1174 A TREATISE ON METAMOEPHISM. 



oxidized and traveled down, the first as gold chloride or a similar salt, and 

 the tellurium as telluric chloride or a similar salt. Below the level of 

 ground water these two compounds would both be reduced where they 

 came into contact with the base sulphides. At the moment of reduction 

 they may have united, and thus the rich tellurides of gold may have been 

 formed. It is thought possible that precipitation was caused in this manner 

 rather than by previously existing lean tellurides of the first concentration, 

 because in the deeper workings of some of the mines the tellurides seem to 

 be very subordinate to the sulphides, and the values are mainly in the 

 sulphides. If the above suggestion proves correct, in the Cripple Creek 

 district the deep, rich tellurides represent a concentration of tellurium as 

 well as of gold. If the amount of tellurium for the upper 500 meters or 

 more of the lodes was not originally greater than in the deeper workings, 

 the tellurium now found in the deep rich horizon must have had a much 

 wider original vertical distribution." 



The formation of the rich free gold near and above the level of ground 

 water in the Cripple Creek district is not materially different from the 

 formation of such products elsewhere. As denudation continued the 

 enriched sulphides and tellurides rose above the level of ground water, 

 the sulphur and tellurium were there oxidized, and some of the free gold 

 was left behind. This chemical process was accompanied by residual 

 concentration. 



CONCENTRATION BY REACTION UPON SULPHIDES COMPARED WITH METALLURGICAL CONCENTRATION. 



One of the more common processes of metallurgy for the separation 

 of gold, silver, copper, and lead from iron is based upon the principle 

 explaining the second concentration given on preceding pages, viz, that 

 iron holds sulphur less strongly than the other elements named. The 

 sulphureted ores are imperfectly roasted, thus partly oxidizing them to 

 oxides and sulphates. The ores are then smelted in a furnace with a flux. 

 The oxides of the valuable metals and the sulphates react on the remaining 

 sulphides of all the metals, producing a matte containing the sulphides of 

 the valuable metals. The iron gets all or nearly all of the oxygen; the 

 iron oxide unites with the fluxes and passes into the slag. 



" Since the above was in page proof I have been informed by Dr. Lindgren, who has closely 

 studied the district, that he doubts the existence of enriched deep tellurides at Cripple Creek. If 

 these tellurides do not exist the two preceding paragraphs need radical modification. 



