76 STUDIES IN GEOLOGY, No. i 



origin of the Corocoro deposits but remarks : "it can hardly 

 be doubted that the presence of copper in the metallic 

 state is due to the intrusion of the dioritic rocks." 



Singewald and Miller consider the close association of 

 the mineralization with the Corocoro fault as indicative of 

 some relation between the two, and think that the parent 

 magma of the diorities was the source of the mineralizers 

 which deposited the ores. 



GENETIC COMPARISON WITH LAKE SUPERIOR DEPOSITS 



The Corocoro copper deposits are often spoken of as 

 analagous to the Lake Superior copper deposits. These 

 have been more closely studied than the Bolivian occurrence 

 and it would seem that an explanation of their genesis 

 might be applicable to or at least suggest the explanation 

 of the origin of the Corocoro deposits. 



A comparison of the geologic features and the ore 

 deposits of the two districts discloses, despite certain 

 features of similarity, features of considerable difference, 

 and renders it rather doubtful whether reasoning concern- 

 ing the genesis of one has any direct applicability to that 

 of the other. A close relationship is implied in 'an article 

 by Alfred C. Lane * on native copper deposits. After 

 mentioning a number of occurrences of native copper ores, 

 of which only the Lake Superior and Corocoro districts 

 are of economic importance, he summarizes the following 

 characteristics as common to them : 



1. All occur in connection with red sedimentaries. 



2. The deposition of the copper is attended by a blanch- 

 ing of the sandstones. 



3. The formation of the red sediments is associated 

 with basaltic dark-colored lavas containing a large 

 amount of ferrous iron and a small percentage of 

 copper. 



* Alfred C. Lane: Native Copper Deposits. Types of Ore De- 

 posits, 1911. 



