Epithermal vein and porphyry-related gold-silver deposits in the Mount Nansen area are mainly hosted in Paleozoic Yukon-Tanana Terrane metasedimentary rocks and Early Jurassic Big Creek Batholith intrusive rocks. Mineralization is spatially, and probably temporally, related to a northwest-trending belt of mid-Cretaceous hypabyssal felsic intrusions and dykes along the Mount Nansen Trend. The proximal relationship between the veins and mid-Cretaceous intrusive rocks suggests that mineralization may be genetically related to felsic magmatism. The Dickson stock yields a U-Pb zircon age of 108.3 ± 0.7 Ma, and proximal dykes in the Flex, Dickson, Brown-McDade and Weber zones give ages of 107.9 ± 0.9 Ma to 109.0 ± 0.7 Ma, similar to the age of the Mount Nansen Group volcanic rocks. Granodiorite that hosts the Dickson deposit gives a U-Pb titanite age of 191.5 ± 2.9 Ma, and is likely part of the Big Creek Batholith. Previous studies indicated two periods of mineralization in the Dawson Range: mid-Cretaceous and Late Cretaceous. Dating indicates that Mount Nansen mineralization is associated with the mid-Cretaceous emplacement of the high-level felsic intrusions.

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.

A detailed methodology has been devised and tested for establishing metal zoning patterns in and about oreshoots within the plane of Ag-Pb-Zn veins of the Keno Hill - Galena Hill mining camp, Yukon, using whole rock vein geochemistry of run-of-mine samples. These ideal metal distribution patterns are easily interpretable in more classical zoning terms as mineral distribution patterns. To establish a zoning model samples that span a wide range of grades are rearranged in order of decreasing silver contents. The resulting "rearranged" profiles for other elements are then evaluated relative to silver. Computer-based curve fitting methods are useful means of generalizing these "rearranged" metal profiles. The foregoing procedure has been used to develop a general model for the Keno Hill - Galena Hill camp based on analytical results from 3 main deposits (Keno, Husky, No Cash) including 6 veins. Essential character of the model is embodied in analyses of Ag, Pb, Zn, and Ca and the Zn/Ag ratio. Additional but in cases ambiguous detail is added to the model by Hg, and Co and/or Ni analyses. These elements allow vein mineralogy to be monitored in a quantitative manner and provide a practical zoning model that can be used as an exploration, tool in evaluating underground workings for proximity to oreshoots in the more than 60 deposits known in the camp. A companion study involving whole rock K-Ar age determinations of small stockwork zones adjacent to Ag-Pb-Zn veins indicated an age of mineralization of about 87±2 Ma. for the Ag-Pb-Zn veins.

Six dikes that are closely associated with the Klaza epithermal vein system in the Mt. Nansen district yield early Late Cretaceous U-Pb zircon ages (78.2-76.3 Ma); this age is similar to that obtained from the porphyry stock that hosts the Cyprus Cu-Mo-Au porphyry occurrence immediately to the southeast. These results support the interpretation that epithermal veins in the Mt. Nansen district are likely genetically related to subvolcanic magmatism. Granodiorite of the Dawson Range batholith that underlies most of the Klaza property gives a U-Pb zircon age of 107.9±0.3 Ma. These dates overlap with previously reported mid-Cretaceous U-Pb zircon ages for felsic dikes associated with the Brown-McDade and related vein and breccia deposits in the Mt. Nansen mine. The new results, together with regional dating and Pb isotopic data from western Yukon, emphasize the metallogenic importance of the “early Late Cretaceous” magmatic-hydrothermal event in this region.

The Keno Hill-Galena Hill mining district of central Yukon has been a prolific silver-lead-zinc producer since the early part of the century. Typical orebodies are extensive vein systems with a mineralogy consisting of siderite, quartz, pyrite, galena, sphalerite, and freibergite in varying combinations. The veins are restricted to steep SE-dipping fault zones principally contained within a brittle graphitic quartzite unit and some concordant greenstone bodies. The main silver lodes form a narrow east-west belt, 25 km long, and have been assigned a mid-Cretaceous age as have nearby granitic bodies and their associated tin and tungsten mineralization. This study of the vein minerals indicates that groups of adjacent deposits have characteristic mineral assemblages distinguishing them from other groups; these form zones along the entire length of the belt. The following summarizes the principal mineralogical zones from west to east:: 1) pyrargyrite in quartz-siderite veins with some native silver, polybasite, stephanite, and acanthite are mainly in the west; 2) siderite, galena, sphalerite, and freibergite occur in most deposits but are found without the other index minerals on top of Galena Hill; 3) pyrrhotite and arsenopyrite are in deep vein exposures in the valley between Galena Hill and Keno Hill; 4) calcite is also in the deep veins along the eastern flank of Galena Hill but extends to the east onto Keno Hill; and 5) boulangerite-jamesonite and abundant quartz-arsenopyrite rich fractions of veins at the eastern end of the district overlap with the calcite zone. Higher gold values are recorded in zones 1, 2, and 5. The changing mineralogical facies record an evolving environment of deposition in a continuous, 25 km long hydrothermal vein system. The western deposits are thought to be higher level, or laterally "downstream" equivalents of the eastern deposits. This zoning sequence is typical and is well established in other regions of the world. Such systems are known to progress further downwards, into gold-quartz veins before attaining tin and tungsten mineralization and associated granitic bodies.

The Kalzas W-Sn-Mo deposit is located in central Yukon, 282 km north of Whitehorse on the northern side of Big Kalzas Lake. Wolframite-molybdenite-cassiterite mineralization occurs in sets of large planar quartz veins which cross-cut Selwyn Basin clastic rocks of the Upper proterozoic Windermere Supergroup, or "Grit" unit. The deposit has a concentric alteration halo with an outer sericite dominated zone, an inner "potassic' core and intense tourmalinization throughout the potassic zone and part of the sericite fringe. Intense fracture and quartz-tourmaline veinlet stockwords are present. No plutonic rocks are exposed in the local area though an underlying pluton is suspected. Kalzas has similarities to many wolframite deposits throughout the world, including those of southeast Asia which contain the bulk of world tungsten reserves. In contrast, North American tungsten mines having wolframite as the dominant tungsten phase are not as common as scheelite skarn deposits which produce most of our domestic tungsten.

Auriferous sheeted quartz veins and silicified shear zones occur along the margins and within adjacent hornfels zones of mid-Cretaceous Tombstone intrusions near the head of Clear Creek in the central Yukon. The lodes are the source for more than 120,000 ounces of downstream placer gold production. These lodes contain variable amounts pyrrhotite, pyrite, and arsenopyrite, with less abundant scheelite - alkali-feldspar, muscovite, biotite and tourmaline are common gangue phases. Grab samples of mineralization often contain gold grades in excess of 1 ounce per ton. Gold-to-silver ratios vary most commonly from 1:1 to 5:1. Gold-rich quartz veins cut all stocks, adjacent hornfels and associated lamprophyre dykes commonly contain greater than 1% arsenic. Bismuth, and less consistently tungsten and stibnite, characterize many of the most highly mineralized veins within and surrounding the stocks. Quartz veins along the intrusive-metasedimentary rock contact around the Pukelman stock are also enriched in lead and silver. R-mode factor analysis of multi-element geochemical data for 111 gold- and sulphide-bearing rock samples indicates that there are two geochemically distinct metal suites in the Clear Creek occurrences. The first is characterized by As-Au-Bi ± Sb, Te ore-related mineral association, which is typical of many intrusion-related deposits in the Tombstone gold belt. Less consistently, anomalous concentrations of Ag, Co, Cu, Fe, and Mo occur within these auriferous rocks. The second metal factor is defined by Ag-Bi-Pb ± As, Au and Te. It characterizes metalliferous vein samples that have uncommonly low Au: Ag ratios and may represent a second hydrothermal episode. Tungsten shows little consistent correlation with the metalliferous veins in either element suite.

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.

not_specified

From 2017-2019, framework metallogenic studies were completed in the eastern Yukon-Tanana upland in eastern Alaska. Numerous previously undated plutons known or suspected to contain components of porphyry, epithermal, and intrusion-related gold systems and associated deposit types were sampled for age and zircon trace element determinations between the Black Mountain area and the Yukon border, north of the Tanana River and south of the Yukon River. A collection of 54 samples were collected by Douglas Kreiner (USGS, Alaska Science Center). Zircon grains were separated from each sample. The samples were examined by U-Pb analysis by laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) in a USGS laboratory in Denver, CO. The samples contain evidence of several discrete periods of magmatic activity, with concordant zircon dates that range from ca. 53.3-2727 Ma. The bulk of analyzed samples are between ca. 68-72 Ma. Other specific periods of magmatism based on zircon dates range from ca. 55 Ma, ca. 100-112 Ma, ca. 130 Ma, and ca. 180-211 Ma. The ca. 340-365 Ma dates are likely inherited from host rocks that were previously unidentified in the field area but are known in the regional framework geology. Archean and Proterozoic zircon dates are not common, but likely represent inheritance from sedimentary and metasedimentary protoliths from the region.