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I.—On the Diamond Fields of South Africa

Published online by Cambridge University Press:  01 May 2009

T. Rupert Jones
T. Rupert Jones
Affiliation:
Professor of Geology, Royal Military and Staff Colleges, Sandhurst
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Extract

Diamond Region.—The diamond-bearing region in South Africa, as at present known, is chiefly within the valley ofthe Vaal River and some of its tributaries (as the Modder and the Vet); but it is known also to extend down the Orange (Gariep) Valley for a few miles after the junction of its two great branches, the Ky Gariep (Vaal) and the Nu Gariep (CradockRiver). Bloemhof on the Vaal, two hours (12 miles) south-west of Potscherfstroom (Trans-vaal), is the reported locality ofthe most northern diamond-find. Below, for a distance of 370 miles, the plain has yielded diamonds, at several places, on both sides of the river, at Hebron, Klipdrift (near Pniel), Zitzikammsi, Vogelstmis Pan, Sitlacomie's Village, Sikoneli's Village, Nicholson's Farm, Kalk Farm (near Litkatlong), etc.; and on the south side of tie Orange River, they have been found some miles north-west of Hopetown, at Probeerfontein, Roodekop, David's Pan, etc. Diamondsare also said to have been found a few miles east of Fauresmith, on a branch of the Modder, about 100 miles south by east of Litkatlong; also a few miles south of Winburg (also in the Orange River Free State), in the upper drainage of the Vet River, about 80 miles from the Vaal.

Type
Original Articles
Information
Geological Magazine , Volume 8 , Issue 80 , February 1871 , pp. 50 - 60
Copyright
Copyright © Cambridge University Press 1871

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References

page 51 note 1 Quart. Journ Geol. Soc., vol. xii. p. 237; 1856.Google Scholar

page 51 note 2 Mr. Bain incidentally mentions that between the Bambus Bergen and “the magnificent Nu Gariep or Orange River … detached hills, separated by extensive and dreary plains,” are the features of the country. Trans. Geol. Soc, 2nd ser., vol. vii., p. 58.

page 51 note 3 “Grahamstown Journal,” January 20, 1869Google Scholar “Cape Monthly Magazine,” September, 1869Google Scholar “Nature,” November 3, 1869.Google Scholar

page 52 note 1 A granilite, or binary granite, is alluded to by Mr. Higson (see further on, p. 53), as being the fundamental rock of the Vaal Valley.

page 53 note 1 This “granilite” may possibly also be the tame as Bain's binary granite of the Paarl and near Bain's Kloof, not far from Cape Town. Geol. Trans., 2nd series, vol. vii., p. 179.

page 54 note 1 Geol. Trans., 2nd ser., vol. vii., p. 57; 1845.Google Scholar

page 54 note 2 Geol. Mag., Vol. III., p. 88, etc.Google Scholar

page 54 note 3 In a paper lately read before the Geological Society of London.

page 54 note 4 The basalt is said by some to be a very different igneous rock from the abundant greenstone of the country to the south and south-west.

page 54 note 5 Dr. J. Shaw remarks that the angular quartz gravel is said to be bad groun for diamonds; and that the pebbly alluvium is better for the finders.

page 55 note 1 Dr. J. Shaw writes of the materials of the alluvium thus:— “The pebbles of sandstone, quartzite, crystalline sandstone, granite, clayslate, agate, tourmaline, iron-pyrites, garnet, garnet-spinel [?], etc., which compose this alluvium, are all roundedly polished and waterworn, and are imbedded at Klipdrift in a brownish fatty earth.”— Nature, Nov. 3, 1870.

page 55 note 2 All philologists must protest against the mongrel word “diamondiferous,” partly English and partly Latin, that the Colonists have adopted instead of “diamond-bearing” or “diamantiferous.”

page 55 note 3 Some of these have been quoted as “Rubies.”

page 56 note 1 See also Prof. Tennant's lecture on South-African Diamonds, Journal Soc. Arts, Nov. 25, 1870, p. 15, etc. Reported in the Geol. Mao. for January last, p. 35.

page 56 note 2 The palæozoic rocks of the Transvaal having been at least a shoal, overlapped, if not wholly covered, by the Karoo formation, it is highly probable that the latter commenced with the boulder-bed here as elsewhere. It is possible, however, that the latest beds only of the Karoo formation reached thus far; and hencethe enigma of Palæozoic coal-plants in the same section with the Mesozoic fossils in the Stormberg.

page 56 note 3 See also Dr. Sutherland's observations on the blocks of porphyritic granite in the arkose, or granitic sand, of the Karoo beds in Natal, as well as in the breccia (which in 1855 he thought to be of volcanic origin). Quart. Journ. GeoL Soc, vol. xii., pp. 466 and 467.

page 56 note 4 There is selenite (small sagittate macles; Grey) of local origin, which may have resulted from decomposition of pyrites in the drift, and reactions with the tufa.

page 56 note 5 Trans. Geol. Soc., 2nd ser., vol. vii., p. 58, 1845.Google Scholar

page 57 note 1 Dr. Rubidge showed me a crystal of topaz in a piece of one of the Karoo auriferous quartz-dykes near Smithfield, described in the Quart. Journ. Geol. Soc, vol. xi., p. 4, and vol. xii., p. 237. Should some of the gold-bearing quartz-veins, such as occur on the Kraai River and near Smithfield, be continued northward to the Vaal, they would be probable sources of rock-crystal, topaz, and gold; but as the yield is very poor at the places named, we cannot reckon on the supply being great elsewhere. Dr. Muskett (in a letter read at a meeting of the Port-Elizabeth Nat. Hist. Society, October 29, 1868) expressed an opinion that the diamonds may have been “set free by the disintegration of the highly ferruginous trap-rocks that abound near the spot where they have been found.” We learn from Mr. Higson (quoted above at p. 52), that both trap-dykes and quartz-dykes of the Karoo series traverse the Vaal.

page 57 note 2 Dr. Grey has sent to England tremolite, amethyst, quartz with galena, a workable variety of steatite, and massive prehnite, from the valley of the Vaal, (Exhibited before the Geological Society, November, 1870.)

page 57 note 3 Chrysolite is common in the Brazilian diamond-drift, though only metamorphic rocks appear to have yielded the débris.

page 57 note 4 The garnet-sand, washed for pyrope, near Bilin, in Bohemia, has been found to contain diamonds. Bull, Geol. Com. Italy, 1870, p. 175 (this fact, however, is doubted in Poggendorf's Annalen); and Geol. Mag., 1870, Vol. VII., p. 348.Google Scholar

page 57 note 5 Agate pebbles are known in the upper part of the Caledon River; and pebbles of amygdaloid rock and rolled agates on the north-eastern branch of the Orange River, and in the Kraai. In 1856 Dr. Rubidgeremarked that “ the amygdaloid rock which supplies the agate-gravel of the Orange, Caledon, Kraai, and Vaal Rivers appears to exist in the ‘Mont-aux-Sources’ (Giant's Castle), in the Draakenberg, as an unworn specimen was found in the Eland River (a tributary of the Vaal), not more than twelve miles from its source.”—Quart. Journ. Geol. Soc, vol. xii., p. 237.

In a footnote at p. 223, Trans. Geol. Soc, Second Series, vol. vii., 1858, mention is made of some drifted ossicles of Encrinites, picked up, when Sir G. Gathcart returned from his unsuccessful attack on Moshesh, by a soldier, near the most easterly branch [Kraai ?] of the Orange River, where they were associated with ferruginous casts of small turreted shells [Murchisonia ?], with fragments of agate, quartz, and fossil wood, and with crystals of mundic The occurrence of Devonian strata at the base of the Draakenberg is indicated in all probability by the fossils referred to; and, whilst the quartz and mundic may be referable to veins in such rocks, or to altered schists of the same or greater age, the agate and fossil wood are sure local signs of the Karoo beds.

So also the river-gravel from near the mouth of the Orange River, referred to in the same footnote, with its Encrinital joints, rolled amygdaloid, waterworn agate, carnelian, cream- coloured chert, and greenstone, and fragments of micaceous shale and copper-ore, points to the Metamorphic, Devonian, and Karoo strata, through which the river runs, in escaping from the interior of South Africa on the western side of the continent. As diamonds are associated with the rains of such rocks in the upper part of this great river's course, possibly they may be found among the detritus of the same rocks crossed by it near its mouth. As Dr. Sutherland has shown that old crystalline palæozoic, and Karoo rocks are all denuded together in Natal, probably among their ruins diamonds are to be found in that country also.

page 58 note 1 For Dr. Rubidge's views respecting the eastern source of the agates, and of the old high-level flats and terraces of agate gravel, see Geol. Mag., Vol. III., p. 89.

page 58 note 2 Dr. John Shaw (“ Nature,” Nov. 3, 1870) thinks that “a series of metamorphic and sedimentary rocks which lay above the present rock-system of the region,” have been slowly worn down; the shifted and reduced débris, and a few local remnants of the series, being all that remain of these old rocks, which he thinks may have been the original seat of the diamonds. Dr. W. G. Atherstone says (Geol. Mao., No 59, p. 212):— “From the great distance of the finding-places apart, and their propinquity to the several river-beds, which all proceed from the Quathlamba or Draakenberg sandstone ranges, I have little doubt that, on careful exploration, the real source of the diamond deposits will be found far to the eastward.”

page 58 note 3 The finding of diamonds at Bloemhof, near Potscherfstroom, if well substantiated, is of great importance in our inquiry; for it shows that the presence of the Karoo beds is not necessary for their occurrence; since the Karoo formation does not reach so far, according to Mr. Higson's observations (“Natal Herald,” August 8, 1867). In this case they must have come from the metamorphic or the granitic rocks of the Transvaal, as the drainage of the Magaliesberg, with its Karoo beds, goes northward.

page 58 note 4 The flexible itacolumite (or sandstone of quartz and rotten felspar), associated with diamond-fields in India, is found beyond the Draakenberg, in Natal; and there it is accompanied with a kind of jade, as in Siberia.

page 59 note 1 Limestone also occurs with these schists, which are thought by Agassiz and Hartt to be probably Silurian rocks, highly altered. See also the Rev. G. J. Nicola's paper in the British Association Report, 1868 (Trans. Sect. p. 74), for an account of one of the Brazilian diamond-fields.

page 59 note 2 Quarterly Journ. Geol. Soc., vol. xi., p. 7; 1855.Google Scholar

page 59 note 3 In the “Academy” for December, 1870, is an imperfect report of a discussion at the Geological Society of London, wherein it is intimated that Prof. Morris expressed an opinion that, as the Bamboo produces tabasheer, so the Conifers of the Karoo formation may hare produced a resin that has since been converted into pure carbon. We must wait for the elucidation of this hypothesis. See also Prof. Morris's “Lecture on Diamonds,” etc., Mining Journal, Sec. 17, 1870, p. 1063.