Overview
ISO 8542:1986 - "Manganese and chromium ores - Experimental methods for evaluation of quality variation and methods for checking the precision of sampling" - specifies experimental and statistical procedures to evaluate heterogeneity (quality variation) of manganese and chromium ores and to check sampling precision. It covers both natural and processed ores and supports definition and validation of sampling procedures using the mass-basis systematic method and the two‑stage method.
Key topics and requirements
- Quality characteristic: primary indicators are manganese content (% Mn) for manganese ores and chromium oxide content (% Cr2O3) for chromium ores; other characteristics (moisture, particle size) may be considered.
- Experimental design:
- Recommended consignment size: ≥ 3 000 t and ≥ 50 increments per gross sample.
- Systematic sampling: divide a consignment (or part) into 5 equal-mass parts, take 10 increments per part; form odd/even subsamples (A and B) and prepare single or paired final samples.
- Two-stage sampling: select 10 wagons at equal mass intervals (random start), take 4 increments per selected wagon (total 40 increments); prepare paired subsamples (C1, C2, D1, D2).
- Experiments are run on a consignment basis and repeated five times; frequency recommended (e.g., biennially).
- Data handling & testing:
- Sample preparation and chemical analysis follow relevant ISO sampling and testing standards.
- Chemical determinations should be randomized (duplicate determinations in some procedures).
- Data recorded on standard sheets (examples provided).
- Statistical evaluation:
- Quality variation quantified by standard deviation (within strata, within wagons, between wagons).
- Procedures for estimating precision of division, measurement and overall sampling precision (variance-based).
- Guidance on handling negative variance estimates and classification of ore variation into categories (“small”, “medium”, “large”).
Practical applications and users
- Useful for mining companies, sampling engineers, QA/QC laboratories, port and terminal operators, assay and analytical labs, commodity traders and quality auditors involved in manganese or chromium ore trade.
- Applies to designing sampling plans, validating sampling precision, auditing vendor consignment quality, and ensuring traceability and statistical confidence in assay results.
Related standards
- ISO 4296-1 - Manganese ores - Sampling - Part 1: Increment sampling
- ISO 4296-2 - Manganese ores - Sampling - Part 2: Preparation of samples
Keywords: ISO 8542:1986, manganese ores, chromium ores, sampling precision, quality variation, mass-basis systematic method, two-stage sampling, standard deviation, consignment sampling.