The TBMB claim group, 4 km southwest of the Dan occurrence in the upper Swift River area of stratiform zinc occurrences, reveals the nature of the host rocks and style of folding. A train of east-southeast-trending, east-northeast-verging, km-scale F1 overturned anticlines and synclines dominates the area. These folds clearly control the distribution of low metamorphic grade tectonites (in map and vertical cross-sections) and a structural model allows definition of general stratigraphy of the TBMB and BOUND claim areas. A lower, an intermediate, and an upper unit of siliciclastic metasedimentary rocks are separated by two intervening units of base-metal -sulphide-bearing strata (acid to intermediate metavolcanic rock and marble, respectively). Based upon the repetitive F1 folds (possibly associated with thrust faults) and the similarity of rock types in the TBMB and Dan areas, the authors propose a structural linkage between them.

not_specified

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

Paleozoic rocks of the Pelly Mountains, central Yukon, preserve greater than 150 m.y. of sedimentation, magmatism and base-metal mineralization. To identify secular trends in regional tectonics and metallogeny, a multi-year project on the stratigraphy of the Pelly Mountains in the Quiet Lake (105F) and Finlayson Lake (105G) map areas was initiated. Field studies during summer 2015 focused on two stratigraphic intervals: (1) mafic volcanic, volcaniclastic and clastic rock successions assigned to the Cambrian-Ordovician Cloutier and Groundhog formations (Kechika group); and (2) felsic volcanic, volcaniclastic and clastic rock successions assigned to the Devonian-Mississippian Black Slate and Felsic Volcanic formations (Seagull group). Cambrian-Ordovician strata were deposited in a marine environment characterized by episodic mafic volcanism and extensional tectonism. Devonian-Mississippian strata record the transition from an extensional turbidite basin to a metalliferous volcanic rift basin, and resemble key rock assemblages of the Selwyn basin (Earn Group) and Yukon-Tanana terrane (Grass Lakes and Wolverine Lake groups).

The Tantalus Formation developed within confined intermontane river valleys during the late stages of collision and amalgamation of Stikinia and associated arc systems with the North American plate in Upper Jurassic and early Lower Cretaceous times. While most of the extensive chert pebble conglomerate in the Tantalus Formation can be interpreted as shallow braided gravel-bed river deposits, some may represent the products of deposition from deeper, braided and meandering gravel-bed rivers. Floodplain and lake deposits are restricted to poorly exposed slope forming intervals. Coal deposits developed locally on abandoned segments of floodplains in confined river valleys, in places associated with high constructive river deposits. The age profiles of detrital zircons indicate major contributions from reworking of older strata, combined with continued un-roofing of the Stikine terrane. In addition more distal sources were tapped in the Yukon-Tanana and adjacent terranes to the north and west of the Whitehorse trough. Much of the chert in the Tantalus Formation appears petrographically similar to chert in the Cache Creek terrane, now preserved only to the south of the Whitehorse trough. As both decrease in maximum grain size, and paleocurrents, are generally south to southwesterly trending, this source is considered unlikely. Chert may have been derived from now eroded supracrustal rocks that once formed the top of the Yukon-Tanana terrane, or more likely from an obducted block of Cache Creek terrane once present to the north and west of the Whitehorse trough. The latter may have been thrust over metamorphosed rocks of the Yukon-Tanana terrane beginning in the early Bajocian, and has subsequently been removed by erosion. A proximal North American cratonic source is excluded, as there are no Archean zircon grains in the Tantalus Formation. The possibility that strata of the Tantalus Formation may host significant conventional reserves of oil or gas is very low, due to lack of trapping mechanisms. There may be some undiscovered coal reserves, and limited potential for coal-bed methane production.

Detailed exploration conducted during 2006 in the western part of the Skukum Creek deposit has revealed new structural, mineralogical and geochemical features. The deposit incorporates a number of (at least six or seven) sub- parallel narrow mineralized zones, coincident with andesite-dacite-rhyolite dyke swarms extending for at least 1 km along strike and for hundreds of metres down-dip. Various mineralized zones differ in size, structural setting, intensity and composition of mineralization, and, in total, form a large mineralized package more than 200 m wide, corresponding to a property- to district-scale fault zone extending for over 10 km and traced by a dyke belt. Significant potential exists for the exploration of these structures along strike and down-dip. The diamond drilling intersected numerous high-grade intercepts of gold and silver mineralization corresponding to the low-sulphidation sub-type of epithermal gold-silver deposits. However, strong enrichment in base metals (up to 25% of combined Zn+Pb+Cu) and arsenic suggests essential differences from typical epithermal mineralized systems.

Upper Devonian and Lower Mississippian metavolcanic rocks of Yukon-Tanana Terrane in southern Finlayson Lake and Frances Lake map areas occur in three thrust sheets, locally modified by a Cretaceous normal fault. The lower thrust sheet, the Big Campbell sheet, comprises the Upper Devonian to Lower Mississippian metavolcanic stratigraphy that hosts the main volcanichosted massive sulphide (VHMS) deposits of the district. Metavolcanic rocks in the middle thrust sheet, the Money Creek sheet, include the Upper Devonian Waters Creek and Early Mississippian Tuchitua River formations. The former comprises primarily felsic metavolcanic rocks and carbonaceous phyllite and is extensively intruded by sheets of comagmatic porphyry. The latter comprises primarily intermediate metavolcanic, volcaniclastic and epiclastic rocks. The upper thrust sheet, the Cleaver Lake sheet, is in part made up of Late Devonian calc-alkaline basalt and rhyolite, the Cleaver Lake formation, and comagmatic felsic to ultramafic plutonic rocks. Of these, the Waters Creek formation and the formations in the Big Campbell sheet have the highest potential to host VHMS deposits.

Reconnaissance geological mapping in the Coal River map area of southeastern Yukon investigated several small mid-Cretaceous plutons. The intrusions are composed of unfoliated or incipiently foliated, fine to coarse-grained, equigranular and porphyritic, biotite ± hornblende quartz monzodiorite to granodiorite. They are metaluminous to peraluminous and have reduced to oxidized geochemical characteristics. The composition of selected samples is consistent with magma formation from partial melting of infracrustal source rocks.U-Pb ages were obtained for nine plutons from five or six zircon single-grain analyses by the isotope dilution thermal ionization mass spectrometry method with chemical abrasion (CA-TIMS). All interpreted ages are concordant within statistical uncertainty. The plutons range in age from 99.80 ± 0.03 to 97.70 ± 0.03 Ma. Given the primarily unfoliated nature of the plutons, contractional, fabric-forming deformation within the Cordilleran orogeny must therefore have largely ceased at the present level of exposure in the Coal River area by the time of intrusion (ca. 98 Ma).The ages and compositions of the plutons in Coal River map area are consistent with their being part of the Tay River plutonic suite, a northwest-trending belt of coeval and compositionally similar plutons and local volcanic rocks (South Fork volcanic suite) that, when augmented by the addition of the Coal River plutons, extends approximately 465 km with a width of up to 150 km.

not_specified

The Rapid Creek Formation, exposed at Big Fish River and Rapid Creek, in the Richardson Mountains of Yukon is well known for its rare phosphate minerals. Mapping, geochemical sampling, and collection of phosphate minerals and nodules from this formation occurred over a three week field program in the summer of 2012. The Rapid Creek Formation is a phosphorite-rich ironstone facies composed of alternating beds of phosphate and siderite-rich mudstones and shale. Secondary minerals collected from crosscutting mineralized veins in this area include unusual apatite, augelite, arrojadite group minerals, dypingite, lazulite, and garyansellite-kryzhanovskite. Phosphate nodules with satterlyite, wolfeite, vivianite-baricite, wicksite, and arrojadite-group minerals have been identified and collected for study.