In modern mineral resource evaluation, data credibility is paramount. Quality Assurance and Quality Control (QA/QC) programs are not merely regulatory check-boxes for JORC and NI 43-101 technical reports; they are the primary defense against catastrophic grade miscalculations.
The Holy Trinity of Geochemical QA/QC
A rigorous exploration QA/QC program relies on three foundational control samples inserted blindly into the analytical sample stream:
- Certified Reference Materials (CRMs): Matrix-matched standards containing known, certified element concentrations. CRMs assess analytical accuracy and instrument bias.
- Coarse & Pulp Blanks: Material containing undetectable analyte concentrations. Coarse blanks test for sample preparation cross-contamination in jaw crushers, while pulp blanks verify clean dissolution and cupellation in the analytical line.
- Field, Coarse Crush & Pulp Duplicates: Replicate samples taken at different stages of the comminution circuit. Duplicates evaluate sampling precision, geological heterogeneity, and fundamental sub-sampling error.
Statistical Rules of Thumb
Standard industry practice mandates a minimum 15% to 20% quality control sample insertion rate (1 CRM, 1 Blank, and 1 Duplicate per 20 routine samples). Any CRM assay deviating by more than 3 standard deviations (±3σ) triggers immediate batch rejection and re-assay from the original master pulp.