72 STUDIES IN GEOLOGY, No. i 



themselves. Second, the aragonite twins, replaced in part 

 by copper, must have formed subsequent to the deposition 

 of the beds enclosing- them or they would be water worn, 

 and their replacement by copper came still later. Third, 

 the copper occurs not only as a cement but also penetrating 

 the grains and pebbles of the mineralized strata of what- 

 ever type of rock they may consist. Hence it was not 

 deposited merely as a filling between the interstices of the 

 constituent particles, but the solutions penetrated the rocks 

 as a whole. Though not specifically stated, the inference 

 from this evidence seems to be that the metal-depositing 

 solutions were more active than ordinary bodies of water 'in 

 which sediments are laid down, and represent subsequent 

 mineralizing solutions. Fourth, the copper occurs in the 

 Ramos and the Vetas and hence in rocks of different age. 

 It is more natural to suppose one period of mineralization 

 occurred subsequent to the deposition of the metalliferous 

 beds. 



Four other features which he regards as significant with 

 respect to the mode of origin of the deposits are cited by 

 Sundt. First, the copper is generally intimately associated 

 with calcium sulphate and barite, and often so intricately 

 as to predicate simultaneous formation. Second, the 

 unmineralized sandstones are usually red in color, due to 

 the presence of ferric oxide. Where they are mineralized 

 they are bleached through the reduction of the ferric oxide. 

 Third, the cupriferous beds usually contain more or less 

 water characterized by high salinity through the presence 

 of sulphates and chlorides of the alkalies and alkaline earths. 

 Fourth, the position of the ore bodies on each side of the 

 Corocoro fault would indicate some relation between the 

 fault and the infiltration of the cupriferous solutions. 



Supported by the above observations Sundt concludes 

 that at some period subsequent to the deposition of the 

 Ramos and Vetas series, possibly when the Corocoro fault 

 was formed or possibly when the high plateau was uplifted, 

 solutions of copper, chlorides, and sulphates impregnated 



