Following years of development and testing, in-situ chemical assay by Pulsed Fast and Thermal Neutron Activation (PFTNA) has been implemented in mining grade control at BHP Western Australian Iron Ore as a world first. Demonstrating the technical capability and aptness of a new methodology, however, is not sufficient to ensure the sustained quality of reported assay data. The success of moving from testing stage to implementation in active mining grade control, is chiefly dependent on the robustness of ongoing quality control and quality management.

This paper shows the steps undertaken to achieve end to end monitoring of data acquired by Blasthole Assay Tools (BHAT) using PFTNA methods. The main challenge for in situ chemical assay by the BHAT is to design a quality assurance/ quality control program (QA/QC) without a physical sample being collected, and in consequence, without the conventional separation into the focus areas sample collection, sample preparation and laboratory analysis. In this context, the BHAT combines all in one instrument, and different ways to monitor data integrity, repeatability and accuracy need to be established as outlined below.

After the validity of a BHAT calibration has been verified and a tool is in operation, data is monitored on a daily basis to check that relevant operational parameters inside the tool are working within defined acceptance limits. Measurement error in the field is monitored with repeat logs in Blastholes, and inter-instrument error by replicate logs of different BHAT units in the same Blastholes. Accuracy and instrument drift over longer periods are monitored by repeated logs in Reverse Circulation (RC) drill holes. Operational parameters, such as neutron output and spectral resolution of the instrument detector are monitored by scheduled logs in dedicated testing facilities. Also, duplicate manual sampling in Blastholes is used to compare grade populations obtained by different sampling methods in mining pits to aid grade reconciliation from mining to production. By routine application of these QA/QC steps, in conjunction with close communication of results to mining teams, the new BHAT technology has been successfully embedded in day to day mining operations.