IRIS Metals Unveils High-Grade Lithium and Rubidium at Tin Mountain

Strategic Drilling Success at Tin Mountain

IRIS Metals Limited (ASX – IR1) has announced compelling results from its Phase II diamond drilling program at the Tin Mountain Project in South Dakota’s Black Hills. The program, comprising eight drill holes totaling 747 metres, has confirmed high-grade lithium mineralisation with lithium oxide (Li2O) concentrations reaching as high as 5.41%. Alongside lithium, the drilling revealed significant concentrations of rubidium, beryllium, caesium, and tantalum, underscoring the project’s multi-commodity potential.

These findings are particularly notable given the absence of any current rubidium production in the United States, a mineral classified as critical by the US Geological Survey. The presence of rubidium at grades up to 0.40% Rb2O positions Tin Mountain as a strategically important asset for domestic supply chains seeking to reduce reliance on foreign sources.

Expanding the Critical Minerals Portfolio

The drilling program successfully delineated the pegmatite’s near-surface lateral extent and down-dip continuity, with a shallow weathering profile that bodes well for future extraction. Untested extensions to the north and east hint at further resource expansion potential. IRIS Metals is now progressing towards a JORC-compliant maiden Mineral Resource Estimate (MRE) for lithium and rubidium, expected in the first quarter of 2026. The company is also evaluating the inclusion of other critical minerals such as beryllium, caesium, and tantalum in the resource estimate.

Matt Hartmann, President of IRIS Metals’ US operations, highlighted the significance of these results – "Tin Mountain has delivered outstanding results, not just confirming the high-grade lithium we’ve been chasing, but also unlocking a unique suite of critical minerals. This solidifies our position as a near-term lithium producer in the US and advances our vision of building a resilient, multi-commodity critical mineral supply chain in South Dakota."

Favourable Jurisdiction and Infrastructure

The Tin Mountain Project benefits from its location in a mining-friendly jurisdiction with robust infrastructure, including proximity to road, rail, and power networks. This logistical advantage, combined with strong federal support for critical minerals, enhances the project’s economic viability and strategic importance. The Black Hills region itself has a rich mining history dating back to the late 19th century, with some of the largest spodumene crystals ever recorded found in the area.

IRIS Metals is also advancing other projects within its South Dakota portfolio, including the Beecher and Ingersoll Projects, and is exploring lithium conversion technologies to produce battery-grade lithium chemicals domestically. The company’s broader strategy includes potential acquisitions to expand its critical minerals footprint in the region.

Looking Ahead

With the Phase II drilling results now in hand, IRIS Metals is poised to deliver its maiden Mineral Resource Estimate early next year, a key milestone that will underpin further development and investment decisions. The company’s multi-commodity approach aligns well with growing demand for diversified critical minerals essential to the US battery and technology sectors.