MINES OF BATTLE MOUNTAIN, EAST GROUP. 
447 
of granite. This is confirmed by the microscope, which shows the material to con¬ 
sist chiefly of finely comminuted microcline and quartz, evidently derived from the 
granite, with usually a little secondary quartz, fluorite,-and pyrite. No volcanic 
fragments were detected in this material. The Bobtail vein is therefore a fissure zone 
which follows not a dike, but an 
older fissure filled with brecciated 
material. This original fissure 
probably dates from the volcanic 
period, but whether it was filled, 
like the great crater, with particles 
which had previously been blown 
into the air, or by the trituration 
of the wall rock by movement along 
the fissure, could not be deter¬ 
mined. The breccia of the fissure 
apparently passes without break 
into the breccia filling the throat of 
the old Cripple Creek volcano. 
Another deposit, unique in the 
Portland mine, and indeed in the 
district, is the Anna Lee chimney 
or stock. No work has been done 
on this deposit for years and little 
can be added to the descriptions 
given by Penrose" and later by 
V G. Hills. 6 
Mr. Hills says: 
This ore chimney occupies the pipe or neck 
of an extinct mineral spring. It follows one of 
the main basalt dikes and extends downward, 
as far as yet followed, some 1,130 feet. It 
has several remarkable features. It is nearly 
circular in plan and varying from 15 to 30 
feet in diameter, and extends nearly vertically, 
but with a sort of a corkscrew form, into the 
earth. The ore filling this pipe consists of 
well-rounded pebbles cemented together with 
material which is composed, for the most part, 
of the same rock pulverized. This ore con¬ 
tains from 9 to 15 per cent of lime and 7 per 
cent iron, thus differing from any other ore 
body in the district. It is also a remarkable feature that the gold values contained in the pebbles and in the 
cementing material are about the same. The values are distributed with remarkable evenness through the 
mass, thus forming a notable exception to the rule of gold deposits. 
Mr. Hills gives a stereogram of the Anna Lee ore shoot, which is reproduced 
in fig. 58. 
Fig. 58.—Stereogram of Anna Lee ore chimney. (After V. G. Hills.) 
a Mining geology of the Cripple Creek district, Colorado: Sixteenth Ann. Rept. U. S. Geol. Survey, pt. 2,1895. pp. 205-207. 
5 Eighth Ann. Rept. Portland Gold Mining Company, 1902. 
