General Surveys of Diamond
Some general surveys of gemstones have become cluttered with repetitious material whose authenticity cannot be established without access to such original sources as can be accessed (this field of study is open only to those
who can deal with oriental and Slavonic languages; no single individual could attempt it – the literature would need to be compared with more modern records). The thought is a daunting one! For this reason I am rec- ommending, as an excellent and up-to-date general survey of the history of diamond discovery, mining, use, testing and synthesis, George S. Harlow’s The Nature of Diamonds (1998; ISBN 0521623957). This is as good a survey as can be found at the time of writing.
The synthesis of diamond is well described in Robert M. Hazen’s The Diamond Makers, 1997 (ISBN 0521654742). Here we meet Hannay and other bold experimenters as well as the scientists who finally succeeded in manufacturing diamond. Hazen has also written The New Alchemists (1993; ISBN 0812922751) in which he describes, in layman’s terms, the development of high-pressure technology, including its use in the man- ufacture of diamond. Amanda S. Barnard’s The Diamond Formula (2000; ISBN 0750642440) is another first-rate overview of diamond at the present time; it includes an account of diamonds grown by chemical vapour deposition (CVD) (I was told at a conference in October 2004 that no CVD diamond had so far reached the trade).
Coloured diamonds, long known as fancies, now have their own large and beautifully presented book, Stephen C. Hofer’s Collecting and Classifying Coloured Diamonds, 1998 (ISBN 0965941019). The book is a catalogue of the Aurora Collection of coloured diamonds which are illustrated in their entirety with many small features closely depicted. This is a particularly important study, as fancies now have their own grading system which is used by the major auction houses in their catalogue descriptions. Another beautifully produced study of coloured diamonds is Fancy-colored Diamonds, by Harvey Harris, published by the Fancoldi Registered Trust, Liechtenstein, 1994; ISBN 39520643).
Diamonds from India were probably the first to be described, the Koh-I- Noor and Jehangir diamonds being now assigned to India. The traveller Jean Baptiste Tavernier (1605–1680) wrote Les six voyages de Jean Baptiste Tavernier, Paris, 1676 [Sinkankas #6499] but also see many subsequent edi- tions and translations of which the best is Valentine Ball’s English version of 1889 and later. Ball includes a biography of Tavernier who travelled in the Near East during 1631–68; he then appears to have begun a fresh career as a jeweller with royal clients. He was buried near Moscow.
Tavernier’s travels in India are agreed to be a significant record rather than a compilation of hackneyed legends; he visited the diamond mines there and the diamond-bearing rivers; one such visit was to the mines at Raolconda.
In the Science and Technology of Diamond, edited by G.S. Bhatnagar in 1999 (ISBN 1898326487), Bhatnagar and Murthy give a valuable introduction to the science of diamond in protohistoric India. As the book is not easy to find, a short resume is given below. Ancient diggings were along the Penner, Krishna and Godavari rivers, stones reaching the temples of south- ern India and later Europe. Valentine Ball’s Manual of the Geology of India, part 3, 1881 and Ritter, Erdkunde von Asien, vol. 4 (2), 1836, are sources. Further information can be found in Murthy, Gemmological Studies in Sanskrit Texts, vol. 1, 1990 and in Sircar, Studies in the Geography of Ancient and Medieval India, Varanasi, 1971.
Diggings along the banks of the Penner, Krishna and Godavari rivers provided first the temples of South India and later Europe with fine dia- monds. No really up-to-date account is available in English but Kautilya’s Arthashastra (Mysore, Mysore Publishing and Printing House, 1967) and Samasatri, Kautilyarthasastram, Oriental Research Institute, University of Mysore, 1960, include considerable data. These sources date back to the third century BC and are especially valuable for the study of the geology, mineralogy and commerce of diamond. Varahamihira’s Brahat Samhita from the fifth century AD is also of great value. Yet more information can be found in other Sanskrit texts. Bhatnagar (1999) gives an excellent bibliography.
The earliest record of diamond is in Rig Veda (see Murthy, op. cit.). The name Golconda, not always linked with a specific location, has often been used as an epithet for Indian diamonds in general, but does cover diamond-bearing ground in areas from which the Penner River discharges into the Bay of Bengal. Nonetheless it is difficult to link ancient names with present-day places though Bhatnagar proposes several connections: sabha- rastraka is identified as diamond from the Vidarbha area, madhyamaras- traka from the present-day Madhya Pradesh, Kasmaka is believed to refer to diamond from near Baranas, Srikatanaka to the place named Vedotkata. Manimantaka is diamond from the mountain Maniman and Indravanaka is from Orissa. Vidharbha region is probably the area known for current dia- mond workings. These attributions are of course conjectural.
Sanskrit sources attribute many properties to diamond so its potential for ornament must have been realized from the earliest times.
The diamond sources on the Krishna in present day Andhra Pradesh are probably the mines which have produced, in present-day Andhra Pradesh, diamonds of the quality of the Koh-I-Noor, a celebrated diamond now in the English crown jewels; disputes over its re-cutting can be found on books devoted to diamond. It is possible that the slaty blue Hope diamond with the remarkable reddish fluorescence (in the National Museum of Natural History, Smithsonian Institution, Washington DC, USA) also comes from the same general area. Details of the major stones in the Crown Jewels can be found in the HMSO publications dealing with them. In general, Indian diamonds are notably limpid though at the time of writing there is no way in which the place of origin of any diamond can be determined by normal gemmological testing. In the state of Andhra Pradesh some diamond pipes were discovered in the 1960s and addi- tional pipes have also been found in the state of Madhya Pradesh. Not all pipes have been found to contain diamonds. The workings in Madhya Pradesh are in the Bundelkhand area; mining is sporadic. Alluvial, pipe mining and investigation of conglomerate rock have all taken place at least from time to time. Well-shaped green octahedra have been found at Majgawan and further investigation of the region has been carried out by government; there has been some recovery of diamond.
Extensive reports on diamonds in India were provided by Bauer in Edelsteinkunde, 1896 (English translation by Spencer, 1904; Dover Press reprint, 1968 [Sinkankas #471]). Those interested are recommended to read them with an eye on accuracy as no original material is cited.
Apart from the Majgawan pipe, the Indian diamonds are found in sandstone or conglomerate, or in the sands and gravels of old river beds. The associated minerals are usually confined to quartz pebbles and variously coloured jaspers. Panna diamonds have been known for 200 years.
Perhaps the best general surveys of Indian diamonds are contained in books by Valentine Ball, once of the Geological Survey of India and the translator of Tavernier’s travels (q.v.). In 1880 he contributed a paper on the mode of occurrence and distribution of diamonds in India to Journal of the Royal Geological Society of Ireland 6, part 1, new series.
The paper [Sinkankas #334A] contains details of Indian diamond deposits, their history and geology. The paper can also be found in Proceedings of the Royal Society of Dublin 2 ns, 1880, pp. 551–89. Pages 69–70 in the first-mentioned journal contain notes on obscure locali- ties, including Raolconda.
In another paper, published in Journal of the Royal Asiatic Society of Calcutta, 50, part 2, 1881, pp. 31– 44 [Sinkankas #334B], Ball identifies those Indian diamond mines visited by Tavernier. Ball’s 1881 book, The Diamonds, Coal and Gold of India, published in London [Sinkankas s#335], discusses, among other topics, the relationship between the Great Mogul diamond and the Koh-I-Noor. The book describes Indian diamond deposits and their geology and the prospect of success if the mines were taken over by Europeans.
Indonesia
Diamonds are found at a number of locations in present-day Indonesia but production appears to be sporadic. Deposits in the general area of Pontianak, a coast town on the west coast of Borneo have been mentioned in unsupported notes by some writers but current evidence is not forth- coming. The same can be said of reported deposits in other locations in Borneo. Information in Webster’s Gems, various editions, appears to derive from Bauer, Edelsteinkunde (various German editions and Spencer’s translation of 1904); for deposits in what is now Indonesia, Bauer cites Edmond Boutan’s book Le Diamant, Paris, 1888 [Sinkankas #838].
Brazil
Diamonds were discovered in Brazil at least as far back as the early seven- teenth century. Panning for gold brought diamond crystals to light, sites adjoining the Jequitinhonha River being particularly prolific. Remarks on Bauer’s account of Indian diamond mines are equally applicable here as none of the admittedly profuse and interesting information is referred to authorities. Those wishing to investigate further into the history of Brazilian diamond deposits should read the second volume of Sir Richard Burton’s Explorations of the Highlands of Brazil, London, 1869 [Sinkankas #1078]. This volume describes his journey to the area now known as Diamantina; there are also descriptions of alluvial diamond deposits in the state of Bahia. This is the major introduction to Brazilian diamond mining.
Another outstanding survey of Brazilian diamond is Wilhelm Ludvig Eschwege’s Pluto Brasiliensis of 1833 [Sinkankas #1947]. Here the author describes gold as well as diamond and other gem minerals, giving, in pass- ing, the regulations of the Portuguese crown for the control of the mining and marketing of diamonds. Gold and diamond smuggling are also cov- ered. Brazil is relatively rich in diamond since in addition to the Diamantina area of Minas Gerais there are occurrences in several other states.
Diamonds have been found in possibly Precambrian rocks overlain by the Itacolomy series, diamond occurring in intrusions of an altered rock. Diamond has also been found in the Lavras series of conglomerates and other rocks and in alluvial deposits.
Most Brazilian diamonds are small but quality can be good. The Presidente Vargas diamond weighs 726 ct.
North America
The best accounts of any gemstone found in North America can be found in the three volumes of John Sinkankas’s Gemstones of North America (1959, 1976, 1997). Occurrences except for those in Canada tend to be adventitious crystals turning up in California in 1849 during gold mining operations. In Merrill’s Handbook and Descriptive Catalog of the Collections of Gems and Precious Stones in the United States National Museum, 1922, only one diamond (yellow, uncut but polished, weight 0.77 ct) is recorded, from Kentucky, and another from Rutherford county, North Carolina, a pale yellow flat- tened octahedron of 0.14 ct. In 1972 the Crater of Diamonds State Park was established in the area of Murfreesboro, Pike county, Arkansas, where three types of igneous rock are found, lamproite, lamproitic breccia and tuff, though only the breccia produces diamonds. A good account of the area and its geology can be found in The Mineralogical Record 21 (6) 1990. Diamonds have been found in Alaska, North and South Carolina (the latter at least possible), Alabama, Georgia, Louisiana, Kentucky, Michigan, Wisconsin, Montana, Iowa, Wyoming and California (Sinkankas 1997). One or two of the reports of diamond crystals (many pale yellow distorted octahedra in general) may be in error. However, some finds have been remarkable; the Uncle Sam diamond from the Arkansas deposit weighs
40.42 ct and the Star of Arkansas 15.31 ct.
The different state mineralogies give more detail and notes in journals can be found listed in the three Sinkankas volumes.
The diamond scene in North America was completely changed when, in the late 1970s kimberlite pipes were discovered in the north-west Territories of Canada when Charles E. Fipke identified diamonds in a kimberlite pipe situated beneath Point Lake in the Lac de Gras area. The story of some of Fipke’s life and work can be found in his picaresque Fire into Ice (1999; ISBN 1551923343). Construction of the Ekati mine was com- pleted in 1998. It is interesting to note that some exploration in Finland has shown the existence of similar pipes and small diamonds have been found.
Australia
Diamonds from New South Wales are well described in A.A. Macnevin’s Diamonds in New South Wales (1972; Sinkankas #4115). The publishers are the Department of mines, Geological survey of New South Wales and the book forms #42 of the Mineral resources series. Diamond is reported to have been found in 1851 at Sutter’s Bar on the Macquarie river near Bathurst. Most diamonds from New South Wales are small and yellowish or off-coloured. Diamonds have also been found in Queensland. In the second volume of The Geology of the Commonwealth of Australia,
T. W. Edgeworth David (1950) briefly describes the deposits in New South Wales. The diamonds occur in stream deposits. Near Inverell, diamonds are found at Copeton, where many stones are recovered from a tertiary wash.
Western Australia
The Ashton Joint Venture’s exploration for diamonds in the furthest north-east area of Western Australia has led to some of the most impor- tant developments in the diamond world for many years. Particularly notable are pink diamonds, some inclining to red.
Exploration of the Kimberley district began in 1972. Up to 28 pipes were found in Ellendale province and the quality of the diamonds recov- ered from the start made it likely that there would be a good proportion of gem-quality crystals. Later, deposits at Smoke Creek produced allu- vial diamonds; a large lamproite pipe, AK-1, was found near Lake Argyle (man-made). Possible yield from Smoke Creek was reported to be as much as 470 ct for each tonne of ore.
The very large pipe AKA, said to be sixth in extent among world pipes, was expected to produce very large quantities of diamonds even though the proportion of gem-quality material might not be exceptional. Certainly the discovery of the coloured Argyle diamonds has led to a growing inter- est in fancy stones.
South Africa
The history of the discovery and mining of diamonds in southern Africa has been told many times and is not examined in detail here; several authorita- tive studies of mining in South Africa itself have already been cited (Gardner
F. Williams, The Diamond Mines of South Africa, second edition, 1905; Alpheus F Williams, The Genesis of the Diamond, 1932 – A.F. Williams was the son of
G.F. Williams and their combined experience of the area made both books essential for diamond studies). It may not be widely known that A.F. Williams also produced a book of essays concerning mining and miners in South Africa, Some Dreams Come True, 1948 [Sinkankas #7225]. The essays include brief biographies of a number of personalities, including Cecil Rhodes.
In 1873 Augustus F. Lindley published Adamantia. The Truth about the
South African Diamond Fields or, a Vindication of the Right of the Orange Free State to that Territory, etc. This rare book was published in London and is Sinkankas #3984. As Sinkankas says [‘the book is] an important histori- cal document in which the seamy side of the acquisition of the diamond fields of South Africa is carefully examined’. The British Parliament and public is told about the actions of their government and the case is sup- ported by considerable evidence.
The Anglo American Corporation of South Africa and the work of Sir Ernest Oppenheimer are described in Theodore Gregory’s Ernest Oppenheimer and the Economic Development of Southern Africa, published in 1962 by Oxford University Press (Sinkankas #2525). Chapters 3–5, pp. 109–383, tell ‘The diamond story’ and the student can find a great deal of information on the exploitation of diamond resources. The estab- lishment of the De Beers organization is described in ‘The Story of De Beers’, by Hedley A. Chilvers (London, 1939: Sinkankas #1287). The appendices, in particular, contain details of mine operations and statistics
while the main text traces the history of the company with commentary on some of the politics involved. The diamond cutting industry in South Africa is also described.
A useful account of the diamond occurrence and mining in the Kimberley area can be found in Cairncross and Dixon, Minerals of South Africa, Geological Society of South Africa, 1995 (ISBN 0620193247). The book includes some useful maps of the mining areas as well as a compre- hensive bibliography.
Zimbabwe
Alluvial diamonds were discovered during 1903 in the Somabula Forest west of Gwelo in Matabeleland, Zimbabwe. There seems to have been little development in recent years.
Namibia
In 1908 diamond was found near the settlement then called Lüderitz in present-day Namibia. Marine beach deposits were later found in separated areas extending around 100 km along the coast north of the mouth of the Orange River.
In 1927 extensive marine beach deposits were found in Namaqualand, south of the Orange river. Rich deposits were located some 25 m above sea level of a terraced beach. A minor diamond field was discovered in 1956 on the Skeleton Coast of Namibia. The area lies in the Kaokoveldt, south of the Kunene river, which forms the border with Angola.
These coastal fields are worked by excavators after overburden has been removed. Diamond-bearing gravel is removed by hand or by exca- vator brought to a central treatment plant. The origin of these marine allu- vial diamonds is open to debate. Was the original source inland, or did the parent rocks lie submerged under the Atlantic Ocean? The size of the stones diminishes as the distance from the mouth of the Orange River increases. It is therefore thought that the source is inland, the stones hav- ing been carried by rivers of former geological ages to the sea to be later cast up on the beaches near the river mouths by ocean currents.
About 1964 the Marine Diamond Corporation commenced diamond recovery from the sea bed off the Namibia mainland, and in 1967 a specially equipped barge operated about a mile off the mouth of the Orange river. The sand of the sea bed, up to 30 m below, is raised by air- lift and suction dredge. The diamondiferous sand is then screened, washed, concentrated by heavy media separation and finally sorted by hand. Shares in Sea Diamond, either the same or a similar venture, never really prospered.
Zaire, Congo and Angola
Diamonds from some areas of Africa are reported to have been sold for arms at various times and have become known as conflict diamonds. There is general agreement that trade in stones known to be conflict diamonds should not take place.
In 1910 diamonds were found in the south-western part of the Congo in alluvial gravels in the valleys of the tributaries of the Kasai river. Farther west, diamond deposits have been located in the Kwilu basin. A more productive area was discovered around the Bushimaie river to the east of the Kasai river and about 600 miles north-west of Lubumbashi in the district of Katanga. Near the Kundelungu plateau, just north of Lubumbashi, a number of kimberlite masses occur, a few of which have proved to contain diamonds. The town of Tshikapa is the centre of the diamond-mining operations in the Congo, which is the world’s largest producer of diamond in terms of quality. Before the West African production came on the market, the Congoproduced at least three-quarters of the crushing boart so widely used in industry.
During 1916 the Congo diamond fields were found to extend into the north-eastern part of Malange in Angola, particularly along the western bank of the Chuimbe river and both banks of the Luembe and Luana rivers. The Angola deposits are alluvial and are derived from an ancient drainage system which no longer exists.
Mining is carried out, in both Angola and the Congo, by removing the overburden to expose the diamondiferous gravel. This gravel is then exca- vated, taken to washing plants and treated in a heavy media separator. The concentrates are processed in a recovery section for the extraction of the diamonds.
Ghana
The discovery, in 1919, of diamond at Abomoso near the Birim river opened up diamond mining in Ghana. Later prospecting disclosed dia- mond in the district south-east of Kade and about 100 km north-west of Accra. Diamonds from Ghana are mostly of industrial quality, although gem crystals are also recovered.
The Ghana deposits consist of gravels from 0.5 to 2 m thick and are interesting in that the rock formations in the area are steeply dipp- ing metamorphosed igneous and sedimentary rocks of Precambrian age. The mining for diamond is carried out by removing the overburden and depositing it in previously mined sections. The exposed diamond-bearing gravel is mechanically loaded into one-tonne trucks and taken to the
washing and recovery plants where, for the smaller diamonds, a method of ‘skin flotation’ is used. Diamond are also found in the Ivory Coast.
Sierra Leone
The history of diamonds in Sierra Leone and the establishment of the diamond trade there is covered by H.L. Van der Laan in The Sierra Leone Diamonds, published by Oxford University Press in 1965 (Sinkankas #6808). The account covers 1952–61. The author does not omit the many political problems associated with mostly tribally organized and alluvial diamond mining; later troubles are described by other authors, and Matthew Hart, in Diamond: The History of a Cold-Blooded Love Affair, London, 2002; ISBN 184115279X, outlines what he sees as a threat to the long-term prospects of the De Beers organization.
From the geological standpoint, useful texts include Grantham and Allen, Kimberlite in Sierra Leone, London, 1960 (Sinkankas #2489) forming vol. 8 no. 1 of Overseas Geology and Mineral Resources. This review described kimberlite dikes with an outcrop map. Alluvial crystals are also described and there are useful crystal drawings.
The diamond fields of Sierra Leone were discovered in 1930, when a small diamond was found in the gravels of the Gboboro stream near the village of Fotingaia. Consolidated African Selection Trust Ltd sent a prospecting party from the Cold Coast to Sierra Leone. During 1932 they found diamonds north of the Bandafayi watershed in the Shongbo stream near Tongoma village. Small-scale mining operations showed the deposit to be worth investigating. The company was granted the exclu- sive right to prospect for diamond over an area of 10 800 km of the east- ern district of Sierra Leone.
Further exploration showed that diamond occurred in the gravels of the Sewa river, an area not included in the licence granted to the Cold Coast company, and in 1934 a new subsidiary company, the Sierra Leone Selection Trust, was floated and was granted the sole right to prospect for diamond in the colony. Owing to the great expanse of diamond-bearing gravels, policing the area was difficult. During the early 1950s it was esti- mated that more diamonds left the country illegally than legally.
The diamonds produced in Sierra Leone are in the main of good quality and are often of large size. Many of the crystals show excellent octahedral form with bright faces. Crystals of 100 ct or more are occasionally found: The Woyie River Diamond recovered in 1945 weighed 770 ct, but this was surpassed by the finding of the Star of Sierra Leone at the Diminco mine at Yengema in February 1972. This crystal weighed 968.9 ct and was the third largest diamond ever found. Natural bottle-green-coloured diamonds are often found and such diamonds will turn light brown on heating.
Mining is carried on in a similar manner as in the other alluvial fields of Angola and Ghana. The Sierra Leone diamond fields are situated some 225 km east of Freetown.
West Africa
Among the first diamonds to be discovered in the former French West Africa were those in the Région Forestière of the Republic of Guinea. A minute dia- mond found in a river in the N’Zêrêkorê district on the border of Liberia was probably the first. A year later, several workable deposits of diamond were found in the Makona river district and in the rivers of Haute Guinée.
The main workings of this diamond field are located some 75 km north- north-east of Macenta. The diamonds are mostly found in alluvial deposits in the upper courses of the smaller streams and in old terraces associated with such minerals as ilmenite, magnetite, zircon, rutile, corundum, mon- azite, epidote, topaz, spinel, staurolite, tourmaline and almandine garnet. The diamond crystals are usually octahedra or dodecahedra and are frequently of a brown colour, or a clear yellow or blue colour. The stones often contain black inclusions. The majority of the crystals are industrial quality only.
Diamonds have been recovered form ancient river terraces along the region of the Mambere river which runs through the western part of the Oubangui-Chari district of the Central African Republic. An economic study of West African diamonds was published by Peter Greenhalgh, West African diamonds, 1919–83, 1985; ISBN 0719017637.
East Africa
In Geology of East Africa by Thomas Schluter (1997; Beitrage zur regionalen Geologie der Erde Bd 27; ISBN 3443110274) there is a brief note stating that alluvial diamonds have been found about 20 km east of the Kichwamba vol- canic field in Uganda but that it was not possible to say whether or not the diamonds originated in kimberlites. The East African rift system has yet to be fully investigated.
Tanzania
Schluter (1997) describes the kimberlites of Tanzania, estimating that there are more than 200 examples. They are concentrated in the Lake Victoria area: John T. Williamson discovered the Mwadui kimberlite pipe in 1940; it was, at least at that time, the largest known pipe in the world (about 1500 1200 m in diameter). Water lain tuffs form a circumventing ring with a diamondiferous gravel halo. The kimberlite has an unusually
high water content. Millions of carats of diamond have been obtained from this mine; the Williamson pink diamond, in the personal jewellery of Queen Elizabeth II, is a celebrated polished stone of 23.06 ct from the original crystal of 54.5 ct. In Famous Diamonds, fourth edition, 2000; ISBN 090343265X, Ian Balfour describes some of the events surrounding the finding and eventual polishing of the crystal, an account also to be found in Emily Hahn, Diamond, 1956 (Sinkankas #2655). The present writer (MO’D) has examined this stone (now set in a brooch) and can assure readers that it is a quite remarkable pink.
Mwadui diamond crystals are often twinned and have an average weight of 0.24 ct. Other diamond-producing kimberlites in Tanzania are the Uduhe mine in Maswa district and the Kahama pipe. Fifteen pipes were discovered in the Shinyanga region by aeromagnetic survey.
Lesotho
During 1958 diamonds were discovered some 2800 m in a valley in the Maluti Mountains of the Mokhotlong area west of the Drakensberg mountain range. Mining was carried on by primitive methods. Lesotho became famous when, in 1967, a miner’s wife picked up a diamond weighing 601.25 ct. It was the largest diamond ever found by a woman. This crystal was cut into 18 stones. Two other large diamonds, one of 527 ct and the other of 338 ct, have also been found in Lesotho. The mine was closed when diamond prices slumped in the late 1970s.
Botswana
The search for diamonds in Botswana probably started in 1955 in the area west of the Limpopo river. A few diamonds were found along the dry Motloutse river at Foley in the Bamangwato tribal territory. Later searches were carried out to the headwaters of the dry river bed. Diamonds were found along the river course but the traces petered out and there was no sign of a pipe from which the diamonds could have come. The De Beers geologist, Dr Gavin Lamont, found traces of a large shallow valley which he connected with a suggestion made years earlier by Du Toit that an earth folding had occurred along this line and would have thrown the source of the Motloutse river much further west. This was proved when a group of pipes were discovered in the area of Letlhakane. One of these, found in 1967, is now the Orapa mine and is the second largest pipe mine, only being surpassed by the Williamson mine.
Sampling showed that diamonds were in payable quantity and in 1969 a pilot recovery plant was put in operation. Although Orapa was said to have come into production in July 1971, it was not officially opened until
1 May 1972. Mining is carried out by the open-cast methods. Since then production has largely increased in Botswana’s diamond mines, with Orapa producing 15 000 ct a day in 1981, though only 15% of this was suitable for gems. In contrast 40% of the diamonds produced from the nearby Letlhakane mine are considered to be of gem quality. A further large diamond mine at Jwaneng has been producing a high proportion of gem-quality diamonds.
Guyana
Diamonds were discovered in the gold washings of the Puruni and Mazaruni basins of Guyana, during 1887. The diamonds, small in size, are found in a gravel of ferruginous clayey or sandy nature which is overgrown with tropical jungle. The nature of the terrain makes trans- port difficult and recovery of the stones uneconomic. Diamonds are also found in the Cuyuni, Potaro and Berbice rivers and their tributaries.
The diamonds of Guyana are commonly worn and pitted octahedra and are most common in the Mearnu-Apiqua district and in the Potaro deposits. The finest quality and the best shapes come from the kurupung and Eping districts. The commonest colour of Guyana diamond is white with a slight yellow tinge, followed by Capes, and light and dark browns. Unusual colours are rare as are blue-white stones, but occasionally a small aquamarine-blue or deep greenstone is found.
During 1948 a diamond deposit was found on the Ireng river which lies along the Guyana–Brazilian frontier, which led to a miniature rush by miners from both sides of the frontier. A cheerful account of the area and his adventures in exploring it for diamonds is given by Victor Norwood in his two books Man Alone! (1956) and A Hand Full of Diamonds (1960) [Sinkankas #4790 and 4791].
Bolivia
Diamonds have been found in the foothills of the Andes in Bolivia. The diamonds were discovered in the river gravels of the Rio Tuichi and have been reported from the Rio Tequeje, Rio Unduma and some other tributar- ies of the upper Rio Beni. The diamonds are found in gravel beds of 1–3 m thick overlying a bedrock of Permian age.
Venezuela
The diamond occurrences along the Cuyuni and Paragua rivers in the state of Bolivar in Venezuela may be said to be an extension of the diamondiferous fields of Guyana. The exploitation of these deposits is
hindered by their inaccessibility but some mining and marketing of Venezuelan stones is carried out. Diamonds from the Paragua river are coated with iron oxide, but fine-quality stones can be cut from them. Green diamonds are frequently encountered at Icabaru. Fancy colours, such as yellow-green, brown, reddish brown, pink, light blue and black, are common in Venezuelan diamond deposits.
Russia
There is still a dearth of literature in Western languages on the dia- mond deposits of Siberia. In Russian, probably the all-time most impor- tant historical and geological account in A.P. Bobrievich et al., Almaznye Mestorozhdeniya Yakutii, 1959 [Sinkankas #732]. This is an account of the Yakutia diamond fields in Siberia, describing the area geology and the pipes as well as the properties of the diamonds themselves. A later study of the diamondiferous placers of the Malo-Botuobinsk region of western Yakutia. Siberia was published by I.S. Rozhkov et al. in 1963 [Sinkankas #5606]. Rock formations in the same area are particularly well described in the same author’s 1967 publication, Yakutskiy Filiala Sibirskogo Otdeleniya [Sinkankas #5609]. A paper in The Mining Magazine 97(6), pages 329–38, 1957, reviews a number of USSR Russian-language publications on diamond deposits.
As in many places, the first diamond appears to have turned up as a pebble which attracted sufficient attention to make further investiga- tion desirable. Again, the diamond crystal was apparently found when gold and platinum were being sought.
In Mineralogy of the Diamond (1997 op. cit.) Orlov reviews some of the occurrences of Russian diamonds. His opinion is that the sources of many diamonds in the Urals are Paleozoic clastic rocks and that dia- monds may have entered these rocks on disintegration of the kimber- lites. Some diamond-bearing pyrope serpentinites in one of the Yakutia pipes have given rise to the theory that they are fragments of completely serpentinized garnet peridotites or olivenites generally associated with a kimberlite magma originating in the upper mantle. A further theory, also originating from Russian sources, is that all diamonds in kimber- lites are genetically associated with deep-seated pyrope periodotites. When these are fused they form kimberlite magma which acts as the transporting agent to the upper part of the crust. In general, the theories can be made to conclude that diamondiferous peridotite rocks must exist at depth.
In 1958 an eclogite xenolith was found in the Mir pipe at Yakutia.
Orlov found that the diamond content was exceptionally high and the octahedra show stepped faces reminiscent of crystals from South Africa.
Other eclogitic sources of diamond have been found in Yakutia and in Africa.
Kimberlites are the only commercial diamond-bearing rocks found in the upper part of the crust. The first diamond-bearing kimberlite pipe in Yakutia was discovered in 1954 and given the name Zarnitsa. The Mir and Udachnaya pipes were located a year later, followed by Aikhal.
Up to 1938 the total diamond yield of placers in various parts of the Urals was 270–300 crystals. The placer deposits are extensively described by Fersman (1922), Precious and Coloured Stones in Russia vol. 1 (in Russian).
China
Occasional reports on the possible occurrence of diamond in China have been noted for more than two centuries but it was not until systematic prospecting began in 1953 in the provinces of Shantung and Hunan that recovery became organized. Orlov (1977) states that the finds in Shantung were in the basins of the rivers I Ho and Shu Ho; in Hunan finds were made in the basin of the Yuan Chiang river, a tributary of the Yangtze. Placer diamond deposits have been found in Yunnan province and on the island of Hainan.
Sorting and Grading
On recovery and after cleaning, diamond crystals, from whatever source, are sorted. Many crystals have no ornamental potential and are classed as industrials. Gem-quality crystals are sorted into categories of size, shape, clarity and colour at various stages before polishing. Details of the sorting process, carried out in different places, can be found in textbooks on the diamond though the closer the student gets to the process of pricing the fewer the details become! Common-sense dictates that the whole sort- ing process as far as gem-quality crystals are concerned is market-driven: this means that in some circumstances a crystal will achieve a higher grade (and price), sometimes a lower grade. The final classification, again according to colour, size, shape and clarity forms the basis of the pricing for the sights (sales) held by the De Beers orgainsation. Sight-holders are allowed a certain percentage of the type of goods they most want and have to accept some less acceptable material so that an unsaleable stock- pile does not form. Not all rough diamonds are sold through De Beers – private enterprise of every kind continues! Previously the sight-holders’ list has been shortened.
Readers are referred to textbooks on diamond for further information;
the whole sorting and pricing process is never static.
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