Compositional studies have been undertaken on gold particles recovered from hypogene ore, eluvial material and placer samples in and around the Klaza property. These data have been correlated with previous descriptions of in situ mineralization to elucidate placer-lode relationships and systematic change in gold compositions between porphyry and epithermal environments. Gold alloy from the porphyry environment is Ag-poor with respect to Au formed in later stage veins. Silver, and to a lesser extent Cu, have been the main discriminants for inferring the source of Au within the placers, and in general, vein mineralization is a more important source-type than porphyry mineralization. The signature of Pb-Bi-Te previously identified in the inclusion suites of Au grains from Nucleus/Revenue, Casino and Sonora Gulch has also been identified at Klaza, demonstrating that generic compositional signatures can underpin a robust exploration methodology. The relative sizes of porphyry and epithermal footprints of detrital Au together with their respective compositions are important considerations when targeting Cu-Au systems.

A copy of this thesis is available at the EMR library – QE446.Y8 M67 1981.

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.

We have determined the major and trace element composition of approximately 2700 gold particles from 21 gold-bearing mesothermal quartz veins and 35 placer gold samples from the Klondike District in western Yukon Territory. Measured Au, Ag, Cu, and Hg contents were used to define a characteristic geochemical signature for each of the vein samples. These signatures were then compared with the various compositional populations that we have distinguished within each of the placer samples. Preliminary conclusions derived from the study include: 1) placer gold in both recent stream deposits and in the Plio-Pleistocene White Channel Gravels is detrital in origin; 2) the placer gold is mainly, if not entirely, derived from mesothermal quartz veins; 3) all lode sources for the placer gold have not yet been located; and 4) composition data can be used to link placer gold to its specific lode source.

The White River copper deposit, in upper Triassic Nikolai Greenstone of southwestern Yukon, is representative of the native copper-basalt association. Native copper and chalcocite are the association. Native copper and chalcocite are the most abundant ore minerals, but a substantial amount of bornite is known, as well as lesser amounts of chalcopyrite, pyrite, digenite, covellite, cuprite and native silver. These minerals are found in crosscutting fractures, amygdules, gas release tubes, small crackle zones, and as local disseminations in basalt; and although concentrated near the margins of a single glomeroporphyritic unit, are neither confined to that unit nor to a single zone within it. Two stages of copper mineralization are postulated: Stage I mineralization is thought to account for most of the native copper as a product of continental weathering of Nikolai basalts. Stage II mineralization is a much later event characterized by copper sulphides in crosscutting structures. Native copper and copper sulphides of Stage II appear to form a stable and primary product of a low grade (regional) metamorphism indicated by such minerals as chlorite, epidote, prehnite, pumpellyite, calcite analcite and apophyllite which have essentially the same mode of occurrence as primary copper minerals. Consequently, metamorphism (prehnite-pumpellyite facies) is interpreted to have been the mineralizing process. Whole-rock potassium-argon dating suggests an age no older than 120 million years for the metamorphic mineralizing event; hence, stage II mineralization post-dated host rock formation by at least 80 million years. It is probabe that many other copper occurrences in Nikolai Greenstone have formed in a similar manner. Also, it is likely that some of these mineralizing fluids could have moved higher in the stratigraphic sequence and precipitated copper minerals in other units.

Speculation regarding the genetic history of the Minto copper-gold deposit in the Carmacks map area (NTS 115I) has existed since its discovery. Minto copper sulphides are hosted in sheet-like expanses of biotite-rich, variably deformed granitoids surrounded by massive granodiorite. Attempts to explain Minto’s unusual mineralization style have ranged from digested red-bed copper, to aborted and deformed porphyry, and recently to an Iron Oxide Copper Gold (IOCG) type system. Although these commonly used genetic frameworks can explain many aspects of Minto-style mineralization, questions regarding chemistry, paragenesis, and structural controls on mineralization still remain. This paper is part of an MSc thesis project that will focus on characterizing mineral textures, mineral chemistry, mineral paragenesis and micro and macro structural analyses to improve our understanding of the Minto copper-gold mineralized system and to enhance regional exploration potential in the district. This paper summarizes some preliminary observations at the Minto deposit and outlines future research.

The Eocene Mt. Skukum gold-silver epithermal deposits are 65 km southwest of Whitehorse in the Yukon Territory. Veins are in nearly flat-lying Eocene andesitic volcanic rocks of the Mt. Skukum Caldera Complex, part of the Sloko Volcanic Province, which unconformably overlies the Mesozoic Coast Plutonic Complex and Paleozoic to Precambrian metamorphic rocks. Significant veins are contained in a regional halo of propylitic alteration centered on a graben in the southwestern corner of the Mt. Skukum Caldera Complex. Zones of steeply-dipping quartz-carbonate-sericite veins are associated with major faults and rhyolite dykes which bound blocks in the graben. Electrum and native silver form fine grains which average 15 to 20 microns and locally exceed 1 mm across, in veins containing only trave amounts of sulphides. Fliuid inclusions indicate that vein minerals were deposited from fluids averaging 313°C with an average salinity of 0.7 weight percent NaCl equivalent. Primary inclusions show that depositional fluids existed under two pressure regimes: one close to hydrostatic, the other approaching lithostatic. Both indicate deposition about 470 m below paleosurface. Oxygen and carbon isotope composition of minerals in the deposit and surrounding wall rocks indicate that depositional fluids were meteoric. Large depletions in O18 content of andesitic rocks in the deposit area indicate a minimum water: rock mass ratio of 0.81:1. Precious metals at the Mt. Skukum deposit were emplaced at relatively low temperature, near surface, by a meteoric water dominated hydrothermal system driven by heat from associated rhyolite dykes. Gold and silver were leached from andesitic and rhyolite stocks and volcanic rocks as well as metamorphic and granitic basement, and precipitated with quartz and carbonate in permeable conduits such as fault zones, and breccia bodies.

A reconnaissance study of the composition of gold from several placer streams in the Stewart River map area was carried out to characterize the likely style(s) of lode mineralization from which the placer gold in each stream was derived. Results of the study indicate that placer gold from Eureka and Black Hills creeks, as well as gold grains from colluvium in exploration pits at the head of Eureka Creek, have relatively low fineness, low copper contents and high mercury contents. These compositions are consistent with both the gold in colluvium and most of the placer gold having been derived from epithermal sources in the Eureka Dome or Henderson Dome area. Gold in placers in the Moosehorn Range is likely derived from intrusion-related, gold-bearing quartz veins exposed in the headwaters of the placer creeks, and is characterized by relatively high fineness, high copper contents and low mercury contents. Placer gold in Thistle, Kirkman and Blueberry creeks is very similar to that from streams in the Moosehorn Range, suggesting that an undiscovered intrusion-related gold deposit is present within the Thistle/Kirkman drainage basin.

Gold-bearing, arsenic-rich pyrite in association with enriched As, Sb and minor Ag is found in two separate mineralization styles at Kaminak Gold Corp.’s Coffee Gold Project, Yukon. Arsenian pyrite replaces primary metamorphic mica by sulphidizing Fe in the host, while pervasive dolomite-illite alteration destroys the host and eventually consumes early mineralized pyrite. Silicification of host rocks is observed with associated arsenian pyrite deposition due to cooling. Brecciation of silicified intervals by coarse grained hydrothermal quartz occurs later with additional pyrite deposition. Mineralized intervals are oxidized by late, meteoric fluids which consume Au-bearing pyrite and release micron-scale free gold from the pyrite crystal lattice into the remnant oxides. Sulphidized biotite within the 98 Ma Coffee Creek Granite constrains mineralization to <98 Ma. Similar metal associations (Au-As-Sb vs. Au-As-Sb-Pb-Zn-Cu) suggest Coffee potentially represents the shallower, epizonal extension of the mesozonal orogenic Boulevard gold deposit, with a late epithermal overprint.