THE TELLURIDE ORES. 1121 



its solutions, forming metallic gold, the tellurium at the same time going 

 into solution. Further, they have proved that the presence of any of the 

 soluble tellurides, including hydrogen telluride, is sufficient not only to throw 

 the gold out of solution, but to prevent it from getting into solution. Other 

 soluble salts, where tellurium acts as an acid, are the tellurites and tellurates. 

 Tellurous oxide or acid is also sparingly soluble. All of these compounds, 

 like tellurides, precipitate gold from its solutions in a metallic form, not as 

 telluride. From the foregoing it appears that if tellurium compounds in 

 which tellurium is a part of the acid are essential for the formation of the 

 tellurides of gold, these tellurium salts and the gold have come into the 

 trunk channel from separate sources. They could not have traveled 

 together; else the gold would have been thrown from the solutions before 

 reaching the trunk channels. 



It is to be remembered that tellurium, besides acting in an acid, also 

 acts as a metal to the halogens (chlorine, bromine, and iodine). The 

 telluric compounds of this class, such as telluric chloride (TeCl 4 ), beino- 

 completely saturated, so far as tellurium is concerned, have no reducing 

 power, and they may therefore travel with gold solutions. But the tellurous 

 combinations with the halogens, such as tellurous chloride (TeCL), can not 

 travel with gold, for Lenher has shown that such tellurous salts in the 

 presence of water and its compounds react upon the water, producing 

 metallic tellurium and telluric chloride according to the following equation: 



2TeCl,+H,0=Te+TeCl i +H 2 



The metallic tellurium would then reduce the gold, which would therefore 

 be precipitated before reaching the trunk channels. 



The almost invariable association of tellurides with sulphides, already 

 noted, naturally leads to the suggestion that the same conditions were 

 favorable to the deposition of the sulphides and the tellurides. In this 

 connection the occurrence at Cripple Creek is especially interesting. Mr. 

 Moore, consulting engineer of the Portland mine, informs me that in this 

 district near the surface the values are found in the oxidized zone as native 

 gold; that deeper, the values are mainly in the tellurides, the associated 

 sulphides being very lean; and that still deeper the values are found both 

 in the tellurides and in the sulphides of iron. The depth at which the 

 sulphides at the Portland mine begin to have value is about 200 meters. 

 mon xlvii — 04 71 



