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RELATED PARTY TRANSACTIONS - Related Party Revenue and Cost of Sales (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023
Related Party Transaction [Line Items] |  |  |  |
Total revenue | $ 62,927 | $ 52,516 | $ 142,869 | $ 212,240
Cost of sales (excluding depreciation, depletion and amortization) | 57,266 | 22,217 | 134,323 | 69,137
Related party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Cost of sales (excluding depreciation, depletion and amortization) | 38,139 | 21,829 | 78,848 | 66,817
Rare earth concentrate |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Total revenue | 43,053 | 52,472 | 107,555 | 212,139
Rare earth concentrate | Related party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Total revenue | 43,053 | 51,502 | 107,555 | 203,186
Other rare earth products |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Total revenue | 695 | 44 | 1,277 | 101
NdPr oxide and metal (including related party) |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Total revenue | 19,179 | 0 | 34,037 | 0
NdPr oxide and metal (including related party) | Related party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Total revenue | $ 5,061 | $ 0 | $ 7,306 | $ 0

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