The Okiep Copper District situated in the north-western Cape Province, covers some 3 000 km and is the oldest mining area in the Republic of South Africa. The O'okiep Copper Company Limited commenced production in 1940 with a proven ore reserve of 9 million tons at 2,45 % cu. Production since 1940 and present ore reserves total some 93 million tonnes at 1,08 % Cu. The rocks comprising the Okiep Copper District are of Proterozoic age and have been subdivided into a meta-volcanosedimentary succession, intruded by various sub-horizontally emplaced granitoid intrusions. The various intrusions occurred at different stages relative to the main structural and metamorphic events. The copper deposits are confined to basic rocks which are the youngest major group of intrusives in the District. They occur as swarms of generally easterly-trending, steep northdipping, irregular dyke-like bodies consisting of diorite, anorthosite and norite. The dominant silicate constituents are andesite ranging to labradorite, hypersthene, biotite and phlogopite. Copper sulphides are preferentially associated with the more basic varieties. The copper sulphides are mainly chalcopyrite, bornite and subsidiary chalcocite. The copper content of the basic rocks is erratic ranging over small distances from a mere trace to several percent. Emplacement of the cupriferous basic rocks is predisposed to a large extent by enigmatic structural features locally referred to as steep structures. The most common manifestation of steep structure deformation is typically a narrow antiformal linear feature along which continuity of the country rocks has been interrupted by piercement folding and shearing. In places, pipelike bodies of megabreccia occur along steep structures, and also act as hosts to the basic rock. Areas of steep structure are thus prime exploration targets, due to their close spatial association with the cupriferous basic rocks. Exploration techiques employed in the Okiep Copper District in~ elude regional and detailed geological mapping, geophysical surveys utilizing magnetic, gravimetric and electrical methods, as well as limited application of soil and stream-sediment geochemistry. Final evaluation is by surface and underground diamond drilling. Exploration has to date discovered 18 new mines with individual ore reserves ranging from 200 000 to 37 000 000 tonnes. All are underground operations, and the sub-level open stoping method of mining is standard.