170 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
hydrated ferric tellurites . and probably other oxidized compounds of tellurium and 
iron. These minerals occur in association with kaolin, alunite, and ferruginous clays, 
which result from the oxidation of the country rock in which the vein is contained. 
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 bv Penrose. _ 
COMPOSITION AND VAI/CTE. 
Gold and silver are the only metals utilized in the Cripple Creek ores. The 
small amounts of copper, molybdenum, antimony, lead, and zinc are of no economic 
importance. Tellurium is likewise allowed to go to waste, as there is insignificant 
demand for it and its recoverv would be verv costlv. The average amount of gold in 
the ores is probably between 1.5 and 2 ounces, or from $30 to $40 per ton. In some 
of the larger mines the average value sinks to 1.25 ounces or even 1 ounce per ton, 
the latter figure corresponding to 0.0035 per cent. From a lower economic limit of 
about $12 per ton the values of individual shipments swing through a wide range up 
to ores carrying $5,000 or even $50,000 per ton. A shipment of 274 tons from level 
10 of the Cheyenne vein. Isabella mine, yielded $219,000, according to reports, and 
in 1904 a shipment of 2.901.42 pounds of El Paso ore afforded on assay 2.592.68 
ounces of gold and 299.33 ounces of silver per ton and yielded $75.24S.79 net. or over 
8 per cent gold. This would indicate that one-third of the cpiantity consisted of pure 
calaverite. on the assumption that this was the only auriferous mineral‘present. 
Oxidized ores which contain free gold only may under favorable circumstances be 
subjected to direct cyaniding and yield a profit with a tenor in gold of about $5. 
The statement is often made that some of the pyrite in the veins contains high 
gold values. In most cases this is due to admixed telluride. Penrose 0 leans 
toward the same view and states that two pure crystallized specimens examined by 
Hillebrand did not contain a trace of gold. A sample was taken of a heavy sul¬ 
phide filling in a cross vein on level S. Last Dollar mine. The vein was several 
inches wide, and consisted of granular pyrite and sphalerite, with a little molyb¬ 
denum. lead, and copper. An assay by Dr. E. T. Allen and a determination of 
tellurium by Hillebrand gave Te. 0.016 per cent: Au, 0.0015 per cent (0.44 ounce 
per ton : Ag. 0.017 per cent (4.9 ounces per ton). The molecular ratio is 126 Te : 7 
Au : 157 Ag. corresponding approximately to a proportion of 42 sylvanite [(Ag. Au) 
Te,] and 225 liessite (Ag,Te\, leaving a surplus of 23 Te. which might possibly 
belong to lead or some of the other baser metals. The pyrite evidently contains 
no gold. 
The pyrite of the altered country rock is always poor in gold. A specimen of 
coarse pyrite with sphalerite from the breccia in the Hull City mine, level 7. near 
Vindicator line, contained only 0.20 ounce of silver and 0.04 ounce gold per ton. 
Whether free gold is present in the telluride ores is a debatable cjuestion. It 
may and probably does occur locally, but it is likely to be in very small amounts. 
Analyses 2 and 3 of the table below show that a small part of the gold in the tellu¬ 
ride ore from the El Paso mine, presumably entirely free from oxidation, would be 
free gold if all of the silver were assumed to be present as tellurides. But as there 
c Mining geology of the Cripple Creek •listrict, Colorado: Sirt -enth Ann. Rept. U. S. Geol. Survey, pt. 2,1SQ3, p. 122. 
