158 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
bowlders being often of large size and very conspicuous in the black matrix. 
This seems to be a result of the thinning of the blue limestone and the con- 
vergence of the Silver and the Contact faults. There are many large and 
interesting caves in the blue limestone just above the Contact fault in this 
mine, which mostly seem to have been formed since the ore deposition. 
The ore occurs along the Contact fault, but chiefly along certain 
parallel zones or shoots in this fault. These shoots, which are three or four 
in number, have a northeast trend and correspond to a system of fractures 
and slight faults which are found in the rocks in this vicinity and which 
are cut in the Durant tunnel. The ore is an altered limestone, containing 
much galena and often a great deal of barite. Pls. XX and XXI are from 
photographs of stopes in the A. M. and S. mine. ‘ 
Durant tunnel The Durant tunnel runs in from the bottom of Aspen 
Mountain to the deep mines, thus affording convenient means of transporting 
ore and of drainage. It starts in the Leadville dolomite very close to the 
Parting Quartzite, and soon encounters a series of northeast faults and 
fractures, which are in general vertical, although some dip northwest and 
others southeast. Along these faults are triturated zones and open water- 
courses. There are many of these faults, and their general effect is to 
shift the formations very slightly back to the east on the south side. The 
strike of the formations at the north is slightly more easterly than the gen- 
eral trend of the tunnel, so that the tunnel tends to go down in the series, 
but the effect of the faults is to keep it along nearly the same horizon, 
near the Parting Quartzite, for the first 1,000 or 1,500 feet. Then comes 
a marked steepening of dip, as has already been noted in the Aspen and 
Durant mines, so that the rocks become nearly vertical. The strike also 
swings round more to the north and the tunnel goes steadily up in the 
series till it strikes the Contact fault. 
Homestake shaft—The Homestake shaft went through 240 feet of drift, 265 
feet of porphyry, and 115 feet of shale to the Silver fault; then through 
225 feet of blue limestone to the Contact fault. These thicknesses, how- 
ever, are taken on a very steep dip, so that the .actual thickness of blue 
limestone is not over 40 or 50 feet. This is also its thickness in the 
northern part of the A. M. and S. mine. Close to the Homestake shaft is 
situated the mouth of the Enterprise tunnel, which runs from this point 
east to the Contact fault. 
