142 



DESCLOIZITE FEOM SOUTH-WEST AFEICA. 



BY 



Percy A. Wagner, Ing.D., B.Sc, F.G.S., M.A.I.M.M.E. 



[Communicated by permission of the HonovrabJe the Minisicr 

 for Mimics and Industries.) 



Read July 11, 1922. 



Superficial deposits of vanadium ore are worked at a number 

 of localities in the Grootfontein district of the South-West 

 Protectorate and form the basis of quite an important industiy. 

 The ores occur for the most part in sand or rubble-filled solution 

 cavities and harremf elder in the surface of the Otavi dolomite, 

 more rarely in open solution fissures and in surface breccias, and 

 finally as actual replacements of the dolomite, these being, how- 

 ever, always connected with one or another of the previously 

 mentioned types of deposit. 



Some of the occurrences have descloizite as the predominant 

 ore mineral, others mottramite, and yet others (Berg Aukas) 

 apparently vanadinite.* Excellent descriptions of some of the 

 earlier discovered occurrences have been published by H. 

 Schneiderhohn,t but no comprehensive study of the deposits has 

 as yet been made. It is evident, however, from what is known, 

 that these are all of the nature of residual accumulations formed 

 by the concentration, at favourable loci, by descending meteoric 

 waters of small amounts of vanadium disseminated through 

 originally overlying deposits of copper-lead-zinc ore in the Otavi 

 dolomite or the ore-bearing aplite intrusive in that formation, t 

 As the vanadium compounds are the last to survive the degra- 

 dational processes, they are evidently peculiarly resistant to 

 chemical erosion, which is all powerful in a karst region such as 

 that under review. 



The object oi the present note is to describe some excep- 

 tionally handsome specimens of descloizite ore recently sent to 

 the writer by Mr. C. G. C. Clarke, of the South-West Africa 

 Company, Limited. They are from two localities, namely, the 

 farm Olifantsfontein W^est, situated 12 miles north-west of Groot- 

 fontein North, and the farm Abenab, situated 20 miles north of 

 Grootfontein. 



At the former, according to the description accompanying 

 the specimens, the deposit takes the form of a well-defined 

 vertical cleft in the dolomite, the walls of which are lined with 

 dark lustrous crystals and crystal aggregates of descloizite forming 

 continuous crusts, several superimposed crusts being in places 

 present. 



* According to a valuable unpublished Memorandum by Mr. G. E. B. 



Frood, Inspector of Mines, South-West Protectorate, 

 t cf. " Die Erzlagerstatten des Otaviberglandes, Deutsch-Siidwestafrika," 

 MctaU. vnd Erz., XVII, 13, 16, 19, 24, and XVIII. 10 and 11. 



* Schneiderhohn, luc. cit., p. 33. 



