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Fluid Inclusions as an Exploration Tool in the Yellowknife Gold Belt, Northwest Territories, Canada
- Author / Creator
- Aksu, Baykan
The Archean Yellowknife greenstone belt hosts world-class orogenic gold deposits including Con and Giant along with active prospects extending several tens of kilometers along the belt. Some common challenges in exploration for orogenic gold deposit include the nugget effect, which can lead to assays not being representative of the gold grade in the samples analyzed. In contrast, fluid inclusions are homogeneously distributed throughout veins such that, if fluids that correlate systematically with gold can be identified, fluid inclusion characterization would effectively distinguish mineralized from barren samples. In this thesis, we evaluate whether a chemical signature of the fluid inclusions can be used to discriminate between auriferous and non-auriferous samples in different geological backgrounds. Crushing stage tests provide a fast and reliable first order estimate on whether high-pressure of volatiles is common in fluid inclusions within a given sample. We have performed crushing analyses in samples from underexplored claims as well as in mineralized samples from the historic mining sites. The majority of the gold-bearing quartz veins from the Quyta-Bell property have been identified by their high-pressure volatile contents. In the Giant gold mine, our results show that high-pressure volatiles can be used as a proxy to the gold-rich zones within 5 meters.
The presence/absence of high-pressure volatiles as evaluated through crushing tests correlates with dominance of specific fluid inclusion types. Type I aqueous inclusions are abundant in the barren samples. The main component of these inclusions is relatively low-pressure H2O and CO2 below the limit of detection. Type II carbonic (CO2 ± CH4) inclusions correlate with gold-bearing samples. Mineralizing fluids at both the Quyta-Bell property and the Giant mine are CO2-CH4 rich and H2O poor to absent (below detection). Application of crushing stage on the field can easily recognize these volatiles and help narrow potential auriferous veins.
In addition to CO2 and CH4, gold-bearing samples from the Quyta-Bell property are characterized by the presence of graphite. Graphite was observed as a solid opaque phase hosted in fluid inclusions and as a hydrothermal product overgrowing and forming in veins with iron sulfides. Graphite overgrowing and in veins crosscutting pyrrhotite indicates that graphite postdates sulfide precipitation. The temperatures calculated from the graphite thermometer vary between 400 to 480 °C for the graphite inclusions and 530 to 610 °C for the graphite in veins. The cooler temperature recorded in the inclusions is probably an artifact of post-entrapment graphite precipitation within the inclusion at lower temperatures as the closed system cooled down. The higher temperatures indicate lower amphibolite facies and are in agreement with the peak metamorphism in the area. The systematic correlation between gold and graphite occurrences in the Quyta-Bell property suggest a genetic relationship between them. Gold precipitation is most likely associated with high-temperature fluids trapped during peak metamorphism. Some possible precipitation mechanisms for graphite include mixing different C-bearing fluids and the reduction of hydrothermal fluid. These mechanisms can be geochemically linked to gold precipitation. Both high-pressure volatiles and graphite in these quartz veins could be used as a vector for gold occurrences in the Quyta-Bell property.
- Graduation date
- Spring 2021
- Type of Item
- Master of Science
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.