How to use radiometric data to prospect for rare earth elements

Rare earth elements (REE) are among the most sought-after critical minerals of the energy transition. Many of their deposits hold a useful relationship with natural radioactivity — and that is where gamma-ray spectrometry becomes a powerful ally for prospecting.

Why thorium points the way

Many REE deposits — carbonatites, alkaline complexes, placers and associated laterites — concentrate thorium (eTh) together with the rare earth elements (commonly in monazite, an REE phosphate that carries thorium). Thorium is radioactive and emits gamma radiation detectable in airborne surveys. Thus, mapping zones of high eTh is an indirect but efficient way to flag where REE may be concentrated.

This does not mean that every thorium high is REE — but it is a first-order vector to narrow the search area.

Ratios that refine the target

Working only with the thorium channel can generate false positives. That is why the interpreter usually uses ratios and combinations:

• A high eTh/K highlights evolved and alkaline rocks, common in REE contexts;
• eTh/eU helps distinguish primary concentrations from supergene enrichments;
• The ternary image (K, eTh, eU) reveals color patterns that quickly separate radiometric domains.

When a thorium high coincides with a favorable geological context — an alkaline intrusion, a carbonatite or a lateritic crust — confidence in the target grows.

Integration is everything

Radiometrics alone points to "where to look", but the target only holds up with integration:

• Magnetometry to identify the intrusive body or host structure;
• Geology and known mineral occurrences;
• Terrain, which controls where the lateritic crusts are preserved.

This is the logic of a modern analysis: cross-reference independent layers until the target stops being an isolated anomaly and starts to make geological sense.

From public data to target

Brazil has public airborne geophysical surveys covering many provinces with REE potential. The work of downloading, processing and cross-referencing this data is what consumes time. Automating this chain — generating the radiometric channels, ratios and integration with geology — makes it possible to reach the thorium map and ratios in minutes, freeing the geologist for interpretation.

How Lithogeo helps

This is exactly the kind of work the Lithogeo platform automates. From an ANM process number or a polygon of your area, it processes and integrates the public data — magnetometry, gamma-ray spectrometry, geology, terrain and mineral occurrences — and delivers the products described here ready for analysis, in minutes and right in the browser.

Educational content. The presence of radiometric anomalies does not confirm REE mineralization; validation requires detailed geology, geochemistry and fieldwork.