ASPEN MOUNTAIN. 161 
south, for 250 feet to the contact between dolomite and granite caused by 
the Pride fault. 
Late Acquisition mine. (See Pl. XL, C).—The Late Acquisition shaft is 125 
feet deep and is entirely in dolomite, which is probably Carboniferous. In 
this shaft there are four levels, of which the upper two are short and 
extend in a westerly direction. The third level, which runs to the east, 
cuts the Parting Quartzite 50 feet from the shaft. On this level a consid- 
erable amount of medium-grade lead ore has been found along the Saddle 
Rock fault and along parallel slips in the dolomite. One hundred feet 
below the third level is the fourth or tunnel level, which runs due north and 
south on a fault plane which is marked by a perpendicular, highly polished 
and striated wall of dolomite on the west side and by blue limestone on 
the east. This is not the main Saddle Rock fault, but a parallel slip about 
50 feet west of the main one. The rock along this fault is mineralized, 
containing considerable lead and zine sulphide, which has replaced the 
dolomite. 
The ore throughout this mine has the general characteristics of the 
West Aspen Mountain ores, as shown in the Pride of Aspen mine. It is a 
high-grade lead ore with only a small amount of silver. There is almost 
no barite, and tons of the ore often average less than 1 per cent of baryta. 
ASPEN MOUNTAIN MINING MAP. 
The Aspen Mountain map (Atlas Sheet XXV) includes the produc- 
tive mines of Aspen Mountain, except those near the pomt of West Aspen 
Mountain. Through the center of the district runs the outcrop of the hghly 
metalliferous zone which is continuous from the Argentum-Juniata up to 
the Durant. In the bottom of the Aspen Mountain syncline little mining 
has yet been done, although it offers a favorable field for exploration, while 
on the west side of the syncline are some long tunnels. 
Besides the structure already shown on the smaller-scale map, some 
additional details appear on the Aspen Mountain map. The Contact fault 
between the limestone and dolomite of the Leadville formation is repre- 
sented, and the distinction between limestone and dolomite is indicated by 
different coloring. An east-west fault which crosses Spar Gulch at the 
southern edge of the mapped area and which represents a system of nearly 
vertical northeast faults, with usually very slight throw, is also shown. 
MON XXXI it 
