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Coscuez, Muzo, La Glorieta-Yacobi, Quipama, Macanal, Chivor, Gachala - Emeralds

Colombia

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The Coscuez, Muzo, La Glorieta-Yacobi and Quipama and the Macanal, Chivor and Gachala and other mines form two narrow NNE trending zones of emerald deposits about 100 km apart in the poorly folded thrust belt of the Eastern Cordillera of central Colombia.

The Coscuez and Quipama districts in the west are around 10 km apart and are both hosted by lower Cretaceous carbonaceous shale deposited in a strongly subsiding rift basin active through the Cretaceous to the Tertiary.   The black shales overlie limestones and are in turn succeeded by Upper Cretaceous arenites.   These sediments were subsequently deformed and uplifted during the Tertiary Andean tectonic episodes.

The Coscuez mine is hosted by carbonaceous shales with intercalated dolomitic limestones, overlain by siliceous shales.   Mineralisation is within a complex fracture system comprising veins, banded stratabound lenses and breccias resulting from hydrofracturing.   Fracturing is present as two sets trending at 10° and 140°.   Hydrothermal fluid circulation was accompanied by strong fluid-rock reactions and metasomatism of the black shales to produce carbonates, albite, pyrite halos to the emerald bearing carbonate veins.

The Quipama mines represent numerous workings in the same sequence and setting as at Coscuez.   There are three fracture sets in the productive zone, at 0 to 10°, 40 to 70° and 110-130° which are filled by calcite, dolomite, REE dolomite, pyrite, quartz, albite and greenish K mica.

Macanal and Gachala are in the eastern belt, about 30 km apart.   They were formed in the Guavio Formation which lies on a Palaeozoic basement and comprises a sequence of siltstone and siliceous black shales, carbonate-bearing black shale with limestone intercalations and anhydrite beds, overlain by siliceous black shales of the Macanal Formation.   The emeralds were formed at 65 Ma at temperatures of at least 250° C below 7 km of sediment cover.   The emeralds occur within carbonate-silicate-pyrite veins and breccias in black shale-limestone hosted deposits.

For more detail consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 2000.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.


  References & Additional Information
   Selected References:
Cheilletz A, Feraud G, Giuliani G, Rodriguez C T  1994 - Time-pressure and temperature constraints on the formation of Colombian Emeralds: An 40 Ar / 39 Ar laser microprobe and fluid inclusion study: in    Econ. Geol.   v 89 pp 361-380
Giuliani G, France-Lanord C, Cheilletz A, Coget P, Branquet Y, Laumomnier B  2000 - Sulfate reduction by organic matter in Colombian Emerald deposits: chemical and stable isotope (C, O, H) evidence: in    Econ. Geol.   v95 pp 1129-1153


Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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