The Quesnel terrane is a distinct package of rocks that runs roughly northwest-southeast across central BC. In the CICGR project area, the Quesnel terrane is buried under thick glacial till. With the Mount Milligan copper-gold mine to the north and the Mount Polley copper-gold mine and Gibraltar copper-molybdenum mine to the south, economic mineral deposits may exist beneath the till.
This project used Geoscience BC’s QUEST project regional electromagnetic data, as well as groundwater well, exploration drilling and outcrop data, to provide a revised overburden thickness model for the central Quesnel terrane. Existing regional gravity and magnetic datasets were used to evaluate the mineral potential of magnetic targets within the central Quesnel terrane, a method that can be used in future mineral exploration to predict the size and shape of subsurface intrusions with porphyry deposit potential.
Past mineral exploration efforts in the extensive till-covered region of the Quesnel terrane between the Mount Milligan, Mount Polley and Gibraltar mines have been limited by the thickness of till. By using existing public datasets, the researchers developed models that will improve mineral exploration targeting under the till cover in this region.
This project fits under Geoscience BC’s Strategic Objective of ‘Identifying New Natural Resource Opportunities’ and our goal to:
- Continue regional-scale surveys that deliver large data sets in support of identifying prospective targets and increasing discovery rates of deposits.
This project is part of the Central Interior Copper-Gold Research series. It included:
- A revised overburden thickness model for the central Quesnel terrane.
- 3-D magnetic and gravity inversion models, including estimates of magnetic susceptibility and density values for each target
- Exploration target prioritization based on similarities to known deposits, overburden thickness and other geographic and human factors
The data, maps and models generated by this project can be used to inform land and mineral exploration decisions, and to attract new investment. They provide an improved model of the thickness of the till cover in central BC and identify potential areas of interest for new copper-gold porphyry exploration.
This project investigated over 32,000 km2 of the Quesnel terrane in BC’s Central Interior (North Central and South Central Regions) and includes communities such as Fort St James, Mackenzie, Prince George, Quesnel, Vanderhoof and Williams Lake.
Project information and results are shared with all First Nations in the project area. Geoscience BC encourages anyone planning mineral exploration work to first contact Indigenous groups in the area. The Province of British Columbia’s Consultative Areas Database can help with this (https://maps.gov.bc.ca/ess/hm/cadb/). The Association for Mineral Exploration (AME) also produces an Indigenous Engagement Guidebook.
View Project Area in Earth Science Viewer
What Was Found?
To understand regional variability of overburden thickness and aid mineral exploration planning, an overburden thickness model was created by interpolating available outcrop, drilling and groundwater well data in conjunction with bedrock depth constraints from interpreted electromagnetic inversion sections. The results show high variability in overburden thickness through the project area, and numerous windows of thinner overburden 25 metres or less, where bedrock may be more accessible, and drilling less expensive.
A suite of mineral exploration targets representing possible porphyry deposit hosts or sources of intrusive rocks were selected. The targets were chosen based on geophysical patterns associated with copper-gold porphyry deposits across the Quesnel terrane, which indicate alkalic style porphyry deposit host intrusions are commonly magnetic. Magnetic and gravity inversions were completed to derive magnetic susceptibilities and densities for each target.
Based on physical property investigations of known porphyry deposit host rocks, higher density targets were deemed most prospective in that they are most like alkalic deposit host rocks in the southern portion of the Quesnel terrane. High density targets likely represent rocks with a greater abundance of dense mafic minerals. If they are intrusive rocks, they would be monzonitic to dioritic. Lower density targets are less like the southern Quesnel terrane porphyry deposit hosts, but are still of interest, with deposits like Mount Polley and Rayfield River correlating with gravity lows. Rocks hosting these deposits may be more syenitic in composition, with smaller mafic mineral components.
Geology inferred from geophysical models can help guide and prioritize targets for exploration. A summary of overburden thickness and land features that may influence mineral exploration decisions are included for each magnetic target chosen for this project and are available in the report.
Full results are published as Geoscience BC 2022-07, which includes a detailed final report (including petrography and TerraSpec findings and inversion methodologies). Data deliverables include magnetic targets, overburden and inversion models, and Geoscience Analyst products.