An international proficiency testing programme devoted to U-Pb dating
Proficiency testing (PT) is a cornerstone of good laboratory practice, providing a valuable route to demonstrating laboratory competence and data excellence. In support of improved data quality in the field of geochronology, the International Association of Geoanalysts (IAG) has developed a new PT scheme that allows laboratories active in the field of U-Pb age determinations to directly evaluate their data quality and to document their competence in this field of metrology.
How the G-Chron programme works
All analytical facilities wishing to participate in the G-Chron programme will be able to register their interest online. Each participating laboratory will be sent a single unit of circa 100 mg of zircon. Participants will have three months in which to determine the age of the material and to report their results. The age of this material has been determined using ID-TIMS determinations by multiple, well established geochemical facilities, and these results will be used to define the target age for the corresponding PT round. Each laboratory submitting data by the deadline will receive a report on the material’s characterisation plus a performance assessment of the submitted data based on z-scores. The target uncertainties will be based on the uncertainties reported by each class of instrument (quadrupole, sector ICP-MS, SIMS, TIMS). The origin of each data set will remain confidential through the use of randomly assigned laboratory code numbers, which will change in each round.
Reasons for participating in the G-Chron programme
There are two major advantages for participating in the G-Chron programme. Firstly, G-Chron provides a unique means for geochronology laboratories to test their data quality, potentially revealing unsuspected bias in their results. Secondly, participants will gain early access to a new generation of the highest quality zircon reference material that can serve as quality control material well into the future. Excess material from a given round will subsequently be made available for global distribution. In view of the large effort invested in characterising the materials used in the G-Chron programme, this new suite of reference materials will be an important resource for the coming decades. Reports for the first three rounds of G-Chron are available here.
Information for G-Chron Round 4:
- Circa 20 mg splits of the mid-Archean Barb-21 zircon material were distributed to participants in November 2025
- A unit of ROM-16401 zircon was also provided to participants as an additional benefit
- The data submission deadline for the Barb-21 zircon is Wednesday, 4 March 2026
- Report will be sent to the participants in June 2026
Information for G-Chron Round 5:
- Several materials are currently under development
- Distribution intended for late 2026
- Subscription fee: £300 (£200 for IAG members)
- Registration for Round #5 via http://www.gchron.info/