Laboratory Quality Assurance and Control Sample Clauses

Laboratory Quality Assurance and Control. Internal QA/QC samples were provided to Atna Resources Inc. by the assay lab. Internal lab protocol consisted of running 1 in 20 to 1 in 40 samples (depending on job size) as internal duplicates to check assay adequacy. Results were posted on the final certificate under the heading “QA/QC Au ppb”. The duplicate sample was taken from the coarse reject with the preparation of an entirely new pulp, and run as blind samples within the job. Evaluation of the results looked at the number of samples falling outside an accepted 10% range. If less than 90% of the samples are within the 10% range, then affected assays falling outside the 10% range should be re-run. Evaluation of the laboratory duplicates compared the original assay to the blind duplicate. A total of 460 duplicates were inserted by the lab throughout the program. To make meaningful comparisons, though, only those samples greater than 30 times detection (above 150 ppb) were used, as variances at lower levels are extreme and meaningless. Given these parameters, only 177 samples were used to evaluate lab internal QA/QC. Of the 177 samples, 10 (5.6%) fell outside the accepted 10% of the original assay (94% of the samples were within the allowable 10% error range). Figure 12-8 represents an x-y scatter plot with red lines representing a 10 percent error. Two samples with the largest variances were found to contain data entry errors. These have been corrected in the database. Other samples exceeding the error limits are unexplained, but given only 5.6% of the samples were bad, the internal lab duplicates validate assay adequacy and accuracy. Figure 12-8. Laboratory Blind Duplicates