Sn-Nb-Ta-T-(Y, REE, Li) deposit associated with the A-type Madeira granite.

Note on the mineral list: Bastos Nero et al. (2009) also mention "waimirite" and "atroarite".

Xenotime-(Y) from the deposit is highly enriched in fluorine, with up to 5.10 wt.% F for the material from core albite-enriched granite.

These pegmatites fit in the CMS (Dill, 2016) classification as the 24dE type because they are hosted in peralkaline igneous rocks and are carriers of REE-Y ores. According to the classification by Černý and Ercit (2005), they belong to the Rare Elements class and the NYF family, as they are rich in REE, Nb, Y and F, and are associated with A-type granites in environments with low pressures and temperatures.

The Madeira granite contains four facies. The early, mostly meta-aluminous porphyritic amphibole-biotite granite (1824 ± 2 Ma) contains plagioclase-mantled K-feldspar mega-crystals, sometimes also showing reverse zonation and thus referred to as the “rapakivi granite”. The amphibole-biotite granite was followed by somewhat younger meta-aluminous biotite granite (1822 ± 2 Ma) which contains its xenoliths. The alkali feldspar hypersolvus porphyritic granite facies (1818 ± 2 Ma) has K-feldspar phenocrysts in a fine- to medium-grained matrix dominantly composed of K-feldspar and quartz. The hypersolvus granite and the AEG were emplaced simultaneously, and then interacted and intruded into the older facies. The age of the AEG is only very roughly constrained at 1822 ± 22 Ma due to the metasomatic alteration of zircons.
The Madeira deposit corresponds to the AEG. It is an oval-shaped body with an aerial extension of approximately 2 km × 1.3 km at the outcrop. It is divided into a subfacies called an albite-enriched granite core (AGC) and an albite-enriched granite border (AGB). The AGC is a peralkaline subsolvus granite, porphyritic to seriate in texture, fine- to medium-grained. The AGB is peraluminous and presents types of texture and essential mineralogy like the AGC, except for being richer in zircon, for the presence of fluorite instead of cryolite, and for the absence of iron-rich silicate minerals, which have almost completely disappeared due to an autometasomatic process.
The ore grade of the disseminated ore (AGC + AGB) stands at 0.17 wt.% Sn (cassiterite), 0.20 wt.% Nb2O5, and 0.024 wt.% Ta2O5 (both in pyrochlore and columbite) within a total of 164 Mt of rock [39]. The potential by-products of the disseminated ore are F (4.2 wt.% cryolite); Y and HREE [xenotime and gagarinite-(Y)]; Zr and Hf (zircon); Th (0.07 wt.% ThO2, thorite); and U (0,03 wt.%, pyrochlore).

The CAG granite is also known to host a massive 10 million tons cryolite deposit at the center of the core facies.

The Pitinga Province is the largest Sn producer in Brazil. The alluvial ore deposits were discovered in 1979 and are now nearly depleted. The primary ores are predominantly associated with the Madeira Granite (Figure 1). The Madeira deposit, which has been actively mined since 1989, corresponds to the albite-enriched granite. The average grade of the disseminated ore (CAG + BAG) is 0.17 wt.% Sn (cassiterite), 0.20 wt.% Nb2O5 and 0.024 wt.% Ta2O5 (both hosted in pyrochlore and columbite). Potential by-products from the disseminated ore include F (4.2 wt.% cryolite), Y and HREE (xenotime), Zr and Hf (zircon), Th (0.07 wt.% ThO2, thorite), and U (0.03 wt.% UO2, pyrochlore).

Geochronology

Mineralization age: Paleoproterozoic : 1885 ± 4 Ma to 1782 ± 4.6 Ma

Important note: This table is based only on rock and mineral ages recorded on mindat.org for this locality and is not necessarily a complete representation of the geochronology, but does give an indication of possible mineralization events relevant to this locality. As more age information is added this table may expand in the future. A break in the table simply indicates a lack of data entered here, not necessarily a break in the geologic sequence. Grey background entries are from different, related, localities.

Geologic Time				Rocks, Minerals and Events
Precambrian
	Proterozoic
		Paleoproterozoic
			Statherian	ⓘ Mica Group 1782 ± 4.6 Ma ⓘ Zircon (youngest age) 1794 ± 19 Ma
			Orosirian	ⓘ Zircon (oldest age) 1885 ± 4 Ma

Other Regions, Features and Areas containing this locality

References