Conglomerates belonging to the Indian River formation (IRF), south of the Klondike goldfield, have recently become the focus of exploration activity owing to their potential as hosts for paleoplacer gold derived from the Klondike. However, textures within the conglomerate have been interpreted as indicative of hydrothermal activity, and the possibility exists of in situ epithermal gold. Paleocurrents in conglomerates indicate dominant transport from the southeast, incompatible with gold transport from the Klondike. Gold grains from unconsolidated conglomerate at Montana Creek reveal an epithermal signature (20-50% Ag, 0.3 to 3% Hg and opaque inclusion suite containing complex polymetallic sulphotellurides and sulphosalts), distinct from the signature of placer and lode sources in the central and southern Klondike (12-20% Ag, Hg absent and opaque inclusion suite of simple base metal sulphides). Gold grain morphology and alteration textures within unconsolidated conglomerates suggests that Montana Creek gold is derived from in situ epithermal mineralization related to that previously reported at Eureka Dome.

Placer gold has been reported in small amounts throughout the South Nahanni river drainage; however, the original source of the gold is uncertain. This study focuses on two types of placer gold in the area: (1) locally abundant grains derived from near Selena Creek, and (2) scattered grains recovered from streams throughout the South Nahanni drainage area. A shape analysis of all gold grains was completed and representative grains from each sample population were selected for imaging on the scanning electron microscope, along with analysis for Au-Ag-Cu-Hg values on the electron microprobe. The gold grains are typically >700 fineness and mercury is below detection levels (<0.20%). Approximately half the grains analysed from the Selena Creek area registered near to, or slightly greater than, detection levels of copper (<0.04%), whereas the majority of grains from the isolated showings had copper contents below detection levels. The results are compared with published morphological and compositional data for placer and lode gold in other regions.

orphyry and epithermal mineralization of early Late Cretaceous (ca. 76-74 Ma) at Casino, Revenue/Nucleus, and Sonora Gulch areas in the central and eastern Dawson Range in west-central Yukon is spatially related to numerous placer gold mining areas. Placer-lode relationships have been established through study of gold alloy compositions and associated mineral inclusion assemblages. At Casino, hypogene gold grains are liberated by erosion and pass into the placer system without compositional modification, as evidenced by the common alloy signatures and a mineral association of Au, (Bi-Pb-Te-S) minerals and chalcopyrite. A second signature of higher-Ag, chalcopyrite-poor gold has been identified in placer populations, but this gold type also exhibited the Bi-Pb-Te-S signature. The results suggest that the placers contain a mixture of gold derived from the porphyry and peripheral or shallow level epithermal mineralization. The Bi-Pb-Te-S association evident at Casino was also recorded at Revenue/Nucleus and Sonora Gulch. This generic signature of gold in Cu-Mo (-Au) porphyry deposits and their associated distal epithermal manifestations could be applied to exploration in areas where placer-lode relationships are unclear.

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A reconnaissance study of the composition of gold from several placer streams in the Stewart River map area was carried out to characterize the likely style(s) of lode mineralization from which the placer gold in each stream was derived. Results of the study indicate that placer gold from Eureka and Black Hills creeks, as well as gold grains from colluvium in exploration pits at the head of Eureka Creek, have relatively low fineness, low copper contents and high mercury contents. These compositions are consistent with both the gold in colluvium and most of the placer gold having been derived from epithermal sources in the Eureka Dome or Henderson Dome area. Gold in placers in the Moosehorn Range is likely derived from intrusion-related, gold-bearing quartz veins exposed in the headwaters of the placer creeks, and is characterized by relatively high fineness, high copper contents and low mercury contents. Placer gold in Thistle, Kirkman and Blueberry creeks is very similar to that from streams in the Moosehorn Range, suggesting that an undiscovered intrusion-related gold deposit is present within the Thistle/Kirkman drainage basin.

The White Channel Gravel (Pliocene) is the most important gold-bearing unit in the world famous Klondike goldfields of west-central Yukon. It is up to 46 m thick and consists of framework-supported, poorly bedded, slightly muddy sandy gravel that was deposited by braided rivers. Historically, this unit is subdivided into a lower 'white gravel' and an upper 'yellow gravel'. The colour of the white gravel is due to an abundance of quartz clasts and an alteration of the sand-mud matrix that has been referred to as 'leaching' or 'bleaching'. Previous researchers concluded that the alteration is hydrothermal in origin, but a review of this research shows that there is no unequivocal evidence supporting hydrothermal alteration. Petrographic examination of in situ samples from both the white and yellow gravel reveals a depositional fabric and an alteration fabric, although the alteration is better developed in the white gravel. The alteration is reinterpreted as the result of weathering, and particularly diagenesis due to groundwater flow.

A new research project was begun in 2002, aimed at better understanding the nature and origin of copper-gold mineralization and its main host rocks at the Minto and Williams Creek (Carmacks Copper) deposits in west-central Yukon. This will also help to further constrain exploration models both on a property and a regional scale. Field work in 2002 confirmed that the main host rocks for both deposits are variably deformed plutonic rocks (diorite and quartz diorite at Williams Creek and mainly granodiorite at Minto). Mineralization formed prior to the ductile deformation that has affected these units. Mineralized granodioritic gneiss from Minto and apparently post-mineralization quartz diorite at Williams Creek yield U-Pb ages of ~194 Ma and ~191 Ma, respectively; thus the mineralization appears to have formed at essentially the same time as the host intrusions. Reconnaissance Pb- and S-isotope analyses of sulphide minerals from both deposits also indicate a likely magmatic source for the mineralization.

Placer gold mining in Clear Creek extends back to 1900, when the discovery claim was staked. Approximately 129,000 crude ounces (4012 kg) of gold have been reported since 1941 which includes 49,637 crude ounces (1544 kg) obtained by dredging operations (1941 to 1955, and 1981 to 1987). Placer gold morphology ranges from crystalline gold in quartz to rounded nuggets to flattened gold. The largest nugget, recovered from the headwaters of Left Clear Creek, weighed 7 ounces (218 g). Clear Creek valley was filled by ice during the pre-Reid glaciation (early Pleistocene). Pre-Reid glacial drift is preserved as till, resedimented till, and glaciofluvial sediments on the lower slopes along main Clear Creek and parts of Left Clear Creek. Alpine glaciers formed at the headwaters of Left Clear Creek, however most of the moraine deposits have been eroded. During the subsequent Reid and McConnell glacial periods local alpine glaciers formed in the headwaters of Josephine and Big creeks. Alpine glaciers, the pre-Reid ice sheet and their melt waters redistributed the gold in the Clear Creek drainage. The distribution of heavy minerals in Clear Creek drainage is varied. Over the years dredging operations intersected pockets of gravel containing cassiterite, scheelite and galena, but their precise locations were not documented. Contemporary placer mining and our heavy mineral studies have located concentrations of pyrite, arsenopyrite, scheelite and galena, in addition to gold. Exploration for the source of placer gold has resulted in the discovery of numerous gold veins in the surrounding area.

Significant economic concentrations of placer gold were first recognized in an intermediate level terrace near Dawson City in the late 1980's Regional surficial mapping has shown the distribution of many high level terraces of pre-Reid, Reid and McConnell age in central Yukon, but the relationship between economic gold concentration and terraces is not well understood. Sedimentological study of an intermediate level terrace near Dawson City suggests two river types have been dominant:: the first, a 'wandering gravel bed river' is characterized by moderate sinuosity, later accretion deposits, limited sand facies, and generally fine gravel; the second, 'proximal braided river' is characterized by multiple channels, very thick and crudely imbricate gravel, low bed relief, and a maximum particle size greater than the underlying wandering gravel bed river deposits. The gold-bearing 'wandering gravel bed river' assemblage is typical of present-day conditions with river processes dominated by lateral migration and high gravel transport rates through the system, conducive to heavy mineral concentration during an interglacial period. The 'proximal braided river' is characteristic of nearby glacial ice and rapid sedimentation resulting in poor heavy mineral concentration. The transition from a wandering gravel bed river to a proximal braided river is suggested to mark the onset of a pre-Reid glaciation in the Southern Ogilvie Mountains. The sedimentology of the intermediate terrace gravels suggests a geomorphic model which may be used for exploration of terrace placer deposits in central Yukon with a similar pattern of regional glaciation influencing terrace formation.

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.