Open pit, bastnaesite (carbonatite) · MP Materials
Mountain Pass rare earth mine, California
Mountain Pass in California holds 29.21 million short tons of proven and probable ore reserves at 5.90% total rare earth oxide (TREO) at a 2.50% cut-off, giving a mine life of about 28 years, according to the operator's September 2025 reserve statement.
From operator reserve statements · reviewed 28 October 2026
Mountain Pass reserves and resources
| Category | Tonnage (million short tons) | Grade (% TREO) | Note |
|---|---|---|---|
| Proven (stockpiles) | 1.05 | 4.16 | Reserve |
| Probable (in situ) | 28.16 | 5.96 | Reserve |
| Proven plus probable | 29.21 | 5.90 | Cut-off 2.50% TREO |
| Indicated resource | 5.29 | 3.50 | Excludes reserves; cut-off 2.15% TREO |
| Inferred resource | 14.15 | 4.65 | Excludes reserves; cut-off 2.15% TREO |
Effective 30 September 2025 (report dated 16 February 2026), dry basis. No measured resource is reported. Contained TREO is not stated in the report; tonnage times grade gives about 1.72 million short tons for proven plus probable reserves (our calculation).
Mountain Pass key facts
| Fact | Value |
|---|---|
| Location | San Bernardino County, California, United States |
| Operator and owner | MP Materials (surface rights MP Mine Operations; mineral rights Secure Natural Resource, both wholly owned) |
| Mineral | Bastnaesite, mined as the primary product (USGS) |
| Mining method | Conventional open pit; contracted drilling and blasting; 30 ft benches |
| Processing | Flotation concentrator rated at 2,000 metric tonnes of ore per day |
| Ore processed | 763,356 t at 8.55% TREO in 2024; 611,704 t at 8.45% TREO in January to September 2025 |
| Concentrate produced | 45,455 t TREO in 2024; 38,609 t TREO in January to September 2025 |
| Mine life | About 28 years: pit mining to Q3 2047, stockpile processing to Q1 2053, closure 2054 |
| Yttrium share | About 0.12% of the rare earths in the ore (USGS) |
Mountain Pass in context
Output in context
USGS estimates US mineral concentrate production at 51,000 tonnes of REO in 2025, valued at $240 million, with Mountain Pass the primary source, against 270,000 tonnes in China. In the quarter to 30 June 2026 MP Materials produced 11,072 tonnes of REO in concentrate and 840 tonnes of NdPr oxide.
From concentrate to oxide
MP has been ramping a separation plant at Mountain Pass that turns concentrate into separated oxides (MP 10-K technical report). USGS records a $150 million Department of War loan in August 2025 for a heavy rare earth separation facility there.
Operator profile: MP Materials. Other mines: rare earth mines. Reserves by country: reserves and production.
Mountain Pass: frequently asked questions
How big is the Mountain Pass mine?
Proven and probable reserves are 29.21 million short tons at 5.90% TREO, with a further 5.29 million short tons indicated at 3.50% and 14.15 million short tons inferred at 4.65% (effective 30 September 2025).
How long will Mountain Pass last?
The reserve statement gives about 28 years: pit mining to Q3 2047 and stockpile processing to Q1 2053.
Who owns Mountain Pass?
MP Materials owns the surface rights through MP Mine Operations and the mineral rights through Secure Natural Resource, both wholly owned, with some mineral rights controlled by the State of California and the US government.
Sources
Information only, not investment advice. Reviewed 28 October 2026.