Matrix VLF-EM

Terraquest now offers the new Matrix Digital VLF-EM frequency system designed and built by Dr. Petr Kuzmin of Magenta Geophysics Ltd. at Terraquest’s request.

The Matrix VLF-EM system is a newly developed, light weight, digital, passive system that utilizes continent-wide communication VLF radio signals as a power source to energize ground conductors. The signals are received by 3 orthogonal coils and recorded independently from up to four VLF stations. Being fully digital, a full range of final outputs is possible including total field amplitude, vertical and planar ellipicities, tilt and azimuth to the transmitter separately for each frequency.

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Benefits of the digital Matrix VLF-EM system:

  • State of the art digital circuitry ensures consistent, high resolution VLF data with minimal operational input
  • Separate data from 3 coils permit cleaner data with increased resolution
  • Simultaneously monitoring of up to 4 independent and customizable VLF frequencies, full advantage of source-target coupling geometries can be achieved
  • Full parameterization of anomalous VLF signals – including angular and ellipticity components – allow for maximum flexibility for integration to achieve advanced modelling and interpretational techniques
  • VLF-EM technology has been repeatedly demonstrated to map structure effectively and economically, to unravel structural complexities
  • Matrix maps fine-grain, low conductivity and more disseminated structures
  • Matrix compliments active EM systems which are designed to identify and delineate other specific targets

The VLF method responds to geological structures (e.g. faults and shear zone) and overburden conductivity variations, but may also respond to bedrock conductors (e.g. graphite and massive sulphides).

Specifications:

The Matrix Digital VLF-EM Receiver contains 3 orthogonal coils mounted in the wing tip or stinger location and is coupled with a receiver-console. The data are recorded using four (or more) VLF frequencies such as:

  • Cutler Maine NAA frequency 24.0 kHz
  • La Moure North Dakota NML frequency 25.2 kHz
  • Seattle, WA NLK frequency 24.8 kHz
  • Puerto Rico NAU frequency 25.2 kHz
# of Channels 1…4
Frequency Range 10…..49 Khz
Sampling Period 0.1 Sec
Coils Diameter 16 Cm
Power Supply V 10….30 V
Temperature Range -30…+60 Degrees C

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Output:

The basic outputs for each frequency are:

  • Total Field
  • Vertical and Planar Ellipicities
  • Azimuth to transmitter
  • Tilt

Final Processed Products:

  • Contours of Total Field Amplitude
  • Conductor Amplitude Peak Detection
  • Profiles of In-Phase and Out-of-Phase
  • Matrix Inversions: resistivity maps, sections and depth slices

Case Study #1: Inversion Modelling of Gold-Vein Mineralization using Matrix VLF-EM

Attached is a recent press release from Signature Resources Ltd. which focuses on the benefits of airborne Matrix VLF-EM inversions to provide cost effective near surface mapping. EMTOMO performed the inversion and to our knowledge, this is the first time airborne VLF-EM data from a typical greenstone terrane in North America have been inverted. The interpretation, performed by Jeremy Brett of MPH, successfully enabled refinement of high priority targets and definition of key geological features. The resistivity modelling shows:

  • enhanced resolution of the controlling contact between felsic intrusives and mafic metavolcanics
  • a distinctive, broad resistivity low that correlates with a known mineralized, gold vein system and alteration (Lingman Gold Deposit) and numerous other occurrences along a 22 kilometre strike, even where known thin surficial conductivity is mapped by the total field VLF-EM surficial data
  • that the depth slices are unimpaired at depth by known surficial conductivity, as shown in the 40 metre resistivity depth slice presented in the press release

In general inversion of VLF-EM data can:

  • Characterize rock types by their inherent resistivity
  • Enhance the resolution of contacts between lithologies
  • Augment the conductor axis provided by the total field amplitude
  • Identify resistivity lows commonly associated with contact zones, alteration and mineralized structures
  • Surface mapping can be continued downwards by progressive depth slices
  • Map the surficial conductivities separately from the deeper bedrock responses.

In summary, resistivity products derived from the inversion of airborne Matrix VLF-EM data from a typical greenstone belt with thin overburden provide an inexpensive technique to identify and map near surface bedrock lithologies, structure, alteration and mineralization. We would be pleased to discuss this technique with you and discuss any application to your ongoing exploration programs including any inversions of existing data.

Link to Client Press Release: https://docs.wixstatic.com/ugd/63a91d_529fe5654c7b43a3b7b2f0b9c1df58cb.pdf

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Case Study 2: Utilization of Inverted VLF-EM data to Map Uranium and Associated Alteration in Athabasca Sandstones

Terraquest performed a Matrix VLF-EM case study for uranium exploration in the Athabasca Basin of northern Saskatchewan. In this geologic model, high grade uranium mineralization located along the unconformity between the basement and overlying sandstones have been remobilized upwards by hydrothermal fluids along steeply dipping faults, creating resistivity breaches in the sediments, characterized by uranium and associated alteration. The purpose of the test was to determine if low-cost, shallow VLF-EM techniques can be effective in identifying these breaches. The VLF-EM data were inverted by EMTOMO and are shown here compared with drill hole information and a DCIP resistivity profile. Complete description is provided in the link to the case study.

  • The inversion of airborne Matrix VLF-EM in upper panel at same vertical scale as the coincident inverted DCIP resistivity section shows excellent correlation with the upper reaches of the DCIP resistivity breaches.

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Attached: Application of Matrix VLF-EM for Mapping Alteration in Athabasca Jan 20.pptx