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.

The AurMac property, located 35 km north of Mayo in central Yukon, includes two metasedimentary rock-hosted gold deposits: the 6158 koz Au Powerline deposit and the 845 koz Au Airstrip deposit. Mineralization at the Powerline and Airstrip deposits is characterized by gold in sheeted quartz veins and mineralized skarn horizons, respectively. The AurMac deposits straddle the Robert Service thrust fault whereby the Powerline deposit is hosted in the Late Proterozoic to Cambrian Hyland Group hanging wall, and the Airstrip deposit is hosted in the Mississippian Sourdough Hill Member of the Keno Hill Quartzite footwall. Host rocks comprise siliciclastic metasedimentary rocks, variably calc-silicate–altered calcareous metasedimentary rocks and magmatic rocks. Magmatic rocks in the Powerline zone consist of foliated mafic horizons that are geochemically similar to Cambro-Ordovician magmatic rocks found in Hyland Group metasedimentary rocks in the McQuesten, Mayo, Clark Lakes and Hart River map areas. In the Airstrip zone, magmatic rocks include a steeply south-dipping, unfoliated, aplite dike. Evidence for intrusion-related gold mineralization at AurMac includes sheeted vein and skarn mineralization similar to the intrusionhosted, intrusion-related gold deposits at Dublin Gulch, as well as the presence of metamorphic porphyroblast assemblages that suggest contact metamorphism. These findings suggest potential for further discovery of mineralized intrusion-hosted zones on the AurMac property and sedimenthosted, intrusion-related gold deposits elsewhere in the region.

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

Magmatism in the Nahanni region, which defines the eastern extent of the Tintina Gold Province, is generally associated with tungsten mineralization and/or gold-copper-antimony-bismuth-lead-zinc metal occurrences. Intrusions are subalkaline, granitic to granodioritic, and contain several types of textural variations and highly evolved phases. The intrusions range from large composite batholiths to small stocks with associated felsic dykes and veins. Initial U-Pb and Ar-Ar geochronology reveals ages of 97.5-95 Ma with short (0.5-1.5 m.y.) cooling periods, although the intrusion associated with the Cantung tungsten-skarn orebody cooled over a relatively long period (3 m.y.). Magmatism in the area has been interpreted as crustally derived, however, the rare earth element primitive-mantlenormalized profile revealed negative niobium, tantalum and titanium anomalies suggesting an arctype setting. Furthermore, the granites lack volumetrically significant, primary peraluminous mineralogies characteristic of S-type granites.

The upper Sixtymile River area is located approximately 128 km west of Dawson City, Yukon. Lithology in this area consists of Precambrian to Paleozoic metamorphic rocks, Paleozoic ultramafic rocks, Middle Jurassic pegmatitic and aplitic dikes, Upper Cretaceous porphyritic dikes and volcanic rocks with intercalated sedimentary rocks, Quaternary alkaline basaltic dikes and Quaternary alluvial sediments. Precious metal occurrences in these volcanic rocks are divided into two types, based on differences in local distribution, petrology and wall rock alteration: a gold-bearing pyrite-arsenopyrite type and a silver-bearing galena-sphalerite type. Both types are characterized by four stages of mineralization.

The Tintina Gold Province (TGP) of east-central Alaska, Yukon Territory, and the southwestern Northwest Territories comprises a very large number of gold (± base metal) deposits and occurrences that are spatially and temporally related to mid-Cretaceous intrusions. Intrusions in the eastern Selwyn Basin, south of MacMillan Pass and east of Frances Lakes, include some of the largest bodies within the TGP and are the focus of this study. Magmatic rocks of the TGP have been divided into individual plutonic suites on the basis of crystallization age, lithology, mineralogy, geochemistry, and spatial distribution, as well as metallogenic association. From -111 Ma to -99 Ma, magmatism is thought to reflect the formation of a southwest-facing continental magmatic arc, represented by the Whitehorse - Coffee Creek suite, and that the coeval Anvil and Cassiar suites formed in a back-arc environment. The younger Tay River, Tungsten and Tombstone plutonic suites successively stepped inboard between 99 Ma to 89 Ma. However, the processes leading to such volumetrically significant magmatism remains poorly understood. Intrusions within the study area range in composition from granite to granodiorite with subordinate diorite and are characteristically calc-alkaline, peraluminous to weakly metaluminous, relatively reduced, and typically contain only biotite as the dominant mafic phase. Sixteen new U-Pb ages, ranging from ~107 Ma to -91 Ma, constrain a temporal framework for plutonism across the region that is consistent with the progressively "inboard younging" pattern of magmatism observed in the northern and western portions of the TGP. - Geochemical (major, trace and rare earth elements) characteristics, together with geochronology indicate that the Anvil, Tay River, Tungsten, and Tombstone plutonic suites as originally defined farther to the northwest do continue southeastward and into the southwestern Northwest Territories. Initial Sr ratios and epsilon Nd values (n=20; age corrected for T = 100 Ma) range from 0.70853 to 0.72243 and -6.0 to -17.5, respectively. Lead isotopic compositions (n=20) show relatively narrow ranges for 2 0 6Pb/2 0 4Pb, 2 0 7Pb/2 0 4Pb, and 2 0 8Pb/2 0 4Pb ratios of 19.397 to 19.772, 15.697 to 15.829, and 39.461 to 39.883, respectively. All radiogenic isotope systematics indicate that these magmas have interacted extensively with or were derived entirely from continental crust. Several spatial and temporal trends are apparent in the data including an increase in overall REE abundance and sNd values, and a decrease in Srjnit ai, values with decreasing age (broadly moving from west to east). These trends may reflect differences in the nature of the underlying basement, potential magma source(s), and/or the melt producing processes that were involved. Lead isotope compositions of feldspars from various intrusions and sulphides from associated precious- and base metal deposits and occurrences define narrow and overlapping ranges indicating that the metals in many of the mineral deposits (and prospects) in the region are mostly derived from the mid-Cretaceous TGP intrusions.

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.

Kalzas, in central Yukon, is a porphyry-style stockwork and sheeted-vein wolframite deposit. Alteration includes a potassic core, a quartz-tourmaline-sericite zone and an outer quartz-sericite-pyrite zone, the latter in excess of 2 km in diameter. Wolframite is confined to the inner two zones, in an oval area 1500 m by 800 m. The wolframite is disseminated within the quartz-tourmaline stockwork and also occurs as coarse crystals in sheeted veins. Mineralization occurs within Neoproterozoic to Early Cambrian Hyland Group quartzites and phyllites, which are likely intruded at depth by a pluton, possibly of the Cretaceous Tombstone Suite. From 1981 to 1984, Union Carbide carried out mapping, soil and rock geochemistry, an airborne magnetometer survey, road building, trenching and drilling of two diamond drill holes. Results from Copper Ridge's 2001 sample program range from 0.3% WO3 to 0.5% WO3 over widths up to 70 m. They demonstrate the potential to define a signifi cant resource of surface-mineable tungsten mineralization at a grade of 0.4% WO3 or better. Drilling is required to confirm grade continuity at depth and along strike.

This report releases whole-rock geochemical assay results of 102 samples collected by the Geological Survey of Canada (GSC) and Yukon Geological Survey (YGS) from four Carlin-type gold zones (Conrad, Sunrise, Osiris and Anubis) in the Nadaleen Trend, Yukon.

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