string(10) "[Minerals]"

Undercover and Deep Geology from QUEST Electromagnetic and Gravity Data

Lead Researcher(s):  D. Mitchinson

Project ID:  2022-002

Key Research Organization(s):  University of British Columbia - MDRU

Project Location:  North Central BC

Strategic Focus Area:  Mineral

Summary



A belt of rocks known as the Quesnel terrane extends roughly northwest-southeast through BC’s interior and is host to many known mines including Mount Milligan (Cu-Au), Mount Polley (Cu-Au) and the Gibraltar (Cu-Mo). However, in the Prince George area, the Quesnel terrane is obscured by a thick layer of glacial sediments. Without a better understanding of the geology under the thick layer of glacial till, mineral exploration and other land use decisions are hindered.

This project used Geoscience BC’s QUEST project regional electromagnetic and gravity data to derive new information about bedrock geology in the central Quesnel terrane. These particular datasets have been underused in interpreting bedrock under glacial till in central BC (when compared to magnetic data) but show interesting correlations with known geology and structures. In this project, the electromagnetic and gravity data sets were used to support an evolving understanding of the geological history of the Quesnel terrane and provide more context for future mineral exploration.

The Need

Due to extensive glacial till overlying bedrock in BC’s central Quesnel terrane, the ability to map and sample the bedrock at surface is greatly limited. As the region has high porphyry copper-gold mineralization potential, research that enhances understanding of the bedrock geology can aid in the identification of specific locations to target for further research and exploration.

Goals

This project fits under Geoscience BC’s Strategic Objective of ‘Identifying New Natural Resource Opportunities’ and our goal to:

  • Undertake research that adds value to existing or ongoing data sets through ground-truthing studies, data interpretation and mining camp compilations

Specifically, this project aimed to:

  • Develop a new interpretation of the bedrock geology for the QUEST area from integrated interpretation of available geophysical data and other datasets that were not available when the bedrock geology map was last updated;
  • Add geologic details, such as internal variability in volcanic domains, buried intrusive bodies, or new contact or structural interpretations, to the existing but largely inferred geological map of the central Quesnel terrane; and
  • Determine whether VTEM and gravity data and models may be a useful tool elsewhere in BC for identifying buried geology and possible mineral deposit environments

Benefits

Gravity and electromagnetic surveys show promise for distinguishing between certain volcanic units and can support the identification of intrusive rocks and structures. As Geoscience BC’s 2007 QUEST project captured this geophysical data over the central Quesnel terrane, this project aimed to utilize this existing data and subsequent interpretations to explore and define the ability for electromagnetic and gravity data to distinguish lithologies under cover, and to corroborate features interpreted previously from magnetic data.

Models of interpretations of newly distinguished or interpreted geological and structural features will be produced for use by geologists and explorers looking to identify potential areas of interest for new copper-gold mineral exploration.

Location

The study area is comprised of the QUEST survey area in BC’s North Central region between Williams Lake and Mackenzie.

What Was Found

The QUEST project electromagnetic and gravity data are very effective for mapping regional scale volcanic, sedimentary, and intrusive geologic domains. Commonly, magnetic data are used for remote interpretation of bedrock geology when areas are under sedimentary cover or difficult to access. But since volcanic stratigraphy in the project area have only a weak magnetic response, magnetic data is not as useful here for mapping volcanic domains. Gravity and VTEM data on the other hand, although lower resolution, identify contrasting volcanic domains through sediment covered areas.

Comparing the electromagnetic and gravity data with recent geological maps validates its use in mapping volcanic stratigraphy and enables an understanding of the composition and coherency of the bedrock. Geophysical interpretations of bedrock geology through the central Quesnel terrane indicate dense and resistive stratigraphy correlate with previously mapped pyroxene-phyric volcanic units and dominate the western part of the terrane. Lower density, lower resistivity rocks correlating with previously mapped basin-fill sedimentary rocks dominate in the east. A compositionally different series of volcanic rocks, containing magnetite and thus producing a positive magnetic response, occurs in the southern part of the project area and extends southward and may be derived from a different magmatic source compared to volcanic rocks in the northern and southern Quesnel terranes. Isolated bodies that correlate with gravity, resistivity and magnetic highs are possible intermediate to ultramafic composition intrusive rocks. Known alkalic type porphyry deposits in the Quesnel terrane are usually hosted in high density, high magnetic susceptibility intermediate composition, and these interpreted bodies may represent targets to focus greenfield porphyry deposit investigations. If further investigations of previously unsampled dense and magnetic anomalies uncover mafic to ultramafic intrusive sources, they could alternately be investigated as potential hosts to magmatic nickel-copper style deposits.

Deliverables


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