THE AGENCY OF MANGANESE IN THE SUPERFICIAL 



ALTERATION AND SECONDARY ENRICHMENT 



OF GOLD DEPOSITS 1 



WILLIAM H. EMMONS 



I. INTRODUCTION AND SUMMARY 



Ferric iron, cupric copper, and manganitic manganese are 

 present in many mineral waters, and under certain conditions 

 any one of them will liberate chlorine from sodium chloride in 

 acid solutions. Nascent chlorine dissolves gold. Each of these 

 compounds releases chlorine at high temperatures, or in concen- 

 trated solutions. In cold, dilute acid chloride solutions, ferric 

 iron will not give nascent chlorine in appreciable quantity in 34 

 days, and cupric copper is probably even less efficient; but man- 

 ganitic compounds liberate chlorine very readily. In a cold solu- 

 tion containing only 1,418 parts of chlorine per million, consider- 

 able 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-man- 

 ganiferous ores. 



Gold thus dissolved is quickly precipitated by ferrous sulphate. 

 It is, therefore, 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 



1 Published, in a more amplified form, by permission of the Director of the U.S. 

 Geological Survey in Bull. 46, American Institute of Mining Engineers, 768-837, 

 October, 1910. 



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