| Basis for focus area |
Outline of the Tertiary syenite complex that hosts the Zortman-Landusky low-grade Au deposit in the Little Rocky Mountains. |
| Identified resources |
Historical production of gold and silver. |
| Production |
Zortman (1884-1985): 727,414 oz Au and 789,000 oz Ag. Zortman-Landusky mines (1960s-1996): >2 million oz Au. |
| Status |
Past mining; Zortman and Landusky gold mines were reclaimed in the mid-2000s. |
| Estimated resources |
Unknown. |
| Geologic maps |
Porter and Wilde (2001); scale 1:100,000. |
| Geophysical data |
Inadequate Rank 3 to 4 aeromagnetic and Rank 4 aeroradiometric coverage. |
| Favorable rocks and structures |
Zortman syenite. |
| Deposits |
Zortman mine (MRDS dep_id: 10124596), Zortman-Landusky mines (MRDS dep_id: 10008952). |
| Evidence from mineral occurrences |
MRDS; Goldfarb and others (2017). |
| Geochemical evidence |
Gold occurs as electrum, native gold and auriferous tellurides associated with pyrite, marcasite, dolomite, and fluorite (Russell, 1991). Gangue fluorite and some records indicate sphalerite is present in places. |
| Geophysical evidence |
Unknown. |
| Evidence from other sources |
Unknown. |
| Comments |
BLM land; ongoing water treatment. Occurrence of Bi and V has been inferred from the mineral system/deposit type table (Hofstra and Kreiner, 2020). |
| Cover thickness and description |
Exposed at the surface, mined to some depth. |
| Authors |
Jane M. Hammarstrom, Jay A. Gunderson, Joshua M. Rosera, Kaleb C. Scarberry. |
| New data needs |
Geophysical and geochemical surveys. |
| Geologic mapping and modeling needs |
Targeted 1:24,000 scale mapping and mine-site mapping would be beneficial. |
| Geophysical survey and modeling needs |
High resolution aeromagnetic and aeroradiometric coverage. |
| Digital elevation data needs |
Lidar complete or in progress. |
