New Mexico Mineral Symposium — Abstracts

Silver, not gold, is the metal that made the American West. Although the discovery of gold in the foothills of the Sierra Nevada in 1848 sparked the great rush to California, it was the tremendous silver deposits that provided the stable mineral economy that led to the rise of cities and states. The first great silver strike was the Comstock Lode (1859), followed by Park City (1869), Silverton (1874), Leadville (1875), Aspen (1879), Creede (1890), Tombstone (1877), and Coeur d'Alene (1885). These great camps produced more than 100,000 metric tonnes of silver (although even more silver was produced as a byproduct of copper mining). Despite this great tonnage of metal, only a modest number of exceptional silver mineral specimens survive to grace modern collections. Historical descriptions of specimens suggest that American silver specimens would rival the great European localities, but interest in specimens in the last quarter of the 19th century, remoteness of the camps, and mining methods conspired to send most of the material to the smelter. The mineralogy of the deposits is varied and rich, and there are a number of silver minerals that are unique (or nearly unique) to the western United States. These include aurorite ([Mn,Ag,Ca]Mn₃O₇•3H₂O), cameronite (AgCu₇Te₁₀), empressite (AgTe), benjaminite (Ag₃Bi₇S₁₂), ourayite (Pb₄Ag₃Bi₅S₁₃), owyheeite (Pb₇Ag₂[Sb,Bi]₈S₂₀), billingsleyite (Ag₇ [As,Sb]S₆), henryite (Cu₄Ag₃Te₄), and treasurite (Ag7Pb₆Bi₁₅S₃₂)•

The Comstock Lode produced more than 250 million dollars worth of silver between 1859 and 1890 and made the United States the world's largest silver producer until the 20th century. The silver ore was mainly disseminated, fine-grained complex veins that contained acanthite, polybasite, and polybasite. The surviving "great" specimens number in the hundreds. The mines of Colorado are largely based on epithermal vein systems associated with voluminous ash-flow eruptions 25-40 million years before the present. Some districts involved significant carbonate replacement (Leadville and Aspen), whereas others are nearly devoid of sediment host rock. The volcanic mineralizing fluids deposited sulphides (principally pyrite, marmatite, galena, and sphalerite), and the range of silver minerals are represented. The mines of the Coeur d'Alene exploit polymetallic views, and the silver is largely bound in galena and other Pb minerals.

The mining history of the West is preserved in the minerals specimens. Although nearly all the mines are extinct, and the silver is long recycled in the economy, the wire silvers from Creede, acanthite cubes from Park City, and silver tellurides from the mountains of Colorado are a testament to the civilizing of the West.