162 ANNUAL KEPOET SMITHSONIAN INSTITUTION, 1917. 



Venezuela. The eastern range, in which the city of Bogota is situ- 

 ated, appears to be lacking in precious metal deposits. 



Heavy gravel deposits containing gold and platinum are found 

 along the coast on the Atrato and San Juan Rivers, but the richest 

 placers, some of which are now being dredged successfully, lie along 

 the drainage trending northward, in the Magdalena, Force, Cauca, 

 and Nechi Rivers. These are deposits of great value though difficul- 

 ties of transportation and climate have interfered with their suc- 

 cessful exploitation. 



The majority of the lode mines are in the departments of Antio- 

 quia, Cauca, Bolivar, Tolima, and Santander, of which the first two 

 are the most important. 



The deposits are mostly typical quartz veins, often with crystal- 

 lized native gold, and more or less pyrite, pyrrhotite, arsenopyrite, 

 chalcopyrite, galena, and blende, occasionally also telurides. They 

 are closely related to the California type and undoubtedly allied in 

 their genesis to intrusive rocks. Though the deposits usually occur 

 in granite and schists of probable pre-Cambrian age, porphyries or 

 monzonites of much later date (probably early Tertiary) are usually 

 found close to them. These intrusive rocks have sometimes been de- 

 scribed as anclesites or rhyolites.^ 



Among the deposits there is also another class, the representatives 

 of which yield gold and silver or silver alone, and which occur in 

 undoubted flow rocks, such as andesite and rhyolite. Many of them 

 contain stibnite, tetrahedrite, pyrargyrite, jamesonite, and stephanite 

 and were formed under materially different conditions and near the 

 surface. Such mines are those at Marmato and Echandia in Cauca, 

 and those near Manizales on the boundary of Tolima and Antioquia. 



Altogether Colombia must be considered as the most promising 

 gold-bearing region of South America. 



Apparently Ecuador is not rich in deposits of precious metals. 

 The coast is occupied by Cretaceous and Tertiary sediments, the 

 former including some intnisive rocks. These are adjoined by a zone 

 of igneous flow rocks of Tertiary or Recent age, surmounted by 

 volcanic cones, while, according to W. A. Wolf, the best authority 

 on the subject, the main or eastern cordillera is built of ancient 

 schists and crystalline rocks. 



Almost the whole of the moderate production of a few hundred 

 thousand dollars comes from the ancient mines at Zaruma near the 

 Peruvian boundary and 50 miles from the coast. According to J. R. 

 Finlay, these veins are contained in a fine-grained diorite. In the 



1 1-I. W. Nicholas and 0. C. Farrington : The Ores of Colombia (Bulletin No. 33, Field 

 Columbian Museum, 1896). 



