4 o WILLIAM H. EMMONS 



make these suggestions with respect to the character of the man- 

 ganese oxides associated with the rich ore, not because I think the 

 reactions which precipitate manganese are well enough understood 

 to give a positive paragenetic value to the oxidized manganese 

 minerals themselves, but in the hope that others will ascertain and 

 report the character of the manganese oxide associated with gold 

 in the deeper zone and in the residual products from that zone. 



5. Lateral migration of manganese salts from the country rock 

 to the ore. — Clarke's analyses 1 show that igneous rocks carry an 

 average of o. 1 per cent of manganese oxide, and many basic rocks 

 carry from 0.2 to 0.9 per cent. Where basic dikes have cut an 

 ore body, they doubtless contribute manganese to the waters 

 circulating in the deposit. The ore of the Haile mine, in South 

 Carolina, is cut by basic rocks; and the ore bodies of the Delamar 

 mine, in Nevada, are crosssed by a basic dike. Both of these 

 deposits show secondary enrichment of gold; and in both the 

 better ore is found along the dikes. In general, however, the 

 manganese from the country rock cannot safely be assumed to 

 have migrated extensively into the ore deposit, for many analyses 

 of mine waters do not show manganese; but where manganifer- 

 ous rocks are intimately fractured and rilled with seams of ore it 

 would be supposed that the reactions requiring manganese could 

 take place. 



In my own experience I have found only trivial stains of man- 

 ganese in those lodes where it was not present in the gangue of 

 the primary ore; and, in view of its wide distribution in igneous 

 rocks, I believe that the lateral migration of manganese into the- 

 ore under the conditions which generally prevail is very subordinate. 

 Though the amount so contributed may facilitate the solution of 

 gold, it is probably inadequate to form sufficient higher manganates 

 or similar salts to suppress effectively the action of ferrous sul- 

 phate. Under such conditions the gold could not travel to the 

 reducing-zone below the water level, but would be precipitated 

 practically at the place where it had been dissolved. 



6. Concentration in the oxidized zone. — -The concentration 

 of gold in the oxidized zone near the surface, where the waters 



1 Bulletin No. 330, U.S. Geological Survey (1908). 



