Big Ben

Region West, Northwest
Mineral systems
Deposit types
Other minerals

Information leading to the delineation of this focus area

Basis for focus area The focus area encompasses the Big Ben porphyry molybdenum resource; REE, Re, Sc, Sn, and W are potential byproducts. A 15 km buffer was applied to encompass undiscovered occurrences in adjacent areas.
Identified resources Identified molybdenum resources.
Production None.
Status Big Ben was drilled and mapped by the U.S. Bureau of Mines in the early 1940s (Herdlick, 1949) and drilled by ASARCO (eight holes in 1958-1959); and then extensively by AMAX in the 1970s.
Estimated resources Big Ben: 245 Mt at 0.092% Mo (Johnson, 1964); 376 Mt at 0.098% Mo (Gammons and others, 2020).
Geologic maps Witkind (1971), scale 1:62,500.
Geophysical data Inadequate Rank 3 aeromagnetic and Rank 5 aeroradiometric coverage.
Favorable rocks and structures The terrane is early Proterozoic metamorphic rocks intruded by Tertiary porphyries and breccia pipes; Big Ben is a silicified pipe (Worthington, 2007). Big Ben porphyry dated at 49.5 Ma (Rostad and others, 1978).
Deposits Big Ben Molybdenum (MRDS dep_id: 10096465).
Evidence from mineral occurrences MRDS; Herdlick (1949); Worthington (2007); Gammons and others (2020).
Geochemical evidence USBM drilling indicated a weighted average of 0.19 to 0.26% MoS2 in core samples (Herdlick, 1949). Molybdenite and molybdite occur with chalcopyrite, galena, fluorite, and quartz.
Geophysical evidence Unknown.
Evidence from other sources Unknown.
Comments Molybdenum resources identified at Big Ben. REE, Re, W, Sn are potential byproducts, but their enrichment has been inferred from the mineral system/deposit type table (Hofstra and Kreiner, 2020).
Cover thickness and description Exposed at the surface, mineralization followed down to 45 m.
Authors Ryan D. Taylor, Albert H. Hofstra, Joshua M. Rosera, Kaleb C. Scarberry.
New data needs Geologic mapping, geophysical, and geochemical surveys.
Geologic mapping and modeling needs None requested at this time.
Geophysical survey and modeling needs High resolution aeromagnetic and aeroradiometric coverage.
Digital elevation data needs Lidar planned over a small portion of focus area and is incomplete for the rest.