Ioneer partner search to H1 2026: Rhyolite Ridge economics for mine planners
Reviewed by Joe Ashwell

First reported on MINING.com
30 Second Briefing
Ioneer now expects to secure a new partner for its Rhyolite Ridge lithium-boron project in Nevada in H1 2026, after Sibanye-Stillwater withdrew from a proposed $490 million, 50% stake and Goldman Sachs-advised talks overran the original four‑month timetable amid weaker markets and geopolitical uncertainty. Backed by a $996 million US government loan and all key permits, Rhyolite Ridge has an updated DFS with a 95‑year mine life, NPV lifted to $1.5 billion, and reserves of 7.8 Mt boric acid plus 2 Mt lithium carbonate supporting an initial 77‑year plan. Average output for years 1–25 is now projected at 24,500 t/y lithium carbonate equivalent and 135,500 t/y boric acid, placing the operation in the global lowest cost quartile on an LCE basis and making co‑product economics central to any JV valuation.
Technical Brief
- Ioneer now targets selling a smaller 40% project stake in any new partnership.
- Sibanye-Stillwater had previously proposed $490 million for a 50% interest before exiting in February 2025.
- Goldman Sachs is running the formal strategic partnering process, which has already exceeded the initial four‑month window.
- Rhyolite Ridge is located 362 km north of Las Vegas, in Nevada’s arid interior basin.
- Over 70% of engineering design is reportedly complete, indicating limited remaining front-end design risk.
- All key permits are already in place, reducing schedule exposure to lengthy US federal approvals.
- Ioneer has been advancing Rhyolite Ridge since 2016, giving nearly a decade of site-specific data and studies.
- Parallel interest in acquiring Rio Tinto’s US boron assets (c. $2 billion valuation) suggests a deliberate boron growth strategy beyond Rhyolite Ridge.
Our Take
With a 95‑year projected mine life and combined reserves of 7.8 Mt boric acid and 2 Mt lithium carbonate, Rhyolite Ridge in Nevada would give any incoming partner unusually long-duration exposure to US-based critical minerals, which is rare among the battery metals projects in our database that are often modelled on 15–30 year lives.
The US government’s US$996 million loan support materially de-risks country and financing risk for ioneer relative to many other lithium projects in our Mining/Projects coverage, which could justify a lower cost of capital assumption in partner valuations despite the drawn-out partner search into H1 2026.
The shift from a proposed 50% stake for Sibanye-Stillwater to a 40% stake on offer now suggests ioneer is aiming to retain more upside in the US lithium-boron market, a pattern seen in several recent critical minerals deals where juniors preserve operatorship while using strategic partners mainly for balance sheet strength and offtake security.
Prepared by collating external sources, AI-assisted tools, and Geomechanics.io’s proprietary mining database, then reviewed for technical accuracy & edited by our geotechnical team.
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