Summary:
Deposit Types
Frontier Lithium’s target or deposit model is the highly evolved, granitic, rare-element lithium-cesium-tantalum bearing (LCT) complex type, petalite subtype pegmatite.
PAK Pegmatite Mineralization
Upper Intermediate Zone (UIZ)
The Upper Intermediate Zone (UIZ) represents a lithium-focused zone within the pegmatite and is dominated by spodumene-quartz intergrowths (SQUI), a term used to describe an isochemical reversion resulting in the replacement of primary petalite by oriented spodumene + quartz (London, 1984). Lesser grey K-feldspar and primary white spodumene in quartz are also present, along with other common accessory minerals such as montebrasite and apatite (phosphates), as well as lithian mica.
Central Intermediate Zone (CIZ)
The Central Intermediate Zone (CIZ) is located in structurally higher portions of the pegmatite and is enriched in tantalum and rubidium. The CIZ is in contact with both the UIZ and Upper Wall Zone and persists to the southeast edge of the outcrop where it is believed the pegmatite continues under the till cover. To the southeast, the CIZ is intersected by channels CH-1 and CH-7 where it consists of similarly sized fragments of randomly oriented coarse K-feldspar (variably altered) + mica + quartz. Blue apatite prisms up to 1 cm wide and several cm long accompany the mica-rich zones. In the adjoining area to the northeast of CH-7, the K-feldspars are strongly altered to lithian mica + quartz. In this area, veinlets and patches of lepidolite are common. Channel 1 (CH-1) contains the highest tantalum grades found to date in the exposed pegmatite, which persists in the subsurface in drill holes PL-13-001 and PL-13-006, in addition to high rubidium and elevated cesium grades. To the northwest, channels CH-8 and CH-19 intersect the central portion of the exposed CIZ where it consists of predominantly grey K-feldspar with minor lithian mica + quartz alteration. Drill holes PL-13-003 and PL-13-004 confirm the extension of the CIZ into the subsurface in this area, where it features notable cm-scale blebs of the rare cesium mineral pollucite, and high tantalum and rubidium grades.
Lower Intermediate Zone (LIZ)
The Lower Intermediate Zone (LIZ) comprises the bulk of the exposed pegmatite and is considered an intermediate stage zone with significant lithium, tantalum and rubidium.The zone comprises predominantly K-feldspar, Na-feldspar, SQUI and lithian muscovite. Pollucite also occurs in an intersection of LIZ in drillhole PL13-005. The zone has undergone both ductile and brittle deformation at the apparently structurally lowest portions of the pegmatite. Ductile deformation is manifested as a banded appearance on surface, where seams of oriented mica provide a planar fabric.
Wall Zones
The wall zones (upper and lower) of complex LCT-type pegmatites are generally characterized by the occurrence of brick-red K-feldspar (perthite) and simple mineralogy (Cerný, 2005; Cerný and Vanstone 1996). The brick-red colouration of the K-feldspar is more common in close proximity to the metasediments; conversely, this colouration does not generally occur where the pegmatite is in contact with the granite. In this latter case, K-feldspar is chiefly light to medium grey, likely a result of lower inherent iron levels in the Pakeagama Lake granite.
The Upper Wall Zone found in the southwest portion of the pegmatite exposure, is in contact with the lithium rich UIZ and is composed of quartz with lesser pale-red coloured K-feldspar, minor phosphates and accessory beryl and lithian mica. The exposure of this zone is limited.
The Lower Wall Zone is mineralogically similar to the Upper Wall Zone.A common feature of the footwall Wall Zone in the more complex LCT-type pegmatites is the presence of bands of sodic aplite (“footwall aplite”). These sodic bands are generally not common in the Upper Wall Zone. The Pakeagama Lake pegmatite is somewhat more complex as bands of what appears to be pre-existing banded sodic aplites are found throughout the pegmatite. The contact with the LIZ is gradational and is defined by the general absence of SQUI within the wall zones and the change in colour of the K feldspars from pale-red to the light grey commonly found throughout the pegmatite. Like the LIZ, this zone has undergone deformation.
Spark Pegmatite Mineralization
Two (2) predominant lithologies occur within the Spark Pegmatite including an early aplite phase that occurs ubiquitously throughout the pegmatite and an apparent later overprint phase of coarser-grained feldspar-quartz-spodumene-muscovite. The aplite ranges from grey to greenish-grey to purplish-grey and is dominated by fine albite and quartz. Intervals containing abundant fine- to coarse-grained muscovite are common, and mm-scale pink garnets are commonly associated with quartz-rich phases. Coarse to megacrystic K-feldspar occurs locally within the aplite, and spodumene abundance ranges from common to absent. Aplite exposed at the surface and intersected in drill core in the eastern portion of the Spark pegmatite are conspicuously purple owing to lithian mica. Common accessory minerals include black prismatic tourmaline, fluoroapatite, and rare coarse-grained loellingite.
The later phase that appears to overprint the aplite at Spark has similar lithology and texture to the Lower Intermediate Zone at PAK and has been geologically classified as such. The LIZ at Spark consists of coarse to megacrystic grey to tan K-feldspar up to 20 cm in size (typically 2 to 5 cm), common to abundant fine to coarse-grained white to light grey spodumene with varying textures, muscovite, and quartz. K-feldspar and quartz exhibit graphic texture in some intersections. Intervals of aplite up to a few metres thick also occur in the LIZ at Spark. Accessory minerals include beryl, black tourmaline, fluoro-apatite and locally arsenopyrite and rare loellingite. Contacts between host metavolcanic rocks and both the aplite and LIZ commonly display a deformed biotite- tourmaline-holmquistite-arsenopyrite contact zone. Greyish white to light grey spodumene occurs throughout the pegmatite varying from fine-grained laths (1-3 mm) to coarse-grained "jackstraw" texture with crystal laths up to 3 cm in length. Grey megacrystic feldspar crystals are typically ~2 to 5 cm in size but can reach up to 20 cm locally. This later phase has been geologically logged as LIZ due to similarities in texture and composition with the LIZ at the PAK Deposit.
There is a narrow interval (~3 m thick) present at the surface and in the subsurface of the western portion of the Spark Pegmatite consisting of dark-coloured muscovite, dark grey quartz, grey megacrystic K-feldspar, and common blue apatite. The mineralogy and texture of this interval are considered similar to the CIZ at PAK.
Both aplite and LIZ at Spark are weakly to moderately deformed with a preferred foliation and/or flow textures that are steeply dipping to sub-vertical and trending 070° to 100°. Locally, surface exposures of aplite tend to display tight folds with vertical axial planes.