This image shows the Total Magnetic Intensity from the airborne survey. The X’s pinpoint the location of magnetic susceptibility measurements, a measure of the ability of a rock to become magnetized.
The photos show the instrument used to measure magnetic susceptibility (A Geo Instruments GMS-2, made in Australia). It is effectively a very small EM survey, sampling about a fist-worth of rock. The output appears on a LCD and the digital data can be stored. Each measurement takes about 10 seconds. A number of measurements are taken at each site to develop an average. The Magnetic susceptibility data are in units of micro-CGS and are shown on the upper right side of the X’s. These can be easily converted to the other common susceptibility standard, SI, by multiplying these micro-CGS values by 4*pi.
The susceptibility measurements are quite variable and don’t seem to correlate exactly to the airborne mag data. This makes sense since the local geology is also quite variable at this site: changing readily on the scale of meters. Also, small magnetite grains in veinlets significantly impact the localized susceptibility measurements. Keep in mind that the airborne magnetic data average a very large volume of rock, thus smoothing or averaging the response considerably.
Despite these inconsistencies, this work quantifies the connection between the airborne geophysical data and geology, improves the rigor of geophysical models, and aids in the overall geologic interpretation. A significant effort is underway to relate these physical property measurements with known geologic units to possibly help outline these units in areas of poor rock exposure and limited mapping.
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