GEOPT1 - INTERNATIONAL PROFICIENCY TEST FOR ANALYTICAL GEOCHEMISTRY LABORATORIES - REPORT ON ROUND-1 (JULY 1996)

The results of the first international proficiency test (GeoPT1) of ge ochemical laboratories are presented. A total of 49 laboratories contr ibuted analytical data on G94, a sample of Threlkeld microgranite whic h had been collected at the International Conference, Geoanalysis 94. Assigned values were derived by robust statistical analysis of contrib uted data for 12 major elements and 39 trace elements, of which 3 (As, Pb and Th) were provisional values. Z-scores were calculated, as requ ired by the protocol using either 'pure geochemistry' or 'applied geoc hemistry' fitness for purpose criteria selected by contributing labora tories. An overview of the z-score results indicates that 28.7 % of co ntributed data fell outside the -2<z<2 range indicating that unsuspect ed analytical discrepancies may be affecting the corresponding results .