The central Yukon Territory has a number of favourable placer deposit settings due to its unique history of multiple glaciations, active stream sedimentation in association with proglacial outwash settings and terrain which has remained unglaciated. Placer gold was found along the Stewart River on point bars in 1884 prior to the discovery of gold in the Klondike area. This was the first indication that the Yukon Territory contained important economic concentrations of placer gold. This study is concerned with the late Tertiary and Quaternary geology in the Lower Stewart River and adjacent Yukon River above Dawson. Previous systematic surficial geological mapping and testing for placer gold on the high-level terraces along these rivers has been limited. This report describes the sedimentology and stratigraphy of key gravelly exposures in this area because similar high-level terraces in the Fortymile River drainage in Alaska had been mined for gold for many years. Work of this type also provides information on the physical characteristics of gravelly deposits (e.g., grain size distribution) which may assist regulatory decisions on placer mining in the lower Stewart and Yukon drainages. Accompanying this report are two 1:50 000-scale surficial geology maps including marginal notes (Garner Creek, NTS 115O/13 and Matson Creek and Ogilvie NTS 115N/9 (east half) and 115O/12), as well as one 1:250 000-scale topographic map (Stewart River - NTS 115N/O) including field study site locations, heavy mineral sample sites and hardrock mineral occurrences.

Alpine glaciers from cirques of Granite and Albert creeks have deformed and reworked sediments in the Granite Creek valley and deposited locally sourced gold. Placer mining operations in the valley allowed detailed study of sedimentary deposits. The main units identified are from at least two glacial episodes which advanced farther than the previously mapped limits. Thick sequences of advance and retreat outwash blanket the till and represent high energy depositional environments. At least one proglacial lake formed due to ice-damming of lower Granite Creek by the Cordilleran Ice Sheet. We provide a stratigraphic record extending approximately 130 000 years and have correlated alpine till units to MIS 4, which has not been identified elsewhere in central Yukon. Multiple gold-bearing sedimentary units are found in the stratigraphy, representing glacial, interglacial/interstadial, and modern processes. This work highlights processes important to gold concentration that can be applied to other alpine glaciated areas with proximal gold mineralization.

The Haggart Creek study area contains unconsolidated sediments, which represent six main geomorphic settings: 1) Reid-age glacial and glaciofluvial deposits; 2) McConnell-age proximal braided stream deposits to periglacial alluvial fans; 3) McConnell-age medial to distal braided stream deposits; 4) post-McConnell wandering gravel bed river; 5) Holocene gulch deposits; and 6) Holocene colluvium. Placer gold within the study area is known to originate from at least two main local lode sources: 1) gold in sheeted quartz veins within a Late Cretaceous-age granodiorite stock; and 2) gold in isolated quartz-sulphide fissure veins found in bedrock along Haggart Creek. Placer gold is believed to have formed as a result of reworking and re-concentration of gold during interglacial times, as well as reworking of older auriferous interglacial gravel by McConnell-age periglacial alluvium. The primary setting for placer gold deposits is Late McConnell to Early Holocene alluvium, on or near bedrock. Sub-crystalline to crystalline placer gold grains recovered from sediments found far removed from currently known local bedrock sources suggests that other lode sources may be present within the study area. A copy of this thesis is available at the EMR library – QE195.W47 1999. This thesis is available online at http://hdl.handle.net/1880/25379.

Preliminary investigation of surficial geology in northern Kluane Range has resulted in new interpretations of Pleistocene ice cover including extensive unglaciated terrain and restricted glaciation during the Last Glacial Maximum. Two glacial limits are identified: a higher limit recording the most extensive glaciation of the area; and a lower limit that records younger, less extensive glaciation. This paper describes Pleistocene limits of the Donjek Glacier and the distribution of surficial materials in the upper Quill, Maple, and Wade creek drainages. The source and transport mechanism of surface materials has particular significance for surficial geochemistry sampling programs and implications for mineral exploration are addressed.

Due to the depletion of traditional economic gold placer deposits in unglaciated areas of the Yukon, the study of the relationship of placer gravels to overlying glacial sediments in ice covered regions is important to future exploration activities. The livingstone Creek area in south central Yukon has supported placer mining operations for over 90 years. Present activity is centred on gold-bearing gravels buried by thick Pleistocene glacial deposits. The placer gravels are associated with coarse interglacial stream and gulch deposits and they are overlain by fine-grained, proximal, glaciolacustrine sediments. During the last glaciation, damming of gold-bearing, high gradient interglacial tributary stream channels by main valley ice caused rapid environmental changes. Depositional processes dominated over erosion in the ice-marginal lakes, and thick sequences of fine-grained suspension deposits, debris flow sediments, and deltaic sands and gravels accumulated. In addition, when glaciers expanded and overrode the area, these thick deposits protected the underlying placer gravels from subglacial erosion and dilution. Subglacial tills were probably deposited by lodgement, meltout and flow. During deglaciation, ice-marginal sedimentation again dominated. Post-glacial streams later cut through the glacial sediments and re-exposed the gold-bearing gravels. Stratigraphic, sedimentologic and geomorphic evidence from the Livingstone Creek area suggests that small tributary valleys, oriented transverse to the former direction of ice flow in the adjacent main valleys would make good exploration targets in regions of new placer interest.

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Regional till geochemistry surveys were conducted in the Finlayson Lake, Glenlyon and eastern Carmacks map areas. Detailed till sampling was completed at the Kudz Ze Kayah and Clear Lake massive sulphide deposits to evaluate glacial dispersal near mineralized rock in a mountainous region and a plateau, respectively. A comparative evaluation of the silt-and-clay-sized fraction versus the clay-sized fraction geochemistry indicates that the clay-sized fraction presents higher metal concentrations than the silt and clay, but both size fractions generally delineate the same base metal exploration targets. The correlation between the high gold concentrations in both size fractions is not as good as for base metals because gold occurrences are only refl ected in the silt- or clay-sized particles of till. The beryllium content of till might provide an indication of the occurrence of beryl in bedrock but the low analytical precision of beryllium analyses limits this approach.

Auriferous sheeted quartz veins and silicified shear zones occur along the margins and within adjacent hornfels zones of mid-Cretaceous Tombstone intrusions near the head of Clear Creek in the central Yukon. The lodes are the source for more than 120,000 ounces of downstream placer gold production. These lodes contain variable amounts pyrrhotite, pyrite, and arsenopyrite, with less abundant scheelite - alkali-feldspar, muscovite, biotite and tourmaline are common gangue phases. Grab samples of mineralization often contain gold grades in excess of 1 ounce per ton. Gold-to-silver ratios vary most commonly from 1:1 to 5:1. Gold-rich quartz veins cut all stocks, adjacent hornfels and associated lamprophyre dykes commonly contain greater than 1% arsenic. Bismuth, and less consistently tungsten and stibnite, characterize many of the most highly mineralized veins within and surrounding the stocks. Quartz veins along the intrusive-metasedimentary rock contact around the Pukelman stock are also enriched in lead and silver. R-mode factor analysis of multi-element geochemical data for 111 gold- and sulphide-bearing rock samples indicates that there are two geochemically distinct metal suites in the Clear Creek occurrences. The first is characterized by As-Au-Bi ± Sb, Te ore-related mineral association, which is typical of many intrusion-related deposits in the Tombstone gold belt. Less consistently, anomalous concentrations of Ag, Co, Cu, Fe, and Mo occur within these auriferous rocks. The second metal factor is defined by Ag-Bi-Pb ± As, Au and Te. It characterizes metalliferous vein samples that have uncommonly low Au: Ag ratios and may represent a second hydrothermal episode. Tungsten shows little consistent correlation with the metalliferous veins in either element suite.

Yukon has over a century of placer mining history, predominately in unglaciated regions. However, as these targets are exploited, focus turns to more complex landscapes where glaciation has buried, eroded and incorporated placer gold. This study examines how Early Pleistocene glaciation in the Mount Nansen area, central Yukon, has affected placer gold deposits. Detailed stratigraphic analysis and sample collection has focused on Back Creek, where placer mining has exposed a 22 m section with several gold bearing units. In the section, sediment from two glacial advances cap sporadically preserved pre-glacial gravel. The section is variably dissected by younger placer gold bearing fluvial gravel with enrichment related to intersection of inter-glacial or pre-glacial placer gold deposits. Analysis at Back Creek reveals the potential for deeply buried placer gold deposits in other glaciated regions of Yukon.