338 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
cides with the Walter lode. According to Penrose® the Raven vein is a sheeted 
zone which crosses the dike at a very small angle. The ore is described as occur¬ 
ring in the sheeted zone and also in the dike where the two coincide. 
The granitic ore of the Thompson mine occurs in very irregular masses, gen¬ 
erally similar to those described in the Ajax and Portland mines. These ore bodies 
are related to fissures and occur mainly on the east side of the basic dike, partic¬ 
ularly where two or more fissures intersect (fig. 36). The dike is small and irreg¬ 
ular in the Thompson ground and is not uniformly present, being at some points 
represented by a mere crack in the granite. The main fissures run approximately 
north and south, and probably correspond to the sheeted zone known farther 
north as the Walter lode. There are also a number of fissures on the east side of 
the basalt dike, which strike about N. 35° W., and a few fissures of northeasterly 
strike. The ore is not confined, as in the breccia, to the actual fissures, but extends 
out very irregularly into the granite, which is locally altered to a porous mass, 
containing much secondary feldspar and quartz, 
together with fluorite and pyrite. This metaso- 
matically altered porous granite constitutes the 
ore, which probably owes its value to the occur¬ 
rence of minute crystals of sylvanite or calaveritc 
in the small drusy cavities with which the rock is 
honeycombed. The tellurides, however, are rarely 
visible. 
Between the Elkton and Thompson shafts, on 
level 7, are two so-called flat ore bodies of some¬ 
what unusual type. The larger of these, which is 
almost midway between the two shafts, while irreg¬ 
ular in detail, is of generally oval plan and corres¬ 
ponds ver} T nearly to the plan of the small pliono- 
lite laccolith in which the ore occurs. Near its 
Fig. 3 G.-Pian of ore body in granite, Elkton western edge this phonolite is cut by the Elkton 
mine, level 4 , showing relation of ore to (Raven) basic dike. Near its eastern edge it is 
rlilrG qtiH fiQQiirpQ 
cut by a zone of fissuring commonly supposed to 
be the Walter lode. The ore occurs chiefly between these two north-south lines, 
which are about 120 feet apart. As the north-south fissures, which collectively 
represent the narrower sheeted zone of the Walter lode as known farther north, 
enter the northern edge of the phonolite mass they become very irregular, split 
up, and in part pass into nearly horizontal fissures. One set of such nearly hori¬ 
zontal fissures lying a few feet above level 7 constitutes a fairly definite sheeted 
zone within the phonolite, and is called the “flat vein.” The bulk of the ore occurs 
along this nearly horizontal sheeted zone, but is very irregular in thickness and 
frequently extends for varying distances above or below it along nearly vertical 
fissures. The ore in the “flat vein” proper, however, apparently averages about 
6 feet in thickness and is of relatively low grade. The most interesting peculiarity 
of this ore body is the fact that the ore is practically confined to the much-fissured 
mass of phonolite, nowhere extending for more than a few feet into the surround¬ 
ing breccia except along the Elkton dike to the south and along the main eastern 
a Sixteenth Ann. Rept. U. S. Geol. Survey, pt. 2, 1895, pp. 181-183. 
