Spectral IP and Resistivity
Spectral Induced Polarization & Resistivity surveys (IP & Res) are excellent methods for detecting disseminated sulphide mineralization that could be associated with gold. The surveys are carried out using surface and borehole modes.
Large Loop TDEM
ClearView Geophysics Inc. owns and operates transient PROTEM receivers and TEM57/67 transmitters built by Geonics. This system has proven itself useful for detecting both good and bad conductor sulphide mineralization located both shallow and 100’s of metres deep. It is also useful for detecting sources of water.
Snowmobile-Mode Cesium Magnetics
Cesium magnetometer surveys are carried out using a custom-built sleigh pulled behind a standard snowmobile. This system has proven itself on numerous large-scale mineral exploration projects during the past 15+ years.
Seismic Refraction
Seismic Refraction surveys are typically carried out for depth to bedrock investigations. The "shot" can be either an explosive or hammer source. Interpex IXRefraX software is used to process the data.
Electromagnetic (EM) and Magnetic surveys
EM and Magnetic surveys are perhaps the most common geophysical methods used on mineral exploration and environmental investigations. The most commonly used EM instruments for environmental investigations are the Geonics EM31 and EM61.
GPR ( Ground Penetrating Radar )
GPR works best in low conductivity areas. Conductive materials (e.g., clay) attenuate the GPR signal to the point that very little depth penetration is achieved. Penetration is greatest in unsaturated sands and fine gravels.
Gravity
Gravity surveys are completed for a number or applications, including mineral exploration (e.g., diamonds) and geotechnical investigations (e.g., escarpments).
Geophysical Interpretation
ClearView has extensive experience interpreting airborne and ground-based geophysical data. We use UBC's suite of inversion software to produce 2D and 3D interpretations of total field magnetics and IP/Resistivity data. Post-processing software is also used to produce various derivative datasets and maps.
A Geometrics Geode with ability to record up to 65,536 samples per record allows high resolution data to map stratigraphy and structure to depths up to 2 km using a trailer-mounted 800 lb weight-drop system. A 'seismic gun' is sufficient for shallower investigation depths.
The Geonics EM34-3XL ground conductivity meter can be applied in 'rover-mode' for high resolution coverage in a short amount of time. The onboard 'Archer2' datalogger collects real-time GPS at 1-second intervals tagged to Apparent Conductivity readings at 5x per second. The low-stretch tow-strap keeps the distance between the receiver and transmitter sleighs close to the optimum 'nulled' 20-metre separation.
The same specially configured plastic sleighs with no metallic components used for the IMAGEM rover surveys are also used here - allowing for stable coverage.
The mode of operation in the case displayed here is 'vertical dipoles, 20-metre Tx-Rx separation' for effective depth penetration of 30 metres.
Abandoned wells need to be located and decommissioned. There are several steps required in order to accomplish this. The first step is to search for drill logs filed with the City/Region or MOE. Some historic inspection files can also have photographs taken at the site to aid with referencing the well to surface structures and features.
The next step is to view historic air photos. The following historic Air photo displays a likely historic well cover that has since been buried.
Sometimes its necessary to apply geophysical methods in unconventional ways. In addition to snowmobile-mode and ATV-mode surveys with various instruments such as cesium magnetometers, TDEM IMAGEM, GPR and others, it is often necessary to use other platforms to carry out the surveys. A few examples are provided here:
Geonics EM31 Ground Conductivity Meter, Scintrex EnviC Cesium Magnetometer and Sensors & Software Noggin 100 were all mounted on an inflatable raft so that a quarry could be scanned. A kayak was used to tow the instruments around to avoid potentially contaminating the water which was also used for organic agriculture operations.
EM31 with GPS linked to DAP logger, mounted on inflatable raft and towed by kayak
FWS (Full Waveform Sonic) borehole surveys can be an alternative to Borehole shear-wave seismic surveys in certain cases.
Borehole Shear Wave surveys use 1 or 2 borehole geophones that are 'clamped' against the PVC cased borehole wall. Ideally the holes are dry. Seismic shear waves are generated near the borehole collar using a hammer against a plank held in place under the wheels of a truck.
FWS can be used to determine Poisson's Ratio by measuring Vp compressional and Vs shear Wave velocities down the borehole in a single self-contained borehole probe. The method requires the borehole to be filled with water. The main disadvantage of FWS compared to borehole seismic surveys is that the borehole needs to be uncased and as small diameter as possible. This might be difficult through soft soils so the borehole should be logged immediately after the casing is pulled by the drill crew. In some cases the drillers may need to fill the borehole with water to allow the survey to commence.
Gravity Surveys are used for many applications, including gold, base metal and diamond exploration. For geotechnical applications it can be used to detect buried bedrock escarpments, for example.
Cross-hole IP/Resistivity Surveys are carried out with C1-C2 transmitter current electrodes at 'infinity' perpendicular to the target strike and on each side of the target. P1-P2 electrodes are placed in the borehole pairs and read in a semi-tomographic mode. A third electrode is typically positioned at one of the collars for quality control and to monitor the transmitter current as the surveys progresses.
ClearView owns and operates a Sensors & Software Conquest 100 System for concrete scanning services. This compact 1 GHz GPR instrument includes an added-on power cable detector.
Joe Mihelcic attended the symposium in Iqaluit and met many interesting government, business and local leaders.
Joe with Paul Okalik - Nunavut's first premier.
ClearView Geophysics Inc. carries out large loop TDEM surveys for base metal, uranium and graphite exploration using Geonics PROTEM receivers and TEM57 transmitters with TEM67 power modules. Low frequency 3D coils or fluxgate sensors are connected to the receiver to measure the responses. Borehole surveys can also be carried out with BHEM probes.
The IMAGEM system is a state-of-the-art high resolution time-domain system that is capable of recording 200 channels of on- and off-time EM measurements.
Geotechnical engineers require accurate parameters for designing buildings, foundations, rock slopes and so forth. The shear-wave velocity of the ground is a useful part for determining common geotechnical parameters such as Poisson's Ratio and Shear Modulus.
ClearView is in the arctic carrying out snowmobile-mode geophysical surveys. These surveys are faster than walking mode, safer, more accurate, higher quality and much higher resolutions than airborne surveys. The project this year is focused on helping exploration geologists pick near-mine targets for further evaluation.
We are proud to say that ClearView Geophysics Inc. has provided professional geophysical services for mineral exploration, environmental investigations and geotechnical applications since it was incorporated in 1996.
ClearView was founded by Joe Mihelcic, geophysicist, after completing his MBA at Ivey Business School in London, Ontario. Since then, ClearView has employed and trained dozens of high-calibre geoscience students, technicians, engineers and specialists. The company was established to allow greater flexibility in applying customized solutions.
Here's to the next 20 years!
Sometimes the simplest and most inexpensive methods from Civil 101 can provide surprisingly high accuracy vertical positioning. ClearView recently completed an elevation survey to complement a complex series of geophysical surveys at a site in Southern Ontario. The elevation data was used to provide 3D capabilities for presenting the geophysical data. A pair of Trimble ProXT GPS receivers were used to provide accurate temporary benchmark data. The level survey data closed to less than 1/8 of an inch over 700 metres in both directions through the 1400 metres long survey area.
MaxMin by Apex is a mature method used over many decades for mineral exploration. ClearView is presently applying the method on a gold exploration project to see if it can detect subtle quadrature (out-of-phase) responses that might indicate stringer mineralization, faults or geologic formation variations.
There are many types of 'targets' that geophysics can be used to detect. For exploration, targets can be gold, base metals, speciality metals, diamonds and sand/gravel deposits, to name a few. Each target type has its own unique response to geophysical methods based on its local geologic environment - this is called its 'geophysical signature'.
The Dipole-Dipole electrode configuration is ideal for detecting off-hole targets because the transmitter and receiver electrodes are always at the same distance apart as the configuration moves down the borehole. This makes detecting anomalies easier because if there weren't any, the resistivity profile would be flat in a uniform half-space.
Snowmobile-mode surveys can be used with different geophysical techniques. Our flagship survey is the cesium-magnetometer survey - almost continually applied and operated in the arctic on small and large-scale projects at spring-time personally by Mr. Mihelcic since 1996. Only the mag sensor and GPS dome are on the sleigh separated by 1.7 metres. Post processing corrections using in-house software correct for this layback and a 0.33-second system latency which is confirmed by speed tests done over anomalies in both directions. The tried and true un-manned aluminum sleigh is located far back from the snowmobile. It has proven durable in boulder fields, steep terrain, extreme cold and wet conditions.
These design features, fine-tuned over 20 years, give extremely low heading errors - far better quality than walking mode and certainly higher resolution than any airborne survey. Productions rates of 40-80 km per day can be acquired depending on terrain, with readings at 10x per second.
This spring we applied a combined cesium-mag and TDEM system on a large-scale project in Nunavut.
The image below shows the magnetometer sleigh followed by the TDEM sleigh on the horizon:
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