200 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
looking across Lenado Canyon and up Silver Creek, from the hillside west 
of the creek, just above the Leadville mine. 
ASPEN CONTACT MINE. 
The Aspen Contact mine has its workings along the Lenado fault, 
which traverses the Lenado district from northeast to southwest. (See 
Pl. XXVIII.) The tunnel starts in Weber shales on the northwest side 
of the fault and runs southeast to meet it. On approaching the fault the 
shale becomes soft and decomposed, and the dip varies constantly from 
horizontal to vertical and pitches steeply in both directions, showing that 
the shale is crumpled into a series of complicated folds. From the 
shale the tunnel cuts into brown dolomite, which is probably Silurian. 
The contact of shale and dolomite is nearly vertical, and constitutes one 
of the parallel sips which make up the Lenado fault. The dolomite near 
the fault is much broken up, containing fragments of ore and of limestone. 
Near the fault workings run through the dolomite on a vein of rich blende, 
which was in places very high in silver and in lead. On the edges of the 
vein the sulphide has altered to zine carbonate, with some lead carbonate. 
This vein was traced continuously for about 200 feet, trending with the 
shale-dolomite contact and only a short distance from it. In places its 
walls are smooth and straight, but they are slickensided, and are probably 
slip walls. In other places the vein is broken and interrupted by breccias 
and by faulted-in blocks of dolomite. It is probable that this ore was not 
formed in place, but existed prior to the faulting. A short distance south- 
east of the fault between the shale and the dolomite comes another fault, 
which separates the dolomite from the Cambrian quartzite. The two 
faults have the same general movement, but the displacement of the fault 
between the shale and the dolomite is greater. The zone between the 
dolomite and the quartzite, however, is greatly brecciated for many feet, 
and the quartzite is softened and decomposed. The ground-up rock is 
called “tale” by the miners, and is distinguished as ‘‘gray tale,” “brown 
talc,” or “blue tale,” according as the quartzitic, dolomitic, or shaly 
material predominates. In this ‘‘tale” the richest ore in the mine has 
been found, lying directly under the quartzite, for here the fault dips 
steeply to the southeast, so that quartzite forms the hanging wall. The 
main ore body extended from the tunnel up to about 40 feet from the 
