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by Carmela Burns on July 19, 2012 technology
The recent rush to find graphite and vanadium deposits to satisfy potential demand in green energy applications is reigniting airborne electromagnetic (EM) methods as highly effective exploration tools.
Graphite and vanadium are both commonly used in steelmaking and both are finding new, high-tech applications such as lithium-ion and vanadium-redox batteries, wind and solar power. In some cases the two materials occur together in nature, allowing geophysicists to use the highly conductive graphite to lead to the more subtle vanadium that can be bound by several different minerals.
As is the case for many accessory minerals, there are no direct geophysical methods for detecting minerals containing vanadium, says Alexander Prikhodko, senior geophysicist with Geotech. Geophysical techniques are able to reflect only indirect indications, or “symptoms”, of the metal and the factors that control its deposition.
Where there is a graphite association, he says, EM methods are highly effective in exploration for vanadium. Tintaniferous magnetite, a common vanadium host, also provides an EM response.
At Triple Nine Resources’ Four Corners iron ore-titanium-vanadium property in Newfoundland, for example, a 2011 helicopter borne VTEM survey conducted by Geotech over newly staked claims extended one high intensity magnetic anomaly and discovered three new ones. The targets occur along (and in close proximity to) the Cabot Fault Zone, part of a globally significant, deep penetrating structure that is the likely source for the mineralized fluids at the Four Corners Property.
Follow-up drilling on the property’s Keating Hill anomaly, which the VTEM survey suggests has double the strike length than that originally outlined, confirmed significant concentrations of all three metals down to a maximum vertical depth of 590 m, including a weighted average grade of 20% Fe2O3 T (total iron), 3.5% titanium oxide (TiO2) and 0.10% vanadium pentoxide (V2O5).
Furthermore, prospecting along the largest of the four anomalies, the Four Corners MAG anomaly (FCMA), confirmed widespread enrichments of titanium – vanadium – magnetite mineralization with assays of up to 48.8% Fe2O3, 12.5% TiO2 and 0.31% V2O5. FCMA has a strike length of at least 4.5 km and a width of is 1.5 km and appears to be part of a large mineralized system that will require more follow up.
The high conductivity of graphite lends itself well to electromagnetic surveys, and there are a number of airborne electromagnetic systems that are being used successfully for vanadium and graphite exploration, including Fugro's HELITEM (time domain) and DIGHEM (frequency domain) systems and Geotech’s VTEM system. Each system has its unique strengths.
Prikhodko notes that there is no single technical characteristic that identifies an EM system as the best for a particular exploration task including finding vanadium deposits. Instead, the electronical and mechanical attributes of the system work together to provide an integrated solution. Just as the loudest singer is not necessarily the best, the EM system with the most powerful transmitter is not necessarily the most appropriate for targeted exploration. The “loudness” of a system must be balanced with timbre, clarity of sound and precision of note, he says.
According to Prikhodko, one of the key technical advantages of Geotech’s VTEM system is the balance between high power and sensitivity. “Balance is achieved through complex engineering, noise reduction in very wide broadband and optimization of the transmitter’s current wave form to use as much of the helicopter’s spare electrical power as possible,” he says.
In this way, VTEM can detect and discriminate between low to excellent conductors using a low base frequency, long pulse width, system calibration and a B-Field derived from integrating data collected at 96 kHz over the entire waveform.
Geotech’s continual development of their technologies has included extensive GX programming within the Geosoft platform to build a highly specialized and integrated solution for quality control, processing, visualizing and presenting VTEM results. “ We utilize Geosoft for QC procedures, data processing, maps creation, parameters calculations and resistivity depth imaging,” said Prikhodko.“ Geotech geophysicists and processors have developed lots of special GXs to accommodate our workflows.”
For vanadium and graphite exploration, and especially when the two materials occur together, EM methods are proving to have the right combination of deep penetration, sensitivity, and spatial and conductance discrimination to detect future deposits of these strategic resources.