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.
Nezinho do Chicão area consists of Lavra do Meio, Maxixe, Tamboril and Murial pegmatites.
Lavra do Meio
The host country rock to the pegmatite dike is a biotite–quartz schist and has similar features to the schist that hosts the Barreiro pegmatite. Garnet and tourmaline have developed near the pegmatite–schist contact.
The dike is concordant with the schist foliation, strikes north–south and dips at 75–80º to the east. Based on drill data, the dike is about 600 m long, 250 m wide, and has an average thickness of 12–15 m. It extends to a depth of approximately 300 m.
The pegmatite mineralization is moderately to highly homogeneous mostly in the centre and deeper part. The upper and lower contact zones are characterized by albite, quartz and mica. In the albite-rich border zone, tantalite and cassiterite can occur interstitial to fan-shaped albite lamellae. In the pegmatite core, medium, to very coarsegrained laths of typically pale green spodumene and coarse to very coarse-grained, colourless, translucent to transparent, petalite crystal aggregates and cryptocrystalline masses occur and compose around 20% of the lithium-bearing minerals. Both spodumene and petalite are set within a micro-fractured, medium to coarsegrained matrix composed of quartz, mica, albite and microcline. The micro-fractures are infilled with pyrolusite.
Nezinho do Chicão
The pegmatite is hosted in a biotite–quartz schist, which is similar to the schist described as hosting the Barreiro pegmatite. The pegmatite body strikes nearly north-south (020º) and dips at 40-75º to the southeast. The dike is about 1,600 m long, 200 m wide and 20-30 m thick. It remains open to the north, south and at depth, with the deepest drill hole reaching 350 m.
The pegmatite shows a classic border, intermediate and central zones. The border zone tends to be more albite rich and the highest spodumene content is generally in the central zone. The NDC pegmatite is a high-grade mix of mainly spodumene but also containing some petalite with a variable ratio depending on the thickness of the zone, although petalite can be found throughout the deposit.
Murial
A similar biotite–quartz schist to that hosting the Barreiro pegmatite is host to the Murial pegmatite.
The pegmatite is a north–south striking body that has fluctuating westerly dips, ranging from 70–85º in the south of the dike, to a much shallower 25–35º in the north. It is about 1,200 m long, 840 m wide, and has an average thickness of 15–20 m. It remains open to the west, east and at depth.
The southern part of the dike generally has lower lithium contents, and the pegmatite has a sub-vertical to nearly vertical orientation. To the north, the lithium concentrations increase, and the dike orientation changes to horizontal to sub-horizontal and becomes more planar in shape.
The pegmatite shows a border, intermediary and central zone. The border zone is enriched in albite, the intermediate zone is typically spodumene-rich, and the central zone contains both spodumene and petalite. The fine-grained border matrix can include tantalite and cassiterite mineralization.
Maxixe and Tamboril
The Maxixe and Tamboril pegmatites are in the hangingwall of the Nezinho do Chicão pegmatite and are southwest and along strike from Lavra do Meio. The pegmatites are very similar geologically to both NDC and LDM.
The host country rock to the pegmatite dikes is a biotite–quartz schist and has similar features to the schist that hosts the Barreiro pegmatite. Garnet and tourmaline have developed near the pegmatite–schist contacts.
The dikes are concordant with the schist foliation, striking approximately north–south and dipping at 60º to the east. Based on drill data, Maxixe is about 400 m long, 170 m wide, and has an average thickness of 10-12 m. It extends to a depth of approximately 300 m and is open at depth and to the north. Tamboril is about 260 m long, 160 m wide, and has an average thickness of about 8 m. It extends to a depth of approximately 250 m.