EVOLUTION OF LA-ICPMS TECHNIQUE FOR DATING AND MEASURING TRACE ELEMENTS IN ZIRCON

Among the first North American rock samples dated in the LA-ICPMS lab at Australian National University was a sample from a Yerington Hb-Bt porphyry (JD-99016) supplied by John Dilles in Sept 2001 with his question, “An accurate age of the porphyry would be interesting for comparison with the already dated porphyry—are these cogenetic or are they different ages?”. The already dated porphyry from 2 fractions gave a TIMS age of 168.5+/-0.4 Ma (Dilles and Wright, 1988, GSA Bull.). In Feb 2002 I reported an age of 166.9+/-0.9 Ma with MSWD of 1.94. This sparked discussion of the handling of uncertainty and propagating uncertainties in the reference material as a part of our reporting. As a retrospective, starting with this experience and giving an updated result, I will examine general and specific aspects of the LA-ICPMS technique, how it has evolved with help from many colleagues, what its real limitations are, and how the explosion of LA-ICPMS zircon ages and their trace element characteristics inform tectonic questions, and the drive for resource companies to find more Au and Cu. Today at QUT we generate tens of thousands of analyses a year mostly on detrital zircon using a novel and effective split stream system comprising two “basic” single quadruple instruments. What is it all good for? What has the community learned about earth history? Have we progressed toward finding metal deposits using these techniques?