Between the Cretaceous granitic rocks (Hake Batholith on the west; Cassiar Batholith to the east) are three belts of metamorphic rocks, collectively part of Yukon-Tanana terrane. These are remnants of oceanic and continental volcanic arcs, and marginal basin sediments of Early to mid-Paleozoic age. At the head of Borden Creek are thick carbonate and andesitic volcanic rocks correlated with Klinkit Group. The Ram Creek fault and Hidden Lake fault are not exposed but deduced to be steeply dipping brittle structures with northeastward thrust or transpressional offset, based upon more complete exposure to the southeast in 105B/3 map area. The former is likely of Cretaceous age; the latter was active between mid-Permian and Early Jurassic time.

Examination of Early Tertiary clastic rocks in the Indian and Sixty Mile River areas has revealed that: 1) sediments are arranged in fining-upward sequences and are dominated by sandstone and to a lesser extent conglomerate; 2) the clastic sequence in the Indian River area is thicker than previously thought; and 3) conglomerate beds consist mainly of white vein quartz, Nasina Quartzite, Klondike Schist and chert pebbles. The metamorphic clasts were probably locally derived and the chert pebbles were eroded from the Ogilvie Mountains. These clastic rocks are interpreted as being deposited in separate, but coeval, continental basins that were mainly fed by southward flowing braided-rivers.

Unconsolidated sediments in the Mount Nansen area can be subdivided into eight clastic facies: 1) clay-rich diamicton; 2) massive/stratified silt/clay; 3) massive/disorganized pebbly sand/sand; 4) stratified pebbly sand/sand; 5) disorganized muddy gravel; 6) massive/stratified sandy gravel; 7) disorganized gravel; and 8) massive to crudely stratified gravel. Diamicton is interpreted as glacial till; other facies are fluvial/glaciofiuvial in origin. Sediments have a number of geomorphic settings, including Holocene colluvium, alluvial fans and stream deposits; Reid periglacial alluvial fans; and pre-Reid glacial and glaciofluvial deposits. Previous workers suggested that significant placer gold concentrations occur only in alluvium that lies either upon bedrock or glacial till. New data from this study suggests that significant amounts of placer gold also occur in the diamicton, primarily at the diamicton/bedrock contact. Gold concentration in the diamicton is likely due to glacial erosion and incorporation of a supergene-enriched bedrock mantle and pre-existing auriferous alluvium. A copy of this thesis is available at the EMR library – QE571 L42. This thesis is available online at http://hdl.handle.net/1880/30694 - embargoed.

Regional-scale thrust faults in the Klondike District separate major lithologic units that include medium-grade metamorphic rocks of the Upper Permian Klondike Schist and middle to late Paleozoic Finlayson (Nasina) assemblage, as well as relatively low-grade greenstone and ultramafic rocks of the Slide Mountain terrane. These units were emplaced in the Jurassic as a series of kilometre-scale stacked thrust slices that are locally separated by additional ultramafic slices. A distinctive set of post-metamorphic compressional structures related to thrusting, particularly a set of ductile recumbent folds and associated spaced cleavage, is preserved in all thrust slices and is well developed near bounding faults. In carbonaceous units within the Klondike Schist, spatially associated with some thrusts, carbonaceous material is locally concentrated along the thrust-related spaced cleavage. Thrust-related fabrics are overprinted by kink-folding that locally affects the Finlayson assemblage, but is mainly developed in Klondike Schist. Gold-bearing veins appear confined to Klondike Schist and were emplaced in local sites of extension controlled principally by axial surfaces of these kink folds.

Unconsolidated sediments in the Mount Nansen area can be subdivided into eight clastic facies: 1)clay-rich diamicton; 2) massive/stratified silt/clay; 3) massive/disorganized pebbly sand/sand; 4) stratified pebbly sand/sand; 5) disorganized muddy gravel; 6) massive/stratified sandy gravel; 7) disorganized gravel; and 8) massive to crudely stratified gravel. Diamicton is interpreted as glacial till; other facies are fluvial/glaciofluvial in origin. Sediments have a number of geomorphic setting, including: 1) Holocene colluvium, alluvial fans and stream deposits; 2)Reid periglacial alluvial fans; and 3) pre-Reid glacial and glaciofluvial deposits. Previous workers suggested that significant placer gold concentrations occur only in alluvium that lies either upon bedrock or glacial till. New data from this study suggest that significant amounts of placer gold also occur in the diamicton, primarily at the diamicton/bedrock contact. Gold concentration in the diamicton is likely due to glacial erosion and incorporation of a supergene- enriched bedrock mantle and pre-existing auriferous alluvium.

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The layered rocks in this area originated as continental shelf sediments overlain by volcanic arc successions. Now called Yukon-Tanana terrane, they tectonically over-rode the western edge of ancient North America beginning in Middle Jurassic time. Three elements are present in the map area. The west half comprises the Big Salmon Complex; the east half is a separate, in part contemporaneous succession composed of the Dorsey Complex and Swift River Group. Unconformably overlying both these elements are less metamorphosed Klinkit Group and Triassic sediments that are here interpreted as overlap assemblages. The unexposed contact between Big Salmon Complex and Swift River Group is inferred to be an east-side-down normal fault.

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. A copy of this thesis is available at the EMR library – QE195 M67 1979. This thesis is available online at http://hdl.handle.net/2429/22257.

The Kluane Ranges, located in southwest Yukon, are underlain by Late Paleozoic to Late Triassic volcanic and sedimentary rocks assigned to Wrangellia. Bedrock mapping completed within the White River area indicates Wrangellian rocks underwent several phases of deformation between Late Triassic and Miocene time. Middle Triassic marine, fine-grained sedimentary rocks are preserved in grabens where they are overlain by basal conglomerates and breccias of the Nikolai formation. The grabens are related to uplift associated with the deposition of Nikolai formation flood basalts and intrusion of ultramafic bodies. Late Jurassic to Early Cretaceous compression resulted in structural stacking of older rocks and northeast- and southwest-verging overturned folds. Latest (?) Cretaceous to Miocene dextral strike-slip along the Denali fault system led to the formation of steeply dipping faults, extensional and compressional basins and refolding of older regional scale folds. Reactivation of Jura-Cretaceous faults also occurred at this time. An enigmatic pre-Middle Triassic deformation event is believed to be preserved locally in rocks of the Hasen Creek Formation.