Overview
ISO 3084:1998 - Iron ores: Experimental methods for evaluation of quality variation specifies laboratory and field experimental procedures to quantify the heterogeneity (quality variation) of iron ores for each ore type and handling plant. It defines two main approaches - interleaved sampling and variographic (variogram) analysis - and gives standardized calculation methods to estimate the within‑strata standard deviation and sampling variance used for quality control and trade.
Key topics and technical requirements
- Two experimental approaches
- Interleaved sampling: consecutive primary increments are alternately combined into paired samples (A and B). This method requires less effort and provides straightforward estimates of variation.
- Variogram method: individual increments (typically 20–40) are measured in duplicate and analyzed by variographic techniques. Variograms give a better estimate of spatial/temporal quality variation and sampling variance and are used to fine‑tune sampling operations.
- Definitions and general conditions: quality variation is expressed as the standard deviation within strata; quality characteristics include Fe, SiO2, Al2O3, moisture, size distribution, etc.
- Investigation types and sampling schemes: procedures are given for different delivery/lot situations (frequent small lots, infrequent large lots, wagon‑borne lots, etc.) and for stratified, systematic and random sampling.
- Data collection and calculation: includes computation of ranges and paired means for interleaved samples, correction for sample preparation and measurement variances, and formulas to derive the estimated standard deviation within strata.
- Variogram processing: how to compute an experimental variogram, correct it by subtracting sample preparation/measurement variance (half the sum), and approximate the variogram by a linear fit to obtain components used to calculate sampling variance.
- Minimum investigation counts: e.g., at least five investigations for type 2/3 and at least ten for type 1/4 to obtain reliable estimates.
- Annex with worked examples: illustrative calculations of standard deviation.
Applications and who uses ISO 3084:1998
- Mining and beneficiation engineers assessing ore heterogeneity and selecting appropriate sampling plans.
- Quality control laboratories verifying sampling precision and separating sampling variance from analytical variance.
- Port/handling plant managers optimizing sampling frequency and protocol for traded iron ore lots.
- Metallurgists, traders and auditors who need standardized, reproducible estimates of sampling variance for contract compliance and dispute resolution.
- Standards developers and statisticians applying variographic methods to bulk material sampling.
Related standards
- ISO 3082 - Iron ores: Sampling and sample preparation procedures (normative reference for sampling).
- ISO 3085 - Experimental methods for checking the precision of sampling.
- ISO 11323 - Iron ores vocabulary.
Keywords: ISO 3084:1998, iron ores, quality variation, interleaved sampling, variogram, sampling variance, sampling standard, ore heterogeneity, ISO 3082.
