CHAPTER VIII.—THE ORES. 
GENERAL CHARACTER. 
The characteristic feature of the Cripple Creek ores is the occurrence of the gold 
in combination with tellurium, chiefly as calaverite, but partly also as the more 
argentiferous sylvanite, a and probably to a minor extent as other gold, silver, and 
lead tellurides. Native gold appears to he absent from the telluride ores, except as it 
may be set free by the oxidation of these tellurides. Pyrite is widely disseminated 
through the country rock and also occurs commonly in small amounts in the fissures, 
associated with tellurides. Galena and sphalerite are sparingly present in the major¬ 
ity of the veins. Tetrahedrite, or gray copper ore, and stibnite are of frequent occur¬ 
rence. Molybdenite in small quantities is probably always present. The tetrahed¬ 
rite is usually rich in silver, and also contains gold. Possibly, however, the latter 
metal is due to admixed calaverite, as the two minerals often are found in intimate 
intergrowth. The galena and zinc blende rarely contain enough of the precious 
minerals to form ore. Auriferous pyrite is often reported, but in the cases investi¬ 
gated the gold was found to be derived from admixed tellurides (p. 170). Metallic 
minerals found only as great rarities are hubnerite, specularite, chalcopyrite, chal- , 
cocite, and arsenopyrite. 
The usual gangue minerals of the ores are quartz, fluorite, and dolomite; more 
rarely chalcedony and opal. Roscoelite and rhodochrosite are also found in a few 
places. Celestite, the sulphate of strontium, occurs as little acicular crystals in quartz 
vugs and forms the gangue of some exceptional veins. Calcite occurs interstitiallv 
in much of the breccia near the ore bodies, hut is rarely found in distinct crystalline 
form with the ore minerals. Secondary potassium feldspar (adularia or valencianite) 
is common in the ores. It is especially abundant in the ores inclosed in granite, par¬ 
ticularly those in the Pikes Peak type. 
Owing to the occurrence of the ore minerals and gangue as the filling of narrow 
fissures, joints, and cracks in the sheeted zones which usually constitute the lodes, or 
as a very incomplete replacement of the country rock, the ores of Cripple Creek as 
mined have approximately the composition of the somewhat altered rocks which 
immediately adjoin the veins. The quantity of metallic or gangue minerals is thus 
in nearly all cases relatively insignificant. By reason of the slight metasomatic alter¬ 
ation the rocks in the lodes approximate somewhat closely to the normal composition 
of the fresh country rock, be it granite or any of the volcanic rocks of the district. 
Oxidized ores, while still worked in many properties, are of relatively less impor¬ 
tance than when Penrose described the district. They contain the characteristic dull 
gold, often in pseudomorphous skeletons, resulting from the oxidation of the tellu¬ 
rides, associated with tellurite (tellurium dioxide), emmonsite or durdenite (both 
a Calaverite, (Au, Ag) Tea; tellurium, 57.4 per cent; gold, 39.5 per cent; silver, 3.1 ner cent. Sylvanite, (Au, Ag) Tea? 
tellurium, 62.1 Der cent; gold, 24.5 percent; silver, 13.4 per ceDt. 
169 
