120 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
Tellurite .—The pure tellurium dioxide, Te0 2 , forms slender orthorhombic 
prismatic crystals and small spherical masses. It is a soft white or yellowish-white 
mineral of adamantine luster, with excellent cleavage. It has been identified by 
Doctor Hillebrand from the W. P. H. mine at Cripple Creek and occurs also at the 
Gold Sovereign and Blue Bird mines. It is confined to the oxidized zone. 
SULPHIDES AND SULPHANTIMONITES. 
Pyrite .—This mineral is the most common sulphide in the district. It occurs 
disseminated in the altered breccia and other volcanic rocks, but is most abundant 
in or near the veins. Disseminated in the rocks, it is usually crystallized, showing 
pyritohedral forms; the small crystals coating quartz crusts in the veins show the 
same form, occasionally also simple octahedrons or combination of cube and octa¬ 
hedron. At the Galena and C. K. & N. mines it forms thin reniform coatings on quartz 
and has a radial fibrous structure. It commonly occurs in massive form, in veinlets, 
or occasionally in large, irregular masses. It was thus observed in the granite ores 
of the Portland, Ajax, and Elkton mines, in the cross veins of the Last Dollar mine, 
and near Vindicator shaft No. 2 on level 3, near the Hull City line. Well-formed 
crystals one-half inch in diameter occur in the Lost Anna vein. The pyrite is usu¬ 
ally very poor in gold, but sometimes cupriferous, as shown by copper stains on 
the 1,000-foot level of the Portland mine. Two pure crystallized specimens exam¬ 
ined by Hillebrand proved to be without even a trace of gold. a At the localities 
just given the pyrite is also nearly barren. It is believed that in most cases the gold 
contents of the pyritic ores of Cripple Creek are due to admixed tellurides. 
Marcasite .—Crystal growths doubtfully referred to marcasite occur in Strat¬ 
ton’s Independence mine on crusts of dolomitic carbonates. 
Molybdenite .—The molybdenum disulphide frequently appears in the ores as 
oft lead-gray scales, particles, and smaller masses, more rarely covering slickensides, 
and is on the whole very inconspicuous. As seen under the microscope it forms 
flocculent aggregates, and is very commonly intergrown with pyrite and zinc 
blende. It has generally been overlooked, but without doubt is a very character¬ 
istic part of the vein matter. It occurs at all depths below the oxidized zone and 
has been identified from the Vindicator, Findley, Last Dollar, Mary McKinney, 
Moose, Portland, and several other mines. 
The mixed ores analyzed at the chlorination mills of the United States Reduc¬ 
tion and Refining Company at Colorado City contain about 0.04 per cent 
molybdenum. 
A little molybdenite was also found in a quartz veinlet 1 mile southwest of 
Cripple Creek, in gneiss. This veinlet is probably older than the gold veins of 
Cripple Creek. 
Stibnite .—The sulphide of antimony is of common occurrence in the Cripple 
Creek district in association with rich gold ores. In the usual groups and bunches 
of brilliant, steel-gray, striated prismatic crystals it is found in the C. K. & N. and 
El Paso veins, in the former in masses weighing up to 50 pounds. Other occurrences 
are in the Mary McKinney, Puzzle, Katinka,*Blue Bird, and Stratton’s Independence 
“Penrose, R. A. F., jr., Mining geology of the Cripple Creek district: Sixteenth Ann. Rept. U. S. Geol. Survey, pt. 2 
1895, p. 122. 
