The origin of green stones
The extraction of emeralds in Colombia dates back to pre-Columbian times, when the Muiscas took them out of the town of Somondoco for commercial exchanges. The Spaniards continued with their exploitation during the Colony, until at the beginning of the 20th century the State assumed it.
Much earlier, a series of geological events occurred that gave rise to the emeralds (see box). A relatively broad central zone of the lower Cretaceous period in Colombia had to play a very important role in the geographical circumscription of the emerald deposits to specific areas of the country, since only in these were all the physicochemical conditions and the geological processes for your generation
Today, the exact geographical margins of that central area are unknown; however, based on geological data compiled by the Colombian Geological Service (formerly Ingeominas) and the Universidad Industrial de Santander, during the exploration of the emerald belts between 2005 and 2008, it is believed that the northern limit is located near Sucre ( Santander), and the south, approximately in La Palma (Cundinamarca). From the west to the east that area would be delimited by the municipalities of Puerto Romero and Santa María (Boyacá).
These geological conditions of the emeralds make their deposits are located in two particular areas of the Eastern Cordillera: one located on its western edge, in the region of Muzo, Quípama, La Palma, La Victoria, Otanche and San Pablo de Borbur, named Western Emerald Belt (CEOC), and the other on its eastern side, in the municipalities of Gachalá, Ubalá, Chivor, Macanal and Santa María, known as the Eastern Emerald Belt (CEOR). Both are part of the pristine depocentral area of the lower Cretaceous.
The potential zones for exploration and exploitation in the CEOC are located in the Muzo (Hauterivian-Barremian age) and Rosablanca (Valanginian age) geological formations; and in the CEOR, in Santa Rosa and Chivor (Berriasian age). The emerald belts are separated from each other by about 110 kilometers and to date no emerald deposits have been found in that area of separation.
The miners extract these gems from what geologists call 'hydrothermal structures', which are formed when the mineralizing fluids bearing the emerald 'penetrate' the sedimentary rock subjected to tectonic deformation (folding, internal deformation and fracturing), which makes that breaks and in those fractures the stone is deposited.
Commonly, the emerald is accompanied by other minerals that are typical of deposits such as albite, calcite and sulfides. Traditional miners have exploited this resource empirically because they learned to recognize these minerals and the different hydrothermal structures present in the rock. Its extraction, in general, is underground, by digging tunnels with branches in different directions, although in other mines its exploitation may be superficial.