Grade Control is a systematic process used in mining operations to accurately identify, delineate, and manage the spatial distribution of ore grades within a mine, ensuring that material of economic value is correctly separated from waste and processed efficiently. In gold, iron ore, bauxite, and diamond mining, grade control involves a combination of geological mapping, sampling, assaying, and data interpretation to define ore boundaries at the scale of individual mining blocks or flitches.
The process begins with blast hole sampling, where cuttings from drilled holes are collected at regular intervals and submitted for laboratory analysis or field testing. Results are then interpreted by grade control geologists using statistical and geostatistical methods to produce block models or ore outlines that guide the excavator operators. Effective grade control is critical to maximising ore recovery and minimising dilution — the unintended inclusion of waste material in the ore stream — which directly impacts mill feed quality and overall metal recovery.
In diamond mining, grade control takes on additional complexity due to the extreme variability of diamond distribution, often requiring larger sample volumes. In bauxite operations, grade control focuses on alumina content and reactive silica levels. Iron ore operations target iron percentage and penalty element concentrations such as silica, alumina, and phosphorus. The accuracy of grade control directly affects financial outcomes, including revenue generated and processing costs.