A deposit boundary in mining refers to the three-dimensional spatial limit beyond which a mineral deposit is no longer considered economically or technically significant for exploitation. Defining deposit boundaries is a fundamental requirement in geological resource estimation and mine planning for bauxite, gold, iron ore, diamond, and other mineral deposits, as it determines the extent of the mineralized volume that is included in resource and reserve calculations. Deposit boundaries may be defined on the basis of several criteria, including: grade cut-offs (the minimum mineral grade below which material is classified as waste), mineralogical transitions (the point at which the dominant ore mineral gives way to barren or sub-economic rock types), structural or lithological contacts (geological boundaries such as fault planes or intrusive contacts that truncate mineralization), or economic limits imposed by mining method constraints and commodity prices. In bauxite deposits, the boundary is often defined by a combination of minimum aluminium content and maximum reactive silica content thresholds. In gold deposits, the economic cut-off grade — typically expressed in grams of gold per tonne — defines the outer boundary of ore relative to waste rock. In iron ore operations, grade boundaries between ore and proto-ore or waste are critical inputs to mine scheduling models. In diamond mining, the deposit boundary of a kimberlite pipe is typically defined by the geological contact between the kimberlite and the surrounding country rock (host rock), supplemented by diamond grade data. Accurate boundary definition requires dense drill hole spacing and rigorous geostatistical analysis.
