Results of a study to determine the origin of alteration in the Plio-Pleistocene White Channel sediments and bedrock using field observations, mineralogical and geochemical analysis. The study was coordinated with a sedimentological study of the White Channel gravel by S.R. Morison in 1985. A copy of this thesis is available at the EMR library – TN414.C32 Y86. This thesis is available online at https://doi.org/10.7939/R32F7JW6S.

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.

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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.

Compositional studies have been undertaken on gold particles recovered from hypogene ore, eluvial material and placer samples in and around the Klaza property. These data have been correlated with previous descriptions of in situ mineralization to elucidate placer-lode relationships and systematic change in gold compositions between porphyry and epithermal environments. Gold alloy from the porphyry environment is Ag-poor with respect to Au formed in later stage veins. Silver, and to a lesser extent Cu, have been the main discriminants for inferring the source of Au within the placers, and in general, vein mineralization is a more important source-type than porphyry mineralization. The signature of Pb-Bi-Te previously identified in the inclusion suites of Au grains from Nucleus/Revenue, Casino and Sonora Gulch has also been identified at Klaza, demonstrating that generic compositional signatures can underpin a robust exploration methodology. The relative sizes of porphyry and epithermal footprints of detrital Au together with their respective compositions are important considerations when targeting Cu-Au systems.

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.

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.

Most of the historic placer gold recovered from the Indian River has been from the modern river gravel; however, a significant amount of placer gold has been mined from older deposits, including low-level, intermediate-level and high-level gravel terraces. Significant placer gold reserves exist in Indian River drainage in various forms. Prospective targets include 1) modern (Holocene) alluvial channels, alluvial fans and tributary gulches; 2) modern (Holocene) low-level buried and/or abandoned alluvial terraces; 3) early to late Pleistocene intermediate-level buried abandoned terraces and alluvial fans; 4) early Pleistocene (pre-Reid) glaciofluvial gravel sequences; 5) Pliocene high-level alluvial terraces (White Channel gravel); and 6) technogenic (tailings) deposits. Fine-grained placer gold existing in size ranges not recovered efficiently by conventional sluicing operations has been found in alluvial and glaciofluvial gravel and tailings deposits. These deposits may represent an important resource and any future mining operations must address the metallurgical implications to maximize recovery.

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.

On-going compositional studies of gold from placer and lode deposits and occurrences in western Yukon provide new insights into their nature and origin. Two main compositional populations are present in placer and lode deposits in the Klondike District. The dominant population has high fineness and low mercury content, and appears to be mainly derived from lode sources in the Lone Star, King Solomon Dome and lower Gold Run Creek areas. A second population of low fineness, high-mercury-content gold is derived from lode sources on the left limit of Eldorado Creek and in the headwaters of Bear and Last Chance creeks. Placer gold in the Sixtymile District was not derived from epithermal vein occurrences like those in the Sixtymile River valley but rather has compositions more similar to Klondike-type metamorphogenic veins. Placer gold in Scroggie Creek in southern Stewart River map area appears to be derived from intrusion-related vein occurrences.