Thursday, 24 January 2013

Diamond's From Mine to Market

Washing for diamonds at Mandango in Brazil, about 1760. The slaves are working under the constant supervision of overseers.
Until the discovery of the first diamond pipes in South Africa in 1871, for centuries the only source of diamonds known to man had been the river. Diamonds had been found on the banks of active rivers or in the beds of rivers that had dried up thousands of years before, but all the sources were clearly alluvial. The methods adopted for the mining and recovery of diamonds were therefore simple and labor-intensive. Tavernier provides us with a graphic account of the techniques of the great mine of Kollur in the Kingdom of Golconda in India around 1650:
After the miners have selected the place where they desire to work, they smooth down another spot close by, of equal or rather greater extent, round which they erect an enclosing wall of two feet in height. At the base of this little wall they make openings, at every two feet, for the escape of the water, which they close till it is time for the water to be drawn off. 

They excavate to ten, twelve or fourteen feet in depth, but when they reach water there is nothing more to hope for. All the earth is carried to this place, men, women and children draw water with pitchers from the hole which they have excavated, and throw it upon the earth which they have placed there in order to soften it, leaving it in this state for one or two days, according to the tenacity of the clay, until it becomes like soup. This done, they open the holes which they made in the wall to let off the water, and then they throw on more, so that all the slime may be removed, and nothing remains but sand. 

It is a kind of clay which requires to be washed two or three times. They then leave it to be dried by the sun, [and it] is quickly effected by the great heat. They have a particular kind of basket made something like a winnowing fan, in which they place the earth, which they agitate as we do when winnowing grain. The fine part is blown away, and the coarse stuff which remains is subsequently replaced on the ground. 

An aerial view of the opencast workings of the Finsch Mine, with the treatment plant in the foreground.
All the earth having been thus winnowed, they spread it with a rake and make it as level as possible. Then they all stand together on the earth, each with a large baton of wood like a huge pestle, half a foot wide at the base, and pound the earth, going from one end to the other, always pounding each part two or three times; they then place it again in the baskets and winnow it, as they did on the first occasion, after which they spread it out again and range themselves on one side to handle the earth and search for the diamonds.
Further to the west, about five days' journey from Golconda, Tavernier noted different methods in use. There the ground was sandy, rock-strewn and covered with coppice, and as he comments, "somewhat like the environs of Fontainebleau." The diamonds were to be found mixed with sand and earth in veins in the rocks, and were extracted by the miners using little iron rods crooked at one end. The earth and sand were then washed two or three times in the search for diamonds. Harry Emanuel, the nineteenth-century mineralogist, recorded that in the diamond-producing district of Sumbhulpore near Panna in the north, the diamond-washing trade had been carried on for centuries by two tribes. These were the Thara and the Tora, who by their appearance had traces of Negro blood and were judged to be the descendants of slaves imported by one of the earlier conquerors of India for that very task.
The methods employed in Brazil a hundred years later were similar. The diamond-bearing gravels, called cascalho, were excavated to a depth of about ten feet and deposited in heaps outside the washing huts. In these huts were long troughs, called canoes, and elevated seats for the overseers who kept a constant watch on the proceedings. The cascalho was then washed in the canoes by means of a stream of water coming in one end and flowing out of the other, often from canals cut into the banks of the nearby river. When a diamond was found, the slave would clap his hands as a signal to the overseer who took it and placed it in a water-filled vessel which hung in the middle of each hut.
After the removal of the sand, the uneven bedrock is then broken up with compressed air drills and shoveled onto conveyor belts set up on the spot.
The early South African diggers on the banks of the Vaal River in 1869 used 'much the same primitive techniques to recover diamonds. The broken ground was taken from the pits and pounded with shovels to break it up even more. It was then placed in a rocking trough fitted out with sieves (sometimes in three tiers of varying mesh sizes) to get rid of both the larger material and any fine sand or dirt. The remaining collection of pebbles, crystals and coarse rock grains was put in a fine sieve and washed in order to concentrate the heavier portion of the material, which of course would include any diamonds. The sieve was then tipped onto a table and the contents hand-sorted. These rockers or cradles were commonly improvised from old gin crates. A slightly more sophisticated type was invented and marketed by an American gun salesman, J. L. Babe. Inevitably his rocker was known as the "Baby" or the "Yankee Baby."
This simple sequence of operations had worked well for centuries, but it quickly became outmoded when mining at the dry diggings began to more than scratch the surface of the earth. As the claims went deeper, mechanical methods had to be employed to bring the yellow ground to the surface. The most common method was the endless rope linked to a pair of pulleys, one in the pit and one at the edge, which carried up the broken ground in hide buckets and took them down empty again. 

Soon there were literally thousands of such ropes and cables coming up from the claim, and staging had to be erected in several tiers around the edge of the mine to cope with them all. As the claims became deeper still, horse whims gradually replaced hand tackle in the lowering and hoisting of buckets. The first one was introduced at the Kimberley Mine in 1874, and in the following year steam engines began to be used to operate the winding gear.
Today's washing pans are mechanically operated and somewhat larger, but they operate on much the same principle.
Panning gravels in the search for alluvial for alluvial diamonds on the banks of River Sewa in Sierra Leone.
What has changed dramatically over the years has been the method of getting the broken ground out of the mine. Because diamond mining has a higher proportion of waste material to product mined than is usual in almost any other mining operation, the emphasis has always had to be on the efficient and economic extraction of diamond-bearing ores in bulk. The open-pit operations of the early days rapidly became uneconomic be-cause of the growing frequency with which the surrounding rock collapsed into the hole. By 1882 no less than three tons of rock and debris had to be removed in order to extract one ton of blue ground from the Kimberley Mine.
Attempts to cut back the sides of the mine proved impractical because of the area involved and the increasing depth of the hole, and an experiment carried out at Dutoitspan in which a protecting wall of blue ground was left around the sides of the pit nearly proved disastrous when all the walls collapsed simultaneously.
Water was not readily available in the semi-desert area of the dry diggings and washing techniques could not be used at first. Instead a hand-operated rotary sieve with 1-inch to 1 1/4-inch mesh called a trommel (Dutch for "drum") was devised for sifting the broken ground. The finer pieces were further pulverized before being shoveled into hand sieves with 1/4-inch mesh. What remained in the sieve went to the sorting table. In due course, rotary washing pans were introduced. These were circular containers about four feet across and nine inches deep with a series of prongs on arms set into the axle. When the axle was rotated by turning the handle, the mixture of water and gravels was swirled around causing the lighter elements to flow over the top of the pan while the heavier ones fell to the bottom.
Underground loading in the Kimberley Mine in 1894.
Today's open-pit mining methods are a far cry from those of the thousands of independent claim holders who crowded into the Kimberley Mine in the 1870s. The whole operation is completely mechanized: towering mechanical diggers and thirty-five-ton dump trucks have replaced the shovels and hide buckets of a century earlier. The problem of the surrounding rock collapsing into the mine, as it did in the early open-pit workings, has been solved by tackling it right at the beginning: the reef is gradually cut back in steps as the mine gets deeper. The result is a much wider and deeper hole. 

The intention is to take the Finsch Mine down to 1,000 feet (330 meters) before switching to underground mining. In the Kimberley Mine the maximum depth reached in open-pit operations was 800 feet (240 meters); and in the Premier, 600 feet (180 meters). Mining in the Finsch is carried out in 40-foot (12-meter) steps which are blasted along the edges and the broken kimberlite is then loaded by mechanical shovels into dump trucks which transport it to the adjoining treatment plant. It is estimated that the open working will continue for approximately fifteen years.
The gradual consolidation of the many claims into fewer and fewer hands paved the way for the introduction of underground mining techniques at Kimberley from 1883, but these were only partially successful. The real breakthrough did not come until 1890, after all the claims were finally consolidated in the hands of De Beers. In that year an excavation technique called chambering was introduced by Gardner Williams, the American mining expert who was also general manager of the company. In this method, a main shaft is sunk in the rock surrounding the pipe and connected to the pipe by main rock tunnels established at the 600-, 1,000- and 1,600-foot levels (180, 330 and 490 meters).
Drilling in the Kimberley Mine in 1894.
At 40-foot intervals, chambering levels are established from which a series of parallel tunnels are driven into the pipe leaving 10- foot-wide pillars between. The tunnels on the level below are staggered so that they are positioned immediately under the pillars on the level above. Mining is carried out by blasting the chamber roofs of the top series of tunnels so that the pillars collapse into the tunnel below. The blue ground is then loaded into trucks, transported to the main shaft and hoisted to the surface.
Chambering was used throughout the mines of the De Beers group until 1953 when it was replaced in all except the Wesselton Mine by a more efficient and less labor-intensive technique known as block caving. In this system a series of parallel concrete-lined tunnels called scraper drifts are driven from the main rock shaft into the pipe some 400 to 600 feet (120 to 180 meters) below the top of the blue ground. Openings known as draw points are left in the roof of these tunnels through which raises are cut to form cone-shaped excavations into the blue ground above. 

The whole block of blue ground above the cone is then mined out to a height of about 7 feet (2 meters) and after a brief interval it begins to crumble and collapse into the cones through the draw points and into the scraper drifts. From here it is dragged out by mechanical scrapers and precipitated into trucks which carry it to an underground crushing plant where it is reduced to pieces of 6 inches (152 millimeters) or less in size before being taken to the surface in skips.
An underground loader in operation in the De Beers Mine at Kimberley.
The advantages of block caving over chambering are that all loading is mechanical and much more blue ground can be mined per shift. Furthermore, since all operations are carried out on one level, supervision is much simpler with consequent benefits in the level of safety and efficiency.
Once the blue ground has reached the surface, it is screened and crushed again, this time to below 11/4 inches (32 millimeters) in size, before being conveyed to the central treatment plant. It is then passed through the rotary washing pans. These pans exploit the high specific gravity of diamonds, which causes them to sink when the blue ground is placed in a state of liquid suspension by mixing it with muddy water called "puddle." On average, about one ton of concentrate is extracted by the rotary pans for every twenty-three tons of waste or "tailings" swept away.
The next step in the recovery process is for the concentrate from the rotary pans to be delivered to the vibrating grease belts. These take advantage of another of the diamond's physical characteristics its inability to be wetted and its tendency to adhere to grease. The concentrate is sluiced over the grease-covered surface of the belt and the diamonds are trapped while the rest is carried away. The diamonds are automatically scraped off the belt by a heated blade and collected, at which point they are ready for boiling in kettles. This will disperse the grease so that only clean diamonds remain.
Two diamond sorters at work in Kimberley at the turn of the century. The sieves help them to sort the rough diamonds into size groups.
An alternative method to the grease belt which is rapidly gaining ground is the X-ray separator. The basis of this method of recovery is that all diamonds fluoresce when exposed to X-rays, whereas all the accompanying minerals in the concentrate do not. The stream of concentrate is fed into the recovery machine, and as it falls toward the collecting bins past the X-ray beams any diamonds present will "light up," trigger a photoelectric cell and activate an air-operated ejector which will blow them into a separate bin.
Another principle method of diamond mining currently in use is beach mining. The richest source of gem diamonds in the world is a stretch of bleak, storm-swept coast in South West Africa extending 50 miles (83 kilometers) northward from the mouth of the Orange River. The diamonds lie under as much as 50 feet (15 meters) of sand in the clefts and gullies of the marine terraces where they were deposited millions of years ago after being swept down ancient water courses from the inland pipes. Their extraction involves Consolidated Diamond Mines (CDM) in the largest continuous earth-moving operation in the world. 

Teams of scrapers and bulldozers remove the overburden of sand at a rate of five hundred tons an hour per machine and on occasions as much as two million cubic meters of sand has had to be stripped to uncover a mining area of only 1,000 feet (300 meters) square. Once the ancient marine terrace has been exposed, bulldozers move in to push the gravel into stockpiles, or if it is very deep, it will be loaded by excavators into thirty-five ton dump trucks and transported to the treatment plant. Finally, the uneven bedrock is examined for trapped diamonds by being handswept with small brushes while back trenchers clean out the deeper gullies.
Rather more complicated techniques had to be employed when attempts were made to mine the deposits in the tidal area, the part of the beach between high and low water marks. Huge coffer dams of sand reinforced with concrete blocks were bulldozed into position and it was found possible to keep the sea at bay long enough to mine successfully. The size of the diamonds recovered was disappointingly small, though, and the operation was discontinued in 1971 for marketing reasons.
Diamond's From Mine to Market
Another marine operation one that has captured more imaginations than it has diamonds is that of mining the seabed by vacuum sweeping. This technique was pioneered by an American oil man, Sam Collins, using one prospecting vessel to map out the payable areas and a recovery barge to do the actual mining. The heavy swell along the coast which could cause the barge to rise and fall by as much as 30 feet (10 meters) presented major technical difficulties and the con-sequent low recovery rate led to the suspension of operations in 1971.
The recovery process for the diamond-bearing gravels of South West Africa follows much the same pattern as that for kimberlite from the inland-pipe mines, and the diamonds which emerge are sent to the same place for sorting and valuing the Central Sorting Office of the Diamond Producers' Association in Kimberley. There the diamonds are cleaned in acid, counted and weighed, consignments from the different mines each being dealt with separately.
First of all, the crystals are separated into broad gem and industrial categories with color and clarity being the principal determining factor. There is obviously some overlap between the two groups and it is the balance of demand from the jewelry trade and industrial sources that determines whether the borderline cases should become gems or be consumed by industry. Roughly 80 percent of all diamonds produced fall into the industrial category. The industrials are dispatched to Johannesburg for further sorting and then marketing.
The gem crystals are sorted according to size, shape, purity and color. First the "sizes" stones weighing about 1 carat or more are separated from the "smalls." The borderline weight varies around the 1-carat mark ac-cording to the state of the market. The next step is to sort the crystals into their basic shapes: stones, which are unbroken crystals of regular or irregular formation; cleavages, or imperfectly formed or fractured crystals; macles, which are twinned stones and tri-angular in shape; and flats, thin, tabular crystals which look like pieces of broken glass.
Having sorted the diamonds into their distinctive shapes, the sorter now grades them according to purity, or quality. In effect, this means that he assesses them in accordance with what he regards as their value to the cutter. Thus an inclusion or flaw near one point of an octahedron will not detract from the value since it will be bruted away early on in the cutting process. On the other hand, a similar flaw nearer the center of the stone would present a major problem to the cutter and the crystal is given a much lower grading. There are ten classes of quality. Broadly speaking, class one would be a clear, un-spotted crystal; class two would have some small spots near the edge; class three, some larger spots, and so on. Beyond class five, gem quality would be in doubt.
 Color sorting is a little more straightforward. Most browns are not favored and are rejected, and shade and clarity determine whether yellows and certain very special browns are classified as gems or industrials. There are many famous diamonds in shades of yellow and brown. The Tiffany diamond is a beautiful canary yellow and the 248.9-carat Earth Star is a deep coffee brown. There is no such ambiguity about a blue, a pink or dark green or the very rare red.
The almost infinite shades of white now remain to be classified, ranging from the finest whites through six grades down to pale yellow. Shade variations will be considered in more detail when the various color-grading systems for polished stones are compared, since at the rough stage color may still be subject to doubt because of the diamond's coating. This is a factor which the chief valuer must take into account at the next stage, which is the valuing of the crystal.

Diamond to Market
Starting with a basic pricing formula for all the classifications, the valuer adjusts his textbook figure according to his assessment of weight recovery and the problems that the stones may set to the cutters. Such formulae are generally applied to stones weighing up to 14.8 carats; anything over that weight is dealt with individually.

After the crystals are sorted into their two thousand or more classifications and valued, they are sold by the Diamond Producers' Association (DPA) down the line to the Diamond Trading Company (DTC) and sent then to their sorting office in London. Here they are sorted into individual parcels which cut across a number of categories, and are then offered to diamond dealers and cutters at sales held ten times a year, known as the "sights." The buyers have already had the opportunity to make their requirements known and the parcels are made up to some extent with these in mind. However, the parcels must be purchased as they stand, and a buyer will have to dispose of any unwanted items through the trade at a later date. 

The Diamond Producers' Association and the Diamond Trading Company together with the cooperative marketing unit known as the Central Selling Organization (CSO) bring order and stability to the whole diamond industry. The CSO basically adjusts the supply of diamonds to the demand by allocating quotas to its producing members through the DPA and by stockpiling certain categories of diamonds when necessary. Thus a period of temporary oversupply of certain types of diamond will be corrected by holding back both their sales and perhaps even their production. After a time the market is likely to adjust to the new situation and demand will revive. In order to finance such stockpiling, the CSO retains a percentage of the selling prices as a handling and marketing charge, but it has also built up a massive reserve fund totaling some hundreds of millions of dollars.
Mine to market diamond'sAbout 80 percent of the world's diamond production is marketed through the CSO. Ghana has its own diamond marketing board, and grades, values and prices its rough production for sale to licensed buyers, as do the Central African Republic, the Ivory Coast and Guinea. The official production of Venezuela, Guyana and Brazil is also disposed of without the help of the CSO. However, it should be noted that in most of these countries, illicit digging and smuggling is endemic and the only semblance of order to their diamond trade is given by the CSO buying on the open market. The production of the USSR was marketed through the CSO from 1959 to 1963, but the Russians now carry out their own marketing.
Similar arrangements govern the marketing of industrial diamonds. These are sold direct to trade buyers through Industrial Distributors (Sales) Ltd., which is also a member of the CSO. Prices are fixed and stocks are retained whenever necessary to stabilize the market. A separate subsidiary deals with the marketing of synthetic industrial production.
As a result of the degree of control that the CSO exercises over the supply and the marketing of diamonds, it can set the selling prices of rough diamonds in accordance with market conditions. Thus in an adverse economic climate it will hold prices steady, and in a favorable climate it will advance them regularly by small amounts.
In a world in which monopoly and cartel have become dirty words, the CSO is only too often the object of bitter criticism. The fact remains, however, that it has achieved for the diamond industry a measure of stability that is the envy of commodity producers every-where.

Having at last emerged from the control of De Beers and the Central Selling Organization and reached the wholesale trade, the diamonds are now ready for distribution to buyers all over the world. The means by which this distribution is effected is a chain of diamond clubs and bourses situated in the world's major diamond trading centers in Amsterdam, Antwerp, London, New York and Tel Aviv. Buyers, sellers and brokers congregate here to bargain over stones in the time-honored fashion of the diamond trade, sealing their bargain with the words Mazel un b'rachah, a Yiddish: phrase meaning "Good luck and blessings." Nothing else is needed to create a binding contract. Of course, disputes can and do arise; but when they do, they are settled within the clubs by a board of arbitrators. Rules and regulations are strict, as befits a trade that relies so much on mutual trust; serious violations can result in a member being disbarred and thus effectively excluded from the legitimate diamond trade.
The rough diamonds make their way to the cutting centers of the world: principally Antwerp, Amsterdam, London, New York, Tel Aviv, Johannesburg and Bombay. There are smaller cutting centers in other countries, notably at St. Cloud in France, Idar-Oberstein and Brucken in West Germany, San Juan in Puerto Rico, Lisbon and in Sierra Leone. And since the discovery of massive diamond deposits in Soviet Russia, a growing cutting industry has been established at Sverdlovsk in the Urals. Traditionally the big centers specialize in certain kinds of work. Antwerp works on everything, but especially on cleavages and chips; New York on stones and shapes; and many of the smalls are cut in Amsterdam, Israel, West Germany and Bombay. The cut diamonds now pass into the hands of the manufacturing jewelers to be made into pieces of jewelry and sold to the public via retailers.  

Writer – George G.Bakey
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