L1N B D ANsoME. ND ] CHARACTER OF THE ORES. 21 



sphalerite occur in small quantities in many of the mines, but rarely 

 contain enough of the precious metals to form ore. Native gold 

 appears to be absent from the telluride ores, except as it may be set 

 free by the oxidation of these tellurides. 



The usual gangue minerals of the ores are quartz, fluorite, and dolo- 

 mite. Roscoelite and rhodochrosite are also found in places. Celestite, 

 or sulphate of strontium, while never present in large amount, fre- 

 quently occurs as little acicular crystals in the quartz vugs of the lodes. 

 Calcite occurs interstitially in much of the breccia near the ore bodies, 

 but is rarely found in distinct crystalline form with the ore minerals. 

 Secondary potassium feldspar is common in the ores; it is especially 

 abundant in the ores inclosed in granite, particularly those in the 

 Pikes Peak type. This feldspar has the composition of orthoclase or 

 microcline, and is formed by the rec^stallization of the original 

 potassic feldspar contained in the rocks. In the granitic ores of the 

 Stratton's Independence, Portland, Ajax, and Elkton mines, this sec- 

 ondary feldspar is the principal gangue mineral. 



Oxidized ores, while still worked in many properties, are of rela- 

 tively less importance than when Penrose described the district. 

 They contain the characteristic dull gold, often in pseudomorphous 

 skeletons, resulting from the oxidation of the tellurides, associated 

 with tellurite (tellurium dioxide), emmonsite or durdenite (both 

 hydrated ferric tellurites), and probably other oxidized compounds of 

 tellurium and iron. These minerals occur in association with kaolin, 

 alunite, and ferruginous clays. The deep workings of the present 

 day show that kaolin is always connected with oxidation, and is not a 

 product of the original mineralization of the district, as was supposed 

 by Penrose. 



The Cripple Creek ores, as a rule, contain very little silver, the 

 average proportion being about 1 ounce of silver to 10 ounces of gold. 

 In the Portland and Stratton's Independence mines the proportion is 

 very much less, the silver from the Portland in 1901 amounting to 

 only 2.4 ounces for each 100 ounces of gold. In the Blue Bird, 

 Doctor-Jack Pot, Conundrum, Pointer, and other mines containing 

 notable amounts of tetrahedrite or galena, the proportion of silver 

 rises considerably above the average. 



The average value of the Cripple Creek ores lies probably between 

 $30 and $40 per ton. In some of the larger mines the average value 

 sinks to about $25 per ton. From a lower economic limit of about 

 $12 per ton the values of individual shipments swing through a wide 

 range up to ores carrying $3,000 or $4,000, or even $8,000, per ton. 

 Occasionally smaller amounts one or two tons have yielded as much 

 as $50,000 per ton. 



