Sigma Mineração S.A. (SMSA) is the Brazilian subsidiary of Sigma and is the owner of the mining rights and the holder of mining concessions ordinance which includes the Xuxa, Barrerio, Murial, Lavra do Meio and Nezinho do Chicao deposits.
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Summary:
The deposits within the Project area are considered to be examples of LCT-type pegmatites.
LCT pegmatites represent the most highly differentiated and last to crystallize components of certain granitic melts. Parental granites are typically peraluminous, S-type granites, although some Archean examples are metaluminous, I-type granites. LCT pegmatites are enriched in the incompatible elements lithium, cesium, tin, rubidium, and tantalum, and are distinguished from other rare-element pegmatites by this diagnostic suite of elements. The dikes typically occur in groups, which consist of tens to hundreds of individual pegmatites and cover areas up to a few tens of square kilometres. LCT pegmatites are known to form as far as 10 km from the parental granite and the more distal the pegmatite, frequently the more fractionated. The most highly fractionated rareelement-enriched pegmatites only constitute 1–2% of regional pegmatite populations.
The Barreiro pegmatite body is emplaced into biotite–quartz schist. Pale greenish–grey coloured, multicentimetre-sized microcrystalline quartz–feldspar intercalations have been noted in the schist, with disseminated green, sub- to one-millimetre-sized amphibole and pink garnet crystals. Pegmatite xenoliths can be found within 3 m of the dike edge within the schist and can range from a centimetre to as much as a metre in size.
The pegmatite strikes northeast–southwest and dips to the southeast at 30–35º. Based on drill data, the dike is about 600 m long, 800 m wide, and has an average thickness of 30–35 m. It remains open to the northeast and at depth. The deepest drill hole reached 374 m. The pegmatite is apparently intruded discordant to the host crenulated biotite schist in surface exposures, but at depth, can be concordant, and emplacement may be related to local fracturing.
The dike is slightly zoned into distinct spodumene-rich and albite-rich areas and is divided into an edge (or border), and a central zone. Overall, spodumene is about 20–24% of the dike mass, albite–microcline is approximately 32–40%, and around 10–18% is mica (muscovite).
The border zone is about 45 cm in thickness, and consists of fine-grained albite, quartz and muscovite. Heavy minerals such as cassiterite and tantalite may occur associated with albite units. The central zone is spodumene-rich and consists of albite and spodumene crystals that are typically 10–25 cm in length but can more rarely can attain as much as a metre in length. Spodumene crystals are also present as short, prismatic, elongated laths. The spodumene laths are colourless or pale green, sometimes displaying a poikilitic texture of fine- to medium-grained quartz and/or pale green sericite. Petalite occurs sporadically, as both colourless, translucent to transparent, coarse to very coarse-grained crystalline aggregates. It can also be present as cryptocrystalline, translucent masses.