27— THE SOMABULA DIAMOND FIELD OF RHODESIA. 



By F. P. Mennell, F.G.S. 

 Curator of the Rhodesia Museum, Bulawayo. 



The last few years have inaugurated a new era in the history of 

 the South African Diamond deposits, inasmuch as rich bodies of 

 diamantiferous ground have been located at great distances from 

 localities which have previously been worked successfully. The 

 group, of which the Premier mine is the best known member, is the 

 most striking example of this extension of area, but the centre of 

 gravity of the diamond-mining industry seems to be gradually shift- 

 ing northward, and the opening up of the interesting deposit of the 

 Somabula Forest, so far North of any other known occurrence, 

 foreshadows the development of an important branch of the industry 

 in the Cinderella of the South African provinces, as Rhodesia has 

 been not inaptly termed. 



No detailed or authentic description of the Somabula field has 

 so far appeared. The writer briefly referred to the occurrence of a 

 remarkably gravelly deposit West of Gwelo in his " Geology of 

 Southern Rhodesia," and ascribed its formation to the Tertiary 

 period, a course which appears fully justified by more recent and 

 detailed investigation. He had already seen diamonds and other 

 gems from the locality, but had not been made aware of their 

 source. Last year he made an examination of the ground on behalf 

 of the South Affican Option Syndicate, who hold a large area on 

 the field, and who have just erected plant for producing diamonds on 

 a large scale. The reports of their preliminary operations will have 

 shewn that a rich deposit of good quality stones has been opened up. 

 A large quantitv were disposed of at a price which works out at jQ^ 

 17s. per carat, and a smaller parcel, sold more recently, fetched ;£6 

 per carat. The following notes, for permission to publish which I 

 am indebted to the Syndicate, are intended to give some idea of the 

 geological and mineralogical features of the field, of which I hope a 

 much more detailed account will be given at an early date. 



The diamond area may be described as a tongue of the Somabula 

 Forest, stretching along the central plateau of Rhodesia from the 

 Uvungu River for about seven miles in the diretion of Gwelo. The 

 beds of which it consists are undoubtedly younger than the Forest 

 Sandstones, as shewn bv their numerous pebbles of agates derived 

 from the lavas interbedded with those rocks, but they are probably not 

 very different in age, and may perhaps be regarded as the uppermost 

 portion of the Forest Sandstone series. They directly overlie the 

 granite of the watershed, on to the apex of which they extend, but 

 further down the Uvungu River the ordinary Forest Sandstones are 

 met with. The general sequence appears to be : — 



('5) Surface rainwnsh. etc., chiefly redistributed 



ijravel and sand (often absent) say 10 ft. 



e , , ( (4) Rs<^ ^"<^ white sands say 40 ft. 



bomahula \ ^^^ Qravel, with partings of clay. etc. say 40 ft. 



^^ ^ ( (2^ White micaceous sand 30 ft. 



resting unconformably upon 

 (i) Granite. 



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