Core sampling is the process of collecting cylindrical rock specimens (cores) from boreholes drilled in the earth's subsurface as part of a mineral exploration or grade control program in mining. In bauxite, gold, iron ore, and diamond mining, core sampling provides the primary source of geological and geochemical data used to characterise the subsurface ore deposit, estimate mineral resources, and support mine planning decisions. The core sampling process involves drilling a borehole using a diamond core drill equipped with a core barrel and diamond-impregnated drill bit. As the bit advances, it cuts an annular ring around a central cylinder of rock, which is preserved in the inner tube of the core barrel. When the inner tube is full (typically after a 1.5 m or 3.0 m run), it is retrieved to surface using a wireline system or by pulling the drill string. The core is then carefully extruded from the tube into wooden or plastic core trays, which are labelled with the borehole identifier, depth interval, run number, and core recovery data. At the core shed, the core undergoes geological logging, geotechnical logging, photographing, and — critically — sampling for laboratory assay. The sampling process involves cutting the core (usually with a diamond core saw) lengthwise along its axis, retaining one half for the laboratory assay and the other half as a reference archive. Sample lengths are determined by the geologist based on geological boundaries and typically range from 0.5 m to 2.0 m. In gold mining, samples are assayed by fire assay for gold content. In bauxite sampling, samples are analysed for alumina (Al₂O₃), silica (SiO₂), iron oxide (Fe₂O₃), and titania (TiO₂). In iron ore sampling, Fe%, SiO₂, Al₂O₃, and P content are the primary assay parameters. In diamond exploration, bulk sampling from large-diameter holes (such as RC or calyx drilled holes) is used to recover actual diamonds for size frequency analysis.
