Gold-bearing quartz-breccia zones in Archean metasediments of the Gordon Lake region, Northwest Territories, Canada.
Date
1991
Authors
Stokes, Timothy Robert.
Journal Title
Journal ISSN
Volume Title
Publisher
Dalhousie University
Abstract
Description
Strata-bound, gold-bearing quartz-breccia zones at Gordon Lake, near Yellowknife, N.W.T., occur within carbon-rich siltstone beds of the Archean Burwash Formation, and are located within the hinge domain of a subvertical regional refold. Structural analysis indicates that although some quartz veining developed before peak metamorphism and formation of a regional cleavage (S$\sb3$), more significant quartz veining, brecciation, and gold mineralization occurred later (late-D$\sb3$ to syn-D$\sb4$), concurrent with formation of a crenulation cleavage (S$\sb4$) and counter-clockwise rotation of the east limb of the refold. Microfractures within the quartz-breccias have abundant fluid inclusions of high salinity ($\sim$25 wt% NaCl-CaCl$\sb2$) and hydrocarbon concentration (e.g., CH$\sb4$ and C$\sb2$H$\sb2$). Gold in the quartz breccias occurs with arsenopyrite, pyrite, and pyrrhotite, and was probably emplaced at ca. 450 $\pm$ 40$\sp\circ$C and a depth of 7-12 km. Hydrothermal alteration enriched the siltstone host in Au, As, Sb, (Br), S, K, Ca, and Na. The high C and low SiO$\sb2$ content of the host siltstone is probably a primary feature of the metasediments rather than a product of alteration. $\sp{40}$Ar/$\sp{39}$Ar dating of a metamorphic hornblende and a muscovite from a post-metamorphic pluton constrain the time of (D$\sb3$) peak metamorphism to ca. 2600 Ma. A plateau age of 2573 $\pm$ 9 Ma for a biotite from the largest quartz-breccia zone gives a minimum age for mineralization, consistent with the late metamorphic timing of the brecciation event. The data are compatible with a genetic model that derives the gold and the fluids from the arc-related volcaniclastic metaturbidite pile, transports the gold as chloride complexes in a moderately saline (and oxidized?) fluid, and deposits the gold, quartz, and sulphides in hydraulically-induced brittle fractures within the reducing carbon-rich silstones.
Thesis (Ph.D.)--Dalhousie University (Canada), 1991.
Thesis (Ph.D.)--Dalhousie University (Canada), 1991.
Keywords
Geology.