ECONOMIC GEOLOGY CfF THE^BAGtllO DISTRICT. 441 



less efficient; but nianganitic compdunda liberate chlorine very, readily. In. a 

 cold solution containing only 1,418 parts of chlorii^e per million, considerable 

 gold is dissolved in 14 days when manganese is present. It should be expected, 

 then, that those auriferous deposits, the gangues of which contain" manganese. 

 Would show the effects of the solution and migration of gold more clearly than 

 non-manganiferous ores. 



Gold thus dissolved is quickly precipitated by ferrous sulphate. It is, there- 

 fore, natural to suppose that gold in such solutions could not migrate far through 

 rocks containing pyrite, since it would be precipitated by the ferrous sulphate 

 produced through the action of oxidizing waters, or the gold solution itself, upon 

 the pyrite. But the dioxide and higher oxides of manganese react immediately 

 upon ferrous sulphate, converting it to ferric sulphate, which is not a precipitant 

 of gold. Consequently, manganese is not only favorable to the solution of gold 

 in cold, dilute mineral waters, but it also inhibits the precipitating action of 

 ferrous salts, and thus permits the gold to travel farther before final deposition. 



These statements apply to the action of surface waters descending through 

 the upper parts of an auriferous ore deposit, since such waters are cold, dilut?, 

 acid (i. e., oxidizing) solutions. In deeper zones, where they attack other 

 minerals, they lose acidity, until the manganese compounds, stable under oxidiz- 

 ing conditions, are precipitated together with the gold. Thus, manganite, as well 

 as limonite and kaolin, is frequently found in secondary (i. e., dissolved and 

 reprecipitated ) gold ores. Moreover, in the precipitation of secondary copper 

 and silver sulphides, ferrous sulphate is generally formed; and, consequently, 

 the secondary silver or copper sulphides frequently contain gold. 



Those deposits in the United States in which a secondary enrichment in gold 

 is believed to have taken place are, almost without exception, manganiferous. 

 Since secondary enrichment is produced by the downward migration, instead of 

 the superficial removal and accumulation, of the gold, it should follow that both 

 gold placers and outcrops rich in gold would be found more extensively in 

 connection with non-manganiferous deposits; and this inference is believed to be 

 confirmed by field-observations. 



For the sake of brevity the process outlined above, can be represented 

 by a series of equations as follows: 



(1) H2S04+2NaCI=:2HCH-Na2SO, 



(2) 4HCl+Mn02=2Cl+MnCl,+2HjO 



(3) 3C1 (nascent) +Au=AuCl3 



(4) 2AuCl3+6FeO+3H20=2Au-f3FeA+6HCl 



Those are the simplest reactions which take place. However, there 

 are others which we shall not discuss here; they may be found in the 

 literature on the subject. 



It is well known, that the chlorination process was formerly very 

 generally used for the extraction of gold, and still is for certain classes 

 of ore. Analyses have shown repeatedly, that chlorine is generally 

 present in mine waters and in fact most underground waters. Even 

 water from very close to the surface has a small amount. An analysis 

 of mine water from one of the upper tunnels (close to the surface) 

 of the Headwaters mine showed some chlorine. Given plenty of time 

 even a small amount of chlorine M'ill take care of the comparatively 



