44 WILLIAM H. EMMONS 



the deeper zone but related to the present surface of the country, 

 the manganiferous lodes should, the other favorable conditions 

 provided, show greater differences in values with respect to gold 

 than lodes free from manganese. 



Gold provinces of the United States. — As Lindgren 1 pointed out 

 in 1902, the principal gold deposits of the United States may be 

 divided into four groups. The deposits of each group belong mainly 

 to one metallogenetic epoch, and certain relationships are clearly 

 shown. This classification, which has thrown much light on the 

 genesis of the deposits, is useful as an instrument for study and for 

 comparison of the deposits with respect to the problem of the 

 migration of gold in them. 



1. The Appalachian gold deposits, and those of the Home- 

 stake type in South Dakota, are the most important representa- 

 tives of the oldest group. These deposits generally yield placers, 

 are usually low grade below the water level, and are singularly free 

 from bonanzas. They are, in general, not greatly leached near 

 the surface, and may have been enriched by the removal of other 

 material more rapidly than gold. At only one of them, the Haile 

 mine, in South Carolina, it is thought probable that gold has 

 been carried below the water level. Judging from descriptions, 

 practically all of these deposits are free from -manganese. 



2. The California gold veins and related deposits in Nevada 

 (Silver Peak) and in Alaska (Treadwell, etc.) are younger than 

 the Appalachian deposits, and were probably formed in the main 

 in early Cretaceous times. These deposits, where physiographic 

 conditions are favorable, have generally yielded rich placers. At 

 many places, moreover, the ore is worked at the very surface, and, 

 there is very little evidence of the migration of gold to the deeper 

 zones. In the places where detailed work has been done, rhodo- 

 chrosite is never a gangue mineral, although manganese oxide does 

 occur in traces in the country rock, and rhodochrosite is found in a 

 few places in veinlets in the mining districts but not associated with 

 the gold veins. 



3. The deposits of the third group are later than the early 



1 "The Gold Production of North America," Trans., XXXIII, 790-845 (1903); 

 "Metallogenetic Epochs," Economic Geology, IV, No. 5, 409-20 (Aug., 1909). 



