This is GMN's first report where in-field radiometry has been applied.
Their MS350 device ( URL ) detects flashes of light in a crystal caused by inbound gamma rays. It counts the flashes over very short sampling periods (200μs). It cannot report Th (ppm) in-field, but under controlled conditions the counts are proportional to the amount of Th that is present. Gamma rays travel for kilometres in air, dissipating with the inverse square of distance. The measured count changes markedly as the distance to source(s) changes.
Five traverses were run, a reference, and 4 surveys.
The reference traverse was run from a location on road BA-250 (-13.53389, -39.79081) near Novo Horizonte, Bahia. A signal was obtained that corresponds well with the variations in Th detected by aero-geophysical surveys (CPRM Project 1021, 1971).
A survey traverse was run near Maracas, Bahia. That survey did detect Th that corresponded with the CPRM survey, but with lower sensitivity. The reason for that is not yet clear. Three other survey traverses were run but each was only a few hundred meters in length. Although the three short surveyed traverses appear prospective in satellite images, the CPRM aero-geophysical surveys indicated that they are not. Their counts were not reported.
The report mentions "very high-grade mineralisation in excess of 4% TREO". No reference to a locatable information source is provided. It is not known by what methods such a grade was found, or where. There is a poor photo inset into Figure 3 that appears to be alongside road BA-250.
About the maps above.
1) 2 maps establish the context of the 5 traverses in Bahia, Brazil.
2) 2 maps show colour coded traverses; the reference traverse, and the traverse near Maracas. They appear as wriggly lines left-center of each map.
Below there is a kmz file that can be used with Google Earth ( URL ) to view the 5 traverse paths in 3D. Just download, drag and drop.
A clickable icon provides a view that seems to match the photo inset into Figure 3. That view is at a location about 1500m NW of the peak Th measurements on the reference traverse.
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Afterburner :
@rexkicker : an all-terrain vehicle mounted with a MS-350 device (with GPS and laptop attached) can perform the data analysis instantly. A following (distant) vehicle can collect (only) the samples that matter. The survey plan for the day can be altered as measurements are made, and survey results reported by email (mobile phone signal strength permitting). The MS-350 device can also measure gamma radiation from the radioactive decay of an isotope of Potassium. When mounted under a drone and flown at altitude a grid of data useful in the search for spodumene might also be obtained. And I see that GMN has more than one MS-350 device !
I wonder how many other explorers think that stream sediment sampling should be followed-up by geophysical surveys ?
Where possible, the others seem to go from geophysics straight to auger or rock chip, then sampling for the lab work. By doing so they minimise wasted time and money.
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GMN ~ Th traverses ~ Maracas Bahia (20240609).kmz.txt
