1 8 WILLIAM H. EMMONS 



similar to mine waters; and Nicholas Sankowsky and Clarence 

 Russell, in a seminar on the Chemistry of Ore Deposits, which I 

 conducted at the University of Chicago, compiled all available 

 analyses of waters from gold and silver mines in non-calcareous 

 rocks. A. D. Brokaw conducted a series of experiments, using cold 

 dilute solutions of compositions suggested by the analyses. He 

 performed other experiments applicable to the study of the pre- 

 cipitation of gold, showing the action of manganese dioxide on 

 ferrous salts. During the progress of this investigation, W. J. 

 McCaughey published his valuable paper on the solvent effect 

 of ferric and cupric salt solutions upon gold, 1 and this in a large 

 measure supplemented the work carried on in the seminars at the 

 University of Chicago. 



The experiments conducted by Brokaw showed that man- 

 ganese in the presence of chlorides and sulphates is very much 

 more efficient in the reactions dissolving gold than are the other 

 salts common in mine waters. To verify these results by field- 

 evidence, the review of the literature was taken up in greater detail, 

 and there also the results indicate a marked difference in the 

 behavior of the cold dilute mineral waters in the presence and in 

 the absence of manganese. 



Lindgren's classification of the gold deposits of North America 

 has been of great value in reviewing these deposits; since in the 

 United States manganese is rarely a gangue mineral in the primary 

 gold deposits as old as the early Cretaceous California gold veins, 

 whereas it is frequently present in appreciable quantities in those 

 deposits which were formed nearer the surface and which are 

 related to intrusives of Tertiary age. 2 I have not attempted to 

 review exhaustively the evidence afforded by deposits outside of 

 the United States with respect to the hypothesis suggested, but 

 some of these deposits appear to supply accurate confirmatory 

 data. 



In a statistical study of outcrops, to ascertain whether gold 

 is more extensively leached in manganiferous lodes than in the 



1 Journal of the American Chemical Society, XXXI, No. 12, 1261-70. 



2 W. Lindgren, "The Relation of Ore-Deposition to Physical Conditions," Eco- 

 nomic Geology, II, No. 2, 105-27 (Mar. -Apr., 1907). 



