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Gold Mountain sees key rare earths rocks in Brazil

Gold Mountain has found extensive charnockite that could contain rare earths. Credit: File

Gold Mountain (ASX: GMN) says it has identified widespread granitoid and related rock types known to possess a strong potential to host rare earths minerals throughout its Down Under project in Brazil.

The company says it has found many examples of leucogranites and charnockite rocks in five of its new tenements within the project where it is undertaking exploration stream geochemistry and other sampling. Both rock types are widely recognised as having the potential to carry higher levels of rare earths mineralisation.

Management has three teams working in the area and recently kicked off a sampling campaign in parts of its ground that sits a mere 1.4km from high-grade rare earths mineralisation reported by Brazilian Rare Earths (BRE) in its 2023 prospectus.

Gold Mountain recognises that while it may not initially identify the same levels of results as those that exist in BRE’s ground, the area constitutes a logical exploration baseline for initial sampling given its proximity to known mineralisation and similar geology.

It is also undertaking remote sensing investigations using satellite imagery that can distinguish various degrees and types of weathering, including lateritisation and the presence and intensity of radioactive thorium, which is often related to or accompanies rare earths mineralisation.

Management says some areas of shearing have been channel-sampled through the entire deep and highly-weathered regolith profile that is typical of parts of higher rainfall areas of Brazil – from the mottled zone through to saprolite and then into semi-weathered rock known as saprock.

That approach will potentially cover any areas of near-surface depletion and/or concentration of rare earths mineralisation that may be hosted, often at lower levels, by the underlying primary rocks of the area. Shear zones of various scales and ages are likely candidates for hosting and mobilising mineralisation for reasons of both tectonic pressures, as well as being open plumbing systems.

Gold Mountain is employing stream sediment sampling as a highly-effective reconnaissance method of testing large regions with relatively few samples. It says it has swept about 64 square kilometres of its selected priority areas with the technique.

The company plans to follow up on the most anomalous areas and will include road cuttings and other exposures of laterite in its sampling program when favourable rock types are found and especially when they register an anomalous thorium responses.

Thorium is a constituent of the mineral monazite, which contains rare earths. Due to its variability in composition, monazite is considered a group of minerals in which the most common species is monazite-(Ce) – the cerium-dominant member of the group.

Leucogranites are a pallid rock-type of the granite family, with magmas interpreted to have been derived by partial melting of pelitic rocks – a kind of metamorphosed sedimentary rock, often mudstones or siltstones.

Interestingly, the rocky tidal island on which the world-famous historic monument of Mont Saint-Michel Abbey and associated buildings are located a few hundred metres off the Normandy coast in France, consists of Cambrian-age intrusive leucogranite that is about 525 million years old.

Charnockites are also related to granites and are among the few suites of rocks called granofels, which are among the few non-foliated rocks to form under conditions of extreme pressure and temperature. That means they can only form at extreme depths under giant tectonic forces and they are therefore characteristic of regional-scale metamorphism, rather than local events.

They are typically formed from metamorphosed clays and shales and can be seen to have a somewhat distantly-related origin with leucogranites.

With a similarly religious connotation, the name charnockite was assigned by geologist T. H. Holland in 1893 with reference to the tombstone of Job Charnock that lies at St John’s Church in the Indian city of Kolkata and is made of the rock.

Both leucogranite and charnockite rock types are known to be associated with the incidence of rare earths mineralisation, probably because their conditions of formation provide for various means of concentrating and remobilising the originally tiny, naturally-occurring amounts of rare earths in the original crustal or mantle magmatic rocks.

Gold Mountain’s stock jumped 66.67 per cent on huge volumes today to an intraday trading high of 0.5c, from yesterday’s close of 0.3c, with nearly 136 million shares changing hands.

And with a vast area of two favourable rock types to play in, it seems almost certain that the company will find one or more targets to follow up in its rare earths hunt.

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