unconformity
An unconformity is a buried surface where a gap in time exists between two layers of rock — older rocks were worn away before new ones formed on top, leaving a kind of missing chapter in the rock record.
Технически: An unconformity is a surface of contact between rock units that represents a significant hiatus in geological time, caused by erosion, non-deposition, or tectonic uplift of the older sequence before deposition of the younger one resumed. In mineral exploration, unconformities are structurally and chemically significant because they can act as pathways for hydrothermal fluids and as chemical or permeability traps that localise ore; the Athabasca Basin unconformity-type uranium deposits are the canonical example. Three main varieties are recognised — angular unconformity, disconformity, and nonconformity — distinguished by whether bedding above and below is parallel and whether the lower unit is sedimentary or crystalline.
Geology
underground mining
Mining that happens beneath the surface, reached by tunnels or shafts, so that workers and machines operate inside the rock rather than in the open air.
Технически: A collective term for any extraction method in which ore is won from workings wholly enclosed within the earth's crust, accessed by shafts, adits, or declines. Underground methods are selected when the orebody is deep, narrow, or high-grade enough that removing the overlying waste rock in an open pit would be uneconomic or impractical. The category encompasses a wide range of techniques — including room and pillar, longwall, cut-and-fill, and block caving — each suited to particular combinations of ore geometry, rock strength, and required production rate.
Mining