Diamond Mine

Mid-20th-century prospecting revealed hundreds of kimberlite outcrops in Brazil, but all mining during the period 1725-1865 took place in alluvial, eluvial or colluvial deposits. Some lithified "bedrock alluvial" sites were worked by benched quarries, and matrix specimens of diamond crystals in coarse conglomerate were sometimes found. Miners to this day may try to sell visitors fake specimens of this type, with the crystals glued onto the matrix (Cassedanne, 1989).

In the early days, mining was done by slaves under the whips of the Portuguese. After Brazilian independence there was much freelance prospecting, and garimpeims often formed co-operative organizations, the miners sharing the work and dividing the profits among themselves and with financial backers, as well as with owners (if any) of the lands hosting successful prospects.

Diamond fields speckle most of the southern half of the country, but the richest sites, and the earliest found, stretch along the Jequitinhonha River for many tens of kilometers north of the town of Tejuco (Diamantina). Diamonds there are found in gupiaras (coluvial terraces high above the streambeds), gorgulho (eluvial plateau deposits), and cascalho (gravel deposits in the streams). In the cascalho deposits, the most important type, gravels were (and are) washed and sorted in complex systems of hoses, pumps, sluices, and washing crates, while women and children comb adjacent parts of the drainages for diamonds. A mechanized dredging operation in the Jequitinhonha River, 80 km downstream from Diamantina, is the only contemporary Brazilian diamond "mine," producing 1 carat of diamond and 1 gram of gold for each 100 cubic meters of gravel (Maillard, 1980; Cassedanne, f989).
The featured collection's only Brazilian diamond is a typically frosty and somewhat irregular crystal measuring 1.3 cm and weighing a little over 11 carats. It comes not from Diamantina, Minas Gerais, but from "Estralla do Sol, Mato Grosso." The province of Mato Grosso is in west-central Brazil, bordering Goias Province on the east and Bolivia and Paraguay on the west; its capital is the town of Diamantino, near which the chief diamond field of the province is located. Prospecting for diamonds (and gold) in this remote region has never been as intense as in the other fields to the east. According to Cassedanne (1989), "A period of excitement and wealth was short-lived, ending in 1847 with the decline in gold production. In the year of 1852 the Mato Grosso Mining Society went bankrupt [and] the Diamantino prospect was abandoned."

In recent years, however, diamond mining activity has picked up in the province. Near Diamantino and north of the city of Cuiaba, a 63,000-hectare claim block now known as the Mato Grosso Diamond Project was host to a large-scale diamond rush in the 1960's, when alluvial diamonds were first discovered in the Morro Vermelho Formation. The proliferation of high-quality diamonds being found by prospectors in the area attracted several major diamond mining companies, and more than 50 kimberlite pipes were discovered. Diamonds collected from the property exhibit pristine or near-pristine surfaces, suggesting a local source for the significant number of alluvial diamonds found on the claims. Eclogitic garnets have also been found in two of the initial heavy mineral samples collected. Iciena Ventures, Inc. is part owner in the project, and recently announced the acquisition of 47 prime diamond exploration permits covering 438,000 hectares in the states of Mato Grosso and Rondonia, Brazil (www.iciena.com).

An area in the southern tip of the state of Rondonia and the northwestern part of the state of Mato Grosso also has large reserves of diamonds. Mining is forbidden there because it is in the protected homeland of the Cinta Larga Indigenous People; however, nearly 3000 garimpieros and miners entered the area illegally to mine diamonds in 1999, and eventually had to be evicted by government troops. The Federal Police estimates that gems amounting to 50 million dollars were smuggled from the region to Belgium last year.

In the juina Diamond Province, Mato Grosso, the Diagem International Resources Corporation currently has 130,000 hectares of mineral claims. The Province has vast deposits of alluvial diamonds as well as 7 identified diamondiferous kimberlite pipes on which basic exploration is complete. Over 130,000 carats of diamonds were recovered during the evaluation phase, including large stones up to 450 carats, and a 100-carat pink crystal. Production began in 1996 (www.diagem.com).

Argyle mine, Western Australia, Australia

No diamonds from Australia reached the world market until 1981, but by 1995 the country had assumed first place in annual diamond production worldwide. Most of this ballooning output has come from the Argyle mine, in the East Kimberley diamond province, situated in the northeastern part of Western Australia. The workings consist of a huge open-pit mine in a lamproite pipe. It is somehow satisfying, though merely coincidental, that this Australian "Kimberley" region was named (in 1880) after the same Earl of Kimberley, then British secretary of State for the Colonies, after whom the great De Beers New Rush diamond mine in South Africa had been renamed the Kimberley mine in 1873 (Grice and Boxer, 1990).

Williamson mine, Mwadui, Tanzania

The Williamson mine is the largest kimberlite mine in Africa, with a main pipe eight times larger than that of the Premier mine. It has yielded diamond crystals to 240 carats; a gorgeous pink 54carat stone was cut to a gem of 23.6 carats and presented to Princess (now Queen) Elizabeth on the occasion of her marriage in 1947.

Mwadui village lies in an area of diamondiferous gravels between Shinyanga and the southern shore of Lake Victoria; some claims were pegged as early as 1910, and limited mining began in 1925 (Webster, 1983; Janse, 1996). In 1934, Dr. John Williamson, a geologist from Quebec, came to prospect in Tanzania (then British Tanganyika), and one of the last star-stories about an individual diamond entrepeneur commenced: "Every geologist dreams of discovering an important diamond mine," wrote G. J. Du Toit in an unpublished manuscript called The Williamson Story, "[and] everybody wants to own one outright. Only one man, Dr. John Thorburn Williamson . . . the discoverer and founder of the now-famous Mwadui diamond mine . . . has ever achieved both ambitions" (quoted in Maillard, 1980).

In 1940 Williamson had worked in three small, unprofitable diamond mines in Tanganyika, and had discovered a few small kimberlite pipes, but was nonetheless down to his last £100 and thinking of joining the army. But on the evening of March 6, 1940, his assistant brought him a soil sample from an abandoned survey trench near Mwadui; processing it, the two men found not only abundant grains of the indicator mineral ilmenite but also a beautiful 2-carat diamond octahedron (other versions of the discovery-story exist, as we might expect- see Janse, 1996). Soon Williamson's systematic work at the site had revealed a massive kimberlite pipe and associated diamondiferous gravels, and the Williamson mine was born. he was able to bootstrap the mine's growth from profits, and built a huge processing plant, a power station, and a township for several thousand employees. After Williamson's death in 1956, his heirs sold the mine to De Beers, and continued economic success followed Tanzanian independence in 1961, and the mine's nationalization (Maillard, 1980).

According to the present owner, Tan Range Exploration Corporation, the Williamson diamond mine is still operating, but on a much smaller scale than previously. Through various modern exploration technologies, e.g. airborne magnetic-anomaly surveys, the company has identified several new, although small, kimberlite pipes in the area and elsewhere in Tanzania. These might be expected to compensate, at least partially, for the expected closing of the Williamson mine sometime in the fairly near future (www.tanzam 2000.com).

The Williamson mine diamond specimen illustrated here is an attractive, nearly colorless 1.3-cm octahedron weighing 7.9 carats.

Kenema, Diamond Fields, Eastern Province, Sierra Leone

The diamond fields of Sierra Leone lie in hilly terrain north of the town of Kenema. Bounded on the west by the Sewa River and on the east by the borders of Liberia and Guinea, the region measures about 80 × 100 km and accounts for about one-third of the total land area of the tiny country. Alluvial diamonds were first found in Gboboro Stream in January 1930 by N. R. junner and J. D. Pollett of the Sierra Leone Geological Survey (Janse, 1996), and there was small-scale prospecting and mining until the end of British colonial rule in 1961. A company called Consolidated African Selection Trust (CAST), through its wholly owned subsidiary Sierra Leone Selection Trust (SLST), acquired a diamondprospecting lease over the whole country, and annual production reached one million carats by 1937 (Janse, 1996). Even during this period, as a harbinger of the chaos to come, more diamonds probably left the country illicitly than were sold by the mining company (Webster, 1983).

 bottle-green. The "Star of Sierra Leone," found at Yengema in 1972 and weighing 969.8 carats, is the largest alluvial diamond of gem quality ever discovered anywhere.

During the last years of British rule the villagers of the region, having learned about how to find diamonds and about their extremely high value, began illicitly collecting and selling them on a large scale, with fortune-seekers from neighboring Guinea and Liberia often joining in too. These are among Africa's poorest countries-Sierra Leone is the poorest-so the diamond mania was not surprising, but it soon threatened the overall economy of the colony. "Farmers neglected their crops and livestock to such an extent that the government had to import commodities like rice, which in normal times Sierra Leone exported. Instead of enriching the country, diamonds were threatening to ruin it. In the region of the diggings there was a severe shortage of food, and prices rose to dizzying heights" (Maillard, 1980).

The British, by issuing diamond-collecting licenses and by encouraging the villagers to dig for the official company SLST, attempted to get control of the situation. But large-scale illegal trading still went on, especially after large numbers of Lebanese merchants moved in to seize control of smuggling activities close to the border of Liberia, in whose capital, Monrovia, diamond dealers and cutters from Antwerp and elsewhere waited to buy smuggled gems at very low prices.

In 1955 the British, in co-operation with DeBeers, countered by authorizing the Diamond Corporation of Sierra Leone (DCSL) to set up a buying office in Freetown, the capital city, with smaller outposts in villages near the sources. "Miners" then could individually bring diamonds to sell at fair prices, and without risk to themselves, and the diamonds could be taxed by the government, then channeled into established international markets. The single SLST concession for all of Sierra Leone was split into two lease areas, called Yengema and Tongo (Janse, 1996).

But since Sierra Leonean independence in 1961, and especially after the country became a republic in 1971, the story of diamonds there has been largely one of civil war, mayhem, deepening poverty, cruelty, and death-one of the world's worst and least noticed "news" stories of recent decades. A series of government coups and counter-coups, these supported or undermined variously by the governments of major powers and by the forces on different sides of the civil conflict going on in neighboring Liberia, have cost tens of thousands of Sierra Leonean lives. Government and rebel forces have both typically formed their armies from underfed children and from alcohol and drug-addled young men, and all sides have employed mercenaries from the U.S., Russia and Europe to "lead" them. In one rebel offensive against Freetown between December 1998 and February 1999, at least 7,000 people died, and, in the overheated (but not necessarily inaccurate) language of one website, "Women and young girls were raped systematically . . . The population was routinely used as human shields. . . . Entire compounds of families have been emptied, the villagers lined up while the rebels jokingly decide which ones to shoot and which to let go . . ." (www.comebackalive.com). Mutilations, especially the chopping-off of arms and legs, have been practiced on a large scale, foreigners have been executed, villages have been starved, and reports of cannibalism persist.

Clearly the most common motive for all this violence is greed for the diamonds which are Sierra Leone's only significant source of wealth and accessible symbol of power. "The diamond mines were the first targets for repossession, as one of the would-be dictators hired [mercenaries] on credit, with a promise of US $500,000 a month payment in diamonds" (www.comeback alive.com). Such are the facts which lurk behind the vaguely, often glibly used term "conflict diamond"-one may or may not choose to bear them in mind while contemplating the two crystals illustrated here, a colorless, modified 1.3-cm octahedron (with a smaller "side-car crystal") weighing 7.5 carats, and a colorless triangular 1.1-cm made weighing 4.6 carats.
Between 1960 and 1996, "official" diamond production from Sierra Leone fell from 2 million to 400,000 carats per year; however, in 1996 a Canadian company was thinking of mining a small kimberlite pipe where gem-quality diamonds seem to comprise an extraordinary 60% of the total yield (Janse, 1996).

Oranjemund district, Orange River, Namibia

Oranjemund lies, as its name specifies, at the mouth ("Mund") of the Orange River, where this river empties into the South Atlantic. Since the Orange River forms the border between Namibia and the Republic of South Africa, Oranjemund is at the southernmost point of Namibia (formerly the South African protectorate known as South-West Africa, and before World War I the German colony of Deutsch Sudwest Afrika). At Oranjemund, the Namdeb Diamond Corporation Limited (owned jointly by the Namibian government and De Beers) maintains a fleet of earth-moving equipment "nearly as large as that owned by the United States army" (Maillard, 1980), and uses it to conduct a mammoth beachmining operation for diamonds.

"Beach" diamonds were first detected along this coast in 1908, near Luderitz, where a railroad worker found a few small crystals in the sand dunes. Soon, discrete beach deposits were being found along a 60-mile stretch north of the mouth of the Orange, and the Germans were mining considerable numbers of small but highquality diamonds. When South Africa took control after World War I, the deposits were sold to Consolidated Diamond Mines (CDM), which was transferred to DeBeers in 1929; the present Namdeb Corporation was organized in 1994. Its current operations include beach-mining, terrace-mining, and seabed-mining-all flourishing nicely, and imparting a new sense to the old term "alluvial diamonds."

For a while geologists wondered whether these marine diamonds had come from kimberlites on the sea floor, or whether they had been transported oceanwards from the great kimberlite swarms of the inland Kalahari Craton. But it is now quite certain that kimberlites do not occur in the ocean basins, only in continental cratons, and moreover a mere glance at a stream-drainage map of southern Africa makes it clear that huge numbers of diamonds from inland kimberlites must have been transported to the sea by the Orange River system (including tributaries such as the Vaal); further, it has been noted that the sizes of the marine diamonds diminish regularly as the distance from the mouth of the Orange increases. Presently it is estimated that over the past 100 million years, up to 1,400 meters have been eroded from the land surface of South Africa and Namibia, and that of all of the diamonds released to the streams by the weathering of the kimberlites, only 10% stayed behind in inland alluvial deposits, the remaining 90% having been carried to, and out into, the ocean. And since the ocean waves shatter the poorer-quality diamonds, 90-95% of marine diamonds are of gem quality (www.amnh.org/exhibitions/diamonds).

Terrace mining for diamonds at Oranjemund takes place well above the high-water level and up to 3 km inland, and seabed mining, carried out by suction-dredging from huge offshore barges, operates more than a mile out from the mouth of the Orange. More important than either of these is beach mining. In the first stage of this process, massive earth-moving equipment removes loose beach-sand overburdens to depths of up to 80 feet, exposing ancient beach terraces as much as 65 feet below present high-water levels. The terraces are broken up and bulldozed into rubble-piles until the tough, irregularly configured bedrock schists are laid bare: this is the level most avidly sought, since the gravels left in the potholes and crevices here have concentrated most of the diamonds.
Backtrenchers with digging buckets gouge out some of the gullies, but mining from this point is largely a matter of hand work: miners known as bedrock cleaners dig, shovel, and sort the highly diamondiferous residual gravels, until the whole schist floor is swept clean (Maillard, 1980). The technology is efficient, and potential yields from the "Oranjemund district" are vast-in 1995 alone, such beach deposits produced 1,300,000 carats of diamond crystals (www.amnh.org/exhibitions/diamonds).

Similar beach diamond deposits have been located in Namaqualand, South Africa, south of the mouth of the Orange, as well as much farther north, on the "Skeleton Coast" of Namibia (Webster, 1983). It is most likely, however, that the specimen illustrated here (a gemmy triangular made twin 1.3 cm across, weighing 4.1 carats) came from somewhere not too far north of Oranjemund-and that the working from which it came has long since been buried again by tide-borne sands.

Bangui region, Central African Republic.

Although only a tiny fraction of the world's diamonds comes from the Central African Republic, diamonds are this poor, landlocked former French colony's principal resource. The colony (which is partially underlain by a small craton), was once known as Ubangi-Chari; it lies just north of Zaire, the latter also known as the Congo Republic. Neither state should be confused with the former French Congo, now the People's Republic of Congo, lying just to the west of Zaire (devotees of dioptase will be familiar with these confusions). The Ubangi (or Oubangui) River marks the border between Zaire and the Central African Republic, and Bangui is a town on the river's north bank. The "Bangui region" (source of the crystal illustrated here, a 1-cm yellow cube weighing 4.1 carats) corresponds to a diamond-producing area between Bangui and Berberati, in the southwestern part of the country (Maillard, 1980; Webster, 1983).

Here, diamonds are recovered by clearing heavy forest and jungle vegetation, then removing a thick bed of topsoil to reach diamond-bearing alluvial gravel; there is also some mechanized dredging in beds of the region's numerous rivers and streams. Further diamond-related developments may follow when the parent kimberlite or lamproite pipes (if they still exist) are finally located in the Central African Republic.

Northern Lunda Province, Cuango River area, Angola

Angola produced 1.8% of the world's diamonds in 1996 (www.amnh.org/exhibitions/diamonds), and a high proportion are of gem quality. Counterbalancing these upbeat observations, though, is the fact that civil wars and insurgencies have intermittently troubled Angola ever since independence from Portugal was declared in 1975. Consequently, as in the case of Sierra Leone, diamonds known to be from Angola may be "conflict diamonds." At least half of all diamonds found in the country are gathered and sold illicitly (Janse, 1996). Even when there is no fighting, demobilized soldiers generally prefer to dig gems rather than return to bare-subsistence farming.

The Angolan diamond regions are all in the northern part of Lunda Province, in the country's northeastern corner, adjoining Zaire,. In fact, the first discoveries of alluvial diamonds, in 1911/ 1912, were byproducts of exploratory surveys just to the north, in what was then the Belgian Congo. A series of parallel rivers run from south to north through Lunda Province before passing into Zaire, and diamonds have been found in many of them. The Cuanga River, forming the border between Lunda Province and Malanje Province to its west, is the largest of these rivers, and had produced about 80% of Angola's diamonds as of 1998 (Harlow, 1998). It is possible, however, that the stated source of the lovely 1-cm yellow crystal illustrated here,"Cuango (or Kwombo) River," is merely a geographically convenient term, and that the diamond was found in one of the region's smaller rivers (candidates include the Chicapa, Luachimo, Chiumbe, Luana and Lembe).

Creative geological fieldwork by R. Delville in the early 1950's succeeded in establishing that diamondiferous gravels and conglomerates were concentrated along two parallel faults in a buried fault-graben structure in Lunda Province, and inferences could then be drawn concerning where the original kimberlite sources lay concealed in the forested wilderness of the province. The first of the kimberlite pipes was found near the Chicapa River in 1952; it is now known to be one of the largest in the world (Maillard, 1980), and one of about 600 pipes in northern Lunda (Harlow, 1998). Ongoing mining and prospecting is in the hands of a consortium, Consorcio Mineiro de Diamantes (Condiama), whose members include De Beers, the government of Angola, and an earlier company called Diameng (Companhia de Diamantes do Angola), which had begun to look for diamonds during Portuguese colonial times.

Ghana

Although Ghana is not represented by any of the diamonds in the collection featured here, it is the locality for the large and amazingly modified cube shown on the cover of this issue, from the collection of Mike Scott. In 1911, British prospectors found small numbers of alluvial diamonds in what was then the colony called the Gold Coast-more famous in history both for its gold and for its infamous slave-trading ports-on the Gulf of Guinea. As of 1980, 3 million carats of diamonds were being produced annually, 85% of the output being merely of industrial grade (Maillard, 1980). In 1996 the country accounted for 0.7% of world diamond production (www.amnh/exhibitions/diamonds).

Alluvial diamond deposits in Ghana are concentrated in the Birim valley, in the Akwatia region midway between the capital city of Accra and the town of Kumasi (Maillard, 1980)-this is the likely provenance of the cover crystal.

The Future of Diamond Mining

Levinson et al. ( 1992) estimate that the total world production of diamonds, both gem and industrial, between remotest antiquity and the year 1990 was 2,213,875,000 carats, equivalent to 450 metric tons weight. This is, they say, a conservative estimate, since it rounds up only slightly from official figures to take into account unreported, illicit production. As mineral species go, even gempotential species, diamond is not really rare-how many tons of jeremejevite or sinhalite do you suppose have been found?-but its enduring appeal, not to speak of its many industrial uses, makes the securing of further supplies a pressing concern.

Since 1870, Africa has spoiled us: in that year, as mining was just beginning at Kimberley and on the Vaal River, only 300,000 carats of diamonds were produced worldwide, but in 1920, 3,000,000 carats were produced, the tenfold increase being entirely due to new production from African sources. Although the classic African kimberlite mines are now in decline (and some are closed), new African mines, Russian mines, and most recently the Argyle mine in Australia have so far kept worldwide production growing rapidly: 42,000,000 carats were produced in 1970, and more than 100,000,000 in 1990 (Levinson et al, 1992). But now several Russian mines, the Williamson mine in Tanzania, and even the Argyle mine are well past their primes-if we keep up the present rate of consumption, where are diamonds to come from in future decades (aside from the vast stockpiles held by the Russian Diamond Fund)?

One plausible speculation is that more and more of them will come from the sea. Marine diamond mining off the Atlantic coasts of South Africa and Namibia was pioneered by two small companies in 1954. Then, in the early 1960's, a Texas oilman named Sam Collins founded a company called the Marine Diamond Corporation, now in the capable, high-tech hands of De Beers Marine (Pty) Ltd. This company currently dominates the available offshore lease areas, which extend up to 5 km out from the shore (Gurney et al, 1991). There are several positive indications about this diamond source: for one thing, a conservative estimate of reserves in the African marine deposits is 1.5 billion carats-almost three-quarters of total world production since antiquity-and, for another thing, 90-95% of the diamonds are of gem quality, natural "sorting" having destroyed the inferior stones along the way between the original drainages of the kimberlites and final deposition on the continental shelf.

To put it in terms of another statistic, these diamonds deposits contain at least 100 times as many gem diamonds (by weight) as are presently being used each year in jewelry (Levinson, et al, 1992). However, diamonds recovered by relatively simple suction equipment, and by divers, in shallower waters are vastly outnumbered by deeper-water diamonds, and these are difficult and expensive to find and retrieve. Much technical progress is being made, but deep-marine diamond mining is still only marginally profitable. It may also be true that the South African/ Namibian marine diamond deposits are an anomaly in the world, since they result from the uniquely favorable combination of a rich inland diamondiferous craton, deep weathering of the craton, and stable drainage over a very long time to a nearby ocean. Prospectors have eyed the Arctic waters north of the Siberian and Canadian cratons, and some sites in the Gulf of Guinea, but climatic as well as geological factors would seem to preclude mining in these areas, even if they should prove to hold diamonds.

Although they acknowledge the importance of the southern African marine fields, and although they regard some inland alluvial diamond deposits, particularly in Angola, as promising, Levinson et al. (1992) predict that the most significant new diamond sources of the 21st century will be newly discovered kimberlite pipes in Siberia and northern Canada. Economically viable kimberlites, they point out, are amenable to large-scale mining and discouraging to illicit "pirates": two-thirds of world diamond production in 1990 came from just eight large kimberlite mines. The Russian and Canadian cratons are vast, and huge swarms of diatremes may well lurk under the glacial cover in under-explored or unexplored regions (the very rich diatreme now being exploited by the Ekati mine remained successfully camouflaged for a long time under the glacial meltwater of Lac de Gras).
Levinson et al. also point to the geological favorability of Antarctica, where a large craton lurks under the ice cover. Perhaps by the end of this century some technology will have evolved for getting at diatremes there. And Janse (1996) suggests that Africa may not only continue to be a major diamond producer, but may again become the major producing diamond province of the world, perhaps thanks to technological breakthroughs at the marine deposits, or perhaps also to new kimberlite discoveries in central and western Africa, where alluvial mining so far has been the only important kind.

As a mineral collector, one might wistfully regret that almost all of the people who customarily seek or mine or study or write about diamonds are interested in them solely for their industrial or gemstone uses, or as objects of scientific research. It would be interesting (though probably depressing) to know exactly how many euhedral, uncut crystals of diamond are preserved today, from throughout the course of the long history of human obsession which has been sketched here. The fine crystals in the private collection illustrated here provide a wonderful glimpse of a unique species in its original state.

ACKNOWLEDGMENTS

My thanks to the owner of the specimens featured here for making them available for study and photography, and to Bill Birch for reviewing the manuscript and making helpful suggestions. My thanks also to Wendell Wilson for executing the photography, for preparing the other illustrations, for providing information on early collectors, and for locating references in the Mineralogical Record Library. It should be noted that the Record Library was an invaluable resource in the preparation of this article.

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