ORIGIN OF THE ORES. 
225 
the tellurides, as well as concerning the water circulation, make the derivation by 
leaching seem improbable (p. 224), and we therefore fall back upon the third alter¬ 
native, namely, to consider the gold, the tellurium, and perhaps the other rarer 
sulphides as emanations from a cooling magma under the influence of diminishing 
pressure. 
RELATIVE QUANTITY OF SULPHIDES. 
Little is to be said of the various sulphides and sulphosalts, except that they 
must have been present in the water and that according to the experiments of 
Becker" and Doelter 6 they were probably dissolved as sulphides in sodium sul¬ 
phide. Among them are sphalerite, galena, stibnite, tetrahedrite, and molybdenite, 
corresponding to zinc, lead, copper, antimony, and molybdenum. Zinc is on the 
whole most abundant, but the proportion does not appear to rise in many cases 
above 0.75 per cent and in places the metal is entirely absent. The other elements 
occur on the average only in minimal amounts, rarely rising above 0.1 per cent 
and more commonly about 0.02 per cent or 0.01 per cent. The quantity of tel¬ 
lurium and even of gold is often found to exceed that of these metals. A solution 
may of course contain sulphides and tellurides without their being precipitated. 
It is assumed that the precipitation is due to slowly changing physical conditions. 
But as the necessary requirement for precipitation is supersaturation, and as some 
of each sulphide has been precipitated, it is reasonable to conclude that the 3 r were 
precipitated in proportion as they were abundant in the solution. Such a pro¬ 
portion, however, if the metals have been leached from the volcanic rocks by 
atmospheric waters, would be highly remarkable. It would indicate that the 
waters contained as much molybdenum as copper and more tellurium than either. 
The average amount of iron deposited as sulphide in open spaces is but slightly 
larger than the tellurium deposited as tellurides. If these elements had been 
gathered by leaching we would be justified in concluding that .they existed in 
approximately similar proportions in the rock from which they were obtained. 
This may be looked upon as a reductio ad absurdum. 
Xo such difficulties appear when the metals are regarded as sulphide exhala¬ 
tions from cooling magmas, for here we have no separation according to solubility 
in water, but only according to the ability of a magma to hold certain substances 
in solution under rapidly changing physical conditions. That rare elements can 
be concentrated by this process is well shown by many pegmatite dikes. 
CONCLUSIONS. 
The waters which deposited the Cripple Creek veins were alkaline solutions 
containing the following compounds and ions, either free or in various combinations: 
SiO,, CO,, H 2 S, C0 3 , SO,, S, Cl, F, Fe, Sb, Mo, V, W, Te, Au, Ag, Cu, Zn, Pb, Ba, 
Sr, Ca, Mg, Na, and K. We believe that at least some of the Si0 2 , SO,, Cl, Fe, 
Ba, Sr, Ca, Mg, Xa, and K, are derived from the volcanic rocks by leaching of 
waters, while the remaining metals, as well as C0 2 , H 2 S, S, and some Si0 2 , Cl, and 
Iv were more probably separated from intrusive cooling magmas at considerable 
depth, and brought up as solutions in magmatic water given off in the same manner. 
a Mon. U. S. Geol. Survey, vol. 13, 1888, chap. 15. 
b Tschermaks Min. u. petrogr. Mittheilungen, vol. 2, 1889, p. 319. 
