Significance of Sample Repeatability Index in the Mining Industry

The objective of this research is to establish the importance of Sample Repeatability Index (SRI) as a measure to ensure error minimisation in exploration drilling protocols, during sample preparation of the prospect areas. Almost all the stages entailed in the exploration stages involve sampling. Samples collected and prepared within the field are well checked for a good Quality Assurance and Quality Control (QA/QC) methods. However, samples sent out for testing in the laboratory outside the field are not under the control of the exploration team, hence a measure must be taken to assess the efficiency of the laboratory and accuracy of the laboratory results. Sample Repeatability Index is one of the tools that can be used to ensure the degree of confidence in the laboratory results. To achieve this, QA/QC procedures were employed to monitor precision, accuracy and potential sample contamination in order to ensure confidence in the sampling system. A total of twelve thousand and eighty-one samples taken from eight different deposits, considered within a 4-year period were used in this study. Field duplicate pairs were used to check sample repeatability, Relative Difference and Half Absolute Relative Difference (HARD) plot were used to calculate Sample Repeatability Indexes for the deposits. Results of the study showed that Sample Repeatability Index for all the deposits with exception of deposit 2 fell below the Customer Specification Threshold (CST). Deposit 2 produced somewhat better of 77% at 20% precision as compared to the other deposits. Deposit 3 recorded poorly of 60% at 20% precision. It is advisable to have sampling protocol designed to suit different geological domain on each individual deposit.