GOLD AND SILVER DEPOSITS LINDGREN. 165 



" saddle reef " type inclosed in slates and sandstones.^ The quartz 

 and free gold are accompanied by pyrrhotite, arsenopyrite, and 

 pyrite. They thus belong to the intermediate type accompanying 

 intrusive rocks. The ore is of low grade. 



Bolivia points with pride to its production of silver. The yield 

 from 1553 to 1910 is stated to have been 48,800,000 kilograms, to 

 which the mines of Potosi are said to have contributed no less than 

 30,000,000 kilograms, making this district the greatest silver mine the 

 Avorld has known. Nor is this large production entirely a matter of 

 the distant past, for it is said that the Compagnie de Huanchaca de 

 Bolivia sent to the markets of the world from its mines, which lie 

 to the south, of Potosi, silver and lead to the value of $50,000,000 

 between the years 1873 and 1888. At present Bolivia yields 80,000 

 to 150,000 kilograms (2,500,000 to 4,800,000 fine ounces) per annum. 

 A large part of this comes as a by-product from the tin mines; 

 another part is derived from the mines near Huanchaca. 



The great mineral belt of Bolivia lies in the extremely rough chain 

 which forms the eastern border of the Altiplanicie or high plateaus 

 of that country, a region of Paleozoic folded slates with intrusive 

 cores of diorite, granite, and porphja'itic intrusions. Volcanoes and 

 lava flows are generally absent. In this range there has been pro- 

 duced a widespread mineralization, in part of gold but more char- 

 acteristically of the peculiar type of Bolivian tin veins first described 

 by Stelzner, and carrying both, silver and tin. All these deposits 

 extending from the Peruvian boundary almost to the Argentina 

 border are certainly of the deep-seated type connected with intrusive 

 rocks. In general, these are porphyritic, and may be designated as 

 quartz porphyry or granitic porphyry. In the literature they are 

 frequently referred to as andesite and rhyolite, which usage tends to 

 produce an erroneous impression. There are probably no deposits 

 in Bolivia of the type formed near the surface in flow rocks. 



Interesting changes are observed in depth. Just as the Cerro de 

 Pasco silver veins turned into low-grade copper veins in depth, so the 

 wonderfully rich silver veins of Potosi are shown, as the gi'eat moun- 

 tain is penetrated by deep adits, to have been transformed into 

 pyritic tin-bearing veins. The silver production from this district 

 is now of smaller moment than formerly. 



Lack of data makes it difficult to review at a distance the 

 deposits of Chile. The Republic of Chile, so progi'essive in other 



1 F. C. Lincoln: Incaoro Mine (Mining and Scientific Press, vol. cvlil. No. 14, p. 561 

 (Apr. 4, 1914)). 



65133°— SM 1917 12 



