Gold Mineralisation in the Lone Star area of the Klondike Gold District, Yukon, Canada

The Klondike Gold District (KGD) is located in north-west Yukon and is well known for the extensive placer deposits that were exploited in the Gold Rush of 1896. Intensive exploration in the region led to the discovery of the White Gold District in 2009 and accompanying metallogenic studies identified a regional episode of orogenic mineralisation, which includes that within the KGD (Allan et al., 2013). This period has produced huge amounts of gold from relatively small areas, which lack the large-scale features associated with well-established orogenic gold deposits. This PhD investigates the largest lode occurrence in the KGD that is located in the Lone Star area and includes the richest placer drainages of the Eldorado and Bonanza creeks. This research project develops a paragenetic evolution for gold bearing quartz veins and a, newly discovered, unit of gold bearing schist to establish a genetic relationship to better understand gold distribution in the Lone Star area. Textural and mineralogical analysis of gold bearing quartz veins has revealed that gold is paragentically late and is associated with a volumetrically minor phase of quartz. Detailed petrographic studies have revealed that gold disseminated in a unit of schist along the Lone Star ridge is epigenetic and formed during a period of permeable fluid flow. The gold-bearing quartz veins and gold bearing schist are genetically linked and formed at shallow crustal conditions from a relatively cool hydrothermal fluid. A tectonic setting proposed by Staples et al. (2016) is consistent with a model whereby metamorphic devolatilisation at depth has generated a fluid which was
driven upwards into fractures. This model accounts for the widespread nature of gold occurrences (as indicated by placer activities) with the formation of multiple fluid conduits formed in an extensional environment throughout the period of mineralisation. The associated lack of fluid focusing distinguishes the mineralisation in the region from other economically important orogenic gold deposits globally. Historical exploration in the area has focussed on auriferous veins, and the apparent discrepancy between in situ and placer gold. The identification of the schist as a potential gold source resolves this problem whilst
providing a template for studies of other areas where similar discrepancies exist.