedure occurs in a closed vessel system and takes up to 4 h. In hundreds of digestions, the precipitation of fluorides was never observed. Replicate decomposition of 100 mg of twenty‐one international reference materials (RMs) of igneous rocks, and also one of a shale presented mostly satisfactory recoveries of forty‐one trace elements. Important exceptions were Zr and Hf in G‐2 and GSP‐2 (mean recoveries of ca. 70%), although for four other felsic rock RMs, the digestion was complete. For ultramafic rock RMs, we present Cr results that indicate quantitative dissolution of Cr‐bearing phases. We discuss the findings and conclude that advances in sample preparation of geological materials for instrumental analysis would benefit from a better understanding of how specific characteristics, such as composition and crystallinity of certain minerals, may affect their reactivity.     

Complete Trace Elemental Characterisation of Granitoid (USGS G-2, GSP-2) Reference Materials by High Resolution Inductively Coupled Plasma-Mass Spectrometry

The United States Geological Survey granitic and granodioritic reference materials G‐2 and GSP‐2 were decomposed in high‐pressure bombs using both HF‐HNO₃ and HF‐HNO₃‐HClO₄ in order to evaluate the feasibility of characterising the entire suite of geologically relevant trace elements through direct analysis with a high‐resolution inductively coupled plasma‐mass spectrometer (HR‐ICP‐MS). The digested samples were diluted to the appropriate levels and analysed at low, medium and high resolution depending on the required sensitivity and potential interferences for each element. Memory effects during analysis of the high field strength elements (HFSE) were negligible when analysed using an all‐Teflon, uncooled sample introduction system and combined with adequate wash times with 4% v/v aqua regia + 0.5% v/v HF between samples. The concentration of the remaining lithophile elements was determined with a conventional, cooled, Scott‐type spray chamber using a wash solution of 1% v/v HNO₃. Total procedural blanks contributed between 0.01 to 0.5% to final sample concentrations and blank subtractions were typically unnecessary. Abundances for Li, Hf, Ba, Zr, Ga, Rb, Sr, La, Ce, Th and U were systematically higher, while those for the heavy rare earth elements (HREEs), Cu and Y were systematically lower in this study compared to USGS values for G‐2 and GSP‐2. This is likely to be related to, respectively, higher recoveries from more efficient digestion of refractory phases (i.e., zircon, tourmaline), and better resolution of interferences when using a HR‐ICP‐MS. Sample digestion experiments also showed that perchloric acid digestion in high pressure bombs resulted in superior recoveries and better precision for the bulk of the trace elements analysed. The concentration of the remaining elements overlapped within uncertainty with recommended reference values and with values determined in other studies using isotope‐dilution TIMS, ICP‐MS and XRF. Concentrations for the elements Cd, Sn, Sb, Ta, Bi, Tb, Ni and Mo are also reported for G‐2 and GSP‐2 reference materials. Our study shows therefore that it is feasible to determine thirty‐nine geologically relevant trace elements accurately and directly in granitoid sample digests when using a HR‐ICP‐MS, thereby negating the need for ion exchange or isotopic spiking.     

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%.     

An Investigation of the Reliability of HF Acid Mixtures in the Bomb Digestion of Silicate Rocks for the Determination of Trace Elements by ICP‐MS

The influence of the mixtures HF‐HNO₃ and HF‐NH₄F‐HNO₃ in bomb digestion for trace element determination from different rock types was studied using ICP‐MS. It is shown that the HF concentration, not the ratio of reagents in the decomposing mixture, controls the digestion process of a rock. Data for Zr in the granite G‐2 as a function of HF concentration gave the same results as reaction mixtures of various compositions. A complete digestion in 50‐mg sample bombs was achieved by 1.0 ml of HF alone, or with a mixture of other acids at a HF concentration of at least 35% m/m at 196 °C over 18 h. The results of the analysis of basalts BCR‐1, BIR‐1, mica schist SDC‐1, shale SBC‐1, granites G‐2, SG‐1A, garnet‐biotite plagiogneiss GBPg‐1, rhyolite RGM‐1, granodiorite GSP‐1, trachyandesite MTA‐1 and rhyolite MRh‐1 are given and compared against available data. The reproducibility of the element determinations by ICP‐MS and XRF as an independent non‐destructive analysis for a quality check in the range of concentrations typical for routine rock samples is given.     

Hydrofluoric Acid‐Free Digestion of Geological Samples for the Quantification of Rare Earth Elements by Inductively Coupled Plasma‐Optical Emission Spectrometry

Rare earth elements (REEs) are very important to technological development as well as to geochemical and environmental studies. In this work, hydrofluoric acid (HF) was replaced by condensed phosphoric acid (CPA) in the digestion of geological samples, and the quantification of REEs was performed by inductively coupled plasma‐optical emission spectrometry (ICP‐OES). Six international reference materials (RMs), named DC86318, CGL 111, CGL 124, CGL 126, OKA‐2 and COQ‐1 and three Brazilian ore samples, named Araxá, Catalão and Pitinga were analysed. Only zircon and xenotime, which are potential REE‐bearing minerals, were not completely dissolved. Nevertheless, no REE associated with zircon was detected. The investigated digestion method presented many advantages: It was relatively fast (3 h), avoided fluoride precipitation, it was less hazardous because handling diluted H₃PO₄ is safer than HF, NH₄F or NH₄HF₂ aqueous solutions, it preserved the quartz fittings of the measurement equipment and the final solution contained lower levels of total dissolved solids than those produced by the fusion method.     

Classical and New Procedures of Whole Rock Dissolution for Trace Element Determination by ICP‐MS

Sample digestion is a critical stage in the process of chemical analysis of geological materials by ICP‐MS. We present a new HF/HNO₃ procedure to dissolve silicate rock samples using a high pressure asher system. The formation of insoluble AlF₃ was the major obstacle in achieving full recoveries. This was overcome by setting an appropriate digestion temperature and adding Mg to the samples before digestion. Sodium peroxide sintering was also investigated and the inclusion of a heating step to the alkaline sinter solution improved the recoveries of thirteen elements other than the lanthanides. The results of these procedures were compared with data sets generated by common acid decomposition techniques. Forty‐one trace elements were determined using an ICP‐QMS equipped with a collision cell. Under optimum conditions of gas flow and kinetic energy discrimination, polyatomic interferences were eliminated or attenuated. The measurement bias obtained for eight reference materials (BCR‐2, BHVO‐2, BIR‐1, BRP‐1, OU‐6, GSP‐2, GSR‐1 and RGM‐1) and intermediate precision (RSD) were generally better than ± 5%. The expanded measurement uncertainties estimated for two certified reference materials were mostly between 7 and 15%. New data sets for the reference materials are provided, including constituents with previously unavailable values and also for the USGS candidate reference material G‐3.     

Precise Determination of Sm and Nd Concentrations and Nd Isotopic Compositions in Highly Depleted Ultramafic Reference Materials

In this study, a high‐precision method for the determination of Sm and Nd concentrations and Nd isotopic composition in highly depleted ultramafic rocks without a preconcentration step is presented. The samples were first digested using the conventional HF + HNO₃ + HClO₄ method, followed by the complete digestion of chromite in the samples using HClO₄ at 190–200 °C and then complete dissolution of fluoride formed during the HF decomposition step using H₃BO₃. These steps ensured the complete digestion of the ultramafic rocks. The rare earth elements (REEs) were separated from the sample matrix using conventional cation‐exchange chromatography; subsequently, Sm and Nd were separated using the LN columns. Neodymium isotopes were determined as NdO⁺, whereas Sm isotopes were measured as Sm⁺, both with very high sensitivity using single W filaments with TaF₅ as an ion emitter. Several highly depleted ultramafic rock reference materials including USGS DTS‐1, DTS‐2, DTS‐2b, PCC‐1 and GSJ JP‐1, which contain extremely low amounts of Sm and Nd (down to sub ng g^?1 level), were analysed, and high‐precision Sm and Nd concentration and Nd isotope data were obtained. This is the first report of the Sm‐Nd isotopic compositions of these ultramafic rock reference materials except for PCC‐1.     

Determination of Chromium, Nickel, Copper and Zinc in Milligram Samples of Geological Materials Using Isotope Dilution High Resolution Inductively Coupled Plasma-Mass Spectrometry

A simple and accurate method for the determination of Cr, Ni, Cu and Zn at μg g^?1 levels in milligram‐sized bulk silicate materials is reported using isotope dilution high‐resolution inductively coupled plasma‐mass spectrometry (HR‐ICP‐MS) with a flow injection system. Silicate samples with Cr, Ni, Cu and Zn spikes were digested with HF‐HBr and Br₂, and subsequently decomposed at 518 K in a Teflon bomb. In this procedure, all sulfides and chromite, major hosts of these elements, were completely decomposed, thus allowing for isotope equilibration between the sample and spike. Magnesium and Al fluorides formed after the digestion of the sample were removed by centrifugation, and the supernatant was directly aspirated into a HR‐ICP‐MS at a mass resolution of 7500, where interfering oxide ions, ArO⁺, CaO⁺, TiO⁺, CrO⁺ and VO⁺, were separated from Cr⁺, Ni⁺, Cu⁺ and Zn⁺. No matrix effects were observed down to a dilution factor of 50. Detection limits for these elements in silicate samples were < 0.04 μg g^?1. The effectiveness of the technique was demonstrated by the analysis of 13 to 40 mg test portions of USGS and GSJ silicate reference materials with a major element composition ranging from andesite to peridotite, in addition to 8‐23 mg of the Smithsonian reference Allende. Both the reproducibility and the deviation from the reference value for most reference materials of various rock types were < 9%, and thus confirm that the method gives accurate analytical results for small sample sizes over a wide range of Cr, Ni, Cu and Zn contents. This method is, therefore, suitable for analysing small and/or precious bulk samples, such as meteorites, mantle peridotites and mineral separates, and for the characterisation of silicate and sulfide minerals for use as calibration samples in secondary ion mass spectrometry or laser ablation ICP‐MS.     

A Rapid Acid Digestion Technique for the Simultaneous Determination of Bromine and Iodine in Fifty‐Three Chinese Soils and Sediments by ICP‐MS

Bromine and iodine are important tracers for geochemical and environmental studies. In this study, a rapid acid digestion (HNO₃ + HF) with ammonia dilution for the simultaneous determination of bromine and iodine in soils and sediments using ICP‐MS was developed. The recoveries of Br and I were controlled by the synergic effect of temperature and time. It took only 15 min at 140 °C for the complete recovery of Br and I in sediment (GSD‐2) and soil (GSS‐24) reference materials, which is a process that needs 2–6 h at 90 °C. A serious loss of Br and I was found at a higher digestion temperature of 190 °C. A 5% v/v NH₄OH dilution effectively eliminated the memory effects and stabilised the signals of Br and I. Moreover, ammonia dilution also avoided the corrosiveness of HF on the sample introduction system and torch of ICP‐MS. Tellurium is a more suitable internal standard element than In in the ammonia medium. To avoid the adsorption of residues of dissolution on Te, addition of Te should be carried out after centrifuging the solution. The developed method was successfully applied to determine Br and I in fifty‐three Chinese soil and sediment reference materials. This simple method shows great potential for the rapid determination of Br and I in large batches of geological and environmental samples commonly analysed for mineral exploration and environmental geochemistry studies.     

A Synthetic Haematite Reference Material for LA‐ICP‐MS U‐Pb Geochronology and Application to Iron Oxide‐Cu‐Au Systems

In both nature and synthetic experiments, the common iron oxide haematite (α‐Fe₂O₃) can incorporate significant amounts of U into its crystal structure and retain radiogenic Pb over geological time. Haematite is a ubiquitous component of many ore deposit types and, therefore, represents a valuable hydrothermal mineral geochronometer, allowing direct constraints to be placed on the timing of ore formation and upgrading. However, to date, no suitable natural haematite reference material has been identified. Here, a synthetic haematite U‐Pb reference material (MR‐HFO) is characterised using LA‐ICP‐MS and ID‐TIMS. Centimetre‐scale ‘chips’ of synthesised α‐Fe₂O₃ were randomly microsampled via laser ablation‐extraction and analysed using ID‐TIMS. Reproducible U/Pb and Pb/Pb measurements were obtained across four separate chips (n = 13). Subsequently, an evaluation of the suitability MR‐HFO in constraining U‐Pb data via LA‐ICP‐MS is presented using a selection of natural samples ranging from Cenozoic to Proterozoic in age. The MR‐HFO normalised U‐Pb ratios are more concordant and ages more accurate versus the same LA‐ICP‐MS spot analyses normalised to zircon reference material, when compared with independently acquired ID‐TIMS data from the same natural haematite grains. Results establish MR‐HFO as a suitable reference material for LA‐ICP‐MS haematite U‐Pb geochronology.     

Major and Trace Element Analysis of Silicate Rocks by XRF and Laser Ablation ICP-MS Using Lithium Borate Fused Glasses: Matrix Effects, Instrument Response and Results for International Reference Materials

Major and trace element compositions of fifteen silicate rock reference materials have been determined by a combined XRF and laser ablation ICP‐MS (LA‐ICP‐MS) technique on glasses prepared by fusing the sample with a lithium borate flux (sample:flux = 1:3). Advantages of this technique include the ability to measure major and trace element abundances on a single sample using a quick and simple preparation that attacks resistant phases such as zircon without the need for acid dissolution. The method is suitable for a wide variety of bulk compositions including mafic, intermediate and silicic rocks. Abundance‐normalized mass response patterns (the ratio of signal intensity to element concentration) of the LA‐ICP‐MS analyses vary systematically with major element composition, demonstrating the presence of a matrix effect that cannot be compensated by normalisation to a single internal standard element. Increasing the sampling distance between the ICP‐MS cone and the torch reduces the magnitude of this effect, suggesting that a mechanism related to residence time of ablated particles in the plasma may be at least partially responsible for the observed variations in mass response patterns. When using a matrix‐matched calibration, agreement of the LA‐ICP‐MS results with published reference values or those obtained by solution ICP‐MS is 10% relative. Analytical precision based on replicate analyses is typically 5% RSD. Procedural detection limits that include contributions from gas background and flux are 0.01‐0.1 μg g‐¹ for the heavy mass trace elements (Rb‐U). Major element analyses by XRF show excellent agreement with results obtained using a conventional heavy element absorbing flux. High quality major and trace element data for silicate rocks can be achieved by a combined XRF and LA‐ICP‐MS analysis of Li₂B₄O₇/LiBO₂ fused glasses provided an appropriate matrix‐matched calibration is adopted.     

An Investigation of Digestion Methods for Trace Elements in Bauxite and Their Determination in Ten Bauxite Reference Materials Using Inductively Coupled Plasma‐Mass Spectrometry

Trace elements from samples of bauxite deposits can provide useful information relevant to the exploration of the ore‐forming process. Sample digestion is a fundamental and critical stage in the process of geochemical analysis, which enables the acquisition of accurate trace element data by ICP‐MS. However, the conventional bomb digestion method with HF/HNO₃ results in a significant loss of rare earth elements (REEs) due to the formation of insoluble AlF₃ precipitates during the digestion of bauxite samples. In this study, the digestion capability of the following methods was investigated: (a) ‘Mg‐addition’ bomb digestion, (b) NH₄HF₂ open vessel digestion and (c) NH₄F open vessel digestion. ‘Mg‐addition’ bomb digestion can effectively suppress the formation of AlF₃ and simultaneously ensure the complete decomposition of resistant minerals in bauxite samples. The addition of MgO to the bauxite samples resulted in (Mg + Ca)/Al ratios ≥ 1. However, adding a large amount of MgO leads to significant blank contamination for some transition elements (V, Cr, Ni and Zn). The NH₄HF₂ or NH₄F open vessel digestion methods can also completely digest resistant minerals in bauxite samples in a short period of time (5 hr). Unlike conventional bomb digestion with HF/HNO₃, the white precipitates and the semi‐transparent gels present in the NH₄HF₂ and NH₄F digestion methods could be efficiently dissolved by evaporation with HClO₄. Based on these three optimised digestion methods, thirty‐seven trace elements including REEs in ten bauxite reference materials (RMs) were determined by ICP‐MS. The data obtained showed excellent inter‐method reproducibility (agreement within 5% for REEs). The relative standard deviation (% RSD) for most elements was < 6%. The concentrations of trace elements in the ten bauxite RMs showed agreement with the limited certified (Li, V, Cr, Cu, Zn, Ga, Sr, Zr and Pb) and information values (Co, Ba, Ce and Hf) available. New trace element data for the ten RMs are provided, some of which for the first time.     

Voltammetric Determination of High Field‐Strength Elements (Ti,Zr, Hf,Nb, Ta) in Geological Matrices

A voltammetric method for the determination of the high field‐strength elements Ti, Zr, Hf, Nb and Ta by adsorptive stripping of their tartrate complexes is presented. The applicability of the method to geological and metallurgical samples is illustrated by the analysis of certified reference materials (USGS BCR‐2 basalt, BCS‐CRM 388 zircon and Euronorm CRM 579‐1 ferroniobium). Suitable sample preparation techniques, involving fusion with LiBO₂ and acidic and basic fluxes, followed by preliminary separation by anion chromatography are described. The method is rapid, affordable and environmentally friendly as it does not require problematic compounds such as hydrofluoric acid or toxic solvents and represents an alternative to more commonly used methods (AAS, ICP‐OES, ICP‐MS).     

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.     

U‐Th Zircon Dating by Laser Ablation Single Collector Inductively Coupled Plasma‐Mass Spectrometry (LA‐ICP‐MS)

Zircon crystals in the age range of ca. 10–300 ka can be dated by ²³⁰Th/²³⁸U (U‐Th) disequilibrium methods because of the strong fractionation between Th and U during crystallisation of zircon from melts. Laser ablation inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) analysis of nine commonly used reference zircons (at secular equilibrium) and a synthetic zircon indicates that corrections for abundance sensitivity and dizirconium trioxide molecular ions (Zr₂O₃⁺) are critical for reliable determination of ²³⁰Th abundances in zircon. When corrected for abundance sensitivity and interferences, mean activity ratios of (²³⁰Th)/(²³⁸U) for nine reference zircons analysed on five different days averaged 0.995 ± 0.023 (95% confidence weighted by data‐point uncertainty only, MSWD = 1.6; n = 9), consistent with their U‐Pb ages > 4 Ma that imply equilibrium for all intermediate daughter isotopes (including ²³⁰Th) within the ²³⁸U decay chain. U‐Th zircon ages generated by LA‐ICP‐MS without mitigating (e.g., by high mass resolution) or correcting for abundance sensitivity and molecular interferences on ²³⁰Th are potentially unreliable. To validate the applicability of LA‐ICP‐MS to this dating method, we acquired data from three late Quaternary volcanic units: the 41 ka Campanian Ignimbrite (plutonic clasts), the 161 ka Kos Plateau Tuff (juvenile clasts) and the 12 ka Puy de Dôme trachyte lava (all eruption ages by Ar/Ar, with zircon U‐Th ages being of equal or slightly older). A comparison of the corrected LA‐ICP‐MS results with previously published secondary ion mass spectrometry (SIMS) data for these rocks shows comparable ages with equivalent precision for LA‐ICP‐MS and SIMS, but much shorter analysis durations (~ 2 min vs. ~ 15 min) per spot with LA‐ICP‐MS and much simpler sample preparation. Previously undated zircons from the Yali eruption (Kos‐Nisyros volcanic centre, Greece) were analysed using this method. This yielded a large age spread (~ 45 to > 300 ka), suggesting significant antecryst recycling. The youngest zircon age (~ 45 ± 10 ka) provides a reasonable maximum estimate for the eruption age, in agreement with the previously published age using oxygen isotope stratigraphy (~ 31 ka).     

GHR1 Zircon – A New Eocene Natural Reference Material for Microbeam U‐Pb Geochronology and Hf Isotopic Analysis of Zircon

We present multitechnique U‐Pb geochronology and Hf isotopic data from zircon separated from rapakivi biotite granite within the Eocene Golden Horn batholith in Washington, USA. A weighted mean of twenty‐five Th‐corrected ²⁰⁶Pb/²³⁸U zircon dates produced at two independent laboratories using chemical abrasion‐isotope dilution‐thermal ionisation mass spectrometry (CA‐ID‐TIMS) is 48.106 ± 0.023 Ma (2s analytical including tracer uncertainties, MSWD = 1.53) and is our recommended date for GHR1 zircon. Microbeam ²⁰⁶Pb/²³⁸U dates from laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) and secondary ion mass spectrometry (SIMS) laboratories are reproducible and in agreement with the CA‐ID‐TIMS date to within < 1.5%. Solution multi‐collector ICP‐MS (MC‐ICP‐MS) measurements of Hf isotopes from chemically purified aliquots of GHR1 yield a mean ¹⁷⁶Hf/¹⁷⁷Hf of 0.283050 ± 17 (2s, n = 10), corresponding to a εHf₀ of +9.3. Hafnium isotopic measurements from two LA‐ICP‐MS laboratories are in agreement with the solution MC‐ICP‐MS value. The reproducibility of ²⁰⁶Pb/²³⁸U and ¹⁷⁶Hf/¹⁷⁷Hf ratios from GHR1 zircon across a variety of measurement techniques demonstrates their homogeneity in most grains. Additionally, the effectively limitless reserves of GHR1 material from an accessible exposure suggest that GHR1 can provide a useful reference material for U‐Pb geochronology of Cenozoic zircon and Hf isotopic measurements of zircon with radiogenic ¹⁷⁶Hf/¹⁷⁷Hf.     

An Evaluation of Methods for the Chemical Decomposition of Geological Materials for Trace Element Determination using ICP-MS

Complete dissolution is essential to obtain accurate analytical results using ICP-MS. In this study, decomposition techniques (i.e. acid digestions using Savillex Teflon vials, a high pressure digestion system and microwave oven, a combined lithium tetraborate fusion - HF/HNO3 acid decomposition and sodium peroxide sinter) for the total dissolution of different types of geological reference materials have been investigated. Savillex Teflon vial HF/HNO3 digestion is effective for basaltic samples. The high pressure HF/HClO4 digestion (PicoTrace TC-805 digestion system, Bovenden, Germany) allows dissolution of basalts and ironstones. Granites and magnetite-rich samples can be dissolved using a high pressure HF/H₂SO₄ method. Geological samples cannot be effectively attacked by microwave acid digestion. A combined lithium tetraborate fusion - HF/HNO3 acid digestion method allows complete dissolution of many different types of geological materials; however, this method precludes the determination of volatile elements due to the high fusion temperature (1000 °C). A sodium peroxide sinter method at 480 °C has the potential for the rapid determination of Y, Sc and REE in different types of geological materials. However, the lack of ultra-pure reagents precludes the use of lithium tetraborate fusion and sodium peroxide sinter methods for the measurement of geological samples with low trace element abundances.     

Rhenium–Osmium Isotope Measurements in Marine Shale Reference Material SBC‐1: Implications for Method Validation and Quality Control

In this study, the USGS black shale reference material SBC‐1 was investigated as a matrix‐matched reference material for both intra‐laboratory calibration and inter‐laboratory comparison of high‐precision Re‐Os dating for organic‐rich sedimentary rocks. This reference material was analysed for Re‐Os isotopic composition by three digestion protocols – inverse aqua regia, CrO₃‐H₂SO₄ and H₂O₂‐HNO₃. The results for SBC‐1 obtained by inverse aqua regia digestion yielded similar Re mass fractions but slightly (~ 5%) higher Os mass fractions and lower ¹⁸⁷Os/¹⁸⁸Os values than the CrO₃‐H₂SO₄ and H₂O₂‐HNO₃ digestions. The data set of inverse aqua regia digestion exhibited strong correlations in plots of ¹⁸⁷Os/¹⁸⁸Os vs. 1/¹⁹²Os and ¹⁸⁷Os/¹⁸⁸Os vs. ¹⁸⁷Re/¹⁸⁸Os, which may signify the incorporation of detrital Re and Os into organic matter in the Re‐Os system. Similar correlations were also observed for the CrO₃‐H₂SO₄ digestion data set, but not for that of H₂O₂‐HNO₃. The data indicate that there is an amount of non‐hydrogenous Os in SBC‐1 and that CrO₃‐H₂SO₄ and H₂O₂‐HNO₃ digestions would minimise liberation of the non‐hydrogenous Os component. We propose that SBC‐1 may be a more suitable reference material to monitor the influence of detrital Re and Os on Re‐Os isochron age data, especially for samples with less organic matter and more siliceous detritus.     

Precise Determination of Silicon Isotopes in Silicate Rock Reference Materials by MC‐ICP‐MS

A HF‐free sample preparation method was used to purify silicon in twelve geological RMs. Silicon isotope compositions were determined using a Neptune instrument multi‐collector‐ICP‐MS in high‐resolution mode, which allowed separation of the silicon isotope plateaus from their interferences. A 1 μg g^‐1 Mg spike was added to each sample and standard solution for online mass bias drift correction. δ³⁰Si and δ²⁹Si values are expressed in per mil (‰), relative to the NIST SRM 8546 (NBS‐28) international isotopic RM. The total variation of δ³⁰Si in the geological reference samples analysed in this study ranged from ‐0.13‰ to ‐0.29‰. Comparison with δ²⁹Si values shows that these isotopic fractionations were mass dependent. IRMM‐17 yielded a δ³⁰Si value of ‐1.41 ± 0.07‰ (2s, n = 12) in agreement with previous data. The long‐term reproducibility for natural samples obtained on BHVO‐2 yielded δ³⁰Si = ‐0.27 ± 0.08‰ (2s, n = 42) on a 12 month time scale. An in‐house Si reference sample was produced to check for the long‐term reproducibility of a mono‐elemental sample solution; this yielded a comparable uncertainty of ± 0.07‰ (2s, n = 24) over 5 months.