MANGANESE IN GOLD DEPOSITS 43 



confirm this statement; for, if calcite is present, gypsum is formed 

 by the reaction of H 2 S0 4 on lime carbonate; and, if the wall- 

 rocks are sericitic, kaolin is formed by the acid reacting upon 

 silicates, the potash going into solution as sulphate. The abun- 

 dant ferrous sulphate must quickly drive the gold from solution, 

 and it apparently follows that there may be no appreciable enrich- 

 ment of gold below the zone where chalcocitization is the prevail- 

 ing process. 



VI. REVIEW OF MINING DISTRICTS 



i. If gold is more readily dissolved in manganiferous deposits, 

 it would be supposed that placers form less readily from pyritic 

 manganiferous lodes than from lodes containing no manganese. 

 If, in areas where the waters carry appreciable chlorine, placers 

 have formed as extensively from such lodes as from lodes free 

 from manganese, then the hypothesis fails. 



2. The manganiferous lodes, in areas of chloride waters, as in 

 the undrained areas of the Great Basin, should in general show 

 less gold at the outcrop and in the upper portion of the oxidized 

 zone than below. In silver-gold deposits, however, silver, on 

 account of the insolubility of the chloride, may remain, or be 

 concentrated, in the oxidized manganiferous zone. Bunches of 

 rich gold ore carrying oxidized manganese in the oxidized zone 

 are not necesssarily fatal to the theory; for, as already stated, these 

 are probably residual from the zone of secondary enrichment. 

 An extensive enrichment in gold of the oxidized manganiferous 

 ores at the surface, which are shown not to be residual from the 

 zone of secondary ores, would indicate that the selective processes 

 lack quantitative value, if the waters carry chlorine, and if the 

 primary ores, from which the manganiferous oxidized ores are 

 derived, carry appreciable pyrite to supply sulphate. 



3. If in certain lodes gold migrates below the water-table, it 

 should be precipitated quickly by ferrous sulphate. But Mn0 2 

 converts ferrous sulphate to ferric sulphate, which does not pre- 

 cipitate gold. Hence, Mn0 2 favors the solution of gold, and 

 converting "the ferrous salt to ferric sulphate removes the pre- 

 cipitant. Consequently, if auriferous lodes show enrichment in 



