Investigation of the Mountain River beryl (emerald variety) occurrence, Mackenzie Mountains, Northwest Territories

Author: 
Date created: 
2012-12-17
Identifier: 
etd7578
Keywords: 
Beryl
Emerald
Mackenzie Mountains
Fluid inclusion
Stable isotope
Re-Os isochron
Abstract: 

Emerald at the Mountain River emerald occurrence is milky green and occurs in extensional quartz-carbonate veins hosted within organic-poor siliciclastic rocks. Oxygen isotope mineral pair equilibration thermometry indicates mineralization temperatures of 379 to 415°C. Fluid inclusion analyses indicate CO2-N2-bearing brines and homogenization temperatures between 118 and 258°C. Fluid pressures were on the order of 2.4 to 4.0 kbar, corresponding to depths of 9 to 15 km. Pyrite intergrown with emerald yields a 5 point Re-Os model 1 isochron age of 345 ± 20 Ma and an elevated initial 187Os/188Os of 3.2, indicating a crustal source. The fluids involved in emerald mineralization were derived from deep-seated hydrothermal brines, and were likely the same fluids involved in producing the Manetoe facies dolomite and extensive carbonate-hosted zinc-lead occurrences throughout the Mackenzie Platform. The Mountain River emerald occurrence shares many characteristics with Colombian-type emerald deposits. The Colombian emeralds are hosted in organic-rich black shales and formed during compressional deformation via thermochemical sulphate reduction of brines by organic matter. However, the Mountain River occurrence is hosted in organic-poor siliciclastic rocks and formed in an extensional back-arc environment via inorganic sulphate reduction. The Mountain River emerald occurrence thus represents a modification of the Colombian-type deposit model.

Document type: 
Thesis
Rights: 
Copyright remains with the author. The author granted permission for the file to be printed and for the text to be copied and pasted.
File(s): 
Supervisor(s): 
Daniel Marshall
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) M.Sc.
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