| Basis for focus area |
Agpaitic lamprophyllite-bearing pegmatites enriched in Ba, Zr, REE, Sr, Nb, and Ti at Gordon Butte. Other alkaline intrusions of the northern Crazy Mountains (Comb Creek stock and dike swarm, the Ibex Mountain sill, and the Robinson anticline intrusive complex) may be similarly enriched in this critical mineral assemblage. |
| Identified resources |
None. |
| Production |
None. |
| Status |
Unknown. |
| Estimated resources |
Unknown. |
| Geologic maps |
du Bray and others (1993), scale 1:24,000. |
| Geophysical data |
Inadequate aeromagnetic and aeroradiometric coverage. |
| Favorable rocks and structures |
Strongly alkaline rocks including Gordon Butte, the Comb Creek stock and dike swarm, the Ibex Mountain sill, and sills from the Robinson anticline intrusive complex. |
| Deposits |
Unknown. |
| Evidence from mineral occurrences |
Unknown. |
| Geochemical evidence |
Agpaitic pegmatites enriched in Ba, Zr, REE, Sr, Nb, and Ti at Gordon Butte. Early-stage: zircon, thorite, Sr-rich loparite. Agpaitic-stage: diverse titano- and zircon-silicates (barytolamprophyllite, eudialyte, wadeite, and rinkite). Deuteric-stage: Sr-REE-Na-rich fluorapatite, Ba-Fe titanates, and REE-bearing carbonates (ancylite, calcio-ancylite, and bastnäsite-parisite series) (Chakhmouradian and Mitchell, 2002). |
| Geophysical evidence |
None. |
| Evidence from other sources |
REE-enriched malignite reported in the "Great Cliffs" area of the Robinson anticline intrusive complex (Hearn and others, 1989). |
| Comments |
Gordon Butte comprises agpaitic nepheline-syenite pegmatites and related alkaline intrusive rocks (malignites, minettes, nepheline microsyenites, and microsyenites). In the Crazy Mountains, alkaline rocks occur as laccoliths, sills, and dikes around sub-alkaline stocks. Pegmatites could be a source for several critical mineral commodities. |
| Cover thickness and description |
Erosion has exposed several stocks of the northern Crazy Mountains. A complete section (120 m) of Gordon Butte is accessible on its southeast margin (Hearn and others, 1989). The "Great Cliffs" are an amphitheater-like scarp of a landslide that expose analcime malignite, analcimite, malignite, some felsic alkalic rocks (Hearn and others, 1989). |
| Authors |
Allen K. Andersen, Kaleb C. Scarberry, Jay A. Gunderson, Joshua M. Rosera. |
| New data needs |
High resolution geophysics, whole-rock geochemistry for all critical minerals, geologic mapping, lidar. |
| Geologic mapping and modeling needs |
Detailed geologic map of the Virginia Peak 7.5' quadrangle. 1:24,000 scale geologic mapping. |
| Geophysical survey and modeling needs |
High resolution aeromagnetic and aeroradiometric coverage. |
| Digital elevation data needs |
Lidar incomplete. |
