U-Pb baddeleyite geochronology by laser ablation multi-collector ICPMS using multi-ion counting

Baddeleyite is a common U-bearing accessory mineral found in many mafic rocks including those associated with many ore deposits. An in-situ U-Pb LA-MC-ICPMS method to date baddeleyite is presented. The method allows for the simultaneous measurement of Hg-202, Pb-204, Pb-206, Pb-207, Pb-208, U-235, U-238, isotopes in Channeltron ion counters. Standard-sample-standard bracketing using FC-4b baddeleyite as the external standard is used to correct for instrumental mass bias. A slow line scan ablation is used with a 4-mu m laser beam to minimize laser induced U/Pb fractionation. The small volume of material consumed by the 4-mu m line scan is ideally suited for the small, elongate nature of typical baddeleyite crystals. Results are presented for three baddeleyite samples of known age. External precisions for Pb-207/Pb-206 dates range from <0.6% for baddeleyites older than 1000 Ma to similar to 5% for baddeleyites younger than 1000 Ma. The described method can be used to date mafic rocks where high-precision data are not required or as a compliment to TIMS analyses when high-precision data are necessary.