Lead Isotope Analysis – Graham Carr – CSIRO

Lead Isotope analysis is a powerful tool in discriminating the source of Pb, and by analogy other metals, in geological samples and relating any metal concentration to known metallogenic events. The use of Pb isotopes in mineral exploration was established for high-Pb geological samples (principally drill core and surface gossans) in the mid 1980’s and since then a series of AMIRA projects have shown that the technique can be used for lower-Pb geochemical media – groundwater, soil and vegetation.
Over this period analysis had been undertaken initially using conventional Thermal Ionisation Mass Spectrometry (TIMS), then a double spike TIMS technique and most recently Multi-Collector ICPMS (MC-ICPMS). These techniques have provided increasing analytical precision but have remained expensive – between $300 and $500/analysis. This cost factor has ensured that Pb isotopes have only maintained a small, but important role in some company mineral exploration programs. Therefore the promise that Pb isotopes have shown for use in large greenfields explorations programs has remained untested.
Recent work in CSIRO has indicated that it should be possible to develop sampling, analytical, data presentation and interpretation protocols for Pb isotopes based on mainstream commercial laboratory capabilities (Quadrupole ICPMS) and provide enough precision to make geologically meaningful conclusions. The aim will be to get the cost of analysis down to