Abstract
The Sixtymile gold district, Yukon, Canada has been mined for placer gold since the late 19th century. However, increasing demand for gold has prompted exploration of new lode deposits. Previous studies in the nearby Klondike gold district have shown correlation between placer deposits and bedrock occurrences. Poor bedrock exposure and a complex deformation history, however, make it difficult to determine structural controls on gold mineralization. Through structural analysis involving mesoscopic-scale field observations of fractures, faults, foliation, and folds, and 3D geophysical inversion, the goal of this study was to determine the structural setting of the Sixtymile district to enhance discovery success. Structural measurements in the Glacier Creek, Miller Creek, Bedrock Creek, and Sixtymile River areas show the relationships among the orientations of foliation, fractures, and veins. In most localities, veins are found both parallel and at high angles to foliation, and there is generally a weaker correlation between fractures and veins compared to between foliation and veins. This correlation between foliation and veins is corroborated by inferred gold-bearing horizons from gold assay data. Outcrops of oblique reverse and strike-slip faults, possibly related to a larger-scale thrust-zone, and to the left-lateral Sixtymile-Pika Fault, respectively, were documented for the first time in this study. The results of the 3D probabilistic inversion of total magnetic intensity data for magnetic susceptibility show that magnetic susceptibility highs are preferentially associated with volcanics, but also point to possible intrusive bodies or hydrothermal alteration zones associated with mineralization. A geologic cross-section through the lithologies demonstrates highly variable deformation styles, including extensive folding, possibly indicative of a multiphase deformational history necessitating further, more detailed investigations of the area.
Highlights
The Sixtymile mining district in the Yukon Territory, Canada is located in the SixtymileRiver watershed which is ~75 km west of Dawson City and ~10 km east of the border with Alaska, USA (Figure 1)
Placer gold deposits in this mining district, and in the vicinity, occur both in low-level creek gravels, and in low- and high-level terraces that were mainly formed by Minerals 2022, 12, 291 in this mining district, and in the vicinity, occur both in low-level creek gravels, and in low- and high-level terraces that were mainly formed by aggradation and incision associated with phases of glaciation and deglaciation aggradation and incision associated with phases of glaciation and deglaciation in the past in the past ~40 ka [3,4]
Veins are associated with foliation, but are found along fractures and fault planes (Figures 5 and 6)
Summary
The Sixtymile mining district in the Yukon Territory, Canada is located in the SixtymileRiver watershed which is ~75 km west of Dawson City and ~10 km east of the border with Alaska, USA (Figure 1). The main streams that were mined in the district are the Bedrock, Big Gold, Little Gold, Glacier, and Miller [1] (Figure 2). Placer gold deposits in this mining district, and in the vicinity, occur both in low-level creek gravels (valley bottoms), and in low- and high-level terraces (resting on schist bedrock) that were mainly formed by 4.0/). Minerals 2022, 12, 291 in this mining district, and in the vicinity, occur both in low-level creek gravels (valley bottoms), and in low- and high-level terraces (resting on schist bedrock) that were mainly formed by aggradation and incision associated with phases of glaciation and deglaciation aggradation and incision associated with phases of glaciation and deglaciation in the past in the past ~40 ka [3,4]
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