Characterization of the fluid-rock interaction in the Colombian emerald deposits

Emerald is a high-value gemstone and a variety of the Beryl group that contains traces of Chromium and Vanadium which give them their characteristic green color.  Colombian emerald deposits have been found within two main narrow belts both of them located in the Eastern Cordillera, one of the three main ranges that constitute the Colombian Andes along with the Central and Western Cordilleras.

Several authors (Kozlowski et al. 1998; Ottaway et al. 1994; Giuliani et al. 1993b) have established that the interaction between hydrothermal fluids and the emerald hosted black shales, leading into an intense albitization and carbonation of the host rocks with the depletion of many major and trace elements, resulting into the emerald mineralization along with the deposition of calcite, dolomite, pyrite, albite, quartz and rarely parasite (Giuliani et al.1995). However, the fluid-rock interaction has not been clearly explained and stablished for both productive and non-productive areas in order to provide a more useful guide for further emerald exploration.   

Inductively Coupled Plasma Atomic Mass Spectroscopy (ICP-AMS) along with X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM) data were obtained from unaltered and altered host rocks including siliceous black shales, carbonated black shales, limestones, and dolomitic limestones. The results were analyzed to establish the geochemical relationships between different lithologies and the occurrence or absence of emerald mineralization for the different emerald belts.

The concentration of major, trace and REE elements and particularly the of  Cr, V and Be in the host rocks and the distribution over the studied areas will provide a better understanding of whether those contents are sufficient not only for the formation of emeralds besides of the different minerals in paragenesis. The results of the ongoing results are expected to be used as a possible exploration tool in favor to identify the areas with low potential for emerald mineralization.