The article cites Wilhelm Klein, a senior manager at the Tsumeb mine, who gave a lecture about "The Minerals of the Tsumeb Ore Deposit" that was delivered on August 25, 1938 in the hall of the Eckleben Hotel, in the town of Tsumeb, in northern Namibia. The lecture is considered as one of the most important published contributions to the descriptive mineralogy of Tsumeb as it provides a detailed account of the distribution of minerals between the surface and a depth of 400 meters.