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DIAMONDS & VOLCANOES

DIAMONDS OF AFRICA

RAREST OF THE PUREST
The volcano of Kimberley in South Africa, justly nicknamed the Big Hole, had been dug for 43 years to become what is now known as the biggest man-made hole on earth. The reason - small little sparkling crystals that girls would die for - diamonds. By definition beautiful, durable and rare, the fascination with human psyche seems fixed for eternity.
Tens of millions of years ago, just as South Africa was settling into volcanic retirement, its innards emitted a last few burps, which reached the surface as kimberlite pipes. There are about 150 such pipes in South Africa, but by far the best known is the Big Hole. The Big Hole yielded 2.72 tons or 14.5 million carats of diamonds before being closed in 1914 - 22 700 000 tons of grounds had to be excavated. No other volcano has undergone such a thorough post mortem.

THE DIAMOND STORY
Let us take you on a journey back in time, when the massive volcanic upheavals created and exposed the most valuable natural mineral within a volcanic pipe that gushed pulverised rock, incandescent bombs and molten lava into the surrounding areas. Lets go to Kimberley, in South Africa, where the ancient volcano triggered the mad scramble for diamonds in the city heyday.


GEOLOGY OF DIAMONDS
Diamonds are mined from volcanic pipes, or alluvial deposits (or secondary alluvial deposits) that originate from these pipes, yet, strangely enough, there is no direct genetic relationship between diamonds and the volcanic rocks that host them. As the magma rises through the diamond bearing layers of the mantle, the diamonds are ripped off the walls of the vent. This also explains why most of magmas do not contain diamonds. Scientific studies proved that the formation of diamonds must have taken place at depths of at least 190 km where pressures reached 350 to 700 MPa at temperatures 1500 to 2400C. Ultra basic rock peridotite in its molten form most likely has provided the right conditions.
The upper limit of diamond stability depends on pressure and temperature. The higher the temperature, the higher the pressure required for diamond to remain stable. Only in the cool, deep ancient roots of continents that have not been deformed or metamorphosed are there sufficient diamonds at shallow enough depths to be brought up by magmatism. Most magmas originate at much shallower levels, in regions of graphite stability and thus are not capable to pick up the diamonds on their way up. Only kimberlites and lamproites are generally below the level of diamond stability, which is why their relationship with diamond deposits is so important for the mining industry.
Both kimberlites and lamproites are formed from explosive gas-rich magmas that are generated at great depths in the earth (200 to 300 km for kimberlites and about 200km for lamproites). Kimberlite magma expands rapidly as it reaches the surface of the earth (kimberlite magma contains more gas than lamproites), producing deep conical explosion crater. The violence of eruptions toward the surface is believed to account for the fact, that so many diamonds are chipped or cleaved. Depending on the magma supply and depth of exposure, these so-called pipes typically range from 50 to 500 metres in diameter. The shape of kimberlite pipes is steeply conical, resembling a carrot shape. Lamproites, by contrast, form conical or irregular bodies that commonly do not continue to great depths. Kimberlites and lamproites are very alkaline volcanic and subvolcanic intrusive rocks. Whether they contain diamonds depends on number of factors, including the depth of erosion that has occurred since eruption.
Kimberlite is named after the town of Kimberley, where it was first time discovered. Below the surface, kimberlite has a bluish colour and is known as blue ground, but on exposure to the atmosphere it weathers to a yellowish powdery rock, which is known as yellow ground. Kimberlite is a complicated mixture of volcanic rock, almost unchanged from its original composition and the plucked-off fragments from the host rock, which may vary from minute pieces to masses weighing thousands of tons. It is a porphyric alkalic peridotite containing abundant phenocrysts of olivine (commonly altered to serpentine or carbonate minerals) and phologopite in a fine-grained groundmass of calcite, titanium-rich ilmenite, red garnets (calcium magnesium iron silicate), the green chrome-rich pyroxene, diopside and phlogopite with accessory minerals. Shiny flakes of mica also occur. The presence of these minerals is a guide to locating kimberlite when prospecting for diamonds.
The volcanic pipes vary in size; the Kimberley pipe being 4 ha at the surface, the Dutoitspan 13 ha, the Premier 32 ha and the Finsch Mine 39 ha. In South Africa about 150 of these pipes have been discovered, often clustered in groups, but only about 25 have proved to contain diamonds. Very ancient diamonds, formed about 2500 million years ago and much older than those in the kimberlite pipes, occur in gold beds at Klerksdorp (South Africa). They are green due to the radioactive irradiation. With cutting, however, the green colour disappears.

MAGNIFICENT
Diamond is a crystalline form of carbon and the hardest mineral known. The name comes from the Greek word adamas meaning indomitable or unconquerable. Diamonds are found from well-formed crystals to crystal fragments and impure or imperfectly crystallised diamond matter, which is known as bort. Bort is used in industry for high-speed and precision tools where extreme hardness is essential. Whether the job calls for brute force or microscopic precision, diamonds cut everything. And only a diamond can cut diamond.
But it is for beauty not utility that diamonds are cherished. They have been called rare and noble productions of nature and fragments of eternity. They have been credited with possession of magical powers and reserved for symbolic and sacred rites. Wars have been waged over them and cities pillaged in search for them. Men would come to treasure them, believing in their supernatural powers. Symbol of virtue, purity and courage, diamonds would protect against evil. Almost without fail, diamonds have attracted determined men, each willing to risk all to secure control of a myth that spawned a business empire of unusual staying power.
Today, it is most often women who adorn their necks, ears and fingers with diamonds. A few centuries back, however, the rarest of gemstones were reserved for men - not for decoration, but to protect them in battle and to guide them safely home. It wasnt until the 14th century that the wearing of jewellery became acceptable dress for women. Of course, prior to that, queens and other women of nobility (Cleopatra, for one) had exploited the allure of these rare magnificent gems. Large diamonds have acquired names, histories and legends on their own.
Diamonds are the most compact form of wealth. They are graded for sale by their colour, purity, perfection of cut and weight in carats. A mere handful of high quality diamonds, is as worth as 200 kg of pure gold. To establish a diamond's quality, jewellers examine each of the 4Cs - cut, clarity, carat weight and colour. The combination of the 4Cs determines the value of a particular diamond. For example, a colourless diamond is at the top of the Diamond Quality Pyramid in colour, but if it lacks clarity, is small, or not well cut, it will be of a lower value. The finest stones possess the rarest quality in each of the 4Cs, and are the most valuable.
A diamond is forever.

THE DIAMOND RUSH
A teenager finds a pretty white pebble on the banks of Orange River near Hopetown. The year is 1866. Had Erasmus Jacobs known that his discovery was to lead to the great South African diamond rush, he might well have called out Eureka! - the name eventually given to this yellow diamond of 21.25 carats. The diamond passed into the hands of a trader, John O’Reilly, who sent it to Grahamstown, where it was identified as a diamond.
But it was the deal made by Schalk van Niekerk, a Hopetown farmer, and a Griqua shepherd called Zwartbooi, which really drew the treasure hunters from around the world. Van Niekerk traded all his possessions for a magnificent 83.5-carat diamond, named as the Star of South Africa. Its discovery prompted Sir Richard Southey, the colonial secretary at the Cape, to declare: “This is the rock on which the future success of South Africa will be built. The diamond rush had begun.
Owned by De Beers brothers, Colesberg Kopje, was an eroded remnant of a volcano. It was the place where in 1871 the Star of Africa was found. The place would later become known as the Kimberley Mine or the Big Hole - the most famous diamond mine in the world. As tens of thousands of diggers rushed to peg out the whole area, the entire hillock quickly vanished as a result of their feverish digging, soon to be replaced by a hole, which eventually reached colossal proportions.
The five mines in the area around Kimberly were originally divided into claims 10x10m, which were worked by individual diggers. By 1872, the tents and shacks of more than 50 000 feverish diggers crowded the mining town surrounding the hillock. Overcrowding, insufficient water, unsanitary conditions, disease, heat, dust and flies were ever-present problems in the mining town. In the fledgling city many gambling dens, cardsharps and loan sharks thrived on a diet of other people’s blood, sweat and tears. The stakes were high and the ruthless ruled as fortunes were made and lost in a day. Some found only despair and heartbreak, but others struck it rich.
Legend says that successful diggers went on mammoth sprees, lighting cigars with bank notes, while the women bathed in champagne. A bawdy shantytown born of a desperation and greed redolent of the American Wild West, Kimberley swiftly donned a mantle of architectural elegance. Suddenly the colony found itself transformed from a debtor to a creditor. The insatiable demands of the diamond fields generated greater shipping activity and railways began to replace the time-honoured ox-wagons. Rumour has it that more millionaires gathered under the roof of the Kimberley Club, established in 1881, than under any other roof in the world.
As the claims deepened, so yellow soil gave way to harder blue ground, assumed by many to be bedrock and largely barren. Those striking the blue ground frequently sold off their claims. But the complex workings made the Big Hole increasingly chaotic as men dug deeper. Fights and riots became commonplace. A some kind of amalgamation was inevitable. Recognising this was one thing achieving it, another, especially since it was also recognised that whoever succeeded would hold the key to fabulous wealth.
Cecil Rhodes, a country parson son, and the flamboyant stage actor Barney Barnato travelled from England for different reasons and eventually cherished the same ideal - the control of all diamond mines around Kimberley. The discovery of the SA diamond fields turned the world diamond industry on its head. It quickly became obvious that an inexhaustible South African supply would easily outstrip demand. Rhodes then took the first steps as possessor of a world monopoly in rough-diamond supply. He established De Beers in 1888.
The discovery of the Premier mine near Pretoria and news that a huge new diamond field had been found in German South West Africa had a profound effect on the already delicate world supply-demand equation. A new master was needed to restore the balance. Ernest Oppenheimer took over the chair of De Beers in 1929. Ever since, the Oppenheimer family has been synonymous with De Beers. Its self-imposed position as custodian of the world diamond industry has been strongly maintained.

THE DIAMOND INDUSTRY
The Big Hole mine ceased operation in 1914, but many others in the area opened up. In 1902 the Premier Mine near Pretoria was opened. It produced the largest diamond in the world; the Cullinan found in 1905 and weighed 3025 carats.
Because every diamond is unique, the deposit cannot be simply described in terms of tonnage and grade. There are some deposits that produce fewer carats with high value while the others produce many carats but their average value is low. This phenomenon makes it very difficult to assess the economics of mining a diamond deposit. On average about 250 tons of ore are mined and processed to yield one carat polished stone. That is a ratio of one billion to one. Success is unlikely to come without effort. The volcano does not give away its treasures easily.
To extract the diamonds, the ore is crushed to lumps between 2mm to 30 mm in diameter and treated in dense-media separation plants, which cause the diamonds to sink to the bottom of the container together with the heavier associated minerals. This sink product is then washed over greased vibrating tables to which the diamonds adhere, as they are water repellent owing to the nature of the electrical bond between the atoms. Another method of recovery, using X-rays separators, is now largely replacing the greased-table process.
A puzzling phenomenon is the diminishing yield and average size of diamonds as a mine gets deeper. It is therefore assumed that far more diamonds have been dispersed across the surface of the earth by erosion than have been extracted from, or remain in, the pipes. The Kimberley volcanoes have been eroded by 800m to 1500m and it is calculated that some 3 billion carats of diamonds have been lost over the ages.
Some of these diamonds found way into rivers and thereby eventually reach the sea. In the Kimberley area, there are many alluvial diggings, ranging from individual claims to large-scale companies. The Orange and Vaal rivers carried diamonds thousands of kilometres to the sea to be pushed northwards up the coast of Namibia by the Benguela Current. In 1908 several diamonds were found near Luderitz, and mining operations began in 1914. Today only a ghost town, partially submerged in sand dunes of the Namib Desert, stands a memory to a successful German mining company of Kolmanskop 10 km inland from Luderitz. Considerable quantities of the diamonds have also been deposited in the sea beyond the coastline.

THE DIAMOND CITY
As the site of the biggest diamond rush in history, the sun-drenched Kimberley is one of the most historically influential cities in South Africa. One can travel to Kimberly by a car. From Johannesburg it is some 467km while from Cape Town the drive takes 960km. Both cities provide regular flights, bus and train services to the city of diamonds. Kimberly is a sprawling city so it is advisable to hire a car but there are also Rikki taxis and a ride on the old tram or horse-drawn cart is a must.
Kimberley is rich in heritage sites and fantastic old buildings. A walk through the streets brings back the glory of its heyday. You feel and see the history that made Kimberley famous. On a quiet night, you can imagine the laughter from the bars as Barney Barnato cracked another joke. Among the most visited sites is the Big Hole itself (Kimberley Mine Museum) with its street scenes from old days. An exciting tour of an operational diamond mine brings a rare opportunity to observe the insides of the volcano and mix with the miners themselves. The Bultfontein mine, with its trains, skiffs, trucks and the deafening sound of blasting and heavy machinery, has been producing diamonds for more than a century. It is like Verne journey into Centre of the Earth in this hot, twilight world over 800m below the surface.
The industrial scale diamond mining is not, however, the only way to exploit diamond fields. Private miners along the banks of the Vaal and the Orange Rivers run their alluvial operations. Many of these are fifth-generation diggers, the know-how and equipment having been passed down from father to son. They are suspicious of the tourists who arrive unannounced and remain fiercely independent.