372 
BOLIVIAN COPPER DEPOSITS 
Lorenzo Sundt ^ discussed the genesis of these deposits at some 
length. He presents four arguments in support of their epigenetic 
origin. First, the sheets of copper filling fractures in the beds 
are naturally younger than the beds 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 
whatever type of rock they may consist. Hence it was not de¬ 
posited merely as a filling between the interstices of the constitu¬ 
ent 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 cop¬ 
per occurs in the Ramos and the Vetas and hence in rocks of dif¬ 
ferent age. It is more natural to suppose one period of mineral¬ 
ization 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 sul¬ 
phates 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 infiltra¬ 
tion 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 some of those beds, preferably the 
7 Boletin de la Sociedad Nacional de Mineria, de Santiago, (2a), Vol. IV, 1892. 
