Trace element analysis of scheelite by excimer laser ablation-inductively coupled plasma-mass spectrometry (ELA-ICP-MS) using a synthetic silicate glass standard

Paul J. Sylvester, Majid Ghaderi

Research output: Contribution to journalArticle

141 Scopus citations

Abstract

Concentrations of W and trace elements in scheelites (CaWO4) associated with Archean lode-gold deposits in Western Australia were determined by ArF (193 nm) excimer laser ablation-ICP-MS with external calibration against a silicate glass standard reference material, NIST 610. The excimer laser beam drilled well-defined pits in both scheelite and silicate glass. With internal standardization against Ca alone, W measurements for the scheelites fall within 5% of the concentrations expected from electron microprobe measurements. A matrix effect between scheelite and silicate glass is apparent in the behaviour of W during laser ablation: W is progressively fractionated from Ca in the glass but not in the scheelite. Proper data reduction, therefore, requires use of the early maximum count rates for W and Ca rather than the mean count rates during ablation. W isotopic ratios measured in the scheelites and an in-house generated silicate glass, ANU 252, are both within ∼2.5% of the accepted values for the natural ratios and are reproducible to ∼1%, if data for the first ∼11 s of ablation are excluded. Using the same data reduction techniques employed for W, concentrations of Sr, Y, Mo, REE and Pb, present at ppm levels in the scheelites, were measured with a precision of 4% or less. Measurements on Th and U, present at the 5-10 ppb level, and P, Mn, Nb and Ta are less precise (∼5-40%) and concentrations of Rb, Zr, Ba, Sn, Hf, Tl and Bi are, for the most part, below detection limits. For Sr, Sm and Nd, replicate ELA-ICP-MS measurements made on 80-μm wide spots in scheelite largely encompass the concentrations determined by ID-TIMS on bulk samples. REE patterns determined by ELA-ICP-MS for the scheelites vary smoothly as a function of atomic number. Most of the patterns are hump-shaped but others are rather flat except for positive Eu anomalies. This suggests that the hydrothermal fluids that formed the scheelites did not have a common composition and source.

Original languageEnglish
Pages (from-to)49-65
Number of pages17
JournalChemical Geology
Volume141
Issue number1-2
DOIs
StatePublished - Aug 29 1997

Keywords

  • Gold
  • Isotopes
  • Laser methods
  • Scheelite
  • Standard materials
  • Trace elements

Fingerprint Dive into the research topics of 'Trace element analysis of scheelite by excimer laser ablation-inductively coupled plasma-mass spectrometry (ELA-ICP-MS) using a synthetic silicate glass standard'. Together they form a unique fingerprint.

  • Cite this