NOTES OX THE ORIGIN OF THE DIAMONDS OF GERMAN 



S.W. AFRICA. 



By R. Marloth, M.A., Ph.D. 



(Raid before llie Cape ChciuicaJ Socicly on the i^lh Oelober, iQog.) 



The diamondiferous area of German South- West Africa is a narrow 

 strip of country in the neighbourhood of the coast, mostly only a 

 few miles wide, but about 200 miles long, extending, as known at 

 present, from Angras Juntas, latitude 28° S., to Conception Bay, 

 four degrees further North. The deposits are generally a few miles 

 away from the sea and very patchy, for large stretches of ground 

 within that belt have not as yet produced any diamonds. 



The diamonds occur either directly on the surface or embedded 

 in fine gravel, and where the latter is deep enough, diamonds have 

 been found several feet below the surface. 



The rocks in the immediate neighbourhood of Angra Pequena 

 are granite, gneiss and hornblende-schist, but south of Elizabeth 

 Bay other older rocks are met with, especially various kinds of 

 limestone. Overlying them, unconformabl}' here and there, are 

 remnants of quartzitic beds of cretaceous age, and in a few 

 places, e.g., on the Pomona table mountains, quartzitic con- 

 glomerates occur, which contain numerous pebbles that are evi- 

 dently waterworn. Still younger are some dykes of lamprophyre, 

 which traverse the country for miles, especially south of the 

 Pomona territory. 



The theories advanced for the origin of the diamonds of these 

 districts may be divided into three groups, namely : (i) they are 

 supposed to be of local origin. (2) to have come from the sea, or 

 (3) from the area of the Vaal River. The first theory, which would 

 mean that the diamonds had been derived from an area in which 

 only gneissose and granitic rocks are known, we may leave out 

 of account, although a few geologists think the occurrence of 

 diamonds in such rocks quite feasible. No pipes with diamondifer- 

 ous blue ground are known as yet from German South- West Africa, 

 although quite a number of pipes, with blank kimberlite. exist 

 further inland. 



Among the prospectors who know the countr}- south of Prince 

 of Wales Bay, the belief is quite common that Pomona diamonds 

 came from some volcanic fissures that occurred there, and which, 

 as mentioned before, are filled with a black volcanic rock, showing 

 large crystals of hornblende. 



Among geologists, however, the belief was fairly general that 

 the diamonds originally came out of some blue ground, but on the 

 question where the pipe or pipes which contained that blue ground 

 were situated much difference of opinion existed. 



Mr. Merensky* assumed that in or before cretaceous times 

 land existed to the west of the present coast, while the j)resent 

 land was still submerged under the waves of the ocean. The 

 ■diamonds were washed into that ocean from the west, and 

 embedded in the sand which went to form the cretaceous 



* Trans. Geol. Soc. of S.A., 1909, \'ol. XII. , pp. 13-23. 



