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UBC Theses and Dissertations

Geology and mineralization at Independence Creek : Dawson Range, West-central Yukon Territory McKenzie, Greg


The Independence Creek (“Boulevard”) area in the Dawson Range district in west-central Yukon has recently received new government geological mapping; however, little is known about the nature or origin of gold mineralization in this region. A regional metallogenic framework for the mineralization is proposed herein, based on geological, structural, geochronological, and fluid inclusion studies. The study area is underlain by Paleozoic metamorphic rocks of the Yukon-Tanana terrane and is flanked to the north by the mid-Cretaceous Coffee Creek plutonic suite, a phase of the Dawson Range batholith to the southwest. Two separate but related mineralizing systems have been identified within the study area: the Sunset Trend, a gold exploration target, and the Toni Tiger molybdenite occurrence. Gold mineralization in the Sunset Trend is hosted in a chlorite-biotite ± actinolite schist along brittle northwest-trending structures. The highest gold grades are associated with fault zones, locally including vein breccia, that are dominated by iron-rich clay gouge. The main rock type at the Toni Tiger occurrence is a diopside-garnet skarn that is cross-cut by quartz-molybdenite veins which commonly trend northeast. Fluid inclusion studies indicate that mineralization in both systems formed from similar H₂O-CO₂-NaCl type fluids at conditions >280°C and 1100bar. ⁴⁰Ar/³⁹Ar dating of post-metamorphic hydrothermal sericite yielded an approximate age for mineralization in the Sunset Trend of 95Ma, which overlaps within error with the 95.0 ± 0.4Ma Re-Os age obtained from molybdenite at Toni Tiger. Both of these ages are significantly younger than nearby intrusions, suggesting that mineralization is not directly related to the intrusions. The Independence Creek gold system is interpreted to have formed in zones of dilation that related to an overall dextral strike slip system that developed following the emplacement of the Coffee Creek granite at ~99Ma. Geological and geochronological evidence suggests that the Independence Creek mineralization, together with the Longline deposit located 75km to the northwest, and possibly part of the Coffee gold system located in the Coffee Creek plutonic suite, are products of a mid-Cretaceous, post-magmatic orogenic event that occurred between 96 and 92Ma, during the exhumation of the Dawson Range batholith.

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