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

Resource type
Thesis type
(Thesis) M.Sc.
Date created
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.
Copyright statement
Copyright is held by the author.
The author granted permission for the file to be printed and for the text to be copied and pasted.
Scholarly level
Supervisor or Senior Supervisor
Thesis advisor: Marshall, Daniel
Member of collection
Download file Size
etd7578_MHewton.pdf 7.83 MB

Views & downloads - as of June 2023

Views: 22
Downloads: 2