April 2017 Monthly Meeting

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The majority of the world’s emerald deposits are formed by the introduction of beryllium (Be)-rich fluids to Cr (±V)-rich host rocks, and can be classified into three major categories: types 1, 2, and 3. Type 1 emerald deposits are associated with granitic or pegmatitic intrusions into mafic or ultramafic host rocks. Other emerald occurrences in Canada, such as the deposits at Tsa da Glisza (Yukon), Lened (NWT), and Ghost Lake (Ontario), are of this type, but the MRB does not appear to have formed in the same way, as suggested by markedly different host rocks, fluids, and chemistry. In contrast, the famous emerald deposits of Colombia are formed from the in-situ mobilization of hydrothermal sulphate brines to liberate and transport Be, V, and Cr in organic-rich black shales. Isotopic, fluid inclusion, and geologic data indicate the Mountain River emeralds formed from non-magmatic fluids and are genetically most similar to the Colombian-type emerald mineralization model.