Assay

A chemical or physical test performed to determine the concentration of a target element or compound in an ore, rock, soil, or water sample. In gold mining, fire assay is the standard method for measuring gold content (expressed in grams per tonne or parts per million). In iron ore and bauxite mining, X-ray fluorescence and wet chemistry assays measure iron, silica, alumina, and other element concentrations critical for ore quality assessment.