MANGANESE IN GOLD DEPOSITS 33 



In an acid solution containing some free chlorine, such as has been assumed 

 to be effective in dissolving gold, there would also be a tendency towards the 

 formation of permanganic acid. On the other hand, the production of the 

 chlorine necessarily results in the reduction of the manganese compound. 

 Now a manganous salt is known to react with permanganate to reproduce 

 Mn0 2 and this illustrates the tendency of manganese to pass with ease from 

 one stage of oxidation to another. The precipitation of manganese will occur 

 more and more as the solution loses its acidity. It is well established that 

 manganous salts in an acid environment are very stable; but in neutral or 

 alkaline solutions they oxidize more vigorously, one stage of their oxidation 

 being the manganic salt which hydrolyzes into Mn 2 3 • H 2 (manganite) , with 

 even greater ease than ferric salts into limonite. 



In these ways the migration of an acidic solution would result in the trans- 

 portation of both gold and manganese. But in a region of basic, alkaline, and 

 reducing environment the manganese would be reprecipitated, the free acid 

 neutralized, the chlorine absorbed by the bases and removed, and owing to 

 the accumulation of the ferrous or other reducing salts, the gold would be 

 reprecipitated. 



V. THE TRANSFER OF GOLD IN COLD SOLUTIONS 



i. Restatement of the processes as related to secondary enrichment. 

 — Every theory of secondary enrichment of the metals consists 

 essentially of three parts: (a) solution, (b) transportation, (c) 

 precipitation. 



a) As already stated, there is in the upper part of the ore 

 deposit, where oxidation prevails, abundance of ferric sulphate 

 and sulphuric acid. A little salt, NaCl, or other chloride, is gen- 

 erally present. The H 2 S0 4 , reacting upon NaCl, gives HC1, which 

 in the presence of Mn0 2 gives nascent chlorine, which dissolves 

 gold. Some manganese goes into solution as sulphate, but certain 

 higher manganates are possibly formed as well. 



b) This chemical system will move downward under hydro- 

 static head. If it comes into a zone containing pyrite it will react 

 upon the pyrite, and in the oxidation of the latter more iron sul- 

 phates and acid will be formed. If manganese dioxide is present, 

 or if permanganic acid has been formed, no gold will be precipi- 

 tated, and the system, with gold still in solution, will move to 

 greater depths before ferrous sulphate can become effective. 



c) But as the system moves downward, where no new sources 

 of oxygen are available, the excess of acid is removed. There are 



