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HISTORICAL INFORMATION

 

 

The deposits were exploited by the natives long before the appearance of European in the 16th century and have been worked more or less continuously since then. Emerald became common in world trade only after the Spanish conquests, in south America they reopened the ancient Indian mines. 

In 1000 A.D. Colombian Indians possessed emeralds: deposits were exploited and stones traded to other countries before the conquest. 

In 1514 the Spanish explorer Pedrarias (Pedro Arias de Avila) obtained the first stones when he landed at Santa Marta (Colombia) enroute to Darien (Panama). 

In 1519 Hernan Cortés received gifts, including splendid emeralds, from Montezuma and later obtained many fine stones during the sack of Tenochtitlan. 

In 1539 Francisco Pizarro sent six "Peruvian" emeralds to queen of Spain and vowed to find the source but was unsuccessful because all "Peruvian" stones were actually from Colombia. 

In 1544 Lonso Luis (Alfonso de Lugo) organized an expedition to explore the Muzo region.
 
In 1555 Hintze claimed that a certain Andres Diaz Venero de Leiva was the first to suspect a local source because of accidentally finding emerald in the helmet of a Muzo Indian: he gave the founding date as 1559. 

Captail Valenzuela worked the Chivor deposit with great energy using enslaved Indian labor.  Inhumane treatment led to complaints to the Crown by resident Catholic priests, which eventually resulted in reform. 

In 1558 mining began at Muzo under Francisco Morcillo and was vigorously pressed despite harassment and repeated attacks from natives. 

In 1568 Muzo began formal mining. Operations were pursued with great energy and many stones were sent to Spain. 

In 1593 Maldonado constructed the aqueduct to bring water to the Chivor mines. Gonzales issued regulations governing use of native labor that decreed freedom from slavery for Indians. 

In 1636 the official chronicler of Bogotà visited Muzo and reported poverty due to decline in mining brought about by local labor troubles and the impossibility of importing Negro slaves or other cheap labor.
 
In 1646 Coscuez deposit was discovered and worked for a short period but was abandoned and eventually lapsed into obscurity when a landslide buried in 30 miners. 

In 1664 viceroy of Nueva Granada sent mineralogist José Antonio de Villegas y Avendano to Muzo to investigate deposits. A favourable report resulted in opening anew site and the use of open cuts in lieu of tunnels, but production remained low. 

In 1672 the probable time when Chivor mines lapsed into obscurity from which they were not to emerge until modern times. 

In 1772 attorney General Francisco Moreno T. Escandon reported to viceroy Zerda on the Muzo mines and noted their profitable working but stated that the the Chivor deposits could no longer be found. Production figures showed that Muzo mines operated continuously from 1766-1772. 

From 1824 to 1848 the first Muzo lessee under the new regime was José Ignacio Paris, friend of Simon Bolivar and Mariano Eonardo de Rivero, colleague of Boussingault and warden of the Natural Sciences Museum in Bogotà. Paris obtained exclusive rights until 1838. The rights were later extended for ten years to 1848, with royalty payments reduced to 5%. 

In 1847 the Colombian government promulgated a law permitting all existing emerald deposits to be exploited only on behalf of the nation under regulations that allowed privately owned deposits to continue working, with production taxed, only so long as the work did not cease for longer than one year, in which event the title to the deposit passed to national owner-ship. As a result of this law, the nation acquired many properties in addition to those at Muzo and those as yet undiscovered. In this year the government issued bid tenders to work Muzo, to take effect upon expiration of the Paris lease. 

In 1849 government operations at Muzo ceased. The mines were leased to London-Bogotà firm principals Juan de Francisco Martìn and Patrick Wilson of Bogotà, and the Stiebel Brothers of London. The contract was to expire February 28, 1861; and the company was titled "Sociedad de las Minas de Emeraldas de la Nueva Granada" 

In 1859 Muzo was crippled by a serious landslide and work ceased. 

In 1860 the government reoffered the Muzo lease, but fear of internal political disorders in Colombia resulted in no takers. 

In 1861 Thomas Fallon was appointed admistrator of the Muzo mines, assisted by Felipe Paul and work carried on until April 1865. 

In 1864 in august the government concluded a contract with a Parisian consortium, represented by Gustave Lehmann, to work Muzo for a ten-year period beginning April 1, 1865. Rights granted to the consortium not only for Muzo but also for all other deposits belonging to the nation, and "other persons are allowed to work only those mines which without doubt belong to private persons." 

In 1871 a government decree of December 14 provided that emerald mine properties must be extended sufficiently to include not only the mining sites but also such areas in which occur exploited veins, water sources, and all land made effective upon expiration of the Muzo lease on April 1, 1875. 

In 1886 terms of the new Colombian Constitution proclaim Muzo and Coscuez the property of the nation.
 
In 1889 Restropo petioned government of Boyacà Province for exploration right to Chivor. 

In 1905 the government decreed on April 5 that henceforth all newly-discovered emerald deposits belonged to the nation. 

In 1906 Muzo mine was leased to a Colombian syndicate for five years under the name Colombian Emerald Company Limited. 

In 1911 Restropo and Klein reopened Chivor. 

In 1912 an attempt by government to tax Chivor was nullified by the Colombian supreme court which reaffirmed that the property was for ever free of such taxation. The government rescinded Muzo lease of Colombian emerald Mining company Limited. Legal steps were taken to restore company rights and eventually the government was forced to pay damages. Muzo became inoperative. According to Hermann and Wussow the annulment of these lease took place on January 1, 1913. 

In 1915 Campania de Minas de Chivor dissolved and a new venture, sociedad Ordinaria de Minas des Esmeraldas de Chivor, S.A. ., formed. Rights to Chivor were sold to Wilson E. Griffiths annd Carl K: McFadden representing the Colombian Emerald Development Corporation of_New York. 

In 1918 Colombian Emerald Sindacate Ltd. obtained option on Chivor to expire in 1919. 

In 1919 Colombian Emerald Sindacate Ltd. Purchased five claims of the Chivor property; and later sold them to Columbia Emerald Development Corporation. The latter then reorganised as Chivor Emerald Mines Inc. 

Between 1925-1927 Muzo closed; production resumed ca. 1935 but from 1928 on the government took charge of selling stones. 

In 1931 work at Chivor was reduced or suspended due to political strife. Mines remained virtually closed until 1936 

In 1933 Muzo reopened under direction of Peter W. Rainier and an American group marketed production on commission basis for the government. 

In 1937 Chivor emerald Mines Inc. lease was made effective September 15 to continue to 1940. 

In 1938 Stockpile size permits closing the Muzo and Coscuez mines. Chivor operated on a restricted scale from about November 1937. 

In 1946 Mining rights to Muzo were granted by government to Banco de Republica, Bogotà. 

From 1948 to 1949 Muzo operated for about one year at considerable loss. Work was reduced or suspended at Chivor but resumed in 1948. 

In 1951 Muzo and Coscuez operated in latter part of year. Chivor Emerald Mines Inc. entered bankruptcy, but workers continued mining and reportedly obtained many fine stones. 

In 1954 emerald discovered at Las Vegas de san Juan, Gachalà Cundinimarca Province. Illegal mining removed large quantities of fine stones. 

In 1960 Muzo, Chivor, Vegas de San Juan, Buenavista and Coscuez were operated. 

In 1965 Chivor operated, along with Muzo and Coscuez and the new Pena Blanca mine at Muzo. Lesser qualities of emerald were sold primarily in Italy, Mexico and Brazil, with India the biggest buyer of moralla: extra fine stones brought U.S. $4.000 per carat for "gem of any appreciable size". 

In 1968 Government sponsored ECOMINAS (Empresa de Colombiana de Minas) was authorized to mine Muzo and buy stones from private sources and cut and sell stone. The company still existed in 1979. 

During 1976 and 1977 anarchy existed at government mines with illegal mining and disposition of emeralds the rule rather than the exception. After extensive negotiations the Muzo lease was awarded to the Sociedad Minera Boyacense Ltda., the Coscuez lease went to Esmeraldas y Minas de Colombia, S.A. (ESMERACOL), and the Pena Blancas lease went to the Quinteroo brothers, who also control the Chivor mine. Over five years ESMERACOL will pay ECOMINAS a total rent of 260 million pesos plus 5% of the gross production at Coscuez in March of 1978 

The main area is being stripped away very rapidly so that a significant portion of the potential emerald production is lost to the gravels of the Rio Itoco. About 15.000 guaqueros (independent miners) mine the riverbed each day.

 

GEOLOGY

 

 

The Colombian Andes consist of three subparallel ranges: the Western or cordillera Occidental; the Central or Cordillera Central and the Eastern or Cordillera Oriental. The Western and Central ranges consist primarily of granites and they are known for gold deposits. The Eastern range consist mostly of sedimentary units, principally limestones and shales with minor igneous and metamorphic rocks. 

The major emerald deposits are limited to the eastern (Chivor) and western (Muzo) margins of Cordillera Oriental where there are visible Cretaceous sediments. The emerald are found in the Villeta formation that dates from the Lower Cretaceous age. This formation  consists of black carbonaceous shale with minor limestone inclusions. The Villeta formation is divided in two members: the Cambiado and Emerald beds. Locally these members are separated by two thin agglomeratic layers of calcite crystals designated the Cama and the Cernicero. The emerald-bearing formations lie along the flanks of the eastern branch and occur mainly in the provinces of Boyacà, Cundinimarca and Santander or generally N-NE or Bogotà. 

The Muzo mine penetrate a series of black pyritiferous argillites (shales) intercalated with thinbedded limestones and folded into varying amplitudes as drag folds which have been intensively fractured and fissured due to compression and torsion forces created during the formation of the horst of Muzo and Coscuez. The formations are laterally limited by faults normal to the N-S direction in the contacts with the Upper and Lower Albian formations. The fractures are filled with calcite-dolomite and their analogs, and in places include emerald. These formations are covered from topsoils called "capas buenas" or "capas esmeraldiferas". They lie above the Cambiado formation, where no emeralds occur. 

Between the emerald-bearing rocks at the top and the Cambiado below occur several rocks of great significance in suggesting the origin of the emeralds: Albite rock (albite apparently replaces calcite; druses -- crusts of tiny crystals lining a rock cavity -- contain splendid crystals of albite, calcite and dolomite), Cernicero (ash bed) and Cama (layers of intergrown large and well-formed calcite rhombs). 

The Cambiado is the visible bottom formation at Muzo and consist of limestone alternative layers of thinbedded argillite. The formations at Chivor are of conformable sediments consisting of light grey calcareous shales with some lenses of carbonaceous matter. The top member is hard grey fossiliferous limestone, the lower member is hard blue thinbedded limestone or calcareous shale. Vertical to near-vertical fissures provided mineralization channels for vein fillings while later faulting resulted in some displacements of earlier formed veins. Large veins, beds, and masses of limonite, and sometimes hematite, formed from alteration of pyrite and are conspicuous features. 

Above the limonitic beds quartz also permeates cracks and fissures. Pyrite appeared after faulting, followed by emerald. Ther appear to have been two periods of mineralization, the first being in-filling of E-W fissures and the second, the mineralization afterwards. No emeralds are found in calcite veins of the uppermost formation at Chivor despite the presence of numerous early Spanish tunnels. The strata below the ferojinosas were exposed that emerald were discovered. Beryl appears to have come  from a "deep-seated" source and crystallized at moderate temperature and pressure in the veins as evidence by lack of vein-wall alteration. The emerald crystal are cemented by limonite, and these must be extracted with care to avoid damage to the crystals.

 

LATTICE PARAMETERS

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

COMPOSITION

 

For each mine we calculated the medium value of lattice parameter.                    

For each mine we calculated the medium value of chemical analyses (analysed 20 point ) by EMPA (Cameca CX 827).

Mn, Se, F, Rb are under detection limits except in few cases. Li and Be are not determined.             

Chemical analyses have been normalized at 85%.                   

It was impossible to calculate the water value because the sample quantity was too low.     

 

INFRARED

 

Reflectance FTIR (Fourier Transform Infrared Spectra) of gemstones have been acquired using a microscope IRscopeII (Bruker) accumulating 200 scans with a resolution of a cm-1 or better, in the range 7000-600 cm-1. Here are given only the skeletal bands which lie in the interval 1500-600 cm-1 When the samples were suitably cut in direction parallel or normal to the c axis, polarized spectra were also obtained on the pinacoid or on the basis respectively or both. According to the group theory 6A2u + 16 E1u infrared modes are predicted: the E1u modes are observed in the spectrum when the electric field is perpendicular to the c-axis (ordinary ray) and the A2u modes are observed for the extraordinary ray (E|| c). Therefore, non degenerate bands (A2u) are observed on pinacoids and show intensity changes in polarization, while degenerate bands (E1u) are detected on basis spectra and show only a lowering in intensity in polarized light.

 

Prisma

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Click here to view Colombian Emerald Samples 

 

BIBLIOGRAPHY

 

1. Bosshart G. "Les Emeraudes de Colombie" Association Française de Gemmolgie p. 1-24 juin 1991 n°. 107 
2. Cheilletz A. and Giuliani G. "The Genesis of Colombian Emeralds: a Restatment" Mineral. Deposita 31, p. 359-364, 1996 
3. Keller P. C. "Emeralds of Colombia" Gems & Gemology p. 80-92 Summer 1981 
4. Kane R. E., Kammerling R. C, Moldes R., Koivukla J.I.,, McClure S. F. and smith C. P. "Emerald and Gold Treasures of the Spanish Galleon Nuestra Senora de Atocha" Gems & Gemoloy p. 196-206, Winter 1989 
5. Ottaway T. L., Wicks F. J., Bryndzia L. T., Kyser T. K. and Spooner E. T. C. "Formation of the Muzo Hydrothermal Emerald Deposit in Colombia" Nature vol. 369, 16 june 1994 p. 552-554 
6. Sinkankas J. "Emeralds and Other Beryls" Pensylvania, Chilton Book Co. p. 542-548, 1981

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