Determination of rhenium and osmium concentrations in molybdenite using laser ablation double focusing sector field ICP-MS Dmitry Malinovsky a, * , Ilia Rodushkin b , Mikael D. Axelsson a,1 , Douglas C. Baxter c a Division of Applied Geology, Lulea˚ University of Technology, S-971 87 Lulea˚, Sweden b SGAB Analytica, Lulea˚ University of Technology, S-971 87 Lulea˚, Sweden c Division of Inorganic Chemistry, Lulea˚ University of Technology, S-971 87 Lulea˚, Sweden Received 19 August 2002; accepted 22 August 2003 Abstract A technique for the in situ determination of Re and Os in molybdenite samples using direct solid sampling by laser ablation- inductively coupled plasma-mass spectrometry (LA-ICP-MS) is described. The sample preparation is limited to molybdenite separation followed by grinding and pressing to pellets. For Re determination, the best results were obtained using external calibration in conjunction with internal standardization. Isotopes of both molybdenum and sulphur could be used as internal standards. This quantification approach provides precision levels generally better than 10% the relative standard deviation (RSD) with similar levels of accuracy. Os concentrations were derived from Re concentrations and measured isotopic ratios of intensities measured at masses 187 and 185, using W isotopes for on-line mass bias correction. As a rule, LA-ICP-MS results for Os agree with corresponding isotope dilution ICP-MS data to within 30%. Reproducibility is strongly dependent on the age of the molybdenite as well as on the precision of isotope ratio measurements, which in turn depend on Re and W concentrations. The proposed technique provides a rapid estimation of Re and Os concentrations for subsequent precise analysis by isotope dilution ICP-MS. D 2003 Elsevier B.V. All rights reserved. Keywords: Molybdenite; Rhenium; Osmium; Laser ablation ICP-MS 1. Introduction The 187 Re– 187 Os geochronometer, applied to molybdenite, has been demonstrated to be remark- ably robust, surviving intense rock deformation and high-grade thermal metamorphism. In contrast to 87 Rb– 87 Sr, 40 K– 40 Ar and 40 Ar– 39 Ar chronometers, the Re–Os system in molybdenite is not susceptible to chemical disturbances and loss or incorporation of Re or Os isotopes is exceedingly rare during episodes of hydrothermal/magmatic activity (Stein et al., 2001). Recent advances in instrumentation enable accurate and precise age determinations on molybde- nite using either negative thermal ionization mass spectrometry (TIMS) or inductively coupled plasma 0375-6742/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.gexplo.2003.08.003 * Corresponding author. E-mail address: dima@sb.luth.se (D. Malinovsky). 1 Present address: Varian Analytical Instruments, S-17122 Solna, Sweden. www.elsevier.com/locate/jgeoexp Journal of Geochemical Exploration 81 (2004) 71 – 79