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Analytical bias

Analytical (assay) bias results from differences in methods, techniques, equipment and calibrations and is an issue in all branches of analytical science (chemical, biological etc).

In exploration and mining, where major decisions are based on assay results, low or high bias analytical results may cause inaccurate and materially unacceptable numbers.

It is a property that can only be measured by inter-laboratory testing and can be detected with a well designed assay quality assurance program using control samples, data quality objectives and control rules. These programs measure assay results for accuracy and precision and assure the required analytical quality at a minimum cost.

What is an acceptable bias? This depends on the absolute affect of the error on the operation, and we can use the financial definition of materiality as a guide. Anything over 5% (+-2.5%) needs to be reported.

Therefore process control and ROM sample bias of <2.5% is probably not material. This should be tighter for concentrate and bullion samples; and could be wider for low grade or tailings samples.