192 GEOLOGY OF ASPEN MINING DISTRICT, COLORADO. 
common and characteristic form of ore contains numerous small veins of 
tetrahedrite, which often form crosses in the barite. This peculiar ore goes 
by the name of “crisscross spar.” The crosses are doubtless deposited at 
the intersection of microscopic cracks, and their occurrence shows that the 
metallic sulphide was later in deposition than the barite. This sulphide is 
highly argentiferous, and is always a valuable ore. On oxidation a small 
amount of green copper carbonate is formed from it, which stains the rock 
and is taken by miners throughout the camp as an evidence of rich ore. 
In places, however, this carbonate has been carried some distance and 
deposited in barren barite. This barren spar has then the appearance of 
ore, while it is actually destitute of value. 
From the phenomena in this mine the following deductions as to the 
manner of ore depositions may be made: First, the formation of the Della 
fault preceded the ore deposition, since this fault has been one of the most 
important factors in determining the locus of the ore. Second, since it is 
on the under side of the Della and other faults that ore has formed, and 
since on the upper side the rock is nearly barren, it is probable that the 
ore-bearing solutions were ascending, and that they came up along the 
Silver fault to the Della, at which point they deposited their metallic 
contents. Third, although the barite is the gangue of the metallic sulphide, 
it was deposited in large measure before the richer metals were, since in the 
crisscross spar and similar ores the valuable sulphides have been deposited 
in cracks which were formed in the barite subsequent to its crystallization. 
These cracks are purely mechanical, such as might arise from any strain in 
the rock. 
Although the Della fault existed previous to the ore deposition, yet 
there has been motion along it subsequent to this period. Indeed, there is 
evidence from the deformation of old raises and drifts that movement 
is going on along the fault at the present day. In most of the other faults 
there is also evidence of some movement subsequent to the ore deposition. 
This is true even of the Silver fault, where broken, angular fragments of 
ore may be found in the breccia. 
Pl. XLII, B, is a section through the Della mine, showing the actual 
occurrence of the ore. Although the shape of ore bodies is somewhat 
generalized, the main ones occur as represented, in connection with the 
Della and Smugeler faults, while the Silver fault has also been very 
fo) 
important in determining the locus of ore deposition. 
