The gift that keeps on giving – diamondiferous beach deposits – southern Namibia and Namaqualand, southwestern Africa

Abstract

The diamondiferous raised beaches that occur onshore between the Orange River mouth and Chameis Bay, southwestern Namibia, have been mined extensively since their discovery in 1928. Towards the late 1990s most of the raised beaches had been mined out and focus shifted to accessing the submerged beaches that occur below current-day sea-level. A process whereby stripped overburden sand that has been made available via the mining process, is used to push the shoreline westward. This process is called beach accretion and has proved highly successful in creating land by which the submerged beaches are accessed. Firstly, the sand is used to build new land out seaward, following which seawalls are constructed to protect the mining area from the Atlantic Ocean and lastly mining paddocks on the landward side of the seawall are dewatered, enabling the submerged beaches to be mined using conventional dry mining techniques.

Upfront sampling for diamond information in the highly energetic shoreline environment is not possible prior to the land being built out; however, breakthrough geophysical and geological modeling has provided insights into the footwall (bedrock) morphology that hosts the diamondiferous gravel beneath up to 40 m of overburden sand and 50 m of water. Subsequently spatial correlation between wavecut platform width and gradient could be established using analog onshore data and diamond sampling results dating back to historical delineation work done for the onshore raised beaches between the 1930s and 1960s. This revolutionary work provided a probability prediction mechanism for relative higher diamond concentration on the narrow ‘skinny beaches’. Since this correlation was first observed in 2018, more than five million square meters have been mined. Results up to 2024 show the initial observed correlation holds up against 500 post-mining diamond samples that were extracted from previously inaccessible submerged beaches.

Likewise, beach deposits have been mined between the Olifants River mouth and Alexander Bay since 1925. This paper expands the detailed model of the current-day Namibian linear beach deposits to a wider regional context spanning from the Olifants river mouth in the south to Chameis Bay in the north.