Recognizing heterogeneous distribution of platinum group elements (PGE) in geological materials by means of the Re–Os isotope system

Abstract

The identification of uncertainties caused by sample inhomogeneity, as distinct from those caused by sample preparation and measurement, is a challenging task. Use of chemometric methods to separate and estimate these contributions to the combined standard uncertainty of a measurement (uc) of an analytical result requires complex experiments. The difficulty of platinum group element measurement makes this task even more complex. But unless it can be demonstrated that sample inhomogeneity is the major contributor to the high variability of an analytical result one should be careful not to mistakenly attribute this to a nugget effect. In this contribution we are able to demonstrate in two special cases that irreproducible results (up to 90% RSD) for analysis of Os and Re in the pg g(-1) to ng g(-1) range are truly caused by a nugget effect and not by inadequacies of the analytical method.

A database of chondrite analyses including platinum group elements, Ni, Co, Au, and Cr: Implications for the identification of chondritic projectiles

“…Despite the fact that the data compilation reflects the recent advances in analytical techniques, sample inhomogeneity remains a major challenge in the analysis of highly siderophile elements in geological materials (e.g., Morgan et al 1985;Meisel et al 2001;Walker et al 2002;Horan et al 2003). Different aliquots of the same chondrite may not contain the same abundance of components rich in highly siderophile elements, such as metals/sulfides and/or refractory inclusions.…”

“…A minimum amount of meteorite required to obtain reproducible results appears to be in the order of a few grams, as can be seen by comparing meteorite data of different authors (e.g., Jochum 1996;Friedrich et al 2003;Horan et al 2003). Homogeneous sampling also strongly depends on the meteorite type (see later discussion for CB chondrites, section The CR Clan (CR, CH, CB), Rumuruti (R), and Kakangari (K) Chondrites) and uncertainties introduced during sample preparation and/or by the actual acquisition should be taken into account as well (e.g., Meisel et al 2001).…”

State-of-the-art and progress in precise and accurate isotope ratio measurements by ICP-MS and LA-ICP-MS : Plenary Lecture

“…Furthermore the mass discrimination effect in TIMS is mass dependent. 4,7 A main advantage of ICP-MS is the Tl for 204,[206][207][208] Pb, 69 Ga, 71 Ga for 70,72,73,74,76 Ge Mass discrimination TIME DEPENDENT TIME INDEPENDENT time-independent mass discrimination effect. In general, the mass discrimination is considered in mass spectrometry by looking at the mass bias correction so that the mass discrimination factor -this is the ratio of the true and measured isotope ratio (R true /R measured ) -can be determined, for example, by using an isotope reference material with a certified isotope ratio.…”

Disequilibrium-induced initial Os isotopic heterogeneity in gram aliquots of single basaltic rock powders: Implications for dating and source tracing

“…Several recent studies have conducted replicate Re-Os isotope analyses of individual powders (~200 mesh in size) of mafic-ultramafic rocks (Meisel et al, 2001;Ishikawa et al, 2014;Li et al, 2014). In these studies, replicate analyses of each sample defined a good apparent isochron; the derived apparent isochron ages and initial Os isotopic compositions were used to constrain the timing of geological events and to trace the characteristics of mantle sources (Meisel et al, 2001;Ishikawa et al, 2014;Li et al, 2014).…”

“…In these studies, replicate analyses of each sample defined a good apparent isochron; the derived apparent isochron ages and initial Os isotopic compositions were used to constrain the timing of geological events and to trace the characteristics of mantle sources (Meisel et al, 2001;Ishikawa et al, 2014;Li et al, 2014). In light of the nugget effect for both Re and Os concentrations, it is possible that the Os isotopic compositions of individual hand-specimen samples were not totally homogenized when the rocks formed.…”