Geology and Initial Resource Estimate of the Zoned, Complex-Type, Li-rich Pakeagama Lake Pegmatite, Northwestern Ontario, Canada

English Abstract:

The Pakeagama Lake pegmatite is a zoned, Li-Cs-Ta (LCT) pegmatite located 175 km north of Red Lake, Ontario. The pegmatite occurs near the margin of the Pakeagama Lake granitic pluton, which intruded proximal to the Bearhead Lake Fault Zone that separates the Sachigo and Berens River domains of the Superior Province. More than 2,400 metres of drilling in 14 drill holes and 21 channel cuts have revealed a significant Li deposit, with an inferred resource estimate of 6.8 Mt averaging 1.56% Li₂O, 105 ppm Ta₂O₅, and 0.30% Rb₂O.

Mineralogically similar to the Tanco pegmatite in southeastern Manitoba, the Pakeagama Lake pegmatite displays intermittent wall zones and three main intermediate zones, which are the Upper Intermediate Zone (UIZ), Central Intermediate Zone (CIZ), and Lower Intermediate Zone (LIZ). The UIZ is dominated by spodumene + quartz intergrowth (SQUI) after primary petalite with lesser grey K-feldspar + mica, and represents the highest grade Li zone within the pegmatite (including 4.2% Li₂O over 18 m). The CIZ consists of predominantly coarse (up to 0.5 m in length) K-feldspar with lesser quartz and mica. Significant portions of this zone display replacement of K-feldspar by a dark to purple-coloured lithian mica + quartz assemblage which hosts euhedral blue apatite. These micaceous zones also contain pollucite (the primary ore mineral of Cs) blebs and the highest Ta grades found to date in the pegmatite (including 236 ppm Ta₂O₅ over 19 m). The LIZ comprises the bulk of the exposed pegmatite and contains predominantly K-feldspar, Na-feldspar, SQUI, lithian muscovite, and rare pollucite. Based on electron probe microanalysis (EPMA), spodumene throughout the pegmatite contains low concentrations of impurities such as Fe, making the ore suitable for use in the manufacture of specialty glass and ceramic products. Lithian micas contain high Rb contents based on EPMA, with concentrations as high as 2.75 wt.% Rb₂O.

The pegmatite has an elongated oval shape striking in a northwesterly direction and dipping steeply to subvertical to the southwest, and is in contact with metasediments along the footwall. Initial indications are the pegmatite represents at least the second intrusion event along a linear structure that had previously been intruded by tantaliferous (up to 1350 ppm Ta₂O₅ in a grab sample) banded sodic aplite.