Otavi Mountain Land Cu-Pb-Zn-V deposits: Namibia, The

The Otavi Mountain Land hosts a wealth of fascinating mineral deposits in addition to the famous Tsumeb and Kombat mines. These include Berg Aukas (Grootfontein), Guchab and Abenab, among others, where world-class descloizite, willemite, dioptase, and the largest known crystals of vanadinite have been found.

INTRODUCTION

The Otavi Mountain Land in northeast Namibia is roughly delineated by the main road that runs from Tsumeb to Grootfontein, through Kombat to Otavi and back up to Tsumeb. The rugged topography of the area is formed by weathered carbonate rocks; the highest mountain lies at an elevation of 1677 meters above sea level. The valleys are characterized by a cover of calcrete (caliche) overgrown by dense thom bush and scrubby vegetation while the mountain slopes contain even more resilient species of shrubs and cacti, the latter attesting to annual temperatures that commonly exceed 30C. Yet the rainfall in the Otavi Mountain Land is the highest in Namibia, with Tsumeb recording an average of 520 mm per annum (King, 1994).

The mineral deposits of the Otavi Mountain Land are famous for several reasons. Tsumeb is located here and has been a premier mineral-producing mine for decades. Similarly, although not on as grand a scale, the Kombat mine has also produced superb specimens from time to time and it is also well known for its suite of rare minerals. The polymetallic Tsumeb and Kombat mines are specifically excluded from this review as it would be beyond the scope of this article to describe these two major deposits. There is already extensive literature, geologically and mineralogically, for these two mines (see, for example, Wilson, 1977; Lombaard et al., 1986; Hughes, 1987; Innes and Chaplin, 1986; Dunn, 1991; and Gebhard, 1991).

The other well-known locality in the Otavi Mountain Land, situated southeast of Tsumeb, is the Berg Aukas mine, which has produced superb descloizite specimens now in collections around the world. There is a host of other Pb-Zn-V deposits, some relatively well-known such as Abenab and Abenab West, Guchab (Cu) and Gross Otavi, and also a myriad of lesser known localities. Berg Aukas and Abenab have also produced high-quality specimens of smithsonite and willemite. Berg Aukas is believed to have contained the largest single deposit of willemite in the world. Average grades and total tonnages (mined and in reserve) for the three largest mines are shown in Table 1.

HISTORY

"Otavi" is the name given to a spring in the area, and comes from the Ovambo word tava which describes the nudging and pushing of a calf when it nurses from its mother (Sohnge, 1967). It appears that the Bergdama tribe introduced copper smelting into Namibia long before the practice was used by either the Herero or the Ovambo people. The evidence obtained from smelting sites at Gross Otavi and other localities such as Otjikoto suggests that the style and technique of the operations were similar to those used in central Africa, which had previously been introduced from north Africa prior to 500 A.D. (Clark, 1957).

Europeans were first made aware of the presence of copper deposits in the Otavi Mountain Land when Sir Francis Galton published his narrative Travels in Tropical Africa in 1852; he described a journey through the Otavi region. Galton, together with Charles Anderson and I. Allen, traveled through Ovamboland in 1851 and camped at Otjikoto Lake, 20 km west of Tsumeb. Here, they met various groups of Bushmen and Ovambos transporting copper ore. Later, in 1857 two Rhenish missionaries, H. Hahn and J. Rath were camped east of Grootfontein where they also encountered Ovambo men transporting copper ore from the Otavi Valley (Sohnge, 1967). The ore was contained in "neatly woven baskets made of palm leaves," with each basket holding approximately 90 pounds of ore. This load, together with adequate supplies of food and water, was being hauled over 250 km! Several years later Hahn undertook a second trip to Ondangwa during which he established that the copper deposits in the Otavi mountains were being excavated by the Bushmen. It is clear from archeological remains that the Bushmen mined copper here and then transported the ore to Ondangwa where it was smelted by the native Omundonga, who specialized in metallurgical work. The copper was then used by these people to barter for various other commodities. Sohnge (1967) relates documented evidence provided by an American trader, Gerald McKiernan, who, together with several British traders including I. Hickey, C. C. Thomas and W. H. C. Wilmer, built a house at Otavi. During a hunting trip, McKiernan and Thomas discovered the site of copper mining at Gross Otavi:

When the wagon came up, we slaughtered the game, and proceeding onward arrived at sunset at a place which answered the description of that given by Brook's as the vicinity of the copper mine. Old smelting places were plentiful. Calcined stones, charcoal and fragments of copper-ore in heaps. Lion-tracks were very plentiful and a close guard was kept on the bullocks. Soon after dark we heard lions roaring and growling at no great distance . The next morning we began searching for the mine, but were unsuccessful for nearly half the day; and when we finally did find it, it was not more than 200 yards from the wagon. Such is the nature of that part of the country, a dense jungle; and notwithstanding the frequent visits of the natives, no footpaths led to the mine. The mine seemed to be of great richness and pits were dug along the line of the lode for a considerable distance. There were masses of ore of many tons in weight exposed in many places, and seemed to have been left for want of proper tools for breaking it up into portable form. We had a large hammer, and I broke off about 300 lbs for a sample. It was very hot work, the thermometer 1060 in the shade. On 20th January 1876, McKiernan and Wilmer left Otavi for Omaruru because of hostility among the Ovambos and Hereros.