GOLD AND SILVER DEPOSITS — LINDGEEN. 171 



appear at some places such as Guanaco, Batuco, and Cerro Blanco, 

 but compared to the deposits of other classes they are rare. This 

 is remarkable, when we consider the widespread occurrence in Cen- 

 tral America, Mexico, and the western United States of deposits of 

 the type of Pachuca, Guanajuato, the Comstock, and Tonopah, all 

 marked by certain well-defined characteristics. 



A large number of deposits in Colombia, Bolivia, and Chile ap- 

 proach the high-temperature veins by their content of pyrrhotite 

 and tourmaline. 



A curious fact is that, so far, no contact-metamorphic deposits are 

 described from Peru and Chile, although metamorphism of the 

 Cretaceous limestone by the granodioritic intrusions is often men- 

 tioned. In the Cordillera Real of Bolivia they would hardly be 

 expected, for there the intruded rock is generally a slate or sandstone. 



The poverty of the eastern front ranges of the Andes is paralleled 

 by the lack of precious metal deposits in the eastern or Rocky Moun- 

 tain Range of Canada. 



North America stands out in its richness of placer deposits derived 

 from veins of the Cretaceous intrusive period. In South America 

 there is no real counterpart to the great placers of California, Idaho, 

 Montana, Alaska, and Yukon Territory. 



The placer deposits of the Andes, which were locally rich, were 

 mostly found on the eastern slopes of the eastern ranges, and were 

 derived from gold-bearing veins in Paleozoic slates, with intruded 

 granite porphyries and allied rocks. 



Colombia stands out prominently as the most valuable gold-bearing 

 region of the Andes, from which, in spite of many difficulties, we may 

 expect a considerably increased production. 



The next region is formed by Peru and northern Chile — a region of 

 very numerous mining districts in which the mineralization is chiefly 

 in the direction of silver and copper with a few gold-bearing locali- 

 ties, which, however, do not seem to be able to achieve great pro- 

 duction. No doubt the silver output could be materially increased, 

 partciularly where silver occurs with copper. In looking over the 

 numerous gold-bearing districts of central Chile the student would 

 like to ascertain the conditions which in so favored a country have 

 held back the production to such a marked degree. 



The third region is formed by the Cordillera Real of Bolivia, with 

 its rich mineralization of tin, silver, and (subordinately) gold. Un- 

 doubtedly this region is one of the most promising in South America. 



Lastly, a striking contrast is presented between the two tips of the 

 cordilleran chain. At the north is Alaska, rich in gold, at the south 

 is the Patagonian cordillera, with its gigantic batholith, so promising 

 theoretically, so barren in reality. It is barely possible that theory 



