MINERALOGY OF THE FISSURE FILLINGS. 
175 
Cripple Creek lodes. Biotite, associated with pyrite, is known only in the abnormal 
Dolly Varden vein where exposed in the Ophelia tunnel. 
The gold in the unoxidized ores of the lodes occurs in combination with tellurium 
as calaverite, sylvanite, or krennerite. Calaverite is the most abundant telluride 
of the three, krennerite being apparently the least common. The identification of 
the various tellurides usually requires refined crystallographic and chemical work, 
though calaverite can sometimes be distinguished from sylvanite by its more yellow 
color. As such refinement is not practicable in every case, the relative abundance 
of the three species, particularly of krennerite and calaverite, which have approxi¬ 
mately the same composition, remains somewhat in doubt. The occurrence of 
native gold, while not unknown in the unoxidized parts of the lodes, is so rare as to 
be regarded as a curiosity. 
For more detailed descriptions of the minerals occurring in the lodes, and for 
an account of the products resulting from the oxidation of the original fissure 
fillings, the reader is referred to the sections on the mineralogy of the district and on 
the processes of oxidation. 
The order in which the vein minerals were deposited (paragenesis) is not the 
same in all fissures nor even in all parts of one fissure. In many of the lodes, more¬ 
over, a mineral which was deposited near the wall and which therefore belongs to 
an early stage in the process of vein growth occurs also in the vugs along the medial 
portion of the crustified vein. Pyrite, for example, while in many cases one of the 
earlier of the vein minerals, is sometimes found in small crystals implanted upon 
the quartz, fluorite, or dolomite which line the vugs, and in the C. Iv. & N. mine it 
incrusts crystals of calaverite. Other minerals which are known to have formed 
successively in the same vein are quartz, fluorite, sphalerite, and tetrahedrite. 
As a general rule the tellurides were formed during the later stages of fissure filling, 
as is shown by their prevalent occurrence as projecting crystals in the vugs. Occa¬ 
sionally, however, tellurides have crystallized simultaneously with quartz, fluorite, 
or dolomite at an earlier stage, so that they are embedded in a compact gangue of 
one or more of these minerals, as in the El Paso and C. K. & N. mines. Sphalerite 
and galena, occasionally associated with barite, as in the Tillery vein of the El Paso 
mine, are usually older than any tellurides that may accompany them, although in 
the Abe Lincoln mine the difference in age seems to be slight. Dolomite, fluorite, 
and quartz are frequently intercrystallized in a way to show that they were formed 
at the same time. In some cases a definite sequence is discernible, as in the Hidden 
Treasure vein, where fluorite w r as followed by dolomite and dolomite by quartz. 
In other cases, as w r as observed in ore from the Findley mine, dolomite is incrusted 
by fluorite. Specimens from the Doctor-Jackpot vein show 7 an early crystallization 
of pyrite and tetrahedrite, followed by dolomite upon which tetrahedrite occurs 
again as implanted crystals, followed by celestite, quartz, and pyrite in the order 
named. While celestite is sometimes one of the youngest minerals in the veins, as 
observed, for example, in the C. K. & N. vein, it is often altered to hollow 7 siliceous 
pseudomorphs and these in turn embedded in quartz. It was evidently formed 
at more than one period, as will be seen when the structure of the Howard flat vein 
is described, and in the Elkton mine (Walter vein) its relation to quartz carrying 
calaverite is such as to indicate that the celestite is the older mineral. Specimens 
