Hi @gemdetector, "Figure 2" in ( ASX Ann 15 February 2024 ) is...

Hi @gemdetector,

"Figure 2" in ( ASX Ann 15 February 2024 ) is a collage of two maps. They join 1 km east of the 40 degrees West meridian. Surprisingly, no feature at the joint continues into the other.

The left side appears to be at a higher resolution. It is possibly a subset of eTh mapped in Project 3072 ( completed in 2007 by a state/private org but not published by Brazil's SGB ). Furthermore "Figure 2" eTh legend shows 2 decimal places, whereas SGB regularly uses 1.

I believe that the map on the right is not eTh. It is “IPR_ILH_THK.tif” from SGB's published Project 3089. That is . . . it is the ratio of Thorium to Potassium with units ppm/%. This is very different from eTh (with unit ppm) !

The difference is apparent near Alunas, Bahia ( -13.22,-39.24 ) and GMN 872427/2023 where "Figure 2" reports the highest of eTh values. At the same location SGB's Project 3089 “IPR_ILH_TH.tif” reports about 20ppm eTh (a low value).

The reason I am pointing out this error is that it leads many to think that high Thorium extends to GMN 872427/2023 and east of Alunas, Bahia. But it does not.

The map above shows "Figure 2" georeferenced, but with the RHS replaced with SGB's published Project 3089 eTh.
Although the colour ramp used by LHS and RHS are different you can see that the features of one always extend across into the other.

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A colour ramp for Thorium ppm is difficult to create because of its extremely wide range of values. But for REE hard rock explorers it is the extremely high values that act as path finders ( for this purpose an excellent result is obtained using log10(eTh) instead ). SGB chooses to clip eTh at around 39ppm, thus limiting its usefulness for REE hard rock exploration.

Prospectivity for IACs is always equivalent to "nearology" to REE Hard Rock. That is . . . if REE Hard Rock is not found, then its derivative IAC will probably not be found. Fortunately REE Hard Rock is easy to find, just follow the eTh gamma rays !

Thorium minerals (like Rare Earths) are both dense and have very high melting points. Volcanoes/intrusions sometimes have sufficient thermal and mechanical energy to bring them near to surface. These features (in Brazil) seem to be round at creation. In some areas (Bahia East and Goias) they have been subsequently plastically deformed by NE bound tectonic forces. In Bahia East this deformation is so extreme that the caldera rims have become ribbons. If any trend (or strike) is to be inferred it is along the lines of deformation that curve from NE around to NW.

In the map above you will see that the GMN (and EQN/AUZ) tenements have avoided the high eTh areas. This makes sense. Having high Thorium levels in an IAC is a potential problem for milling, extraction and reclamation. The experience of IAC miner “Serra Verde” ( pdf ) may be of interest.

I look forward to seeing the multispectral study soon.

ASX Ann 21/03/2024 :

The multispectralstudy will then allow surfaces to be discriminated into lateritised and nonlateritised so the focus for IAC deposits will then be clearly focussed.
Potential for high grade hard rock deposits will still remain but in areaswithout laterite, it becomes a lower priority.

GLTALTH