Sources of Emerald, Beryls


Emerald

Despite the fact that emeralds, are exceedingly rare in gem quality, crystals have been found in a number of localities throughout the world. The historical Egyptian mines, referred to earlier, have been worked only sporadically since their rediscovery, for the output consists primarily of pale-green stones containing many fractures and inclusions. By today's standards, the stones are suitable primarily for carving or
for inexpensive cabochon-cut stones. In the early days, the mining was done by very primitive methods; however, from the condition of the mines when they were relocated, it was clear that they had been worked extensively, because the workings extend to a depth of more than eight hundred feet. The mines are located in northern Egypt, about fifteen miles to the north of Aswan. There are two localities, about ten miles apart, in a range of mountains that extends for some distance parallel to the west coast of the Red Sea.

By far the most important emerald localities today are those in the South American Republic of Colombia. Here, four groups of mines produce sporadically the bulk of today's solitaire size gem emeralds. The Muzo mines, discussed previously, produce the fines material, as they have throughout their history. Mining operations are carried out intermittently by the Colombian Government by open pit methods. Water stored in reservoirs is washed over the workings periodically to clean away debris and re-expose the veins of white calcite in the dark shale and limestone. It is in the calcite veins that the emerald crystals are found. The output is held at the Bank of Colombia and released to the market only as demand requires. When the supply is exhausted, operations are resumed. Between times "poachers" work the property
on a clandestine basis, and a certain number of stones reach the market in this manner. The Muzo mines are near the village of the same name, about seventy-five miles to the north of Bogota, the capital of Colombia.

The Chivor mine, which was re-discovered in 1896, has been worked by private organizations. Ownership has changed a number of times in recent years, but the property has been worked fairly steadily. At the present time, the most recent company is in bankruptcy and the mine is being worked under a permanent receiver. It lies near the village of northeast of Bogota. The government owned Coseuez mine, situated approximately ten miles northeast of Muzo, has not been worked for a number of years.

The Colombian emerald mines are restricted to just a few areas of the Cordillera of the Andes Mountains in the Department of Boyaca and Cundinamarca, and are situated on the western side of this great range. The Muzo region is in the basin of the Minero River, and the Chivor district is in the Tenza Valley. According to the geological studies that have been made of the area, the emerald, bearing strata are confined to the Villeta formation of Lower Cretaceous age.

It is interesting to note that the emerald deposition may have occurred at approximately the same time as the emplacement of of the diamond pipe in Africa, since the rocks that the emerald veins traverse are not very many million years older than the diamond pipes, and the mountain building activity of the Andes must have been underway near the end of the Cretaceous Period, when the diamond pipes were formed. The emerald bearing veins are in a formation that lies on steeply uptilted rocks similar to the veins themselves. They are separated by a fault that was the probable path of the solutions and gasses from which the crystallization took place.

 There is some mineralization in the rocks below the fault. It seems likely that the solutions followed the fault and that the gaseous portions thereof affected only the rocks above the fault, whereas the non economically mineralized liquid portions permeated the rocks below the fault. Just above the fault is a zone of strong, change to albite, and above this, in the old carbonaceous shale and limestone, are the calcite - and emerald bearing veins.

In contrast to the open-pit mining at Muzo, where the very steep hillsides are terraced, the Chivor mine is now worked by cutting drifts into the hillside. Ore of the reasons for this is that they are considerably easier to lock and guard at night. When a pocket is opened late in the day at Muzo, it is sealed with clay and the foreman and mine manager put their signatures in the wet clay to make sure that the miners do not tamper with the cavity. "High grading" is a serious problem in the mines. At Chivor, this is avoided by preventing access to the mine tunnel. Pyrite is found in most of the veins and in Chivor emeralds, but it is absent in Muzo and Cosquez stones. Crystals found in a pocket are usually covered with iron stains and anything other than well-shaped crystals must be scraped to be recognized. The presence of a pocket or a series of pockets is usually heralded by the discovery of what the miners refer to as "morally", the word they use for very low-quality massive beryl. Well-formed crystals are called "canutillos".

The Gachala mine, which was discovered about 1956, is located in the Department of Cundinamarca, about five miles from Chivor. Purportedly, it was discovered by a local
farmer who was leading his mule down a steep mountain trail when the animal tripped over a boulder and exposed a rough emerald. It is reached only after a number of hours on horseback from the town of Gachala. Stones are taken from boulders that were evidently displaced from higher on the mountainside. Apparently, the new discovery is too recent to have been worked out or to have led the miners to search out the original formation. The rock would seem to be the same as that at Chivor. It is the same geological formation as that in which the emerald bearing veins occur.

The government has taken over the mine, so presumably it will be worked on a comparable basis to the Muzo mine. Early reports indicate that the emeralds are of fine quality, but perhaps lightly too bluish. They are said to be nearly the equal of the Muzo output and of better color than the usual Chivor production.

Another historic source of emeralds was on the eastern side of the Ural Mountains, about fifty miles east of Sverdlovsk. In this region, a mica-schist contained topaz and tourmaline, as well as chrysoberyl and other beryllium minerals. Sverdlovsk was formerly called Ekaterinburg, which was to pre Soviet Russia what Idar-Oberstein is to Germany today. The principal industries of the area were mining and cutting gemstones. In general, the Russian material was much more heavily flawed than that from South America. Also, the color of large crystals was inferior to that of the South American stones, although the smaller stones were more strongly colored and therefore satisfactory for calibre. Today, Sverdlovsk is a metropolis with a population in excess of 500,000 and is still a major mining center, probably for lithium, beryllium, columbium, tantalum and other pegmatite metal sources. It is possible that emeralds and other gemstones are being produced even now; if so, however, they are not affecting the market. Many of the Russian emeralds known to be reaching the trade are those from estate pieces, but recently it has been reported that it is possible to purchase freshly mined stones in Moscow.

Emeralds have been produced in Brazil, as well as quantities of pale-green beryl too light in color to be ethically called emerald. In 1913 emeralds were discovered in Bahia in an altered clolomitic marble associated with quartz and calcite; the locality name was Bam Jesus dos Meires. The pale color of these stones was such that the mine has never been exploited on any large scale.

Several new discoveries were made between 1960 and 1970. One, the Salininha district in Brazil, produced medium quality green stones colored by vanadium rather than chromium. For this reason, European gemologists refused to call them emeralds, even though they were deeper green and of better quality than some beryl colored by chromium. A second recent source, Carnaiba, produces probably the best emeralds in Brazil, but very few of them approach Colombian quality.

The most recent emerald discovery of importance occurred in Southern Rhodesia, Africa, in the Sandawana Valley. The discovery was made by two veteran prospectors, Lawrence Contat and Cornelius Osthuizen, who had been prospecting in Rhodesia since 1954 for beryl, tantalum and lithium ores, and other pegmatite minerals. Their efforts had centered in the Sabi Valley, in a remote part of Southern Rhodesia. They had discovered some deposits and had been mining on a small scale in that area, but their principal interest was in prospecting. Accordingly, they continued their search for further mineral deposits, concentrating on finding pegmatite dikes. Their interest in pegmatite led them to prospect an area four hundred miles to the south of their mining properties in a very remote and mountainous district. This was an area of very ancient (pre-Cambrian) schistose rocks, traversed in some areas by large pegmatite dikes. Within two days of their entry into the new region, Osthuizen discovered beryl in large quantities and a good sized deposit of spodumene, which is much in demand as a lithium ore. The two men started to examine a large pegmatite dike and soon discovered the first emeralds.

The stones were of low quality but they decided that they were worth investigating, so they searched the surrounding area. In October, 1955, within ten days after their arrival, they had discovered these first emeralds, but it was seven months later before they finally found a second deposit, this one important.  Because their first camp had been at Sandawana, this name was applied to the emeralds, despite
the fact that the discovery was made in an adjoining valley.

It is wild country, infested by crocodiles and rich in other wildlife. In the dry season, the scarcity of water and the distance from the nearest road and railroad pose serious problems. Pits dug below the outcrop show that the soil has been enriched by numerous emeralds left from the erosion and departure of the softer, less durable portions of the host rock through the ages. Most of the stones are very small, usually cutting to less than one quarter of a carat in size, although larger stones are sometimes obtained. In this small size, the color is magnificent; it is so intense that the stones are ideally suited for guard rings and other jewelry utilizing emerald calibre. For a number of years, there has been a dearth of emeralds with the necessary intensity of color to be useful for the production of calibre. Thus, the discovery in Rhodesia will provide a very important addition to gem sources.

There are a number of other sources of emerald. India produces stones from two localities, both discovered in the 1940's. The first came as an accidental discovery in the World War II search for beryl and mica in the Arawalli Mountains in Rajasthan; this was at Kaliguman in Udaipur. Initial mining efforts from the mica-schist by a Jaipur emerald dealer and his partner in 1945 were successful. Later, prospecting turned up deposits elsewhere in Udaipur and Ajmere-Merwara. The Rajgarh mine, fifteen miles south of Ajmere, started operations in a talc-biotite mica-schist in 1947.

Stones from this mine and elsewhere in the district are of a better average quality than those from Kaliguman. India has become more important as a source of emeralds since the later discoveries in Ajmere-Merwara. The Rajgarh mine is operated from a shaft from which drifts extend on a number of levels. The shaft operation has proved to be rather expensive, since excessive timbering is required to support the somewhat friable rock.

Some years ago, emeralds were discovered in the Transvaal, in the Union of South Africa where they occur in conjunction with a series of pegmatite dikes traversing ancient schists.

The mine is not too far from the Sandawana deposit. The Sandawana deposit is on the north side of the Murchison Range and the Transvaal deposit on the south. It is a small-scale, open-pit operation that is worked only spasmodically. The output is made up of a wide range of qualities, from almost colorless beryl to fine green material with few inclusions. Although the finer stones are of good quality, they do not compare with the more expensive grades of the South American production. The Rransvaal deposit which was discovered in 1927, has not had any great impact on the emerald market, because the general quality did not lead to a significant demand.

Other emerald sources include the Habachtal Valley, in the Austrian Alps; Western Australia and New South Wales; and Alexander Mitchell, Creve lend and Macon Counties, North Carolina. All of these sources are commercially unimportant.

 Recently, however, in Hiddenite, North Carolina, a rough emerald crystal weighing approximately sixty carats was found, and subsequently fashioned into a richly colored 13.14 carat stone.

 Aquamarine and Other Beryls

Aquamarine and the other beryls of gem quality are found almost exclusively in pegmatite dikes. The principal source today is the State of Minas Geraes, Brazil. Although varied in size and quality. Brazilian production usually tends toward rather light colors.

Another important producer for many years was the same general area of Russia from which Chrysoberyl was mined: in the vicinity of Sverdlovsk, on the east side of the Ural Mountains. This area produced a volume of beryls in all colors, including emerald. Production was sufficient to make Sverdlovsk a major cutting center.

Madagascar is also a source of significance. This island has been called "the country of beryls" for it produces fine gem material of unusually beauty. Its aquamarine has a color more akin to that of Ceylon sapphires than to other aquamarine, and its morganite is a rich purple-red color.

 

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