The central Pelly Mountains in southeastern Yukon Territory consist of imbricate thrust sheets, which have undergone syn- and post-thrusting deformation and metamorphism. The local geology is further complicated by intrusion of Upper Cretaceous batholiths, and by strike-slip faulting related to the Tintina Fault, a major northwest-trending transcurrent fault of uppermost Cretaceous or early Tertiary age. This faulting disrupts the northeast edge of the study area. Upper Devonian and Mississippian strata are present in at least two of the thrust sheets, but the Mississippian volcanic rocks occur in only one of them. The volcanic rocks consist of volcaniclastic material with minor interbedded flows, and were deposited in a submarine environment. Several coeval and cogenetic syenite and trachyte domes and small stocks are the remains of vent areas. Although the volcanic rocks are all highly altered and show evidence of widespread chemical mobility, trace element data indicate that the rocks are meta-luminous trachytes, most closely resembling peralkaline volcanics generated in extensional environments. This suggestion of a predominantly extensional tectonic setting in mid-Mississippian time in the Pelly Mountains is consistent with recent tectonic syntheses for the area. Stratabound and stratiform massive base metal sulphide deposits that occur within the Mississippian volcanic sequence are similar in many respects to the Kuroko-type volcanogenic massive sulphide deposits of Japan. The Pelly Mountains deposits, however, are among the first known occurrences in the world of Kuroko-type mineralization in a rift environment. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The Kluane Ranges are underlain by a sequence of stratified rocks ranging in age from Permian to Triassic, cut by .Cretaceous and Tertiary intrusions. Flow and pyroclastic rocks of Lower Permian Station Creek Formation were probably part of a volcanic arc environment. Argillaceous and tuffaceous rocks of the Transition Zone of Station Creek Formation and overlying sedimentary rocks of Lower Permian Hasen Creek Formation were deposited in a subaqueous environment, possibly a back-arc basin. Upper Triassic basalts of the Nikolai Greenstone are largely subaerial and were probably a product of rift volcanism. Lower Triassic Kluane gabbro-ultramafic complexes are sill- or sheet-like bodies, divisible into a Lower Group (within the Transition Zone) that consist of peridotite and dunite with associated nickel-copper sulphide deposits, and an Upper Group (within Hasen Creek rocks) that consist of gabbro and peridotite but with no known associated nickel-copper deposits. The ultramafic rocks are piagioclase-bearing and chemically are pyroxenitic and peridotitic komatiites. Bulk chemical composition of the Quill Creek complex is similar to that of pyrolite and calculations show the complex could have formed from an upper mantle diapir, affected by 40 percent partial melting and composed of residual olivine crystals and ultramafic liquid. Prominent copper lode deposits in the Kluane Ranges include: (1) vein and disseminated types in Station Creek volcanic rocks; (2) nickel-copper associated with Kluane complexes; and (3) vein-type in the Nikolai Greenstone. A narrow, positive range of sulphur isotopic compositions for vein sulphides in Station Creek Formation contrast sharply with a large range for those in the Nikolai Greenstone. The former deposits resulted from only local mobilization of sulphur (and metals) during metamorphism in a closed system, whereas mineralization in the Nikolai Greenstone involved considerable variation in chemical parameters of ore fluids in an open system with more than one source of sulphur. Anomalously negative sulphur isotopic values for nickel-copper sulphide bodies resulted from contamination of magmatic sulphur by 30 to 60 percent sulphur from wall rocks. Much of this contamination occurred prior to or during segregation of an immiscible sulphide liquid as at Quill Creek, with further contamination during injection of still liquid sulphide bodies into footwall rocks in the case of Canalask deposit. Substantial contaminant.sulphur may have been crucial in achieving sulphur saturation of magmas of Lower Group Kluane complexes and subsequent formation of associated nickel-copper sulphide deposits. Isotopic data for both magmatic sulphides and sulphur-bearing country rock support a strong case for a general sulphur contamination model for nickel-copper deposits related to mafic and ultramafic intrusions on a worldwide scale. Pyrite in wallrock is considered to be the most likely general source of sulphur contributed to ultramafic magmas and several different stages of sulphur contamination are possible throughout consolidation of the magmas and its associated sulphides. Sulphur transfer to the magma can occur by bulk country rock assimilation or by fluid ingress where the fluid derives sulphur from the contact zone by incongruent melting of pyrite or by complete dissociation of pyrite. Important features of this model, having economic implications, are: (1) emplacement of the ultramafic complex as a magma; (2) presence of sulphur-bearing country rocks; and (3) presence of a sulphur-depletion halo adjacent to the ultramafite. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

[Truncated abstract] The Tintina Gold Province (TGP) comprises numerous (<15) gold belts and districts throughout interior Alaska and Yukon that are associated with Cretaceous plutonic rocks. With a gold endowment of ∼70Moz, most districts are defined by their placer gold contributions, which comprise greater than 30 Moz, but four districts have experience significant increases in gold exploration with notable discoveries at Fort Knox (5.4 Moz), Donlin Creek (12.3 Moz), Pogo (5.8 Moz), True North (0.79 Moz), and Brewery Creek (0.85 Moz). All significant TGP gold deposits are spatially and temporally related to reduced (ilmenite-series) and radiogenic Cretaceous intrusive rocks that intrude (meta-) sedimentary strata. The similar characteristics that these deposits share are the foundation for the development of a reduced intrusion-related gold deposit model. Associated gold deposits have a wide variety of geological and geochemical features and are categorized as intrusion-centered (includes intrusion-hosted, skarns and replacements), shear-related, and epizonal. The TGP is characterized by vast, remote under-explored areas, unglaciated regions with variable oxidation depths and discontinuous permafrost, which, in combination with a still-evolving geological model, create significant exploration challenges. Twenty-five Early and mid-Cretaceous (145-90 Ma) plutonic suites and belts are defined across Alaska and Yukon on the basis of lithological, geochemical, isotopic, and geochronometric similarities. These features, when combined with aeromagnetic characteristics, magnetic susceptibility measurements, and whole-rock ferric:ferrous ratios define the distribution of magnetite- and ilmenite-series plutonic belts. Magnetite-series plutonic belts are dominantly associated with the older parts of the plutonic episode and comprise subduction-generated metaluminous plutons that are distributed preferentially in the more seaward localities dominated by primitive tectonic elements. Ilmenite-series plutonic belts comprise slightly-younger, slightly-peraluminous plutons in more landward localities in pericratonic to continental margin settings. They were likely initiated in response to crustal thickening following terrane collision. The youngest plutonic belt forms a small, but significant, magnetite-series belt in the farthest inboard position, associated with alkalic plutons that were emplaced during weak extension. Intrusion-related metallogenic provinces with distinctive metal associations are distributed, largely in accord with classical redox-sensitive granite-series. Copper, Au and Fe mineralisation are associated with magnetite-series plutons and tungsten mineralisation associated with ilmenite-series plutons. However, there are some notable deviations from expected associations, as intrusion-related Ag-Pb-Zn deposits are few, and significant tin mineralisation is rare. Most significantly, many gold deposits and occurrences are associated with ilmenite-series plutons which form the basis for the reduced intrusion-related gold deposit model