| Basis for focus area |
REE- and Nb-rich carbonate veins and lenses range from a few inches to 10 feet in width, with strike lengths of <10 feet to >450 feet. The veins are crudely parallel to the NW-striking and NE-dipping metamorphic foliation. Including the Mineral Hill district in Idaho, REE- and Nb-rich veins have been found in a NW-trending belt that is at least 18 miles long (Heinrich and Levinson, 1961). |
| Identified resources |
Minor production of REE and Nb took place in the late 1950s by the Sheep Creek Mining Company, a subsidiary of the Continental Columbium Corporation of California (Heinrich and Levinson, 1961). |
| Production |
Unknown. |
| Status |
Past exploration; trenching and minor underground workings. Diamond Creek drilling slated for summer, 2022. |
| Estimated resources |
Diamond Creek prospect has an estimated total reserves of 2,600 metric tons (2,870 tons) of total rare-earth oxides and total probable potential resources of 836 metric tons (921 tons) of total REO. Average grade of 1.22% total REO/ton (Staatz, Armbrustmacher and others, 1979). Similar to Lemhi Pass. |
| Geologic maps |
Kaiser (1956), scale 1:16,000; Berg (1977), scale 1:40,000; Lopez (1982), scale 1:48,000; Lund, Rehn and Holloway (1983), scale 1:50,000; Spence (1984), scale 1:31,250; Berg and Lonn (1996), scale 1:100,000; Lewis and others (2002), scale 1:100,000; Evans and Green (2003), scale 1:100,000; Burmester and others (2016), scale 1:100,000. |
| Geophysical data |
A high-resolution Earth MRI airborne magnetic and radiometric survey was funded by Earth MRI in 2020. Flying is complete, but at this time the data have not been released. Survey covers Idaho REE+Nb occurrences, but not Sheep Creek area in Montana. |
| Favorable rocks and structures |
Mineralized monazite-actinolite-carbonate pegmatite cutting Mesoproterozoic amphibolite gneiss, granite augen gneiss, and lesser biotite-feldspar-quartz schist of the Lemhi Group in the upper plate of the Brushy Gulch thrust fault. The veins are crudely parallel to the NW-striking and NE-dipping metamorphic foliation. |
| Deposits |
Sheep Creek mine (MRDS dep_id: 10070412), Spring Creek mines, Diamond Creek deposit, Mineral Hill District (USMIN Site_ID: ID00046). |
| Evidence from mineral occurrences |
MRDS; USMIN. |
| Geochemical evidence |
Sheep Creek-Spring Creek, Montana: monazite, ancylite, REE fluorocarbonates (bastnäsite, parisite, synchysite), columbite, pyrochlore, fersmite, allanite, Nb-rich rutile (up to 13%), barite, fluorite, apatite, thorite. Sulfides include pyrite, pyrrhotite, chalcopyrite, molybdenite, galena, marcasite, cobaltite, and siegenite. Mineral Hill (Lemhi County, Idaho): monazite, apatite, Nb-rich rutile, allanite, barite, titanite, ilmenite, calcite, magnetite, pyrite, pyrrhotite, chalcopyrite, biotite, actinolite, glaucophane, garnet. Additional REE minerals may be present, similar to Sheep Creek in Montana. Diamond Creek, Idaho: monazite, brockite, thorite, xenotime, bastnäsite, fluorite, rutile, gold. |
| Geophysical evidence |
Unknown. |
| Evidence from other sources |
Unknown. |
| Cover thickness and description |
Varies; extensive colluvium cover in Diamond Creek area. |
| Authors |
Virginia S. Gillerman, Reed S. Lewis, Christopher A. Tate, Karen Lund, Thomas P. Frost, Joshua M. Rosera, Allen K. Andersen. |
| New data needs |
Geologic analysis, high resolution geophysics on the Montana side (Sheep Creek), whole-rock geochemistry for all critical minerals, geologic mapping. |
| Geologic mapping and modeling needs |
Geologic mapping adequate. Work needed is reanalysis of archived ore samples and modern revision of deposit descriptions based on available modern geologic mapping and dating. |
| Geophysical survey and modeling needs |
New Rank 1 geophysics covers mineralized areas in Idaho (Mineral Hill-North Fork area). |
| Digital elevation data needs |
Lidar in progress. |
