562 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



sulphide, or sulpho-salts, of silver under the conditions of time and supply 

 which probably prevailed during the process of decomposition of the orig- 

 inal ore deposits. From such a solution the chlorine in the limestone might 

 have precipitated the silver at the same time that the sulphide of barium 

 was transformed into sulphate. 



Manganese. Another empirical generalization of the miners in this region 

 is that, where a large amount of manganese is found in the iron vein mate- 

 rial, rich chloride deposits are likely to be found in the immediate vicinity. 

 It is worthy of note in this connection that barium is a most frequent con- 

 stituent of manganese ores. The fact that the oxides of manganese when 

 treated by hydrochloric acid evolve chlorine is also suggestive. If it is 

 assumed that silver in its passage from sulphide to chloride passes through 

 sulphate, and that hydrochloric acid was formed in the surface waters, say, 

 by the action of sulphuric acid formed in some of the reactions that may 

 have taken place, the presence of manganese oxide would favor the libera- 

 tion of chlorine, which, in turn, would form chloride of silver from the sul- 

 phate when the latter came in contact with carbonate of lime, and the lime 

 be earned away as sulphate. 



OBES DEPOSITED AS SULPHIDES. 



That the ores were originally deposited as sulphides would legitimately 

 be assumed, from the almost universal observation in nature that such oxid- 

 ized ores pass into sulphides in depth. So generally is this accepted as a 

 rule in ore deposits that it would require special demonstration to prove 

 beyond a doubt that the native metals or their oxides and chlorides (except 

 perhaps gold, tin, and the platinum group of metals) are in any particular 

 case original, and not the result of secondary alteration from sulphides. 

 Analogy with the deposits in the neighboring Ten-Mile district affords more 

 direct evidence in favor of this assumption. Moreover, since the comple- 

 tion of the field work of this investigation, explorations on the dip in Car- 

 bonate and Iron Hill have proved that the oxidized ores actually do pass 

 into sulphides. As yet no systematic description of these sulphide deposits 

 has been published from which it may be learned whether the metals exist 

 exclusively as sulphides, but in the absence of any statement to the con- 

 trary it seems fair to assume that such is the case. 



