160 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
It is rather remarkable that the contact between the breccia and the sur¬ 
rounding granite is so rarely the seat of ore deposition, though some of the most 
important ore bodies in the district are found in its immediate vicinity. The contact 
itself seems to contain ore only where, as in the case of the Independence vein and the 
No. 2 vein of the Portland mine, it is locally coincident with a zone of Assuring 
which is productive also at other points. A possible exception to this last statement 
is the Contact vein in the W. P. H. and Damon mines, which follows the contact 
between schist and breccia for at least 300 feet in depth, dipping steeply southwest. 
It is ore bearing in places. 
The Wild Horse vein, with its long curved course, deserves special mention. 
Near the surface it follows approximately the contact between the granite and the 
breccia, but in depth it passes entirely into the granite. The dip is irregular, being 
in some places vertical and in others to the west at a high angle. 
STRUCTURAL FEATURES. 
The structure associated with the deposits most characteristic of the district 
is that known as a sheeted zone. As here developed, such zones consist of a vary¬ 
ing number of narrow, approximately parallel fissures which 
collectivelv form a lode ranging from a few inches to 50 or 60 
feet, or rarely 100 feet, in width. Within such uncommonly 
wide belts of fracture, however, can usually be distinguished 
two or more zones of concentrated Assuring which lie close 
enough together to be mined as a whole. In other words 
the very wide belts are compound 
sheeted zones, of which the most con- 
Rich ore 
Fig. 4.—Structure of La Bella 
vein, Golden Cycle mine, 
level 9. Rock is very fresh 
latite-phonolite. Central 
seam carries visible calaver- 
ite. Screenings across whole 
width assay 2 ounces per ton. 
Captain veins in the Portland mine. 
Usually the sheeted zones are from 2 
to 10 feet in width. 
As a rule the fissures are mere cracks, 
showing no brecciation, slickensiding, 
or other evidence of tangential move¬ 
ment of the walls. There are some 
notable exceptions to this statement, as will presently be 
seen, and appreciable displacement has occurred along some 
of the veins. But the movement of one wall past the other 
has probably in few instances exceeded 1 or 2 feet. 
A sheeted zone on a small scale is well shown by PI. XIII, 
from specimens from the mineralized basic dike of the Conun¬ 
drum mine. In this case the fissures are filled with fluorite. 
Very often, however, a single narrow fissure is accom¬ 
panied by irregular fracturing of the adjacent rock. Such a 
structure, which is not properly a sheeted zone, is illustrated 
in fig. 4, a sketch of the La Bella vein on level 9 of the Golden 
Cycle mine. The country rock in this case is latite-phonolite. 
Scale 
5 
10 ft. 
_I 
Fig. 5.—Legal tender vein. 
Golden Cycle mine, level 10. 
Fresh breccia with oxidized 
seams. Main clay seam as¬ 
says 300 ounces. All seams 
carry values. 
A few lodes, also, 
are associated with more curved and irregular Assuring than pertains to a sheeted 
zone, and might be called stringer lodes. This type, which is not characteristic 
4 
