Zortman syenite

Region West, Northwest
Mineral systems
Deposit types
Other minerals

Information leading to the delineation of this focus area

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.