for a copy of this paper please contact the Yukon Geological Survey; geology@gov.yk.ca.

Geology of Thirty-Seven Mile Creek map area (1:50,000 scale), southern Yukon Territory (NTS 105D/13) including geological cross sections and mineral occurrences.

Geology including geological cross sections and mineral occurrences.

Grew Creek epithermal gold prospect, in south-central Yukon Territory, is adjacent to and southwest of the Robert Campbell Highway, halfway between the communities of Ross River and Faro. The prospect is within the Tintina Trench, which from Late Cretaceous to Tertiary time was a zone of major right lateral movement that juxtaposed the Cambrian and Ordovician slate and phyllites of the Pelly-Cassiar Platform (to the southwest) against rocks of the Anvil Allochthon (to the northeast). Grew Creek rocks are mid-Eocene based on K-Ar dates of basalt of 51.4 ±1.8 Ma and 50.7 ±1.8 Ma and pollen spores in volcaniclastic rock dated at 56 to 46 Ma. Felsic volcanic and volcaniclastic rocks were overlain by a sequence of interbedded coarse clastic sediments, basaltic flows, and basaltic volcaniclastic rock. Late Tertiary uplift and faulting resulted in graben formation and consequent preservation of Eocene rocks in a structurally complex graben bounded to the south by the Grew Creek fault and to the north by the Danger Creek fault. Mineralization at Grew Creek occurs at the tip of a westwardly pointing wedge of dominantly felsic, crystal lithic lapilli tuff. The zone of precious metal deposition is truncated to the northeast by steeply dipping clastic sediments and to the southwest by the Grew Creek Fault. Gold, electrum, pyrite, and silver selenide were identified in a high grade sample from the discovery outcrop. Alteration at Grew Creek is both surficial and hydrothermal. Surficial alteration is ubiquitous, pervasive, and characterized by mixed-layer clays and carbonates. Hydrothermal alteration, responsible for the gold-silver mineralization is closely associated with rhyolitic dykes and is of three types:: silicic, acid sulphate, and argillic acid sulphate. K-Ar dating of sericite indicates hydrothermal alteration is mid-Eocene (51.5 ±1.8 Ma and 47.0 ±1.7 Ma) and synchronous with deposition of the volcanics. Quartz associated with mineralization at Grew Creek is enriched in heavy oxygen isotopes. A deep magmatic source for the mineralized fluids is one explanation for this enrichment.

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Geologic mapping within the Quill Creek area identified complex stratigraphic and structural relationships that characterize much of the Kluane Ranges in southwest Yukon. Bedrock in the Quill Creek area consists of Late Paleozoic to mid-Mesozoic volcanic and sedimentary rocks belonging to the Wrangellia Terrane. These rocks are intruded by Upper Triassic mafic and ultramafic sills and dykes and Early Cretaceous to Oligocene granitic rocks. At least two phases of folding are recognized that affect rocks throughout the mapped area. Early phase folds are likely associated with large, low-angle thrust faults. Reactivation of thrusts during younger strike-slip faulting may be responsible for refolding of the early folds. Several known mineralized showings occur within the Quill Creek area, including extensive nickelcopper- platinum group element mineralization associated with the ultramafic sills. Samples collected during 2004 mapping indicate potential for copper-silver mineralization at the base of Upper Triassic volcanic rocks.

for a copy of this paper please contact the Yukon Geological Survey; geology@gov.yk.ca.

The study area provides a clear record of the Proterozoic geological evolution of northern and central Yukon Territory. The area lies in the Wernecke Mountains of east-central Yukon, approximately 150 km north-northeast of the town of Mayo, and 20 km west of the Yukon-Northwest Territories border. The rocks record events of sedimentation, magmatism and deformation ranging in age from Early Proterozoic to Tertiary. Rocks of Early Proterozoic age predominate, but strata of Middle Proterozoic, Late Proterozoic, and Early Paleozoic ages are also abundant.

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