Stable isotope composition and geochemistry of calcite and dolomite in the Mountain Pass carbonatite: A lens into petrogenesis
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Abstract
Carbonatites host most of the global rare earth element (REE) deposits. The petrogenesis of these rocks, including magmatic and post-magmatic processes, are poorly understood but critical in forming and upgrading these deposits. The Mountain Pass carbonatite, which hosts the only active REE mine in North America, is lithologically variable but consistently contains >50% calcite and/or dolomite. Multiple generations of carbonates are evident, suggesting bulk analysis of carbonate minerals would generate a mixed isotopic and geochemical signature. In-situ stable carbon and oxygen isotopes, combined with geochemical analysis and petrography, distinguish carbonate generations, trace the source region of the carbonatite magma, and link carbonate genesis to REE mineralization throughout the intrusion. Primary carbon and oxygen isotope values outside the accepted mantle range may suggest a subduction-related carbon and oxygen source in the mantle. Deformation textures in primary calcite indicate syn- or post-crystallization ductile flow. Carbonates with secondary textures and heavy δ13C and δ18O values are associated with ore mineralization, suggesting fluid mobilization was important in concentrating REE and upgrading of the Mountain Pass deposit.
| Publication type | Conference Paper |
|---|---|
| Publication Subtype | Conference Paper |
| Title | Stable isotope composition and geochemistry of calcite and dolomite in the Mountain Pass carbonatite: A lens into petrogenesis |
| Volume | 2 |
| Year Published | 2025 |
| Language | English |
| Publisher | Society for Geology Applied to Mineral Deposits |
| Contributing office(s) | Geology, Minerals, Energy, and Geophysics Science Center, Geology, Geophysics, and Geochemistry Science Center |
| Description | 4 p. |
| First page | 623 |
| Last page | 626 |
| Conference Title | 18th SGA Biennial Meeting |
| Conference Location | Golden, CO |
| Conference Date | August 3-7, 2025 |
| Country | United States |
| State | California |
| Other Geospatial | Mountain Pass Intrusive Suite |