Unearthing the mysteries of the Sperrgebiet
T
he 29th Colloquium of African Geology (CAG29), which took place in Windhoek in September, provided a multitude of opportunities, such as offering a variety of field excursions and workshops. I was one of the fortunate few to have the privilege of embarking on an extraordinary journey to Tsau ǁKhaeb National Park, formerly known as Sperrgebiet (Prohibited Area). The park was established in 2008 with the aim of conserving the unique desert landscape and biodiversity of the area. While the park is under protection, a significant portion of it remains inaccessible to travellers, or only with a guided tour, but our group of geologists had a chance to explore this wild landscape. The Sperrgebiet is part of the Namib Desert, one of the oldest deserts in the world. It covers the entire coastline of Namibia, extending into Angola to the north and South Africa to the south. The Sperrgebiet, an expanse of some 26 000 km², lies in the southern part of this vast area. Upon entering the Sperrgebiet, one is not only confronted with the relentless force of the wind but also captivated by how it has significantly shaped its morphology and landscape for millions of years. The geology of the Sperrgebiet is characterised by ancient rocks and desert landforms. The deposition of these rocks occurred during different periods, from Precambian gneisses of the Namaqualand Metamorphic Complex (ca. 1200 million years) and metasedimentary and metavolcanic rocks of the Gariep Supergroup (ca. 600 million years) to the deposits of the Namib Group, the oldest of which are late Cretaceous (ca. 70 million years). But one of the prominent geological features of the Sperrgebiet is the Orange River Basin. The Orange River, which rises in the Lesotho highlands, drained this part of southern Africa for millions of years. During that time it transported an
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enormous sediment load downriver, depositing it partly along its banks as terraces, off the Orange River mouth in the Atlantic Ocean, and along the seashore, where it was transported and redistributed by ocean currents and winds. And contained within these sediments were diamonds, which accumulated in alluvial deposits, both onshore and offshore. But have you ever wondered where and how these precious gems originated? It is widely accepted among geologists that the diamonds found in the Sperrgebiet come from Cretaceous diamondiferous kimberlites in the interior of South Africa, where graphite was converted to diamond under enormous pressures and temperatures deep within the earth. After being transported to the surface by volcanic processes, complex weathering and the action of streams and rivers, these diamonds embarked on a journey that ultimately deposited them on the western margin of the continent, as well as along the lower reaches of the Orange River. A combination of geological and atmospheric factors, including the interaction of river systems, coastal processes and wind regimes led to the accumulation of the diamonds in a variety of deposit types throughout the Sperrgebiet and off the Namibian and South African coast. As soon as the first diamond was discovered near Lüderitz in 1908 by railway worker Zacharias Lewala, the Namibian diamond rush began. During its initial stages, diamonds were easily found and could be collected by hand in large quantities – especially on a full moon night, when they sparkled in the sand! The Sperrgebiet still retains remnants of the early diamond rush, notably gravel heaps, open-pit mining sites, mining equipment and infrastructure, the latter providing our group with shelter during our visit to this fascinating area. Apart from diamond recovery – now largely offshore – Namdeb Diamond Corporation is working to restore the
