46 WILLIAM H. EMMONS 



these deposits (Comstock, Exposed Treasure, Tonopah); it is 

 very sparingly present in others (Little Rockies) ; in still others 

 (Goldfield) it is almost entirely absent. 



A few small placers are associated with the manganiferous lodes, 

 although at some places they seem to have been derived from 

 veins near by which are not manganiferous. Many of the Cali- 

 fornia veins carry rich ore at the very surface, but the Tertiary 

 gold veins are generally richer in gold a few feet below the surface 

 than at the outcrop. Doubtless, many of them would have been 

 overlooked if it had not been for the concentration of horn silver 

 and argentiferous pyromorphite at the surface. 



It thus appears that practically all of the manganiferous gold 

 deposits of the United States, so far as they have been described, 

 may be included in groups 3 and 4; that nearly all described 

 deposits where relations indicate a migration of gold belong to 

 the same groups; that placers are much less abundantly devel- 

 oped than in groups 1 and 2; and that outcrops less frequently 

 supply gold; that secondary enrichment below the water-table, 

 if carried on at all, proceeds with extreme slowness in groups 

 1 and 2, but may be more pronounced in deposits of groups 3 and 

 4. Not all deposits of 3 and 4 carry manganese, however, and 

 those which do not carry it show relationships more nearly approxi- 

 mating those which hold in the California gold veins. The migra- 

 tion of gold in the more important auriferous deposits of the 

 United States is discussed in some detail in Bull. 46, Amer. Inst. 

 Mining Engineers, 817-37. 



