Critical Resources Confirms Highly Fertile Lithium Pegmatites at Mavis Lake Northern Prospects

Geochemical Breakthrough in Northern Claims

Critical Resources Limited (ASX:CRR) has unveiled compelling geochemical evidence from its 2026 field program at the Mavis Lake Lithium Project in Ontario, Canada, pointing to a cluster of highly fertile lithium-caesium-tantalum (LCT) pegmatites within its Northern Prospects Area. The standout finding: pegmatites within the northern claim package, acquired only last year, are exhibiting potassium-to-rubidium (K/Rb) ratios as low as 17.4 alongside rubidium concentrations up to 5,510 ppm, caesium at 221 ppm, and tantalum at 53 ppm. These signatures are classic markers of advanced magmatic fractionation and pegmatite fertility, setting the stage for targeted exploration.

The program collected 106 rock samples from 14 pegmatite bodies, six of which are newly identified, over a 10-day campaign that combined geological mapping, structural measurements, and whole-rock lithogeochemistry. This comprehensive approach has sharpened the focus on granitic-hosted pegmatites as the highest-priority drill targets across the northern corridor, about 4 km north of the existing 8.0 Mt @ 1.07% Li₂O Mineral Resource.

Differentiating Fertility Across the Mavis Lake Corridor

While the Corona Pegmatite Field remains prospective, its pegmatites display only slight to moderate fractionation, reflected in higher K/Rb ratios and lower pathfinder element enrichment. In stark contrast, the Northern Prospects Area, especially the recently acquired claims, hosts the most highly fractionated pegmatites identified to date, validating Critical Resources’ acquisition strategy from August 2025.

The granitic host rocks appear to provide a favourable geological environment for the evolution of these fertile pegmatitic melts. This spatial association offers a valuable vector for follow-up exploration, with the potential to uncover spodumene-rich cores that grab samples, focused on margins, have yet to confirm. The next steps will integrate these geochemical insights with geological, structural, and geophysical datasets to prioritise drill targets with high confidence.

Advancing a Multi-Deposit Lithium District

Critical Resources' broader district-scale strategy hinges on expanding beyond its current Mineral Resource base. The Northern Prospects Area, featuring targets such as Gullwing, Tot, Little Wing, Coates, Drope, and Corona, forms a pipeline of lithium-bearing pegmatites poised for further evaluation. Gullwing remains the flagship target here, boasting an Exploration Target of 7–10 Mt at 0.3–1.2% Li₂O, with strong surface spodumene mineralisation and structural controls well defined by integrated geochemistry and UAV magnetics.

The company’s Managing Director, Tim Wither, emphasised that these results refine the exploration focus and validate the northern claim acquisition, underscoring the value of systematic regional exploration in unlocking growth opportunities beyond the existing resource. The ultimate aim is to develop Mavis Lake into a multi-deposit lithium district, leveraging disciplined, technically driven exploration.

Next Steps in Exploration

With this geochemical groundwork laid, Critical Resources plans to combine assay data with existing geological, structural, and geophysical information to rank and prioritise drill targets across the northern corridor. Follow-up activities will include detailed mapping, surface geochemistry, mechanised stripping where appropriate, and scout diamond drilling to test the highly fractionated granitic-hosted pegmatites.

While whole-rock analyses returned low lithium values, consistent with sampling pegmatite margins rather than mineralised cores, the elevated rubidium, caesium, and tantalum levels provide reliable vectors for mineralisation. Confirmation of lithium grades awaits drilling results, which will be critical to advancing these targets from conceptual to defined resources.