222 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
HYDROGEN SULPHIDE. 
The abundance of pyrite, which without notable addition of iron has been 
found throughout the rocks affected by the solutions, shows that hydrogen sulphide 
or sodium sulphide, or both, must have acted on the iron oxides and silicates. This 
is amply confirmed by microscopic examination. The widespread pyritization, indi¬ 
cating great capacity for diffusion on the part of the sulphur-bearing compound, 
would indicate that H 2 S as a gas dissolved in water was the chief reagent. But if 
sodium carbonates were present sodium sulphydrate would form;" this, by heating 
or by the presence of certain metallic sulphides, may partly change to Xa 2 S, so that 
it is quite possible that both substances were active. 
Neither the granitic nor the phonolitic rocks are knowm to contain sulphides 
which could have jdelded the necessary sulphur. Hydrogen sulphide might, of course, 
have formed by the reduction of sulphates by organic matter; but very large quan¬ 
tities of sulphur compounds were evidently active at Cripple Creek, and here also 
w T e would attribute the sulphur to emanations from cooling intrusive magmas. This 
position is strengthened by the fact that sulphur in various forms is usually given 
off during eruptions of lavas at the surface. 
IRON. 
It has already been pointed out that the quantity of pyrite in the veins is very 
small. In the ores this mineral rarely exceeds 5 per cent. (See analyses, p. 172.) 
Most of this pyrite is contained in the altered country rock, which in mining can not 
be separated from the tellurides and quartz of the fissure filling. The iron in this 
pyrite is almost wholly derived from the original iron silicates in the rock. Probably 
less than 10 per cent of the pyrites in the ores was deposited in the filling of the 
fissures. We arrive thus at the conclusion that the solutions contained very little 
iron in a condition to form pyrite. 
CALCIUM AND MAGNESIUM. 
Dolomitic carbonates are of widespread occurrence in the altered rocks, but are 
nowhere present under conditions suggesting an introduction of either of these metals. 
The silicates of calcium and magnesium are simply converted into carbonates, and 
in some cases the percentage of the former metal is notably decreased, giving evi¬ 
dence of a partial leaching by the vein-forming waters. It is a noteworthy fact 
that the mines situated in areas of syenite and latite-plionolite, the rocks in which 
lime is most abundantly present, contain the largest amounts of dolomitic carbonates, 
both in the altered rocks and as filling of seams. There is thus strong evidence that 
the lime and magnesia contained in the v T ater were, to a large extent, at least, 
derived from the surrounding country rock. As the waters contained carbondiox- 
ide, the metals must have been present chiefly as bicarbonates. 
ALKALI METALS. 
The substitution of potassium for sodium in the newly formed silicates suggests 
that the waters were originally richer in the former metal, but this can not be said 
o Becker, G. F., Geology of the quicksilver deposits of the Pacific slope: Mon. U. S. Geol. Survey, vol. 13, 1S88, p. 427. 
