58 MINERALS OF CHILE. 



What is here said of the geological structure of the country 

 east of Copiapo is true of many other parts of Chile from the 

 coast eastward. From these general views of the geology of 

 Chile I next pass to the consideration of the minerals collected 

 by the expedition, accompanying the mineralogical discription 

 of them with an account of the manner of their occurrence. 

 For the latter I am also indebted to the geologists already 

 made mention of. 



NATIVE GOLD. 



The specimens of this metal were contained in quartz-rock, 

 exhibiting all the usual characteristics of auriferous quartz. 

 The gold contains silver with but a trace of copper. In Chile 

 this metal is found in veins as well as in the drift; the whole 

 granite of the country is traversed by quartz containing more 

 or less gold associated with the peroxide of iron, and at some 

 depth from the surface with iron pyrites ; sometimes with 

 cupreous pyrites, arsenical pyrites, blende, galena, and sul- 

 phuret of anatomy. These veins by their decomposition fur- 

 nish auriferous deposits of considerable extent, that are now 

 worked. 



Mention is made by M. Crosnier of a number of gold de- 

 posits irregularly disseminated in the midst of decomposed 

 granite and red clay, which contains a large quantity of per- 

 oxide of iron, and which appears not to have originated from 

 the decomposition of regularly -formed veins. This fact is 

 apparent in the neighborhood of Yalparaiso. It is also stated 

 that gold is found in clay more or less ferruginous, arising 

 from the decomposition of the granite in the most elevated 

 portions of certain mountains ; consequently in a situation 

 where it should not have been carried by water. 



It is supposed that the gold came up with the mass of 

 granite at the time of the elevation of the latter, and not by 

 subsequent injections of veins ; and in most instances iron 

 pyrites is regarded as its original associate. This character of 

 auriferous formation is of course the exception, as in most 

 instances the gold is traceable to regular veins, or to the de- 

 composition of these veins. Although gold seems to be quite 

 generally distributed through Chile, but few of the deposits 

 remunerate exploration; the most extensive are on the flanks 



