Thallium Mass Fraction and Stable Isotope Ratios of Sixteen Geological Reference Materials

Abstract

Thallium stable isotope ratio and mass fraction measurements were performed on sixteen geological reference materials spanning three orders of magnitude in thallium mass fraction, including both whole rock and partially separated mineral powders. For stable isotope ratio measurements, a minimum of three independent digestions of each reference material was obtained. High‐precision trace element measurements (including Tl) were also performed for the majority of these RMs. The range of Tl mass fractions represented is 10 ng g−1 to 16 μg g−1, and Tl stable isotope ratios (reported for historical reasons as ε205Tl relative to NIST SRM 997) span the range −4 to +2. With the exception – attributed to between‐bottle heterogeneity – of G‐2, the majority of data are in good agreement with published or certified values, where available. The precision of mean of independent measurement results between independent dissolutions suggests that, for the majority of materials analysed, a minimum digested mass of 100 mg is recommended to mitigate the impact of small‐scale powder heterogeneity. Of the sixteen materials analysed, we therefore recommend for use as Tl reference materials the USGS materials BCR‐2, COQ‐1, GSP‐2 and STM‐1; CRPG materials AL‐I, AN‐G, FK‐N, ISH‐G, MDO‐G, Mica‐Fe, Mica‐Mg and UB‐N; NIST SRM 607 and OREAS14P.

Geostandards and Geoanalytical Research Bibliographic Review 2018

“…Brett et al . () publish precise thallium isotopic compositions for sixteen geological RMs from different providers such as the USGS, CRPG, NIST and others. High‐precision cadmium isotope ratios for a series of standard solutions and geological RMs from various providers such as BAM, IGGE and others are reported by Li et al ().…”

Assessing Thallium Elemental Systematics and Isotope Ratio Variations in Porphyry Ore Systems: A Case Study of the Bingham Canyon District

“…Both the mantle and continental crust display restricted isotope compositions of ε 205 Tl = −2.0 ± 1.0 [31,41], although some natural variability is implied by the fact that this range is slightly larger than the long-term, external 2 s.d. (standard deviation) analytical reproducibility, which is conservatively estimated to be ±0.5 epsilon units [31,42]. Magmatic processes do not appear to cause significant Tl isotope fractionations [33], allowing Tl isotopes to be applied, for example, as useful tracers of different sediment types in variably evolved arc lavas [43][44][45][46].…”

“…The grey box represents the nominal mantle value of ε 205 Tl (−2 ± 1 [31,41]); long-term external 2 s.d. reproducibility of several reference materials of ±0.5 [31,42] shown as error bars for reference.…”

“…The Aldrich solution standard has been run by multiple laboratories over the last decade (ε 205 Tl = −0.8 ± 0.3, 2 s.d. ; [31,42]) and provided additional quality control. Machine performance was considered acceptable when the variation between bracketing NIST SRM997 Tl solutions was <4 × 10 −5 and the Aldrich solution returned ε 205 Tl within its documented long-term reproducibility.…”

“…Without further detailed investigation, it is not possible to infer the exact cause, but we suggest that low temperature alteration (200-300 • C) has resulted in Tl isotope fractionation in this sample, with preferential mobilization of 205 Tl out of altered K-feldspar and/or biotite, accompanied by K removal. This isotopic shift may have been exacerbated by pre-existing 203 Tl-enrichment in biotite (Figures 2 and 7; [36,42]).…”