Mineralogical Significance of Fluids in Channels of Colombian Emeralds: A Mass-Spectrometric Study

Quadrupolar mass-spectrometric study of fluids trapped in inclusions and channels is used to characterize the qualitative and quantitative composition of fluids within emeralds from 10 deposits located on the eastern and western margins of the Eastern Cordillera of Colombia. Fluids in channels and in fluid inclusions have the same qualitative composition. The bulk composition of the fluid phase is: H₂O (80 to 92 mol%), N₂ (3 to 10%), CO₂ (2.5 to 5%), H₂ (1 to 5%), CO (0.1 to 1.5%), CH₄ (<0.5%), organic compounds (<0.05%), and inert gases. Hydrogen and carbon monoxide in large part come from water and carbon dioxide reduction. Fluids trapped during emerald growth belong to an aquo-carbonic fluid phase with CO₂/N₂ ratios near 1 (0.8 to 0.84 in fluid inclusions, 1 to 1.3 in channels). Fluid contents in channels are higher by ～20% in emeralds from the western group compared to those in the eastern deposits. The concentration of H₂O in channels in emeralds from the eastern group is lower (1.35 < H₂O < 1.45 wt%) than in those of the western group (1.63 < H₂O < 2.19 wt%), and it corresponds to the lowest contents of H₂O found worldwide for emeralds from different deposit types. Colombian emeralds are quite different because their hydrothermal-sedimentary genesis is unique.

Emeralds from the western zone also have higher Na₂O contents than those from the eastern zone. A strong correlation exists between channel H₂O and Na₂O in the emeralds, which also is the case for beryls and emeralds from different geological environments. Such an enrichment is indicative of the presence of Na⁺ in the structural channels of beryl. This correlation between channel H₂O and Na₂O of the crystal is evidence for the introduction of channel H₂O as Type-II water molecules in beryls.