340 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
The ore in “basalt” presents at least two aspects. In the northern part of 
the mine the mineralized “basalt” is a compact gray rock, containing abundant 
microscopic crystals of pyrite thickly disseminated through it. The gold occurs 
in the form of calaverite in little veinlets of quartz which are usually a fraction 
of an inch in width and occur most abundantly near the walls of the dike. Some 
of these veinlets contain druses of fluorite, dolomite, and celestite, as well as quartz. 
In the southern part of the mine the altered “basalt” is light gray and has a porous 
texture, and the crystals of pyrite are larger. The rock contains numerous little 
cavities of dissolution lined with adularia and pyrite. The gold probably occurs 
with the pyrite as calaverite, but this mineral is rarely visible. 
Under the microscope this porous gra} T ore is seen to be an aggregate of adularia, 
sericite, apatite, and pyrite, with probably some calaverite. The sericite occurs 
in exceedingly minute form and its identification is not entirely satisfactory. The 
apatite, which is remarkably abundant, is in slender greenish-white prisms distinct 
in habit and appearance from the stout prisms of smoky apatite that occur in the 
latite-phonolite. The pyrite is chiefly in small pyritohedrons, which are sometimes 
clustered into aggregates. 
The ore found in the volcanic breccia also exhibits two varieties similar to 
those shown by the basaltic ore. In the northern part of the mine, in the Walter 
vein, the ore occurs as calaverite in the usual little quartz-fluorite veinlets of a 
sheeted zone in pyritized breccia. The calaverite is usually most abundant in 
the open vuggy portions of the veinlets and often associated with little hollow 
quartz pseudomorphs after celestite. In the southern part of the mine most of 
the ore in the breccia is found near the basalt dike. Much of this ore has an open 
cavernous structure, apparently due to the removal by solution of some of the 
finer interstitial material of the breccia. The remaining fragments are coated and 
cemented together by drusy incrustations of quartz and pyrite, with locally a 
little fluorite. Associated with these minerals, sometimes in crystals of visible 
size, occur calaverite, sylvanite, and molybdenite. The breccia fragments them¬ 
selves are more or less porous and contain irregular cavities of dissolution lined 
with quartz, pyrite, tellurides, and molybdenite. They also contain disseminated 
pyrite. In some places in the southern part of the mine, particularly in the first 
“flat stope” south of the shaft on level 7, fluorite is very abundant not only incrust- 
ing the fragments of the breccia, but often cementing it into a solid mass. Some 
of the fragments of breccia inclosed in the granular fluorite are rounded and embayed 
and appear to have been partially replaced by the fluorite. It is probable, how¬ 
ever, that their angles received a preliminary rounding by solution before the 
deposition of the flourspar. The microscope shows that between the fluorite 
and the phonolite fragments of the breccia there is usually an intervening zone 
of quartz and adularia. These two minerals have formed by metasomatic replace¬ 
ment of the breccia. 
Another variety of breccia ore occurring in the same flat stope consists of a 
dark-gray spongy mass, looking much like a frothy slag, which fills the interstices 
between masses of shattered breccia. The microscope shows that this porous 
crystalline material consists chiefly of adularia, pyrite, and an obscure opaque 
mineral, bluish gray in incident light, which is intimately associated with the 
