| Basis for focus area |
Thirty-five diatremes and dikes produced by mantle-derived alkalic ultramafic magmas of alnoitic and kimberlitic affinity occur in a 140-km long band that trends N80°E from Haystack Butte, close to the Highwood Mountains, to the Little Rocky Mountains (Hearn and others, 1989). Diatremes show genetic connections to alnoitic, kimberlitic, and carbonatitic magmas. Carbonatite blocks within diatreme are reported. Potential for REE-rich carbonatite intrusions at depth. |
| Identified resources |
None (nearby mining mostly related to Zortman alkalic porphyry). |
| Production |
None. |
| Status |
Unknown. |
| Estimated resources |
Unknown. |
| Geologic maps |
Porter and Wilde (2001), scale 1:100,000; Wilde and Porter (2001), scale 1:100,000. |
| Geophysical data |
Inadequate aeromagnetic and aeroradiometric coverage. |
| Favorable rocks and structures |
The igneous rock types include alnoite (melilite-bearing), monticellite peridotite (melilite-free), carbonate-rich mica peridotite, kimberlite, and carbonatite (Hearn and others, 1989). |
| Deposits |
None. |
| Evidence from mineral occurrences |
Unknown. |
| Geochemical evidence |
Past geochemical analysis suggest the presence of REE, Nb, Ta, and Ti. Chemical compositions of the Missouri Breaks igneous rocks are similar to alkalic ultramafic rocks and kimberlites elsewhere in the world. The chondrite-normalized rare-earth element patterns are linear, steep, and show strong light REE enrichment (Hearn and others, 1989). |
| Geophysical evidence |
None. |
| Evidence from other sources |
The similarity of the Missouri Breaks intrusions to similar alkalic ultramafic and kimberlites elsewhere in the world suggest they may be a resource for critical elements. |
| Comments |
Enrichment in barite, niobium, REE, scandium, strontium, zirconium has been inferred from the deposit-type and mineral system table (Hofstra and Kreiner, 2020). |
| Cover thickness and description |
Surficial. |
| Authors |
Allen K. Andersen, Stanley L. Korzeb, Joshua M. Rosera. |
| New data needs |
High resolution geophysics, whole-rock geochemistry for all critical minerals, geologic mapping, lidar. |
| Geologic mapping and modeling needs |
1:24,000 scale geologic mapping. |
| Geophysical survey and modeling needs |
High resolution aeromagnetic and aeroradiometric coverage. |
| Digital elevation data needs |
Lidar complete over eastern half of focus area; in progress over western half. |
