Overview
ISO 6139:1993 - "Aluminium ores - Experimental determination of the heterogeneity of distribution of a lot" specifies experimental procedures to quantify how aluminium ore is spatially distributed within a lot. The standard defines the distribution variance (heterogeneity of distribution) and prescribes how to separate it from composition variance by measuring sampling variance at two increment masses. It supports sound design of sampling schemes and determination of the minimum number and mass of primary increments.
Key topics and requirements
- Objective: Evaluate heterogeneity of distribution to determine the minimum number of primary increments and an effective sampling scheme.
- Data collection:
- Determine the minimum increment mass per ISO 8685.
- Collect a minimum of 30 increments (preferably at the intended sampling interval).
- Analyze each increment separately.
- Repeat with a substantially larger increment mass (e.g., increase by a factor of 10).
- Variance components: The measured sampling variance includes both composition variance and distribution variance. The standard requires subtracting sample preparation and analysis variance (per ISO 10277) from measured variances.
- Permitted analysis methods:
- Visman’s theory of sampling (classical statistics): Produces conservative estimates of sampling and distribution variances.
- Variogram method: Accounts for serial correlation between adjacent increments and their spacing, giving a more realistic estimate and better basis for optimizing sampling schemes.
- Calculations: From two increment-mass datasets, derive composition variance and distribution variance; then compute sampling variance for any increment mass and estimate the number of increments needed to achieve a target sampling error.
- Practical recommendations: Compute corrected experimental variograms for lags (recommended t = 1 to 20), estimate intercept and slope, and use these to compute sampling variance for systematic sampling.
Applications and users
ISO 6139 is practical for:
- Mining companies and sampling engineers designing ore-sampling programs for production and reserve estimation.
- Quality assurance and control teams specifying sampling frequencies and increment masses.
- Metallurgists, mineral statisticians, and consultants optimizing sampling strategy to meet required sampling error limits.
- Laboratories and auditors validating sampling precision and variance partitioning.
Key outputs include distribution variance, recommended number of increments, and a validated sampling scheme minimizing sampling error for aluminium ores.
Related standards
- ISO 8685:1992 - Aluminium ores - Sampling procedures.
- ISO 10277 - Aluminium ores - Sample preparation and analysis; methods for checking precision of sampling.
Keywords: ISO 6139:1993, aluminium ores, heterogeneity of distribution, distribution variance, sampling variance, Visman’s theory, variogram method, sampling scheme, increment mass.
