Araxa. Some information.Perhaps the easiest source is the Porter...

Araxa. Some information.

Perhaps the easiest source is the Porter Geoscience data base.

Araxa is dated at being intruded some 80-90 Mya.

The description of the main ore source comes from this source.

A circular lateritic cover 1800 m in diameter and up to 230 m thick occurs in the central part of the domal structure of the complex. Residual bariopyrochlore (barium rich pyrochlore) has become concentrated (Mariano et al. 1997), giving rise to the largest known niobium reserves in the world.

Further in Porter's text the same plus...
A circular lateritic cover sheet ~1800 m in diameter and up to 230 m thick occurs in the central part of the domal structure of the complex. Residual bariopyrochlore has become concentrated within the lateritic profile, giving rise to the largest known niobium reserves in the world. The laterite mineralogy is composed of limonite, goethite, barite and magnetite as major phases, with subordinate bariopyrochlore, gorceixite, monazite, ilmenite and quartz.

Two types of niobium ores are found at Araxá, the primary ore as described above, with a mean grade of 1.5% Nb2O5, and a maximum grade of 8% Nb2O5, and the friable residual ore with a mean concentration of 2.5% Nb2O5. Only the latter is exploited by open-pit mining. Weathering enriched the niobium ore minerals, which were physically preserved but chemically modified during leaching, and concentrated through through volume reduction during the lateritisation process. Pyrochlore was progressively transformed into bariopyrochlore along fractures and at grain boundaries by the substitution of calcium and sodium by barium, probably due to the action of meteoric waters. The deposit has a resource of residual ore up to 250 m thick, totalling ~450 Mt @ 2.5 % Nb2O5, although drilling in 2001 revealed additional zones with 4.6 to 7 % Nb2O5

The ore above is lateritic and comes in two forms. Still searching for comments on the protore - fresh unweathered material which presumably contains Nb + Phosphates and probably REEs.

Shallow high grade tends to be the jewellery box but sometimes the bulk low grade is the treasure chest. A correction to a post above where the lateritic high grade REEs at Mt Weld is probably the jewellery box to the much larger primary zone which may be the treasure chest if mining of the .hundreds of millions of tonnes potential is ever realised. [Maybe a pipe dream but such a "exploration size" resource exists below the current mine outline albeit at a much lower grade.]
Araxa may be similar.
Luni also?