224 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
be reduced to tellurous salts, which, as already explained, would decompose into metallic tellurium and telluric 
salts, and the tellurium would precipitate the gold. Under these or some other conditions, the gold and 
tellurium go down together, with a definite composition, and thus form the tellurides. 
We are not able to agree with these conclusions; on the contrary, we think 
the evidence from the general occurrence is very strong that gold and tellurium 
existed together in the solutions, and, with the assistance of Dr. W. F. Hillebrand, 
we have been able to show that they do so exist in a combination of two solvents 
which are believed to have been contained in the alkaline vein-forming solutions— 
i. e., sodium sulphide and sodium carbonate. 
Doctor Hillebrand sums up his experiments as follows: 
The first attempts with bicarbonate of soda solution at ordinary temperatures led to the erroneous conclu¬ 
sion that this solvent exerted an appreciable action upon the telluride. It was found, however, that the tel¬ 
lurium going into the,solution undoubtedly came from a coating of tellurite upon the calaverite grains, for subse¬ 
quent treatment of this same powder with the bicarbonate solution gave entirely negative results. That 
such a coating existed upon the calaverite grains was rendered further evident by the fact that a first treat¬ 
ment with hydrochloric acid showed tellurium in solution, while subsequent treatments of the same powder 
gave negative results. A further experiment with bicarbonate solution on calaverite powder thus purified 
was made by sealing mineral and solution in a glass tube, after expelling the air by a current of carbon 
dioxide. The tube was then heated to 150° for many hours. When opened and the powder separated from 
the solution by filtration, no tellurium whatever could be detected in the filtrate. 
The case was quite dilferent, however, if, instead of the bicarbonate solution, one saturated to a greater 
or less extent with hydrogen sulphide was employed. Under these conditions it was a matter of ease to detect 
tellurium, as well as gold, in the filtrates, even after only one or two hours’ exposure at room temperature 
with exclusion of air. It was found possible to estimate quantitatively, with a fair approach to accuracy, 
both the tellurium and the gold. The amounts thus found accorded fairly well with the preparations in 
which these two elements combine to form the mineral calaverite. The absolute amounts were, in one case, 
for tellurium, 0.0011 g., for gold, 0.0008 g. The amount of calaverite which furnished the above quantities 
of tellurium and gold to the alkaline solution was approximately 0.4 g. in a moderately coarse state of division. 
As to the actual conditions existing in these solutions of calaverite, we are 
still in the dark; doubtless a partial dissociation has taken place, as in most electro¬ 
lytes, but we incline to the belief that the tellurides were dissolved as such and 
precipitated by supersaturation due to various physical changes. The synthesis of 
the tellurides offers a fruitful field of investigation which circumstances have not 
allowed us to enter. 
Concerning the derivation of the gold telluride we confess to a lack of con¬ 
clusive evidence. It may have been leached from the granitic rocks or from the 
volcanic rocks bj r ascending surface waters, or it may have been separated as 
exhalations from cooling intrusive magmas and brought up by ascending surface 
waters or by magmatic water. That it was leached from granitic rocks by surface 
waters is exceedingly improbable, for this hypothesis furnishes no explanation of 
the confinement of the deposits to the volcanic area. Whether the volcanic rocks 
now contain gold and tellurium, and if so, whether the surface waters would be 
able to extract them, we can not say. Determinations of gold in the volcanic 
rocks now accessible on the surface or in the mines would have little value, owing 
to the general permeation by solutions that has taken place and to the fact that 
an almost invisible seam in the rock might contain enough telluride to vitiate the 
result. Considerations concerning the quantitative relations of the sulphides and 
