The Coscuez mine: a major source of Colombian emeralds.

Abstract

This mine, in the Muzo district of Boyaca Province, is a major source of high-quality Colombian emeralds. The mine, currently worked by open-cut methods, has been operated intermittently for >300 years. The history, location and access, geology, mining methods and physical properties are treated. Most of the emeralds occur in calcite veins that transect the carbonaceous shales and limestones of the highly folded and faulted Lower Cretaceous Villeta formation. Associated vein minerals include pyrite, quartz, dolomite, parisite, fluorite, apatite, albite and baryte. Although the properties of the emeralds are essentially the same as those of the better known Muzo mine stones, the Coscuez stones exhibit a broader range of hues and saturations of colour.-R.V.D.