Assaying

Assaying is the laboratory process of determining the content and/or concentration of a specific substance within a sample. In mining and metallurgy, assaying refers most often to determining the amount of valuable metals, such as gold, silver, or platinum, in ore, concentrates, bullion, or alloys. The goal is to provide an accurate, representative measure of content that can inform ore valuation, smelter charges, process control, or regulatory compliance. Assaying encompasses qualitative identification of components as well as quantitative determination of their quantities, usually reported as percentages, grams per ton, parts per million, or fineness.

One of the oldest and most widely used techniques is fire assay, especially for precious metals. The sample is fused with fluxes to form a material that concentrates the metal, which is then separated and weighed or chemically analyzed. Modern instrumental methods include atomic absorption spectroscopy (AAS), inductively coupled plasma optical emission spectrometry (ICP-OES), and inductively coupled plasma mass spectrometry (ICP-MS); X-ray fluorescence (XRF) is common for rapid on-site analysis. Wet-chemical gravimetric and titrimetric methods remain in use for certain elements and matrices.

Critical to reliable results are careful sampling and preparation to achieve representative test material, calibration with standards, and quality control measures such as blanks and certified reference materials. Detection limits, precision, accuracy, and matrix effects influence interpretation; assays are typically reported with uncertainty estimates.

Assaying underpins mineral exploration, ore grading, refining, and trade, and has legal and economic implications wherever assay results determine value or regulatory compliance.