Here's a rare, vintage sample of gold ore from Gunnison County, Colorado's Vulcan Mine (next to the Mammoth Chimney Mine & Good Hope Mine).  The mining area is at the “town” of Vulcan, north of the Iron Hill Carbonatite Complex and south of the eastern end of the Blue Mesa Reservoir (= dammed Gunnison River).


Little geologic literature appears to be available on the geology of the Vulcan Mine.  The specimen shown below was the subject of a short article published in 1898.  The grayish & purplish-gray banded portions of the rock were identified by Lakes (1898) as opalite (opal rock, composed of hydrous silica - SiO2·nH2O).  Another source of information suggests that the banded areas are cryptocrystalline quartz (SiO2) - chert.   Peripheral to the banded rock is breccia.  Finely-disseminated native gold (and/or gold telluride?) occurs throughout the rock.


Locality: Vulcan Mine, southern Gunnison County, southwestern Colorado, USA (~38º 20' 37" North, ~107º 00' 26" West).


Vulcan Mine gold ore (Colorado School of Mines Geology Museum, Golden, Colorado, USA).


Vulcan Mine gold ore (Colorado School of Mines Geology Museum public display, Golden, Colorado, USA).


Vulcan Mine gold ore - line drawing of slice from same block of rock shown above (from Lakes, 1898).



Reference cited:


Lakes, A.  1898.  Ores of the Vulcan Mine.  Mines and Minerals 18: 562-563.



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