TY - JOUR
T1 - Trace element analysis of scheelite by excimer laser ablation-inductively coupled plasma-mass spectrometry (ELA-ICP-MS) using a synthetic silicate glass standard
AU - Sylvester, Paul J.
AU - Ghaderi, Majid
N1 - Funding Information:
Development of the ANU ELA-ICP-MS system has been a team effort with major contributions from S. Eggins, L. Kinsley, R. Loucks, M. Shelley and N. Ware. In particular, S. Eggins suggested to us that the ‘intercept’ method of reducing ELA-ICP-MS cps-ratio data might be superior to the ‘mean’ method. The geologists and mine staff at St. Ives Gold Mines, Western Mining Corporation Ltd., particularly R. Watchom, T. Sugden and K. Hein, are thanked for their assistance with the fieldwork. V. Bennett, L. Kinsley, C. Martin, G. Mortimer and N. Ware helped with the analyses. F. Brink and R. Heady assisted with the SEM imaging. M.G. was supported by a PhD scholarship from the Ministry of Culture and Higher Education of Iran. G. Gautbier and S. Jackson provided helpful reviews.
PY - 1997/8/29
Y1 - 1997/8/29
N2 - 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.
AB - 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.
KW - Gold
KW - Isotopes
KW - Laser methods
KW - Scheelite
KW - Standard materials
KW - Trace elements
UR - http://www.scopus.com/inward/record.url?scp=0031423393&partnerID=8YFLogxK
U2 - 10.1016/S0009-2541(97)00057-0
DO - 10.1016/S0009-2541(97)00057-0
M3 - Article
AN - SCOPUS:0031423393
SN - 0009-2541
VL - 141
SP - 49
EP - 65
JO - Chemical Geology
JF - Chemical Geology
IS - 1-2
ER -