English: Gold ore from the Tertiary of Colorado, USA. (cut surface)

This is a rare gold ore sample from the Camp Bird Mine in Colorado's San Juan Mountains. The rock is dominated by quartz, which is often stained grayish to blackish. Golden brassy-colored chalcopyrite (CuFeS2, iron copper sulfide) is present as small patches. Some small areas of green malachite and blue azurite are present. Clusters of tiny specks of native gold occur throughout the rock, often in the darkest-colored quartz. Under the microscope, the color and luster of the chalcopyrite and native gold are almost identical, but the native gold is very slightly more lustrous. Many of the chalcopyrite patches have rinds of brown iron oxide (possibly goethite). An undetermined mineral with metallic. luster and silvery-gray color is also present as clusters of tiny specks - probably a sulfide mineral.

This rock comes from the Camp Bird Vein, an almost east-west trending, 68° to 70° south-dipping hydrothermal vein hosted in Tertiary volcanic rocks of the San Juan Volcanic Field.

Age of mineralization: possibly similar to the age of other gold-bearing veins in the area (e.g., Argentine Vein), which is Early Miocene (~17 Ma)

Provenance: pile of vintage gold ore found below the Camp Bird Mine's Chicago Tunnel, atop a decomposed canvas bag (possibly dropped long ago on its way down to a tram station and mill)

Locality: Chicago Level, Camp Bird Mine, Camp Bird Mining District, ~east-northeast of the town of Telluride & southwest of the town of Ouray, San Juan Mountains, southwestern Colorado, USA

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See info. at: www.mindat.org/loc-8702.html and

en.wikipedia.org/wiki/Camp_Bird_Mine