Gemstones are found in many parts of the world, singly or grouped together. Groups that are quite large are called deposits. Places with a single find are called the location of discovery, place of discovery, or point of discovery. The word occurrence refers to any four of these terms.
For the past 50 years Colombia has been the leader in the largest emerald production in the world. Colombia’s mining towns supply about 60% of the world’s output and 80% of the highest quality emerald available on the market today.
The two principle Colombian mines are located in the “Cordillera Oriental” region of the Colombian Andes mountains. Also referred to as The Emerald Belt. (mining region shown in the shaded area of map) The Chivor mine in the eastern region is the only major privately owned emerald mine in Colombia. The Muzo mine in the western region is leased to the government for 10 year periods to the Sociedad de Mineros Boyancences.
There are hundreds of “Cortes” or mine shafts unknown to the government which are undocumented. The unofficial miners (guaqueros) wait for the slurry (water mixture) to flow down the mountains below the main mining operation and they pan or prospect in these murky waters for emerald of any grade, usually of very low quality. These unofficial guaqueros dwell in very unstable or dangerous areas, Colombia is often referred to as “Locombia” or the mad country.
Bulldozers, dynamite and hydraulic jacks are used in the mining process. Large quantities of water are very important and is pumped to a reservoir above the area being worked and then is time released washing the area free of debris. This process in turn loosens up the emerald bearing material (shale and salt) and exposes calcite veins. The host rock is a dark carbonaceous limestone. Once a calcite vein is exposed all heavy machinery is shut down and workers hand pick and shovel the emerald bed that is within the calcite veins, under the watch of armed guards.
Large quantities of mud are produced in these mountains which makes the mining process extremely dangerous even in the dry season. The need for water accounts for the slow production in the mines during the dry season of March through May. Which in turn explains one reason for price increase of material during this time. A special problem of gem production world-wide is the smuggling of the gems out of the mines by the workers themselves which again will bring a price increase to the marketplace. Many methods of prevention for gemstone theft is becoming more severe.
Colombian Emerald the ultimate choice
Which mine produces better emeralds? The terms Muzo and Chivor are often used in the trade, they do not always determine the origin of the emerald but rather describe the quality and color. “Muzo” is used to describe a warm, grassy-green emerald, with yellow being the secondary color. “Chivor” describes a deeper green (pine-green), with blue being the secondary color. All gemstones are a rare geological occurrence, and emeralds are one of the rarest, even more so than diamonds. When looking for an emerald it is all a matter of preference to the individual. Beauty is in the eye of the beholder. Both stone types are highly sought after and are characterized as clear, brilliant, full of color and can be quite expensive. To the miners it is called “green gold”. To the collector it is “green fire”.
Emerald is traced thoughout the ages dating back as early as the Egyptians and highly valued. Today, gems are not worn as much to demonstrate wealth, but jewelry is bought for pleasure and appreciation of its beauty.
Colombian emerald mines are found in the lower cretaceous level of the eastern range in veins, dikes and filled fractures of sedimentary rocks. They are found in two different stratigraphic and tectonic areas: Guavio ( eastern side) and Muzo (on the western)
Western Emerald Belt:
The mining districs of Muzo, Quipama and Coscuez in the Paja formation (Lower Cretaceous – Middle) consisting of a thick package of black shales or fine carboniferous lutite sheets alternating with more siliceous lutites.
These mines are found in two c haracteristical structures: tractures, veins and small capillaries. These fractures consist of black fragmented lutites cemented inly by calcite, quartz and pyrite. In some cavities, a second gcneration of calcite is observed.
The veins and capillaries vary between 1 and 30 spore centimeters. Generally they are found by cutting through the stratification, although in some instances the cut is a parallel one and consist mainly of calcite and pyrite with quartz, emeralds, fluorite and rarely, parisite (Ca (Ce, La) 2 (Co3) 3h2) and codazite (dolomite with Ce).
The Peñas Blancas deposit within the Rosablanca formation, all Calcareous (lower Cretacecms) and its lithological mineral and structural characteristics are, in general terms the same, with the exception perhaps of the absence of Calcite II.
The Yacopi mines are found within the Villeta Group (Cretaceous-Midd le) consisting of diverse layers of black carbonic lutites, black siliceous Intites, claylutites and limelites.
In every case, emerald mines on the Western Belt are associated with regional type faults towards N 20 grade – 40 grades E and in their intersection with minor faults towards v N 50 grades – 7 – grades W.
Eastern Emerald Belt:
The Chivor mines are embedded within the Lutite formation of the Cáqueza Macanal Group of the lower Cretaceous Age. Lithologically they correspond to a thick package of black carboniferous lutites withthin layers of clay, limolites, thin sand and pockets of plaster. It has been demonstrated that a direct relation exists between regional faults and their transversal intersections with the mineralization of emeralds, and that a clear tectonic control is present, therefore preparing conduits for the circulation of hydrothermal fluids.
In the mining district of Gachalá, mineralizations are generally present in fault zones with angular fragmentation of black and gray lodolites with calcite, feldespato, quartz and pyrite. Veins, composed essentially of plagioclase, quartz and pyrite are also present.
Southwards, mincralized sites are found embedded in thc Guavio Caliza hormation (Lower Cretaceous) consisting of sheeted very fine black dolomites, with thick clay banks. The tectonic model of this part of the Eastern Range is the result of an upper positioning of various regional events that currently are manifested in a group pf inverse regional faults towards N25 grades – 35 grades E, affected by other more recents events towards NW – SF and E-W.