A sequence of Permo-Triassic rocks within a 260 square kilometre part of the Kluane Ranges, southwestern Yukon, consists of Lower Permian volcaniclastic and sedimentary rocks, disconformably overlain by upper Triassic amygdaloidal volcanic rocks. Mafic to ultramafic rocks occur within the upper part of the Permian section and in the Triassic flows. Folding and faulting of this sequence is intense. The ultramafic rocks are peridotite-dunite complexes in the form of sills. Some gabbroic bodies have intruded along sill boundaries, but most are separate sills or dykes. Nowhere have they been found cutting rocks younger than the upper Triassic volcanics. Ni-Cu mineralization is spatially associated with the gabbros and peridotites. Dunite portions of ultramafic complexes are barren. Sulphide minerals include pyrrhotite, pentlandite and chalcopyrite, locally with pyrite, sphalerite and galena. Occurrences are classified as follows:: 1. Massive to stringer within country rock adjacent to gabbro intruding peridotite. 2. Massive to heavily disseminated at the country rock contact of gabbro intruding peridotite. 3. A) Heavily disseminated to nearly massive within gabbro intruding peridotite. B) Disseminated within separate gabbroic bodies. 4. Very weakly disseminated within peridotite. The mineralized gabbro-ultramafic intrusions are spatially related to the Triassic volcanic flows. The mafic and ultramafic rocks, their Ni-Cu deposits, and volcanic flows are believed to be related genetically. This report is accompanied by five geological maps as follows:: 1) Arch Creek (1::4760 scale; NTS 115 G/5 northeast); 2) Wellgreen area (1::4800 scale; NTS 115 G/5 northeast); 3) Linda Creek (1::2380 scale; NTS 115 G/6 northwest); 4) White River (1::4760 scale; NTS 115 F/15 northeast); and 5) Quill Creek (1::80 000; 115 G/5,6 north and 115 G/11,12 south).

Occurrences of placer platinum-group minerals (PGM) were reported in several gold placer deposits in Yukon. The source rock and the type of platinum mineralization are not known for these localities. We investigated five grains of Pt-Fe alloy from Burwash Creek (map area 115G and F), one grain from Scroggie Creek (map area 115O and N) and one grain from Wolverine Creek (map area 105C and D). Results of multiple electron microprobe analysis display elevated levels of Pd, Rh, Ir and Cu in these Pt-Fe alloy grains. The grains host micro-inclusions of various species of PGMs and silicate-melt inclusions with diopside, albite and sodic-calcic amphiboles. Trace element composition of the silicate inclusions determined using laser ablation ICP-MS shows a notable enrichment in large ion lithophile elements. We infer that the reported association of PGM and the trace element composition of silicate-melt inclusions observed in the studied grains are likely derived from a subduction-related Alaskan-type mineralization.

Between the Swift and Nisutlin rivers, unmetamorphosed granite to ultramafic intrusions of four ages (from Permian through Cretaceous) span the amalgamation of Cassiar Platform with Yukon-Tanana and Cache Creek terranes. The mid-Permian granitic Ram Stock and two plutons cutting the Sylvester Allochthon lie at the edge of the Dorsey Complex, a remnant of an ancient passive margin succession that underlies the volcanic arcs of Yukon-Tanana Terrane. Middle Jurassic, locally foliated granodiorite to gabbro intrusions are metaluminous, and high in Sr and low in Ti compared to the Cretaceous suite. These `I-type volcanic arc plutons may be the remnants of an overlapping arc correlative with the Quesnel Terrane. The Cretaceous (113 to 98 Ma) meta- to peraluminous granites are late orogenic incipient `A-type plutons from highly fractionated F- and Cl-rich magmas. These generated extensive hydrothermal systems that produced tin, tungsten, molybdenum and beryl occurrences.

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New U-Pb zircon dates from Permian rocks of the Yukon-Tanana terrane in the Klondike district of western Yukon provide new constraints on timing of intrusions and deposition. The new data shows that significant Pb-loss affected zircon in metamorphic rocks of the Yukon-Tanana terrane. The new, high-precision CA-TIMS dating shows that all intrusions in the region are ca. 261 Ma and eliminate previous constraints on the Klondike orogeny. A review of lithogeochemical data and new Lu-Hf isotope data for zircon support development of the Klondike assemblage in back-arc to continental arc settings. New 40Ar/39Ar data for Permian metaplutonic rocks indicates cooling below 300-350°C in the Early Jurassic.

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

Quantitative mineralogy, U-Pb geochronology of zircon and monazite, 40Ar/39Ar geochronology of muscovite and sericite, and Pb isotopes from galena in veins and feldspar in plutons provide insight into the age of metamorphism, mineralization, intrusion emplacement and the sources of metals at the Plateau South (MINFILE 105N 034, 035, 036) occurrences in central Yukon. Orogenic mineralization and metamorphism is ca. 110 Ma to 100 Ma, and possibly as old as ca. 130 Ma. Following deformation and regional metamorphism, two biotite-muscovite plutons, the Russell stock and Armstrong pluton, were emplaced at 95.39 ± 0.03 Ma and 95.51 ± 0.03 Ma, respectively. These plutons are here reassigned to the Tungsten suite based on mineralogy, chemistry and age. Coeval with these plutons are contact metamorphism and possibly intrusion-related mineralization. Lead isotopic data from galena cluster into two groups: Group 1 is enriched in thorogenic Pb with 206Pb/204Pb values between 18.31 and 18.14, 207Pb/204Pb between 15.62 and 15.55 and 208Pb/204Pb between 38.77 and 38.30. Group 2 is isotopically evolved with 206Pb/204Pb values between 19.13 nd 18.91, 207Pb/204Pb between 15.78 and 15.63 and 208Pb/204Pb between 39.24 and 39.07. We suggest that late Early Cretaceous mineralization is related to large-scale orogenic fluids that tapped primitive (deep?) metal sources and early Late Cretaceous mineralization, coeval with local intrusions, sourced isotopically distinct metals from the intrusions. Alternatively, all mineralization could relate to Early Cretaceous orogenic fluids but with heterogeneous, locally derived metal sources and thermal resetting of Ar ages near the intrusions.