Gems - Occurence Of Diamond
( Originally Published 1919 )
THE whole of the diamonds known in ancient times were 0btained from the so-called Golconda mines in India. Golconda itself, now a deserted fortress near Hyderabad, was merely the mart where the diamonds were bought and sold. The diamond-bearing district actually spread over a wide area on the eastern side of the Deccan, ex-tending from the Pinner River in the Madras Presidency northwards to the Rivers Son and Khan, tributaries of the Ganges, in Bundelkhand. The richest mines, where the large historical stones were found, are in the south, mostly near the Kistna River. The diamonds were discovered in sandstone, or conglomerate, or the sands and gravels of river-beds. The mines were visited in the middle of the seventeenth century by the French traveller and jeweller, Tavernier, when travelling on a commission for Louis XIV, and he afterwards published a careful description of them and of the method of working them. The mines seem to have been exhausted in the seventeenth century ; at any rate, the prospecting, which has been spasmodically carried on during the last two centuries, has proved almost abortive. With the exception of the Koh-i-nor, all the large Indian diamonds were probably discovered not long before Tavernier's visit. The diamonds known to Pliny, and in his time, were quite small, and it is doubtful if any stones of considerable size came to light before A.D. 1000.
India enjoyed the monopoly of supplying the world's demand for diamonds up to the discovery, in 1725, of the precious stone in Brazil. Small stones were detected by the miners in the gold washings at Tejuco, about eighty miles (129 km.) from Rio de Janeiro, in the Serro do Frio district of the State of Minas Geraes. The discovery naturally caused great excitement. So many diamonds were found that in 1727 something like a slump took place in their value. In order to keep up prices, the Dutch merchants, who mainly controlled the Indian output, asserted that the diamonds had not been found in Brazil at all, but were inferior Indian stones shipped to Brazil from Goa. The tables were neatly turned when diamonds were actually shipped from Brazil to Goa, and exported thence to Europe as Indian stones. This course and the continuous development of the diamond district in Brazil rendered it impossible to hoodwink the world indefinitely. The drop in prices was, however, stayed by the action of the Portuguese government, who exacted such heavy duties and imposed such onerous conditions that finally no one would undertake to work the mines. Accordingly, in 1772 diamond-mining was declared a royal monopoly in Brazil, and such it remained until the severance of Brazil from Portugal in 1834, when private mining was permitted by the new government subject to the payment of reasonable royalties. The industry was enormously stimulated by the discovery, in 1844, of the remarkably rich fields in the State of Bahia, especially at Serra da Cincora., where carbonado, or black diamond, first came to light, but after a few years, owing to the difficulties of supplying labour, the unhealthiness of the climate, and the high cost of living, the yield fell off and gradually declined, until the importance of the fields was finally eclipsed by the rise of the South African mines. The Brazilian mines have proved very productive, but chiefly in small diamonds, stones above a carat in weight being few in comparison. The largest stone, to which the name, the Star of the South, was applied, weighed in the rough 254 1/2 carats; it was discovered at the Bagagem mines in 1853. The quality of the diamonds is good, many of them having the highly-prized bluish-white colour. The principal diamond-bearing districts of Brazil centre at Diamantina, as Tejuco was re-named after the discovery of diamonds, Grao Magor, and Bagagem in the State of Minas Geraes, at Diamantina in the State of Bahia, and at Goyaz and Matto Grosso in the States of the same names. The diamonds occur chiefly in cascalho, a gravel, containing large masses of quartz and small particles of gold, which is supposed to be derived from a quartzose variety of micaceous slate known as itacolumite. The mines are now to some extent being worked by systematic dredging of the river-beds.
Early in 1867 the children of a Boer farmer, Daniel Jacobs, who dwelt near Hopetown on the banks of the Orange River, picked up in the course of play near the river a white pebble, which was destined not only to mark the commencement of a new epoch in the record of diamond mines, but to change the whole course of the history of South Africa. This pebble attracted the attention of a neighbour, Schalk van Niekerk, who suspected that it might be of some value, and offered to buy it. Mrs. Jacobs, however, gave it him, laughingly scouting the idea of accepting money for a mere pebble. Van Niekerk showed it to a travelling trader, by name John O'Reilly, who undertook to obtain what he could for it on condition that they shared the proceeds. Every one he met laughed to scorn the idea that the stone had any value, and it was once thrown away and only recovered after some search in a yard, but at length he showed it to Lorenzo Boyes, the Acting Civil Commissioner at Colesberg, who, from its extreme hardness, thought it might be diamond and sent it to the mineralogist, W. Guybon Atherston, of Grahamstown, for determination. So uncertain was Boyes of its value that he did not even seal up the envelope containing it, much less register the package. Atherston found immediately that the long-scorned pebble was really a fine diamond, weighing 21 3/16 carats, and with O'Reilly's consent he submitted it to Sir Philip Wodehouse, Governor at the Cape. The latter purchased it at once for £500, and dispatched it to be shown at the Paris Exhibition of that year. It did not, however, attract much attention ; chimerical tales of diamond finds in remote parts of the world are not unknown. Indeed, for some time only a few small stones were picked up beside the Orange River, and no one believed in the existence of any extensive diamond deposit. However, all doubt as to the advisibility of prospecting the district was settled by the discovery of the superb diamond, afterwards known as. the ` Star of South Africa,' which was picked up in March 1869 by a shepherd boy on the Zendfontein farm near the Orange River. Van Niekerk, on the alert for news of further discoveries, at once hurried to the spot and purchased the stone from the boy for five hundred sheep, ten oxen, and a horse, which seemed to the boy untold wealth, but was not a tithe of the L11,200 which Lilienfeld Bros., of Hopetown, gave Van Niekerk.
This remarkable discovery attracted immediate attention to the potentialities of a country which produced diamonds of such a size, and prospectors began to swarm into the district, gradually spreading up the Vaal River. For some little time not much success was experienced, but at length, early in 1870, a rich find was made at Klipdrift, now known as Barkly West, which was on the banks of the Vaal River immediately opposite the Mission camp at Pniel. The number of miners steadily increased until the population on the two sides of the river included altogether some four or five thousand people, and there was every appearance of stability in the existing order of things. But a vast change came over the scene upon the discovery of still richer mines lying to the south-east and some distance from the river. The ground was actually situated on the route traversed by parties hurrying to the Vaal River, but no one dreamed of the wealth that lay under their feet. The first discovery was made in August 1870 at the farm Jagersfontein, near Fauresmith in Orange River Colony, by De Klerk, the intelligent overseer, who noticed in the dry bed of a stream a number of garnets, and, knowing that they often accompanied diamond, had the curiosity to investigate the point. He was immediately rewarded by finding a fine diamond weighing 50 carats. In the following month diamonds were discovered about twenty miles from Klipdrift at Dutoitspan on the Dorstfontein farm, and a little later also on the contiguous farm of Bultfontein ; a diamond was actually found in the mortar used in the homestead of the latter farm. Early in May 1871 diamonds were found about two miles away on De Beers' farm, Vooruitzigt, and two months later, in July, a far richer find was made on the same farm at a spot which was first named Colesberg Kopje, the initial band of prospectors having come from the town of that name near the Orange River, but was subsequently known as Kimberley after the Secretary of State for the Colonies at that time. Soon a large and prosperous town sprang up close to the mines ; it rapidly grew in size and importance, and to this day remains the centre of the diamond-mining industry. Subsequent prospecting proved almost blank until the discovery of the Premier or Wesselton mine on Wesselton farm, about four miles from Kimberley, in September 1890; it received the former name after Rhodes, who was Premier of Cape Colony at that date. No further discovery of any importance was made until, in 1902, diamonds were found about twenty miles northwest-north of Pretoria in the Transvaal, at the new Premier mine, now famed as the producer of the gigantic Cullinan diamond.
The Kimberley mines were at first known as the ' dry diggings' on account of their arid surroundings in contradistinction to the ' river diggings' by the Vaal. The dearth of water was at first one of the great difficulties in the way of working the former mines, although subsequently the accumulation of underground water at lower levels proved a great obstacle to the working of the mines. The river diggings' were of a type similar to that met with in India and Brazil, the diamonds occurring in a gravelly deposit of limited thickness beneath which was barren rock, but the Kimberley mines presented a phenomenon hitherto without precedent in the whole history of diamond mining. The diamonds were found in a loose surface deposit, which was easily worked, and for some time the prospectors thought that the underlying limestone corresponded to the bedrock of the river gravel, until at length one more curious than his fellows investigated the yellowish ground underneath, and found to his surprise that it was even richer than the surface layer. Immediately a rush was made back to the deserted claims, and the mines were busier than ever. This ` yellow ground,' as it is popularly called, was much decomposed and easy, therefore, to work and sift. About fifty to sixty feet (15—18 m.) below the surface, however, it passed into a far harder rock, which from its colour is known as the `blue ground ' ; this also, to the unexpected pleasure of the miners, turned out to contain diamonds. Difficulties arose as each claim, 30 by 30 Dutch feet (about 31 English feet or 9'45 metres square) in area, was worked downwards. In the Kimberley mine (Plate XVI) access to the various claims was secured by retaining parallel strips, 15 feet wide, each claim being, therefore, reduced in width to 22i feet, to form roadways running from side to side of the mine in one direction. These, however, soon gave way, not only because of the falling of the earth composing them, but because they were undermined and undercut by the owners of the adjacent claims. By the end of 1872 the last roadway had disappeared, and the mine presented the appearance of a vast pit. In order to obtain access to the claims without intruding on those lying between, and to provide for the hauling of the loads of earth to the surface, an ingenious system of wire cables in three tiers (Plate XVII) was erected, the lowest tier being connected to the outer-most claims, the second to claims farther from the edge, and the highest to claims in the centre of the pit. The mine at that date presented a most remarkable spectacle, resembling an enormous radiating cobweb, which had a weird charm by night as the moonlight softly illuminated it, and by day, owing to the perpetual ring of the flanged wheels of the trucks on the running wires, twanged like some gigantic aeolian harp. This system fulfilled its purpose admirably until, with increasing depth of the workings, other serious difficulties arose. Deprived of the support of the hard blue ground, the walls of the mine tended to collapse, and additional trouble was caused by the underground water that percolated into the mine. By the end of 1883 the floor of the Kimberley mine was almost entirely covered by falls of ` reef' (Plate XVI II), as the surrounding rocks are termed, the depth then being about 400 feet (22 M.). In the De Beers mine, in spite of the precaution taken to prevent falls of reef by cutting the walls of the mine back in terraces, falls occurred continuously in 1884, and by 1887, at a depth of 350 feet (107 m.), all attempts at open working had to be abandoned. In the Dutoitspan mine buttresses of blue ground were left, which held back the reef for some years, but ultimately the mine became unsafe, and in March 1886 a disastrous fall took place, in which eighteen miners—eight white men and ten Kafirs—lost their lives. The Bultfontein mine was worked to the great depth of 500 feet (152 m.), but falls occurred in 1889 and put an end to open working. In all cases, therefore, the ultimate end was the same : the floor of the mine became covered with a mass of worthless reef, which rendered mining from above ground dangerous, and, indeed, impossible except at prohibitive cost. It was then clearly necessary to effect access to the diamond-bearing ground by means of shafts sunk at a sufficient distance from the mine to re-move any fear of falls of reef. For such schemes co-operative working was absolutely essential. Plate XIX illustrates the desolate character of the Kimberley mine above ground and the vastness of the yawning pit, which is 0ver 1000 feet (300 m.) in depth.
A certain amount of linking up of claims had already taken place, but, although many men must have seen that the complete amalgamation of the interests in each mine was imperative, two men alone had the capacity to bring their ideas to fruition. C. J. Rhodes was the principal agent in the formation in April 1880 of the De Beers Mining Company, which rapidly absorbed the remaining claims in the mine, and was reformed in 1887 as the De Beers Consolidated Mining Company. Meantime, Barnett Isaacs, better known by the cognomen Barnato, which had been adopted by his brother Henry when engaged in earning his livelihood in the diamond fields as an entertainer, had secured the major interests in the Kimberley mine. Rhodes saw that, for effective working of the two mines by any system of underground working, they must be under one management, but to all suggestions of amalgamation Barnato remained deaf, and at last Rhodes determined to secure control of the Kimberley mine at all costs. The story of the titanic struggle between these two men forms one of the epics of finance. Eventually, when shares in the Kimberley mine had been boomed to an extra-ordinary height, and the price of diamonds had fallen as low as 18s. a carat, Barnato gave way, and in July 1889 the Kimberley mine was absorbed by the De Beers Company on payment of the enormous sum of 5,338,650. Shortly afterwards they undertook the working of the Dutoitspan and the Bultfontein mines, and in January 1896 they acquired the Premier or Wesselton mine. The interests in the Jagersfontein mine were in 1888 united in the New Jagersfontein Mining and Exploration Company, and the mine is now worked also by the De Beers Company. Thus, until the development of the new Premier mine in the Transvaal, the De Beers Company practically controlled the diamond market. The development of this last mine was begun so recently, and its size is so vast—the longest diameter being half a mile—that open-cut working is likely to continue for some years.
Though varying slightly in details, the methods of working the mines are identical in principle. From the steeply inclined shaft horizontal galleries are run diagonally right across the mine, the vertical interval between successive galleries being 40 feet. From each gallery side galleries are run at right angles to it and parallel to the working face. The blue ground is worked systematically backwards from the working face. The mass is stoped, i.e. drilled and broken from the bottom upwards, until only a thin roof is left. As soon as the section is worked out and the material removed, the roof is allowed to fall in, and work is begun on the next section of the same level; at the same time the first section on the level next below is opened out. Thus work is simultaneously carried on in several levels, and a vertical plane would intersect the working faces in a straight line obliquely inclined to the vertical direction (Fig. 60). When freshly mined, the blue ground is hard and compact, but it soon disintegrates under atmospheric influence. Indeed, the yellow ground itself was merely decomposed blue ground. No immediate attempt is made, therefore, to retrieve the precious stones. The blue ground is spread on to the ` floors' (Plate XXI), i.e. spaces of open veldt which have been cleared of bushes and inequalities, to the depth of a couple of feet, and remains there for periods ranging from six months to two years, depending on the quality of the blue ground and the amount of rainfall. To hasten the disintegration the blue ground is frequently ploughed over and occasionally watered, a remark-able introduction of agricultural methods into mining operations. No elaborate patrolling or guarding is required, because the diamonds are so sparsely, though regularly, scattered through the mass that even of the actual workers in the mines but few have ever seen a stone in the blue ground. When sufficiently broken up, it is carted to the washing and concentrating machines, by means of which the diamonds and the heavier constituents are separated from the lighter material.
Formerly the diamonds were picked out from the concentrates by means of the keen eyes of skilled natives ; but the process has been vastly simplified and the risk of theft entirely eliminated by the remarkable discovery made in 1897 by F. Kirsten, of the De Beers Company, that of all the heavy constituents of the blue ground diamond alone, with the exception of an occasional corundum and zircon, which are easily sorted out afterwards, adheres to grease more readily than to water. In this ingenious machine, the ' jigger' or ' greaser' (Plate XXIII) as it is commonly termed, the concentrates are washed over a series of galvanized-iron trays, which are covered with a thick coat of grease. The trays are slightly inclined downwards, and are kept by machinery in constant sideways motion backwards and forwards. So accurate is the working of this device that few diamonds succeed in getting beyond the first tray, and none progress as far as the third, which is added as an additional precaution. The whole apparatus is securely covered in so that there is no risk of theft during the operation. The trays are periodically removed, and the grease is scraped off and boiled to release the diamonds, the grease itself being used over again 0n the trays. This is the first time in the whole course of extraction from the mines that the diamonds are actually handled. The stones are now passed on to the sorters, who separate them into parcels according to their size, shape, and quality.
The classification at the mines is first into groups by the shape: (1) close goods, (2) spotted stones, (3) rejection cleavage, (4) fine cleavage, (5) light brown cleavage, (6) ordinary and rejection cleavage, (7) flats, (8) macles, (9) rubbish, (10) boart. Close goods are whole crystals which contain no flaws and can be cut into single stones. Spotted stones, as their name suggests, contain spots which necessitate removal, and cleavage includes stones which are so full of flaws that they have to be cleaved or split into two or more stones. Flats are distorted octahedra, and macles are twinned octahedra. Rubbish is material which can be utilized only for grinding purposes, and boart consists of round dark stones which are invaluable for rock-drills. These groups are afterwards graded into the following subdivisions, depending on increasing depth of yellowish tint : (a) blue-white, (b) first Cape, (c) second Cape, (d) first bye, (e) second bye, (f) off-colour, (g) light yellow, (h) yellow. It is, however, only the first group that is so minutely subdivided. After being purchased, the parcels are split up again some-what differently for the London market (cf. p. 136), and the dealers rearrange the stones according to the purpose for which they are required. Formerly a syndicate of London merchants took the whole of the produce of the Kimberley mines at a previously arranged price per carat, but at the present time the diamonds are sold by certain London firms on commission.
The products of each mine show differences in either form or colour which enable an expert readily to recognize their origin. The old diggings by the Vaal River yielded finer and more colourless stones than those found in the dry diggings and the mines underlying them. The South African diamonds, taken as a whole, are always slightly yellowish or ` off-coloured' ; the mines are, indeed, remarkable for the number of fine and large, canary-yellow and brown, stones produced. The Kimberley mine yields a fair percentage of white, and a large number of twinned and yellow stones. The yield of the De Beers mine comprises mostly tinted stones—yellow and brown, occasionally silver capes, and very seldom stones free from colour. The Dutoitspan mine is noted for its harvest of large yellow diamonds; it also produces fine white cleavage and small white octahedra. The stones found in the Bultfontein mine are small and spotted, but, on the other hand, the yield has been unusually regular. The Premier or Wesselton mine yields a large pro-portion of flawless octahedra, but, above all, a large number of beautiful deep-orange diamonds. Of all the South African mines the Jagersfontein in the Orange River Colony alone supplies stones of the highly-prized blue-white colour and steely lustre characteristic of the old Indian stones. The new Premier mine in the Transvaal is prolific, but mostly in off-coloured and low-grade stones, the Cullinan diamond being a remarkable exception.
To illustrate the amazing productiveness of the South African mines, it may be mentioned that, according to Gardner F. Williams, the Kimberley group of mines in sixteen years yielded 36 million carats of diamonds, and the annual output of the Jagersfontein mine averages about a quarter of a million carats, whereas the total output of the Brazil mines, for the whole of the long period during which they have been worked, barely exceeds 13 million carats. The average yield of the South African mines, however, perceptibly diminishes as the depth of the mines increases.
The most interesting point connected with the South African diamond mines, viewed from the scientific standpoint, is the light that they have thrown on the question of the origin of the diamond, which previously was an incomprehensible and apparently insoluble problem. In the older mines, just as at the river diggings by the Vaal, the stones are found in a gravelly deposit that has resulted from the disintegration of the rocks through which the adjacent river has passed, and it is clear that the diamond cannot have been formed in situ here ; it had been suspected, and now there is no doubt, that the itacolumite rock of Brazil has consolidated round the diamonds which are scattered through it, and that it cannot be the parent rock. The occurrence at Kimberley is very different. These mines are funnels which go downwards to unknown depths; they are more or less oval in section, becoming narrower with increasing depth, and are evidently the result of some eruptive agency. The Kimberley mine has been worked to a depth of nearly 4000 feet (200 m.), and no signs of a termination have as yet appeared. The blue ground which fills these ` pipes,' as they are termed, must have been forced up from below, since it is sharply differentiated from the surrounding country rocks. This blue ground is a brecciated peridotite of peculiar constitution, to which the well-known petrologist, Carvil Lewis, who made a careful study of it, gave the name kimberlite. The blue colour testifies to its richness in iron, and it is to the oxidation of the iron constituent, that the change of colour to yellow in the upper levels is due. Owing to the shafts that have been sunk for working the mines, the nature of the surrounding rocks is known to some depth. Immediately below the surface is a decomposed ferriferous basalt, about 20 to 90 feet (6—27 m.) thick, next a black slaty shale, 200 to 250 feet (60—75 m.) thick, then 10 feet (3 m.) of conglomerate, next 400 feet (120 m.) of olivine diabase, then quartzite, about 400 feet (120 m.) thick, and lastly a quartz porphyry, which has not yet been penetrated. The strata run nearly horizontal, and there are no signs of upward bending at the pipes. The whole of the country, including the mines, was covered with a red sandy soil, and there was nothing to indicate the wealth that lay underneath. The action of water had in process of time removed all signs of eruptive activity. The principal minerals which are associated with diamond in the blue ground are magnetite, ilmenite, chromic pyrope, which is put on the market as a gem under the misnomer 'Cape-ruby,' ferriferous enstatite, which also is sometimes cut, olivine more or less decomposed, zircon, kyanite, and mica.
The evidence produced by an examination of the blue ground and the walls of the pipes proves that the pipes cannot have been volcanoes such as Vesuvius. There is no indication whatever of the action of any excessive temperature, while, on the other hand, there is every sign of the operation of enormous pressure ; the diamonds often contain liquid drops of carbonic acid. Crookes puts forward the plausible theory that steam has been the primary agency in propelling the diamond and its associates up into the channel through which it has carved its way to freedom, and holds that molten iron has been the solvent for carbon which has crystallized out as diamond under the enormous pressures obtaining in remote depths of the earth's crust. It is pertinent to note that, by dissolving carbon in molten iron, the eminent chemist, Moissan, was enabled to manufacture tiny diamond crystals.
Water trickling down from above would be im. mediately converted into steam at very high pressure on coming into contact with the molten iron, and, in its efforts to escape, the steam would drive the iron and its precious contents, together with the adjacent rocks, upwards to the surface. The ferriferous nature of the blue ground and the yellow tinge so common to the diamonds lend confirmation to this theory. The process by which the carbon was extracted from shales or other carboniferous rocks and dissolved in iron still awaits elucidation.
Diamonds were found in New South Wales as long ago as 1851 on Turon River and at Reedy Creek, near Bathurst, about ninety miles (145 km.) from Sydney, but the find was of little commercial importance. A more extensive deposit came to light in 1867 farther north at Mudgee. In 1872 diamonds were discovered in the extreme north of the State, at Bingara near the Queensland border. Another discovery was made in 1884 at Tingha, and still more recently in the tin gravels of Inverell in the same region. In their freedom from colour and absence of twinning the New South Wales diamonds resemble the Brazilian stones. The average size is small, running about five to the carat when cut ; the largest found weighed nearly 6 carats when cut. They are remarkable for their excessive hardness ; they can be cut only with their own dust, ordinary diamond dust making no impression.
The Borneo diamonds are likewise distinguished by their exceptional hardness. They mostly occur by the river Landak, near Pontianak on the west coast of the island. They are found in a layer of rather coarse gravel, variable, but rarely exceeding a yard (t m.), in depth, and are associated with corundum and rutile, together with the precious metals gold and platinum. Indeed, it is no uncommon sight to see natives wearing waistcoats ornamented with gold buttons, in each of which a diamond is set. The diamonds are well crystallized and generally of pure water; yellowish and canary-yellow stones are also common, but rose-red, bluish, smoky, and black stones are rare. They seldom exceed a carat in weight ; but stones of t 0 carats in weight are found, and occasionally they attain to 20 carats. In 1850 a diamond weighing 77 carats was discovered. The Rajah of Mattan is said to possess one of the purest water weighing as much as 367 carats, but no one qualified to pronounce an opinion regarding its genuineness has ever seen it.
In Rhodesia small diamonds have been found in gravel beds resting on decomposed granite near the Somabula forest, about 2 miles (19 km.) west of Gwelo, in association with chrysoberyl in abundance, blue topaz, kyanite, ruby, sapphire, tourmaline, and garnet.
The occurrence of diamond in German SouthWest Africa is very peculiar. Large numbers of small stones are found close to the shore near Luderitz Bay in a gravelly surface layer, which is nowhere more than a foot in depth. They are picked by hand by natives and washed in sieves. In shape they are generally six-faced octahedra or twinned octahedra, simple octahedra being rare, and in size they run about four or five to the carat, the largest stone as yet found being only 2 carats in weight. Their colour is usually yellowish.
Several isolated finds of diamonds have been reported in California and other parts of the United States, but none have proved of any importance. The largest stone found weighed 231 carats uncut; it was discovered at Manchester in Virginia.