Tsumeb

The pipe that gave mineralogy some of its rarest species

Tsumeb, a town of around 35,000 in Namibia's Oshikoto region, grew over a single mineralised pipe. The International Union of Geological Sciences describes the pipe as about 120 by 15 metres in cross section, dipping steeply from the surface to a depth of roughly 1,700 metres through the limestone and dolomite of the Otavi Group, and filled with altered sandstone and breccia. The deposit is about 530 million years old. Copper, lead, silver, gold, arsenic and germanium were won from its ore, some of it so rich that it went straight to the smelter near the town without passing through the enrichment plant.

The name comes from the Otjiherero Otjiisume, the place of the frogs, for the varied colours of the rocks, and from the Khoekhoe Tsomsoub, to dig a hole in loose ground, for the mining done here in prehistoric times, though those early workers barely scratched the surface. Imperial Germany founded the town in 1905, in what was then German South West Africa, and the OMEG company and later Tsumeb Corporation Limited worked the mine through the twentieth century, mostly by cut-and-fill. The lower workings are now closed.

The mine is renowned among mineral collectors. Inside the pipe, three zones of oxidation let groundwater carry the metals downward and set them out again as new minerals, many in crystals of extreme beauty, and rare elements such as germanium and gallium gave rise to extremely rare minerals. The IUGS counts about 489 minerals in the deposit, 72 of them first described from it and more than 25 known only from Tsumeb, among them tsumebite and stottite, and in 2022 it included the Tsumeb Ore Deposit in its list of 100 geological heritage sites.

The country around holds more. Lake Otjikoto and Lake Guinas, two sinkhole lakes near the town, vanish into lateral caves at the bottom, so neither has been sounded; Guinas, well over 100 metres deep, has its own fish, Tilapia guinasana, and retreating German forces threw their weapons and supplies into Otjikoto in 1914. Etosha National Park is close, and the Hoba meteorite, about 60 tonnes of nickel-iron and the largest known, lies about forty minutes' drive to the southeast. The town holds a copper festival every year on the last weekend of October.