Rhyolite Ridge Project: Can Ioneer still deliver a U.S. critical minerals breakthrough in 2028?

The Rhyolite Ridge Project, led solely by Ioneer Ltd (ASX: INR, NASDAQ: IONR) as of June 2025, is shaping up to be one of the most strategically critical lithium-boron mining operations in the Western Hemisphere. Once slated as a joint venture with Sibanye-Stillwater, the Nevada-based lithium-boron project has re-emerged with 100% Ioneer control, full federal permitting, and $996 million in loan commitments from the U.S. Department of Energy (DOE). If equity funding is secured in time, the project could move into construction by the end of 2025, with commercial production expected by 2028.

Why the Rhyolite Ridge Project Is Central to U.S. Lithium Supply Strategy

Rhyolite Ridge is no ordinary lithium mine. The project is based on a rare sedimentary deposit that allows for the co-production of lithium carbonate and boric acid from a single ore body. With a revised Ore Reserve of 247 million tonnes and a total resource exceeding 510 million tonnes, Ioneer estimates a mine life of over 90 years. The dual revenue model—approximately 75% from lithium and 25% from boron—significantly enhances resilience against commodity price volatility. Importantly, this structure helps place the project’s lithium production cost within the bottom quartile globally.

The U.S. Department of Energy’s $996 million commitment, issued under the Advanced Technology Vehicles Manufacturing (ATVM) Loan Program, reinforces the Biden administration’s push to localize supply chains for critical EV battery materials. Ioneer estimates the Rhyolite Ridge lithium-boron project could produce around 22,000 tonnes of lithium annually in Stage 1—enough to supply nearly 370,000 electric vehicles per year.

Fully Permitted and Shovel-Ready, But Partner Search Now Critical

One of the few lithium projects in the U.S. to have cleared full federal permitting, Rhyolite Ridge received its final Record of Decision from the Bureau of Land Management (BLM) in October 2024. This included a resolution on the endangered Tiehm’s buckwheat issue—once a regulatory flashpoint for environmental groups. The project now holds all major state and federal approvals.

However, in February 2025, Sibanye-Stillwater withdrew from its 50% stake in the joint venture, citing capital reallocation priorities and ongoing lithium market weakness. This has left Ioneer in full control, but also with the burden of raising the remaining equity to match the DOE loan. Goldman Sachs has since been engaged to run a strategic partner search, with the process reportedly launched in Q2 2025 and expected to take at least four months.

Without an equity partner, the project’s Final Investment Decision (FID) remains on hold. If equity financing is secured in H2 2025, construction could begin shortly thereafter, with a projected 36-month development timeline leading to first production in 2028.

How Ioneer Plans to Lower Costs and Maximize Output

The economic case for Rhyolite Ridge remains compelling. According to Ioneer’s June 2025 presentation, the project has a levered post-tax internal rate of return (IRR) of 18.3% and an average annual EBITDA of $406 million over the first 25 years. Capital costs are estimated at $1.67 billion, with a Class 2 AACE estimate status indicating a high level of engineering confidence.

Operating costs are a key focus area. Reagents and their transport currently account for over 50% of total operating expenses. To counter this, Ioneer is optimising leaching processes and acid recovery. Preliminary results suggest throughput improvements could boost lithium and boric acid output by 7–14%. These gains are not yet included in current economics but are expected to be reflected in updated mine plans.

Crucially, the co-production of boric acid adds a revenue buffer during periods of lithium price weakness. Historical pricing data from Ioneer shows that boric acid has demonstrated far lower volatility than lithium, copper, or nickel over the past 15 years.

Global Relevance and Export Potential Beyond the U.S.

While the Rhyolite Ridge Project is tailored to meet domestic EV supply chain goals, it holds broader relevance for global lithium and boron markets. Ford Motor Company, EcoPro, Prime Planet Energy & Solutions (a Toyota–Panasonic JV), and Dragonfly Energy have already signed binding lithium offtake agreements. A boron supply agreement is also in place, targeting industrial and specialty chemical customers.

Rhyolite Ridge’s direct geographic positioning makes it well suited to serve U.S., Canadian, and Asian markets. With full vertical integration—from mining to chemical conversion on-site—the project avoids the geopolitical and logistical risks that plague other lithium supply routes through China or South America.

The potential for exports to the EU and U.K. also aligns with tightening emissions mandates and EV battery traceability requirements under the EU Battery Regulation. For countries like India and Australia, the project provides a blueprint for sedimentary lithium resource development in politically stable jurisdictions.

What Are Investors Watching at Rhyolite Ridge in 2025?

Market sentiment around Ioneer has improved modestly post-reserve update, though the absence of an equity partner continues to cap valuation. As of May 30, 2025, Ioneer’s ASX stock was trading at A$0.12, with a market capitalisation of approximately A$283 million. The NASDAQ-listed ADR (IONR) stood at $3.43, reflecting ongoing U.S. investor interest driven by the DOE loan and offtake visibility.

Ownership remains diversified, with institutional investors accounting for 27.3% of total shares and retail investors 28.6%. Geographically, 47.6% of shares are held in Australia, 34.5% in North America, and 8.4% in Asia, according to the April 2025 shareholder report.

Investors and analysts are watching three key milestones in H2 2025: (1) closure of a strategic equity partnership, (2) integration of throughput optimisation into the financial model, and (3) any shifts in lithium pricing that could further stress-test the project’s low-cost thesis.

Future Outlook: Can Ioneer Deliver on a 2028 Startup?

With the mineral reserve now quadrupled, all federal permits in place, and a U.S. government loan secured, the Rhyolite Ridge Project stands as one of the most advanced lithium-boron plays in the Western Hemisphere. Yet the path to execution hinges on securing a new equity partner in a market still recovering from 2023–2024 lithium price volatility.

If that milestone is met by late 2025, construction can begin and first production could arrive by 2028—bringing not just lithium supply but a critical boron stream to market. Ioneer’s vertically integrated model, co-product advantage, and alignment with U.S. energy and industrial policy could make it a blueprint for future mineral development in North America.

But with financing windows tightening and geopolitical risks reshaping the global battery value chain, Rhyolite Ridge lithium-boron project must now transition from promise to performance.