38 WILLIAM H. EMMONS 



known to have formed elsewhere by processes of secondary sulphide 

 enrichment, are clearly later than primary ore, there is a strong 

 presumption that they were deposited by cold descending waters. 

 If it can be shown, in addition, that they do not extend to the 

 bottom of the mine, but are related to the present topography of 

 the country, then this presumption may be regarded with consid- 

 erable confidence as confirmed. 



With respect to gold, the problem is difficult, because the 

 native metal is the only stable gold mineral known to be depos- 

 ited from cold dilute solutions. Consequently, the applicable 

 criteria are limited; and the vertical distribution of the richer 

 ore, though suggestive, is not in itself conclusive. Lindgren 

 ajid Ransome, in their studies at Cripple Creek, have shown that 

 the richer ore bodies may have in general a relationship to eleva- 

 tion, where there is little or no evidence of deep-seated secondary 

 enrichment. The maximum deposition by ascending hot waters 

 may be greater at one horizon than at another; and the rich ore, 

 though showing broadly certain variations with depth, is in no 

 way related to the water-table. If, however, it can be shown that 

 rich seams of ore cross the primary ore and do not extend down- 

 ward as far as the lowest level in the primary ore, but are related 

 to the present topography of the country, and if it is known that 

 the associated minerals which fill such openings are those which may 

 be deposited by cold waters, the evidence of their secondary 

 origin is practically conclusive. As already shown, seams of gold 

 with limonite and manganese oxides occur in such relations. 

 Similar ore frequently contains chalcocite and argentite also. 

 Such occurrences could with great confidence be attributed to 

 descending waters. 



In the practical application of such reasoning to gold-bearing 

 deposits it will sometimes be necessary to discriminate between 

 the oxidized manganiferous gold ore which has resulted simply 

 from the oxidation of a primary manganiferous ore like one con- 

 taining rhodochrosite, and that which has been deposited in 

 fractures in the sulphides lower down. In other words, it is 

 desirable to know whether rich manganiferous ore in the upper 

 part of a mine is residual from a primary ore body, and there- 



