PROCESSES OF ALTERATION-OXIDATION. 
197 
ORIGINAL WATER LEVEL. 
According to the few data available, the original water surface of the district 
stood at an elevation of about 9,500 feet in the western part. Doubtless it rose 
slightly underneath the Bull Cliff region, reached 9,557 (910 feet below the surface) 
in the Isabella mine, and is even reported at 9,730 (516 feet below the surface) in 
the Hull City mine. In the southeastern part of the district the original water 
level in the Portland stood at 9,459, or about 540 feet below the collar of Xo. 1 shaft; 
in Stratton’s Independence at 9,576, or 274 feet below the surface; and in the Gold 
Coin mine at 9,403, or 368 feet below the surface. 
ROCK OXIDATION. 
As stated above, the general oxidation of the rocks does not correspond to the 
water level, but ceases long before the latter has been reached and usually at a 
depth of at most 200 feet below the surface; sometimes, and especially in the case 
of massive rocks, such as granite or latite-phonolite, fresh material appears a very 
short distance below the surface. At Stratton's Independence the oxidation of 
the breccia is only partial at a depth of 100 feet below the surface. To the general 
rule given above there are one or two notable exceptions. Over a large area on 
Globe Hill, embracing the Deerhorn, Lady Stith, Plymouth Rock, and Ironclad 
shafts the breccia is throughly oxidized and traversed by irregular systems of joints 
and short fissures. Globe Hill is opened in depth by the Chicago tunnel, the portal 
of which is located near the Abe Lincoln mine and has an elevation of about 9,700 
feet; the total length is 4,200 feet and it extends to the vicinity of the Plymouth 
Rock shaft. For the greater distance from the portal the tunnel is in unoxidized 
breccia, but 1.200 feet from the breast evidences of oxidation begin to be apparent, 
and near the end, about 700 feet underneath Globe Hill, the breccia is entirely 
disintegrated, forming a soft, clayey, red material which necessitates stout timbering. 
This condition extends at least to the bottom of the Plymouth Rock shaft, about 
150 feet below the tunnel level, or an elevation of 9.550 feet. Similar complete 
oxidation reaches at least to 700 feet below the surface in the Ironclad shaft. In the 
middle of this area is located the Deerhorn shaft, the lowest level of which is 565 
feet below the surface. Exploratory crosscuts extend from this shaft 600 or 700 feet 
in several directions without change of formation. A mass of gypsum, with some 
fluorite and a little pyrite, is exposed in the lower 300 feet of the shaft (p. 284). 
Oxidized material appears to surround it on all sides. The explanation of this 
unusually deep oxidation is probably that extensive shattering preceded a local 
and very intense thermal-spring action, which by dissolving much material rendered 
the breccia so porous as to fall an easy prey to oxidizing processes. A somewhat 
similar case is that of the Wild Horse mine, where the shattered and pyritic granite 
breccia, as well as the vein contained in it, is entirely oxidized to a depth of 1,150 
feet, or to an elevation of 9,500 feet. 
