The 7 Tools for Geophysical Exploration

Geophysical surveying is a technique of the mining industry which uses a specialized instruments to measure the physical properties of rocks and soil in the surface and subsurface. The goal of geophysical surveying is to detect and/or predict the presence and position of elements and minerals, ground water, oil and gas and other components of geological structure.

 

There are seven main tools and instruments commonly used in geophysical surveying. Many other techniques have been developed but they are less commonly used due to their cost in relation to overall effectiveness. The most conventional geophysical surveys consist of:

Seismic methods measure seismic or elastic wave fields to estimate different properties of the Earths subsurface. This technique uses controlled explosions or vibrating controlled sources of energy to create vibrations which pass through the different layers of the subsurface and are reflected back. Seismologists study the resulting wave patterns to map geological structures, faults and rock structure.

 

Gravity surveying employs highly sensitive gravimeters to detect minute fractional changes in the Earth's gravity field by comparing gravity values between locations . The more common relative gravimeters essentially use the physics of a weight on a string whereby the weight is pulled down due to the increase in gravity due to the presence of an anomaly. Metals in high quantities are typically responsible for slightly increased gravity anomalies, an ideal cause.

 

Magnetic surveying is a very common airborne geophysical technique where a magnetometer is towed behind or onboard an aircraft. As the aircraft passes over terrain, it detects changes in the Earth's magnetic field. If the field increases, it may be as a result of a be a deposit of magnetic material such as magnetite.

 

Electrical surveying involves testing the electrical resistivity of the subsurface. By placing electrodes into boreholes, mapping and even imagery can be created of the subsurface electrical resistance. A more conducive subsurface will suggest higher quantities of conductive elements, and the opposite result is true of less conductive elements.

 

Electromagnetic surveying methods involve imaging the earth's subsurface by measuring variations of magnetic and electrical fields. This is done with ground penetrating radar which can demonstrate various structures causing reflection and with magnetotellurics which is used for nickel or precious metals.

 

Borehole geophysics involves creating a very detailed record of each geological formation found during the digging of a borehole. As the borehole is drilled, visual inspection of samples or by borehole instruments document what is found as the hole is dug deeper and deeper. If the same samples come up in holes drilled over various locations it is a strong indicator that it may be of high quantity.

 

Remote sensing is a technique, typically involving hyperspectral imaging, where the electromagnetic spectrum is collected and processed for an area. The human eye sees red, green and blue; however hyperspectral sensing is able to image various minerals and oil in spectrums the human eye does not see. This makes it a highly valuable geophysical tool for the mining industry.

 

These seven common geophysical surveying tools aid the mining industry in finding minerals and elements for extraction and provide companies with detailed data on a property's geophysical composition.

 

 

Terraquest was established in 1984 and since then, our dedicated team has flown over 1,500 airborne geophysical surveys using both fixed wing and helicopter platforms.  Our professional crews provide significant experience having carried out airborne magnetic surveys, airborne gravity surveys, airborne radiometric surveys, and airborne electromagnetic surveys on five continents.

 

Our quality data sets have been utilized in the exploration for base and precious metals, kimberlite, hydrocarbons, uranium, rare earth minerals and water.  The company has performed exemplary surveys for both small and large exploration groups as well as many government agencies.  References can be provided upon request. Visit www.terraquest.ca.

 

Ed. GMH