In order to monitor the accuracy of the laboratories, several gold CRMs, covering a
range of gold grades, were purchased from CDN Resource Laboratories in Canada
and Rocklabs in New Zealand. The program design does not encompass silver, but
three of the standards have low certified silver values. CRMs were inserted into the
regular sample stream at a ratio of 1:20, according to a predetermined schedule based
on the geological sample number. The CRMs until 2008 were not blind to the
laboratory. Garagan (2006) commented that the large number of different samples,
some with very similar gold grade, help prevent the laboratory from guessing at values.
From 2008, submission of CRMs has been blind to the laboratory. Control charts
plotted monthly show the performance of individual standards. The data entry
personnel note all failures and corrective actions taken in the database. The data show
few failures and no indication of significant precision or bias problems.