INFLUENCE OF DEPTH ON ORE SHOOTS. 
215 
It may thus be concluded, without necessarily advocating promiscuous explo¬ 
ration below the 1,000-foot zone, that any ore bodies existing below that depth are 
far less likely to be discovered than those above, where from the surface to depths 
of several hundred feet the rocks of the district are riddled with shafts, drifts, 
crosscuts, and adits. It is difficult, however, to determine the relative importance 
of this factor in the problem. It is probably safe to assume that the chances of 
discovering a given ore bod}' within the 1,000-foot zone are at least ten times those 
of discovering an ore body below that zone, and the ratio may be very much greater. 
While it is also very probably true that there was originally more ore within the 
1,000-foot zone than there is in a corresponding zone below, this disparity is not 
necessarily anything like so great as is indicated by the vertical distribution of 
known pay shoots. 
Another important line of inquiry bearing upon the relations of the ore bodies 
to depth is concerned with the question of the relative size and abundance of the 
fissures near the surface and at greater depth. It has been shown that all the ore 
bodies are intimately connected with fissures. If such fissures are generally smaller 
and less abundant below the 1,000-foot zone than they are within it, obviously 
there is introduced a factor which diminishes the supposed importance of secondary 
enrichment by affording an anterior and physical explanation for the decrease of ore 
with increase of depth. 
Detailed examination of practically all the accessible mines in the Cripple Creek 
district has led to the conclusion that the fissures, which ordinarily are narrow and 
often appear as mere cracks, do become less abundant and less conspicuous as 
greater depth is attained. No mine exhibits this feature better than Stratton’s 
Independence, in which the very complex systems of productive fissures on the 
fifth and higher levels contrast most strikingly with the few insignificant and 
unproductive fractures visible on level 14. In less degree the same feature is shown 
in many others of the deep mines, but the rule is not without some very marked 
exceptions. 
There are thus at least two factors to account for the smaller development of 
ore shoots below the 1,000-foot level: First, difficulties of development and explo¬ 
ration; and, second, the disappearance of many fissures in depth. These two do 
not, however, seem to completely explain the facts, and it is believed that there is 
a' third cause which is related to temperature and solubility and which favored 
deposition near the surface rather than in depth. 
The minimum depth of rock removed from the district by erosion may be esti¬ 
mated to be 1,000 feet in the central part and 400 or 500 feet about the periphery 
(p. 38). Possibly it was somewhat more. The shape and number of the ore bodies 
formerly existing in this eroded zone can be only conjectured, but it is probable 
that they were large and numerous. The veins were evidently formed shortly after 
the close of igneous activity, while the volcano yet possessed a greater height than 
at present and had a more or less pronounced conical shape. 
If further development substantiates the dependence of the maximum devel¬ 
opment of the ore shoots on the depth from the surface irrespective of the elevation 
of the croppings, this would, according to the preceding explanation, be due partly 
