162 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
by other flat veins in the Mary McKinney mine and by the Doctor-Jackpot, Chance, 
Matoa, and many other lodes, particularly those in the breccia. 
There are a large number of sheeted zones in breccia and in granite, which are 
composed of many parallel or nearly parallel fissures, but which differ from the type 
just described in the absence of a well- 
defined medial zone and in the rather 
less regular character of the fractures. 
This type is admirably illustrated by 
the wider Captain veins in the breccia 
of the Portland mine, some of which 
are stoped to a width of 120 feet. It 
is not in these widest parts, however, 
that the sheeted structure is best seen, 
for in the large stopes the jointing, as 
appears in PL XV, B, is often so irregu¬ 
lar that the lode-like character is lost. 
In the narrower Captain veins, on the 
other hand, the fracturing as shown in 
PI. XIV and in fig. 8 retains the charac¬ 
ter of a sheeted zone. Fissures over 
half an inch in width are rarely seen in 
the Captain stopes and the ore often 
occurs in scarcely visible cracks. Other 
good examples of such broad zones of 
general sheeting are the Anaconda lode 
(PI. XIV) and parts of the No. 2 vein 
of the Mary McKinney mine. In the 
granite the sheeted zones, while similar 
in character to those just described in the breccia, are usually narrower. As exam¬ 
ples of this general type of structure in granite may be mentioned the Diamond 
vein in the Portland mine, the No. 6 
vein in Stratton’s Independence 
mine, the Granite vein, and the 
C. K. & N. vein. In the Ajax mine 
there is a peculiar association of a 
sheeted zone with the flat fissures, 
illustrated in fig. 9. These flat fis¬ 
sures carry ore for 30 or 40 feet from 
the main sheeted zone. 
There is sometimes one fissure 
of a sheeted zone which is distinctly 
larger than the others and which 
usually contains the richest ore. 
The dominant fissure of the C. K. & N. 
vein, for example, is in some places 4 
inches wide, and contains slabs of country rock which were loose before they were 
cemented by ore. The Pointer lode, in syenite, also has a dominant fissure which 
Fig. 8.—North face of No. 8 Captain vein, Portland mine, level 
fi, showing sheeting in brecei^ 
Fig. 9.—Sheeted zone and “ flats” of the Apex vein, Ajax mine. 
