Grade Distribution refers to the statistical and spatial variation of ore grades within a mineral deposit or defined mining area, describing how concentrations of a target commodity — such as gold in grams per tonne, iron as a percentage by weight, alumina content in bauxite, or carats per hundred tonnes of kimberlite in diamond deposits — are spread across a volume of rock. Understanding grade distribution is fundamental to resource estimation, mine planning, and metallurgical process design.
Grade distributions in natural deposits are rarely uniform; they typically follow log-normal or other skewed statistical distributions, meaning that most of the deposit consists of low-grade material while a small portion contains high-grade zones that contribute disproportionately to overall metal content. In geostatistical terms, grade distribution is analysed using variograms, kriging, and simulation methods to quantify spatial continuity and uncertainty.
For mine planners, knowledge of grade distribution informs decisions about cut-off grades, selective mining strategies, and the blending of different ore types to achieve consistent plant feed grades. In bauxite mining, grade distribution maps guide the sequencing of extraction to maintain target alumina-to-silica ratios. In gold operations, high-grade zones may be prioritised for early mining to accelerate cash flow.
Grade distribution data is also essential for reconciliation between resource models and actual mined tonnes and grades.