Bear Lodge Mountains Rare Earth Element Deposit

The Bear Lodge Mountains are located in Crook County, in northeastern Wyoming along the northwestern edge of the Black Hills uplift. They are the largest of several domal uplifts in the region that are cored by exposed Tertiary alkalic intrusions and flanked by steeply uplifted Paleozoic and Mesozoic sediments. REE mineralization in the Bear Lodge Mountains is part of the Paleocene and Eocene alkalic igneous intrusive and volcanic rocks that crop out in northeastern Wyoming in the form of sills, plugs, dikes, and irregular plutonic bodies. These intrusions and resulting uplifts have exposed Precambrian crystalline rocks both in the Bear Lodge Mountains and in the Tinton-Mineral Hill area near the South Dakota border. Other domes in the region, such as Green Mountain, Strawberry Mountain and Lime Buttes might also have unexposed igneous cores. The area is included within the WSGS 30’ x 60’ Sundance and Devils Tower geologic quadrangles (maps published by the WSGS and available via the agency’s Online Store).

Prospecting in the Bear Lodge began in 1875, following the discovery of gold in feldspar porphyry near Warren Peak. Recent exploration in the area has been fostered both by historic mineralization, and by similarities of the Tertiary intrusive complex to that of Cripple Creek, Colorado. In addition to gold, historic economic interest has included barium, copper, silver, lead, zinc, manganese, niobium, tantalum, thorium, fluorite, phosphate, and REE.

REE mineralization occurs in carbonatite and in iron-manganese-rare-earth-element (FMR) dikes, veins, and stockworks that range in depth from the surface to 500 feet (152 m) or more. FMR refers to the major constituents of the highly oxidized, former carbonatite dikes named for F (FeOx), M (MnOx), and R (REE minerals).

FMR dike in one of Rare Element Resources’ 2011 exploration trenches. WSGS photo by Wayne M. Sutherland.
FMR dike in one of Rare Element Resources’ 2011 exploration trenches.
WSGS photo by Wayne M. Sutherland.

Map of Rare Element Resources, Ltd. Bear Lodge Project area.
Map of Rare Element Resources, Ltd. Bear Lodge Project area.
Courtesy of Rare Element Resources, Ltd.

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