The Coffee Project comprises numerous gold occurrences, including the structurally-controlled gold-only Coffee deposit, which is hosted in poly-deformed Paleozoic basement rocks of the Yukon-Tanana terrane and Mesozoic plutons situated in the northern Canadian Cordillera, west-central Yukon. The deposit has been interpreted as having characteristics of numerous deposit types over the project’s history including epithermal, reduced intrusion-related, Carlin-type, and orogenic gold, as well as combinations of deposit types. Recent mapping efforts and new geochronology highlight a previously unknown secondary phase of the Permian Sulphur Creek suite and led to the relocation of the Coffee Creek fault which is interpreted as a primary controlling structure of the Coffee deposit. A new structural analysis builds on previous depth estimates and suggests that the deposit formed at a relatively shallow depth of 1–3 km and together with the new map has outlined the structural history of the deposit in greater detail. New dike geochemistry suggests some mineralized Coffee dikes may be related to the Carmacks group volcanics or Prospector Mountain suite intrusives, which implies a Late Cretaceous age of formation. Field relationships and timing of regional faulting together corroborate a minimum age of formation of ~57 Ma. Available multi-element geochemistry highlights a subtle Au-As-Sb ± Ag-Pb-Te-W-Zn-K metal association that suggests a possible magmatic component to the mineralizing fluids at Coffee. Newly drilled shallow mafic intrusions adjacent to the Coffee Creek pluton serve as a potential source and may be coeval with movement on the Coffee Creek and Big Creek fault systems.

A new widespread, structurally controlled gold mineralizing system has been identified during the 2010 exploration drilling program at the Coffee Project, west-central Yukon. The Coffee Creek area is underlain by a sequence of shallowly to moderately south to southwest-dipping Paleozoic metamorphic rocks that are considered to be part of the Yukon-Tanana terrane and are intruded by the Cretaceous Coffee Creek granite along a west to northwest-trending contact. During the 2010m drilling program, structurally controlled gold mineralization was discovered in all major lithological units underlying the Coffee property. Importantly, these mineralized zones correspond to a number of discrete structural corridors. The gold zones are steeply dipping and characterized by extensive silicification in addition to sericite and clay alteration accompanied by variable As-Ag-Sb-Ba-Mo enrichment. Polyphase breccias of both hydrothermal and tectonic origin, in addition to andesitedacite dykes, are common within the gold-bearing structural corridors. The dominant sulphide is pyrite, although trace arsenopyrite, chalcopyrite and stibnite are observed locally. The similarity of breccia textures and alteration/sulphide mineralogy between all gold zones currently defined on the Coffee property implies a common mineralizing event.

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.

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.

The Coffee gold deposits are controlled by east and north-striking structures that initiated in the Jurassic and were re-activated in the Cretaceous. Cretaceous igneous rocks and Jurassic-altered Paleozoic rocks were overprinted by Late Cretaceous (or younger) gold mineralization and the paragenetic sequence for the main prospects has been established. Jurassic alteration is characterized by zones of pervasive quartz sericite alteration of metamorphic minerals and disseminated brassy pyrite. Jurassic pyrite is locally anomalous in gold, but is generally barren. Cretaceous gold mineralization overprints Jurassic sericite alteration and is characterized by veins and breccia infilled with gold-bearing, dark grey, ‘sooty’ arsenian pyrite. In biotite-rich host gneiss, disseminated arsenian pyrite extends outwards from fracture zones along biotite-rich metamorphic foliation and pre-existing Jurassic shears. In altered Late Cretaceous igneous rocks, gold-bearing arsenian pyrite replaces primary biotite. Compared to other nearby prospects, the Coffee gold project is most similar to the Boulevard trend but textures suggest it formed at shallower levels.

Structure imparts a significant control on the distribution of Carlin-type gold mineralization recently discovered in the Nadaleen trend, Yukon. An improved understanding of the structural framework for gold mineralization is essential for continued exploration success and interpreting ore fluid controls. Structural observations from the Osiris cluster of the Nadaleen trend indicate that NW-verging F1 folds were refolded in response to later SSW-NNE directed contraction. F2 folds have a subvertical ESE-striking axial plane with subvertically plunging axes on steep F1 limbs and subhorizontal fold axes in shallow F1 limbs. F2 folds have a pervasive axial planar cleavage that is recognized regionally. The steeply dipping Osiris and Nadaleen faults appear to cut all folds. Mineralization is spatially associated with later NW-striking faults in the Conrad zone. Much of the folding within the mineralized Conrad limestone is synsedimentary and its geometry reflects its emplacement as an olistostrome.

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 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.

not_specified

Skarns in the Whitehorse Copper Belt occur in both dolomitic and calcareous carbonate rocks near contacts with the diorite contact phase of the Whitehorse Batholith. The skarns are mineralogically and compositionally similar to typical copper skarns. The bulk of sulphide mineralization is associated with retrograde alteration. Chalcopyrite and pyrite are preferentially associated with actinolite and chlorite, whereas bornite and chalcocite are preferentially associated with epidote and locally serpentine. The other important copper mineral, valleriite, is restricted to magnesian rocks and is commonly associated with phlogopite, serpentine, and chlorite. Overall, the Whitehorse system is copper-rich and sulphur-poor; iron sulphide minerals are not abundant. Significant amounts of gold and silver have been recovered from the Whitehorse skarns. Cu, Ag, and Au metal raiots of spot sample assays can be used to discriminate among the different Whitehorse skarns. Deposits formed from relatively pure limestone appear to have low precious metal ratios. Deposits formed from more magnesian protoliths appear to be silver-rich. Deposits with the highest gold ratios appear to have formed from mixed limestone-dolostone lithology.