Summary:
The Raleigh Lake rare-element pegmatite field is located immediately west of Raleigh Lake, confined to the mafic volcanic portion of the mafic-intermediate volcanic package of the supracrustal greenstone belt.
Mafic To Intermediate Meta-Volcanic Rocks
The metavolcanics in the Raleigh Lake area are comprised predominantly of meta-basalts (which are likely flows) and interbedded pillowed horizons. Where observed, pillows range from exceptionally preserved and undeformed, to highly flattened and recrystallized. These mafic units are intercalated with lighter coloured, more siliceous, volcanic rocks that range in composition from calc-alkalic basalts to rhyolites. All varieties are generally fine-grained, semi-massive, with moderate foliation, and are dark green-grey to yellow-grey in colour. Chloritization ranges from absent to strong and is present in zones of intense silica flooding and remobilization, in large part due to metamorphic recrystallization. In sections of silica flooding breccia textures are common, along with the hematization of fine-grained, disseminated sulphides, and can be observed in drill core from the 1998 and 2001 drill programs. Quartz veins commonly contain epidote and ankerite. Mafic units are locally moderately to strongly magnetic in the presence of disseminated pyrrhotite. Calcareous horizons are also common and occur with silica flooding. These horizons contain distorted nodules and bands of quartz-epidote-calcite-diopside-grossular garnet. The grossular garnets are commonly very coarse and range in size up to several centimetres.
Felsic To Intermediate Intrusive Rocks
Feldspar porphyries have been noted mainly in the vicinity of the 1998 drilling program near Microlite Pond, but also occur randomly as narrow cross-cutting dykes distributed throughout the property. They are massive, medium-grained, and medium to dark grey in colour, with 1 to 2 mm subhedral feldspar phenocrysts. The matrix is aphanitic to fine-grained, commonly with fine-grained biotite and locally disseminated sulphides. They are generally unaltered and are associated with local zones of silica flooding and brecciation. Trace to minor pyrite, pyrrhotite, and chalcopyrite occur in the siliceous zones. The porphyries are granodioritic to dioritic.
Pegmatites
The rare-metal-bearing pegmatite dykes on the Property occur in a south¬-southeast striking zone approximately 1.5 kilometres wide and at least 4 kilometres long with a trend of tantalum-mineralized albitic dykes occurring south of Raleigh Lake. The main pegmatite trend, which includes Pegmatite 1 through 3 and the Johnson Pegmatite, belong to the albite-spodumene sub-type of rare metal pegmatites. These pegmatites are at least partially hosted within a sheared, coarse grained gabbro which is a common feature of rare-element pegmatite fields. Most of the pegmatites trend north-northeaster and dip to the east. The dyke mineralogy consists of K-feldspar + albite, including secondary cleavelandite, quartz and spodumene. Accessory minerals identified include microlite, tantalite, and bismuthinite.
The known pegmatites form shallowly to moderately dipping, north-northeast trending, undeformed sheets with a significant potential for extensive lateral continuity. Strong fractionation of contained minerals and weak zonation within the pegmatites suggests that strongly enriched rare-metal zonation may exist within other domains of the pegmatites. The pegmatites are hosted in both mafic and intermediate volcanic rocks. Crude zonation is evident in the wider pegmatites, with albitic “wall” zones and “core” intermediate zones of albite–quartz-muscovite or spodumene-K-feldspar-albite. The pegmatite zonation can be broken down into six crudely defined zones (Table 7-1). This includes the upper wall zone, the upper intermediate zone, quartz + spodumene + k-feldspar core, lower intermediate zone, lower wall zone, and late-stage albite zone. These zones are not as distinct as in some other pegmatite occurrences, and spodumene distribution within the Raleigh Lake pegmatites is homogenous. Spodumene crystals are generally green to pale green in colour, exhibiting tan colours locally in the presence of albite. Grains typically range in size from < 1 cm to > 8 cm, and display ragged, corroded grain boundaries that have undergone complete replacement by a dark green, aphanitic, serpentine-like assemblage.
Several “main” pegmatites have been identified within the property. These include Pegmatite 1, 2, 3 and the Johnson Pegmatite. Pegmatite 1 has a minimum surface exposure of 200 m, an average width ranging from 3.90 to 8.00 m, and has been traced along strike for 300 m and down dip for over 400 m. Average Li2O% are ~1.0% and up to 2.7% locally. It is crudely zoned with local strong albitization with heterogeneous intermediate zones consisting of light green to tan spodumene and K-feldspar in an albitic matrix with local muscovite. These zones are bounded by albitic "wall" zones. Pegmatite 1 is the widest and most laterally continuous pegmatite intercepted to date and forms a train of outcrops up to 10 m wide that extend for 200 m. Drilling has shown that Pegmatite 1 flattens down-dip from 15–20° easterly to a horizontal position. The country rock is albitized and contains exomorphic minerals of holmquistite and biotite adjacent to the dyke. This pegmatite, along with Pegmatite 3, is characterized by a strong crescumulate texture defined by elongate spodumene crystals up to 1.5 by 75 cm oriented normal to pegmatite contacts.
Pegmatite 2 was discovered and subsequently mapped by Breaks (1993) owing to the presence of several bright blue, holmquistite, bearing boulders nearby. The pegmatite is located approximately 800 m west of Microlite Lake and specifically noted to have a lithium dispersion halo greater than the Johnson Pegmatite at two metres. Lithogeochemical analyses show Pegmatite 2 to have the highest lithium assay of 2290 ppm to date.
Pegmatite 3, located SE of Microlite Lake, is exposed for ~50 m and is at minimum four metres thick at surface. It is crudely zoned with feldspathic wall zones and heterogeneous intermediate and "core" zones comprised of albite-quartz-muscovite, and spodumene-K-feldspar-albite. Diamond drilling has shown that Pegmatite 3 ranges up to 1.20 metres in thickness at depth but does show strong lateral continuity having been identified over approximately 300 m of strike length.
The Johnson Pegmatite, located 1400 metres north of Pegmatites 1, is exposed on surface for 83 metres along strike, with an apparent width of 3 to 4 metres. It consists predominantly of coarse white to pink K-feldspar and accessory muscovite and trace tantalum oxides. Diamond drilling of hole RL01-06 produced an average grade of 0.017% Ta205 over a core length of 2.65 metres.
Deposit Type
The Raleigh Lake project falls under the classification of rare-metal pegmatites. The Project can be further sub-categorized as albite-spodumene type pegmatites. The Raleigh Lake Project contains lithium-caesiumtantalum (“LCT”) pegmatites which are enriched in Li, Cs, Ta, Be, B, F, P, Mn, Ga, Rb, Nb, Sn, and Hf.