ORIGIN OF THE ORES. 
221 
t 
to this would perhaps be found in the hot waters of the Comstock lode, which are 
exceptionally rich in these constituents. 
The phonolite, syenite, and latite-phonolite contain appreciable quantities of 
sulphuric acid combined in the mineral hauynite of those rocks. The maximum 
amount found is 0.37 per cent. As this mineral is very easily decomposed under the 
influence of vein-forming solutions with the formation of sericite, it is evident that 
the waters would carry away soluble sodium sulphate. This origin of a part of the 
sulphates in the water may be considered established, but it is probable that the 
magma brought up from great depths and cooling at a level still far below the present 
mine workings gave ofl part of its sulphur trioxide, which ascended, together with 
so much of the magmatic water as was set free. 
CARBONATES. 
The metasomatic processes clearly indicate that the waters contained carbon diox¬ 
ide, either as dissolved gas, as bicarbonates, or as normal carbonates of the alkalies. 
It has been shown that an active decomposition of silicates proceeded in the rock 
accessible to the vein solutions. This could be explained under any of the three sup¬ 
positions, but the most plausible view seems to be that bicarbonates and an excess of 
carbon dioxide were present. The processes outlined indicate distinctly that sodium 
was carried away as a carbonate and that the waters gradually became more charged 
with this substance on their upward journey. The metasomatic processes observed 
also suggest that the waters originally contained more potassium, which gradually 
was substituted for the sodium in the rocks. 
No adequate explanation is available for the occurrence of C0 2 in the waters on 
the supposition that they were ascending surface waters. It can not have been 
leached from the volcanic rocks nor from the granitic rocks, since neither contain 
carbon dioxide or carbonates/' 
Inasmuch as all cooling volcanic rocks give off carbon dioxide and as emanations 
of this kind are abundant in the district to-day, it appears certain to us that the 
carbonates in the veins and in the altered rocks of Cripple Creek were formed from 
the carbon dioxide exhaled by crystallizing magmas. 
HYDROCARBONS. 
The purple color of the fluorite of Cripple Creek is very characteristic and often 
very intense; in thin sections parts of a crystal may be almost opaque, but the color 
is very irregularly distributed. Wyrouboff and Von Lasaulx have shown that this 
color is due to a hydrocarbon, and thus we may conclude that the waters contained 
some of this substance, the derivation of which must remain problematical. Possi¬ 
bly it is derived from the small quantities of bituminous coal occasionally found in 
the breccia. Hydrocarbons are by no means entirely unknown in mineral veins, the 
quicksilver deposits offering one conspicuous example. 
a The supposed derivation of carbon dioxide from fluid inclusions in the granite is altogether improbable; moreover, the 
explanation is quantitatively insufficient. Inclusions of carbon dioxide in granite-quartz are of comparatively rare occur¬ 
rence. Aqueous solutions assuredly predominate. 
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