Deposit delineation is the process of defining the three-dimensional shape, extent, grade distribution, and structural characteristics of a mineral deposit through systematic drilling, sampling, geophysical surveys, and geological interpretation. It is an essential phase of exploration and resource development that follows initial discovery and precedes the formal estimation of mineral resources and reserves for bauxite, gold, iron ore, diamond, and other commodities. The primary tool for deposit delineation is drilling — whether rotary air blast (RAB), reverse circulation (RC), or diamond core drilling — which provides subsurface samples at defined intervals and locations across the deposit footprint. Drill hole data are used to build geological cross-sections and three-dimensional wireframe models that capture the geometry and grade variability of the deposit. Geophysical methods such as ground electromagnetics, induced polarization, gravity surveys, and airborne magnetics complement drilling by providing information about the lateral and vertical continuity of mineralization between drill holes. In bauxite delineation, closely spaced hand-auger or RAB drill programs across lateritic plateau surfaces are common, given the shallow, blanket-like geometry of many bauxite deposits. Gold deposit delineation may require deep diamond drill holes to trace high-grade ore shoots down plunge in structurally controlled lode systems. Iron ore deposit delineation relies on dense RC and diamond drilling grids to establish grade continuity and product quality parameters. In kimberlite diamond deposits, delineation drilling defines the pipe geometry, internal geological domains, and grade distribution with depth.
