CRIPPLE  CREEK  GOLD  ORES

 

The Cripple Creek Gold District of central Colorado, USA is famous for its unusual gold and silver mineralization.  Precious metal mineralization occurs in the Cripple Creek Diatreme, the root zone of a deeply eroded volcano dating to the Early Oligocene (32 m.y.).

 

The dominant lithology at Cripple Creek is the scarce igneous rock phonolite, an alkaline, intermediate, extrusive igneous rock.  Cripple Creek gold can be found in its native state (Au), but it typically occurs in the form of gold telluride minerals (for example, sylvanite - (Au,Ag)₂Te₄, calaverite - AuTe₂, petzite - Ag₃AuTe₂, krennerite - (Au,Ag)Te₂, and nagyagite - Pb₅Au(Sb,Bi)Te₂S₆).  Silver also occurs in some Cripple Creek minerals, including sylvanite, petzite, krennerite, hessite - Ag₂Te, tennantite - (Cu,Ag,Fe,Zn)₁₂As₄S₁₃, acanthite - Ag₂S, and tetrahedrite - (Cu,Fe,Ag,Zn)₁₂Sb₄S₁₃.

 

 

Gold after calaverite lining fracture in phonolite from the Cripple Creek Diatreme, Early Oligocene, 32 m.y. (Colorado School of Mines Geology Museum, Golden, Colorado, USA).  The gold has taken on the crystal form of the original calaverite mineral.

 

 

Calaverite (AuTe₂) (gold-colored) (field of view ~1.7 cm across) in a purple fluorite vein, from the Cripple Creek Diatreme (Early Oligocene, 32 m.y.) of central Colorado, USA.

 

 

Sylvanite ((Au,Ag)₂Te₄) (silver-colored) from the Cripple Creek Diatreme (Early Oligocene, 32 m.y.) of central Colorado, USA (ER # 1956, Ed Raines loan to Colorado School of Mines Geology Museum, Golden, Colorado, USA).

 

 

Sylvanite (dark metallic - (Au,Ag)₂Te₄) and fluorite (purple - CaF₂) from the Last Dollar Mine, northern slope of Battle Mountain, Cripple Creek Diatreme (Early Oligocene, 32 m.y.), central Colorado, USA (ER # 486, Ed Raines loan to Colorado School of Mines Geology Museum, Golden, Colorado, USA).

 

 

The gold telluride minerals common in the Cripple Creek Diatreme lack the wonderful, deep rich yellow color of native gold.  Some Cripple Creek rock samples have been artificially “roasted” to drive off the tellurium.  With heat, the Te readily volatilizes, leaving behind relatively pure gold.  The gold patches on the rock below are surficial blisters and crusts of gold having a fine-scale vesicular texture (lots of tiny holes, like a pumice or scoria).

 

Roasted gold ore (~6 cm across) from Cripple Creek, Colorado, USA.  Artificial heating has driven tellurium (Te) away from the original telluride mineral (calaverite), leaving behind vesicular blebs of gold.  Specimen owned by Mason Davis.

 

Roasted gold ore (same sample as above; ~6 cm across) from Cripple Creek, Colorado, USA.

 

Roasted gold ore (same sample as above; ~6 cm across) from Cripple Creek, Colorado, USA.

 

 

Some info. from Carnein & Bartos (2005) - Mineralogical Record 36(2): 143-185.

 

 

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