CHAPTER VII-STRUCTURE OF THE GOLD DEPOSITS. 
PRINCIPAL TYPES OF DEPOSITS. 
With few exceptions the ore bodies, of whatever shape, are causally connected 
with fissures. The 'most important types of auriferous ore bodies occurring in the 
district are: 
(1) Tabular in form and strictly following simple fissures or sheeted zones. A 
subtype comprises lodes in which the sheeted zone follows “basalt” or phonolite 
dikes. 
(2) Irregular bodies adjacent to fissures and formed by replacement and 
recrystallization of the country rock, usually granite. 
These types are not always sharply distinct, but may be connected by deposits 
of intermediate character. 
All the ore bodies, of whatever type, exhibit certain common features which 
serve to distinguish the deposits of Cripple Creek from those of most other mining 
districts. In the first place, the actual openings in the rocks available for the depo¬ 
sition of ore are, as a rule, remarkably narrow. In the second place, the amount of 
material carried in the mineralizing solutions and deposited as gangue and ore 
minerals was comparatively small. In consequence of these two conditions, the 
district contains no such massive veins, solidly filled with quartz or other vein 
minerals, as are characteristic of the San Juan region in Colorado or the Mother Lode 
region in California. Even the small fissures of the Cripple Creek district are 
seldom completely filled, but have a characteristic open or vuggy structure. Where 
the fractures are unusually wide, or where the rocks are extensively shattered, as in 
the Midget and Moose mines, the small volume of available vein matter is particularly 
noticeable. The walls of such fractures and the fragments of the shattered rock are 
often merely coated with a thin deposit of quartz, fluorite, and other minerals. As 
the rich telluridps were usually among the minerals last to form, and are particularly 
abundant on the walls of the vugs, it is probable that had quartz, fluorite, or other 
gangue minerals been more abundantly deposited, the ores would have been of much 
lower grade. 
LODE FISSURES. 
DISTRIBUTION. 
As elements of geological structure, the lode fissures of Cripple Creek are 
exceedingly inconspicuous. They are marked neither by bold outcrops of quartz 
nor by superficial bands of ferruginous gossan. They seldom fault perceptibly the 
structures which they traverse and they are not sufficiently different from the mass 
of the rocks, as regards resistance to erosion, to have perceptibly influenced the 
topographic development of the district. It is this obscurity that, as already 
153 
