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Soil-Gas Detection of Bedrock Mineralization and Geological Faults Beneath Glacial Deposits using Economic Electronic Gas Sensors

Lead Researcher(s):  D. Sacco, R. Lett

Project ID:  2018-028

Key Research Organization(s):  Palmer

Project Location:  Central Interior

Strategic Focus Area:  Minerals

Summary



Previous research indicates that fluctuations in soil gas can be associated with faults and mineralization. This project developed a practical, real-time soil gas measurement system to detect evidence of geological faults and sulphide mineralization buried beneath glacial sediments in the central interior of British Columbia.

The original prototype was developed in 2020, with functional testing at two MINFILE occurrences in the Quesnel terrane. The project was extended to include further testing in partnership with Centerra Gold Inc. at the Mount Milligan Mine.

The Mount Milligan survey was completed in 2021 using a refined soil gas measurement system. The knowledge of bedrock structures and mineralization provided verification of the results, which showed a positive correlation between carbon dioxide (CO2) and oxygen (O2) concentrations in soil associated with observed geological structures and sulphide mineralization. These results provide a framework for designing effective surveys using real-time soil gas measurements to support mineral exploration in areas where bedrock is covered by sediment.

The Need

BC’s North Central and South Central Regions are characterized by thick glacial sediments that conceal bedrock known to host copper-gold occurrences. New, cost-effective tools that ‘see through’ the sediment can improve the efficiency of mineral exploration in central BC and beyond.

Project Goals

This project fits under Geoscience BC’s Strategic Objective of ‘Advancing Science & Innovative Geoscience Technologies’ and the goal to:

  • Increase research and development of innovative exploration and mining methods, tools, approaches and geoscience technologies.

Specifically, this project:

  • Developed, tested and refined a real-time, portable and cost-effective soil gas survey technology and field-tested it where structures and mineralization are buried beneath a layer of glacial sediments.
  • Determined survey design and sampling protocols for property-scale programs.

Project Benefits

Soil gas sampling has the potential to help identify new natural resource opportunities in an area of BC that may host undiscovered mineral deposits. The project has developed an innovative and practical mineral exploration method for BC and elsewhere in the form of a portable device that can allow for faster exploration decisions by reducing the need for lab analyses.

Survey Area

The method was tested at three field locations:

The Mouse Mountain and Shiko locations were chosen based on the occurrence of faults, the existence of copper-gold porphyry-style disseminated sulphide mineralization and a cover of glacial deposits. The Mount Milligan Mine location was chosen as the testing allowed for corroboration with detailed descriptions of the bedrock and surficial geology provided by Centerra Gold Inc.

What Was found?

Soil gas and soil were sampled over bedrock structures associated with mineralization to compare the soil geochemistry with CO2 and O2 concentrations in soil (‘soil gas’). The soil gas over the inferred structures is enriched with CO2 and depleted in O2 compared to the soil gas over the surrounding geology. Results of the soil chemistry testing indicate the soil gases likely reflect oxidizing sulphides within the bedrock.

In the initial project phase, researchers found that the system reliably measured CO2 and O2 variations in soil gas in real time and that the equipment was field-portable and efficient compared to conventional surface sampling methods that require collection of material (gas or sediment) and lab analysis. With the functionality of the system verified, it was determined that it would benefit from additional testing where the location of the structures were known and could be used to validate the results, and to help determine if buried mineralization could be detected through varying thicknesses of glacial deposits.

The project extension saw modifications to the prototype soil gas analysis system. This included improving functionality by simplifying components. The CO2 and O2 sensors, battery pack and pump were integrated into a single waterproof case. The battery pack was upgraded, and the gas control valves reconfigured. A longer probe was also constructed to allow collection of soil gas in variable surface conditions, which also reduced the potential for atmospheric contamination.

With these refinements complete, the Mount Milligan sampling was conducted. Here, soil-gas CO2 and O2 were measured at 163 sites over two surveys in October 2020 and July 2021. A subsequent trenching program completed by Centerra provided direct observations to corroborate the soil gas survey results.

The survey results showed a spatial correlation between CO2 and O2 anomalies and mapped bedrock fracturing (structures) exposed in the trench excavated parallel to one of the soil gas sampling traverses. The modified system has shown good potential for detecting bedrock structures and associated mineralization beneath areas covered by glacial sediments; however, further opportunities for improvement include additional testing over thicker and different types of sediments, and alterations to the soil gas collection probe to reduce the potential for atmospheric contamination in different soil conditions.

The device also offers potential for application in other fields such as geothermal resource detection, or (in a static format) to monitor seismic activity.

Deliverables