PUBLICACIONES

Chromium and vanadium from host rock to emerald: tracing differences between the two main emerald zones in Colombia and their gemological implication

Javier Garcia-Toloza, Valeria Ramírez-Juya, Camilo A. Betancur-Acevedo, Valentina González, Gabriel Angarita, Holman Alvarado

We have analyzed 1321 samples of emerald, euclase, carbonates, micas and host rocks from the Western and Eastern emerald belts in Colombia: 738 from the Western emerald belt (WEB); and 583 from the Eastern emerald belt (EEB). Results enable trends in chemical composition to be identified, and the pathways followed by key elements in emerald formation to be identified. Colombian emeralds are distinguished chemically by lower concentration of iron. The Cr/V ratio in EEB emeralds is 3:1, it is 1:1 in WEB. This contrasts with host rock compositions where the Cr;V ratio is near 1:1 in both belts. Nevertheless, next to emerald there are several minerals able to catch the elements leached from the host rock and that could be a key role in the characteristic emerald’s chromophores concentration from both zones and it could generate into different hues in emeralds

Geochemical and mineralogical characterization of emeralds from La Arcadia mine, Colombia

Valeria Ramírez-Juya, Javier García-Toloza, Valentina Gonzalez-Ruiz, Luis G. Angarita-Sarmiento

Analyses were carried out on 514 emeralds, 439 from Colombia (15 from La Arcadia, 276 from other mines of Muzo district, 102 from other districts of the western belt and 46 from the eastern belt) and 75 from other countries, to find systematic trends or chemical composition characteristics that discriminate the Arcadia emeralds for provenance purposes. Principal Components Analysis (PCA) was carried out to compare La Arcadia mine against emeralds from other deposits around the world, mines from the eastern belt, mines from other districts, and mines of the same district. Additionally, petrographic analysis was performed on 20 polished thin-sections of representative veins and breccias from the La Arcadia mineralization. The chemical composition of Colombian emeralds is characterized by a high concentration of Vanadium (>2000 ppm), however, La Arcadia emeralds have a lower concentration than other deposits from Colombia, also the elements that substitute for Al have low concentrations. Emeralds observed in La Arcadia are associated with a hydrothermal alteration that affected a conspicuous black level of  siltstones and the typical paragenesis consist of dolomite, albite, mica and emerald in veins and breccias.

Guía de buenas prácticas de la esmeralda colombiana

Bonilla German et. al

La Guía de Buenas Prácticas de la Esmeralda Colombiana o GBPEC, se realiza basada en una serie de recomendaciones enfocadas en cada una de las etapas de un proyecto minero, a lo largo de cuatro capítulos se establecen parámetros, observaciones, errores comunes y enlaces que llevan al profesional a profundizar en cada aspecto articulándose con el actual Estándar Colombiano de Recursos y Reservas Minerales ECRR, publicado en el 2018. El desarrollo minero de las esmeraldas colombianas tiene dos objetivos generales que son: la explotación de nuevos depósitos y la reducción del riesgo exploratorio a medida que se avanzan los trabajos. Para lograr estos objetivos, se requiere generar una secuencialidad en los procesos exploratorios, interconectar las diversas etapas del proyecto minero y analizar los resultados obtenidos para tomar decisiones sobre las sostenibilidad del proyecto

Luis Gabriel Angarita, Holman Alvarado, and Javier Toloza

Two important internal features in gemstones are inclusions and fissures. Inclusions are an important source of information in the gemological evaluation process. They can often provide indications about geographic origin, growth conditions, natural or synthetic origin, and whether the stone has been treated to improve clarity.

Geoquímica y mineralogía de la mina La Pava, Muzo-Quípama: implicaciones en la exploración de esmeraldas en Colombia

Andrés Felipe González-Durán et. al

La mina La Pava es parte del distrito esmeraldífero de Muzo-Quípama, Colombia; allí la presencia de esmeraldas se asocia con pelitas de la Formación Muzo. La mineralización es controlada espacialmente por el Anticlinal de La Pava —un pliegue por propagación de falla— y se restringe a zonas que han experimentado intensa alteración hidrotermal (albitización y carbonatización). Los principales rasgos observados en las venas productivas son las asociaciones paragenéticas de albita-xenotimo-fluorapatito y calcita-dolomita, los cuales van acompañados de anomalías geoquímicas positivas de Y, P, Mn y Mg. Adicionalmente, se presentan anomalías negativas de Li-Cs-Be-Ti que representan indicadores consistentes de la lixiviación de estos elementos en las rocas y su posterior concentración en venas y brechas hidrotermales. Se concluye que en La Pava existen parámetros estructurales, estratigráficos, mineralógicos y geoquímicos que permiten identificar bloques potenciales para hospedar mineralizaciones de esmeraldas.

Mineralogy and fluid inclusions of the Cunas emerald mine, Maripí – Boyacá, Colombia

Fernando Romero, Andrés González-Durán, Javier García-Toloza, Jimmy Rotlewicz, Carlos Cedeño Ochoa, Holman Alvarado, Luis Angarita

The Cunas mine is currently one of the major producers of fine emeralds in Colombia; its emeralds typically display a magnificent green hue,  which is highly appreciated globally. The mineralization is found in vanadium-rich black shales of the Muzo formation. Emeralds occur in pockets within hydrothermal veins and breccias, mainly consisting of calcite, dolomite, albite, quartz, minor pyrite, parisite-(Ce), and fluorite.  Hydrothermal alteration is pervasive and dominated by albitization and carbonatization. Emerald-hosted fluid inclusions are highly abundant and remarkably large and complex. Poly-phase inclusions are ubiquitous, occur both in emeralds and gangue minerals, and consist of two daughter crystals (typically halite and calcite or siderite; exceptionally parisite-(Ce)), a liquid brine, a CO2-N2-CH4-rich gas bubble, and occasionally minor liquid CO2. Vapor-rich inclusions were observed in quartz, and two-phase inclusions were identified in calcite and dolomite, thus suggesting a complex fluid evolution. Microthermometry analysis indicates that emerald-forming fluids were trapped at relatively low temperature ~260-340°C and pressure ~850-2400 bar, with relatively high density 1.03 g/cm³, and elevated salinity ~39 wt% NaCl eq.; other aqueous components detected include CaCl2, KCl, and FeCl2. Based on these data, authors propose the emerald mineralization at the Cunas mine was originated by the mixing of two hydrothermal fluids of different sources; one fluid with high salinity derived from evaporite dissolution, responsible for the albitization of the host rocks; the second is a calcium-rich fluid evolved from connate waters, which was equilibrated by the interaction with calcareous and organic-rich wall rocks. As a result, emerald mineralization took place at structurally favorable sites proper for fluid mixing. The described geological and physicochemical features for the Cunas mine agree with epigenetic sediment-hosted mineralization —Colombian-type— formed by the circulation and mixing of relatively low-temperature non-magmatic fluids

Darwin Fortaleché, Andrew Lucas, Jonathan Muyal, Tao Hsu, and Pedro Padua

Colombia is synonymous with fine emerald, and production is believed to date back well over a thousand years. Over the centuries the beautiful verdant gemstone, which emerges from areas that are also a lush green, has been linked to violence and human exploitation. Nevertheless, the desire of the Colombian people to mine for this treasure and strike it rich has endured, with enough dreams coming true to drive their passion.

Carlos Julio Cedeño Ochoa, Miguel José Herreño Daza, Darwin Fortaleche and Juan Fernando Jiménez

This is a preview of the study currently being developed by the Gemological Laboratory of the Technological Development Center of the Colombian Emerald, CDTEC, on the use of some parameters, both chemicals as spectrals, in order to differentiate Colombian emeralds among local areas as well as emeralds from other sources. To this end, techniques have been selected that meet the following requirements: avoid injuring gems, are easy to apply, and do not involve a delay in the issuing of reports. Moreover, the parameters studied should normally be present in the gems.