GOLD AND SILVER DEPOSITS LINDGREN. 151 



A number of scattered deposits of this kind are found in the cor- 

 dilleran region of the United States, but they contribute only small 

 amounts to the total production. The most important occurrence is 

 the copper deposit of the United Verde mine in Arizona. Its copper 

 bullion yields a considerable amount of gold and silver. 



Compared to the deposits of the cordilleran or younger period in 

 North America the yield — both total and annual — is small. Out of 

 an annual gold production of about $130,000,000, the sum to be 

 credited to the old group of deposits is at present (1913) not more 

 than $10,000,000. 



Very little silver is obtained from the gold deposits, but a small 

 amount comes from the copper deposits of the Lake Superior dis- 

 tricts. Until the discovery of the Cobalt district in Ontario the pro- 

 portion of silver in the eastern region to the total output was even 

 smaller than that of gold ; but the native silver yielded by the deposits 

 of this district (of a type almost unique in America) has changed 

 this so that the old deposits of the East are now credited with about 

 800,000 kilograms out of an annual production for North America of 

 over 5,000,000 kilograms. The great output of the Cobalt district 

 emphasizes again how highly the precious metals may be concentrated 

 Pampas formation or by lavas of the same age. 



SOUTH AMERICA. 



In South America we find extremely similar geological conditions,, 

 but here the older group of deposits yields decidedly more gold than 

 that furnished by the belt of the Andes. On the other hand, the 

 silver production of the older deposits is insignificant. A somewhat 

 more detailed review will perhaps be acceptable. Figure 2 shows the 

 distribution of the deposits in South America. 



Gold deposits of the older type are known from Venezuela, the 

 three Guianas, Brazil, Uruguay, and Argentina. Except in the 

 Guianas they do not form continuous belts, but rather a series of 

 scattered occurrences separated by barren ground or by younger 

 transgressing fluviatile or marine deposits. South of the latitude of 

 Buenos Aires the deposits, if existing, are covered by the Tertiary 

 Pampas formation or by lavas of the same age. 



The northeastern region extends 650 miles from the Yuruari Basin 

 in eastern Venezuela to the Franco-Brazilian border of the Guianas. 

 The occurrences worked are mostly placers, to the formation of 

 which the conditions are very favorable; but quartz veins or min- 

 eralized dikes have also been exploited. The best example of the 

 veins is furnished by the great Callao mine in Venezuela, which, 

 during its life of 30 years (1865-1895), is said to have yielded $28,- 

 000,000 in coarse gold. Active exploitation of the placers and some 

 veins is going on in the three Guianas at present, the French colony 



