Short answer: in exploration practice one reference material is typically inserted per 20–30 samples, blanks at a similar rate, plus duplicates. In total QC samples make up about 10–15% of a batch. Your project's QA/QC protocol sets the exact numbers.
What QC includes
- Reference materials (CRMs) check accuracy: how close the lab result is to the certified value.
- Blanks check contamination: gold-free material inserted after high-grade samples.
- Duplicates check precision: field, coarse-reject and pulp duplicates.
Which grades to choose
Usually two or three standards: near cut-off grade, near the deposit average and high grade. The matrix should resemble your ore: oxide or sulphide, with or without copper. For a porphyry Cu-Au project, choose materials certified for both gold and copper.
How to evaluate results
A standard's result is compared with the certified value and standard deviation (SD) from the certificate. A common rule: a result outside ±3SD is a failure, and so are two consecutive results outside ±2SD on the same side. Failed batches are sent for re-assay.
How this relates to sample bags
If bag numbers are printed in advance, leave gaps in the numbering for QC samples. We print numbers to your scheme, see sample bags with printed numbers.