File:Silver-replaced gastropod in fossiliferous limestone (Leadville Limestone, Lower Mississippian; mineralization between 70 and 55 Ma; Smuggler Mine, Aspen, Colorado, USA) 1 (24282644251).jpg

Silver-replaced fossiliferous limestone from Colorado, USA. (DMNH 138, Denver Museum of Nature & Science, Denver, Colorado, USA)

This remarkable rock is fossiliferous limestone that has been replaced by native silver (Ag). The large, whitish fossil near the center is a gastropod (snail) - it appears to have been truncated by a fault. This specimen comes from a famous silver mining area in Colorado - the Aspen Mining District. Barite, various sulfides and sulfosalt minerals, plus native silver occur principally in breccia zones in the Aspen District. The breccia zones occur within and at the top of the Leadville Limestone, a Lower Mississippian unit that includes dolostone and limestone. Silver and sulfide mineralization in the area occurred during the Late Cretaceous and Paleocene, between approximately 70 and 55 million years ago. This mineralization accompanied the Laramide Orogeny, a mountain building event that formed the true Rocky Mountains of New Mexico, Colorado, Wyoming, and Montana.

Locality: Smuggler Mine, Smuggler Mountain, Aspen Mining District, central Pitkin County, west-central Colorado, USA

Example references on Smuggler Mine area geology:

Bryant (1979) - Geology of the Aspen 15-minute quadrangle, Pitkin and Gunnison Counties, Colorado. United States Geological Survey Professional Paper 1073. 146 pp.