PROCESSES OF ALTERATION-OXIDATION. 
199 
The only generalization which can be safely deduced from all these data is 
that the limit of complete vein oxidation as a rule coincides with the water level, 
but that in many cases this process may partially, rarely completely, alter the 
veins for about 300 feet below this water surface. Owing to the peculiar conditions 
of underground drainage in Cripple Creek, it is unlikely that the water level has been 
subjected to great fluctuations. It may have been somewhat higher, but it is 
doubtful whether it ever stood much lower than when the district was first dis¬ 
covered, for, as stated in the chapter on the ground water, the volcanic mass holds 
water somewhat like a sponge in a cup. At any rate, no evidence indicating notable 
fluctuations can be adduced. 
STRUCTURE OF THE OXIDIZED VEINS. 
Thorough oxidizing decomposition will destroy the original structure of this 
vein. In sheeted lodes with many small parallel fissures and joints the latter may 
become effaced and the lode appears as a homogeneous brown, soft mass. In other 
cases a central seam may be retained and usually appears as a streak of soft, more 
or less impure kaolin; in other cases it maybe filled by white compact alunite, more 
rarely by jasperoid or opaline silica. Crusts of comb quartz, if originally present, 
lie included in the clayey seams, but neither the original fluorite nor the carbonates 
are ordinarily preserved. Ver} T rich oxidized ore sometimes fills the central cavities 
of the lode like a thick brown mud of limonite, kaolin, and quartz sand, and easily 
flows out when the vein is opened. Such material often fills the open seams in veins 
where the oxidation is only very partial, as in level 12 of the Gold Coin mine. When 
this level was unwatered, after having been allowed to fill up and stand for a long 
time, the floor was found to be covered by a thick mud up to 2 feet deep, which was 
said to have contained 2 ounces of gold per ton. The Dorothy vein here consists 
of one main seam in granite, coated with quartz, fluorite, and tellurides, besides 
some pyrite, zinc blende, and galena, and normally showing an open space in the 
center a couple of inches wide. 
OXIDIZING PROCESSES. 
In general oxidation tends to transform sulphides, sulphosalts, and tellurides 
to oxygen salts and native metals, both of which may, under certain circumstances, 
be further changed or carried away by surface waters. The silicates in the veins 
are changed to a few minerals most stable under atmospheric influences, i. e., 
kaolin, quartz, manganese dioxide, and limonite. Th6 carbonates of the earthy 
metals are carried away in solution, while those of manganese and iron are changed 
to oxides. As waters of acid reaction, frequently containing free sulphuric acid, 
prevail during oxidation of vein deposits, original quartz will not be attacked. 
New silica, generally hydrated, may be deposited by solutions derived from the 
decomposition of the silicates. 
The processes are more difficult to follow and to establish by means of analyses 
than those due to primary vein formation, for it seems to be a characteristic feature 
of oxidation to segregate the new minerals in larger masses and thus produce a 
less homogeneous product; this is no doubt due to the energetic action of oxygen 
