The Muzo emerald deposit

The Muzo emerald deposits are located on the western flank of the Eastern Cordillera basin, 100 kilometers north of Bogotá. Emerald occurs in black shales intercalated with dolomitic limestones of Valanginian-Hauterivian age, the Rosablanca and Paja Formations. The deposits are linked by tear faults and associated thrusts formed during a Paleogene compressive phase; contemporaneously, circulation of hydrothermal fluids and emerald deposition occurred. All the tectonic contacts are marked by hydrothermal breccias, emerald-bearing banded carbonate veins and dykes, en-echelon sigmoidal tension gashes and drag folds indicating shearing in the roof of the breccia zones (Branquet et al., 1999). The veins are filled by calcite, dolomite and pyrite with accessory quartz, barite, fluorite, bitumen, Cr-muscovite, emerald and parisite-(Ce).The Muzo deposits are famous also for trapiche gem emerald disseminated in black shales (Pignatelli et al., 2015). Detailed geological and geochemical studies have led to a genetic model based on a hydrothermal-sedimentary origin. Key aspects of formation involve hot brines due to interaction of fluids with evaporites, resulting in intense albitization, carbonatization, and pyritization of black shales, and coeval leaching of Be, Cr and V necessary for emerald formation. The thermochemical reduction of sulphates led to precipitation of pyrite, calcite, dolomite, bitumen and finally emerald.