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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.

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.

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Gold mineralization in the Clear Creek area is associated with ca. 92 Ma Tombstone Plutonic Suite intrusions (TPS) emplaced into metasedimentary rocks of the Neoproterozoic to Early Cambrian Hyland Group. Hyland Group rocks have undergone four ductile deformations (D1-D4 ) in the structurally thick (>10 km) Jura-Cretaceous Tombstone high strain zone. Kinematic features indicate overall top-to-the-northwest movement on shallow shear planes. Four different types of quartz veins developed during ductile deformation and are associated with a progression from ductile to brittle-ductile behaviour. Three major brittle structural trends postdate ductile deformation. A set of sinistral ~165° striking faults developed and are crosscut by secondary east-west fracture zones in Hyland Group rocks. The Tombstone Plutonic Suite was then emplaced in a broadly east-west oriented belt, with some local control exerted by the ~165° oriented faults. Continued development of the east-west fracture set after the Tombstone Plutonic Suite intrusion, resulted in an extensive system of gold-bearing sheeted quartz veins. Finally, sinistral reactivation and associated quartz-tourmaline veining occurred on ~165° oriented structures. Preliminary analysis of fault geometry and connectivity suggests the most favourable sites for mineralization are east-west fracture zones connected to ~165° oriented faults. Other favourable structural sites include misoriented segments of ~165° faults and possibly northeast-striking structures connected to ~165° faults. Mapping has delineated a large area of contact metamorphism suggesting extensive shallowly buried intrusions. The highest priority in any exploration program should be given to sites that are coincident with shallowly buried, or that are near Tombstone Plutonic Suite intrusions and have the above fault/fracture geometries.

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.

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A reconnaissance-level study of post-mining hydrogeochemical conditions was carried out at the Brewery Creek gold deposit within the Tintina Gold Province. The deposit is characterized byepizonal mineralization with a consistent arsenic-gold-mercury-antimony geochemical signature. Surface discharges and seeps in the area are naturally alkaline (pH=7.6-8.2), Ca-HCO3 ¯-SO4²¯ waters. Upstream from the recognized mineralization, waters contain <3 ¿g/L As and <1 ¿g/L Sb. Water samples immediately downstream from the ore bodies show maximum concentrations of 18 ¿g/L dissolved and 47 ¿g/L total arsenic, and 18 ¿g/L dissolved and 21 ¿g/L total antimony. Two kilometres below the mineralization, on lower Laura Creek, arsenic concentrations are diluted to background levels of <3 ¿g/L, and antimony levels are still slightly elevated at 9-10 ¿g/L. Comparison with hydrogeochemical data from Donlin Creek, an undeveloped epizonal deposit in Alaska, indicates that elevated concentrations of a few tens of ¿g/L arsenic and antimony are typical of waters draining such gold systems, regardless of their state of development. In addition to their usefulness for the construction of geoenvironmental models, these data also provide information for establishing exploration programs utilizing water sampling.

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Gold mineralization has been identified on the foliated margins of Paleozoic gabbroic intrusions, where a protracted series of structural preparation events has enhanced rock permeability. Rheological contrasts between these mafic rocks and amphibolite facies metasedimentary hosts have resulted in variable foliation development, especially at margins of mafic bodies. Initial foliation development centred on granitoid material in magmatic intrusion breccia, and was enhanced by syn-metamorphic biotite formation. Early mineralized quartz vein development occurred under greenschist facies conditions during and/or after regional Mesozoic thrust stacking of kilometre scale rock slabs. Initial vein emplacement was largely controlled by the foliation in mafic gneiss, and minor chloritic alteration and later hydrothermal generations cut across all structures. Gold mineralization involved only minor introduction of As, Sb, and S, and the hosting quartzite has higher As, Sb, and S content than most mineralized veins. Au is accompanied by elevated Bi, Mo, and Te in quartz veins.