Hydrocarbons in soil as pathfinders for base and precious metal exploration : an orientation study at the Mt. Washington epithermal Au-Ag-Cu prospect, British Columbia, Canada

The goal of this research is to advance hydrocarbon-pathfinder techniques as non-proprietary geochemical exploration tools for base- and precious-metal mineralization. Three objectives were set to achieve this goal: 1) identification of the physical, chemical, and biological links between buried economic mineralization and hydrocarbon concentrations and compositions at surface; 2) development of a robust, commercially viable and cost-effective analytical techniques for hydrocarbons applied to non-petroleum-based exploration; and 3) to optimize hydrocarbon sampling methodologies and strategies. To better understand hydrocarbon-sulphide interactions, hydrocarbon sampling methodologies were tested with a geochemical orientation survey over the Mt. Washington epithermal Au-Ag-Cu occurrence on Vancouver Island, British Columbia. A novel analytical technique, solid phase micro-extraction gas chromatography with flame ionization detection (SPME-GC-FID), was developed in conjunction with the commercial laboratory GeoFrontiers Corporation to determine hydrocarbon concentrations in soil. Soil gas samples, ground, and surface waters were also collected and analyzed for hydrocarbons. Surficial geology mapping shows that major and trace element distributions in soil are strongly controlled by the depositional facies of glacial cover. Epithermal pathfinder element concentrations in B-horizon soil and groundwater indicate that hydromorphic dispersion is also a significant factor in this study area. Key hydrocarbon pathfinder concentrations in soil and soil gas are highest proximal to sulphide mineralisation. Anomalous tridecane and hexadecane plume geometries in the surface environment are linked to epithermal mineralization in bedrock and commodity and pathfinder element anomalism in soil. Hydrocarbon anomalies in soil and soil gas at Mt. Washington are interpreted to be of biogenic origin. Hydrocarbons are naturally present in soils as products of biosynthesis by microbes, plants, fungi, yeast, and insects. Sulphide oxidising environments contain distinct microbial ecologies including primary producers such as Acidithiobacillus Ferrooxidans. which contribute to hydrocarbon cycling in soil. Thermogenic hydrocarbons interact with basin-hosted hydrothermal systems and may also contribute to anomalous concentrations of organic compounds associated with sulphide minerals.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat