240 W. LINDGREN — CALIFORNIA GOLD-QUARTZ VEINS. 



and that the large granite areas are almost wholly void of veins, though 

 fissures and fractures are not absent from them. 



Second, that in the metamorphic series the gold-quartz veins occur in 

 almost any kind of rock, and that if the countrj^-rock exerts an influence 

 on the contents of the veins, it is, at best, very slight. 



Third, that the principal contact of the metamorphic series and the 

 granitic rocks is in no particular way distinguished by rich or frequent 

 deposits. 



It is further apparent that gold deposits have been formed at different 

 periods, though by far most abundantly in later Mesozoic times. Some 

 of these later veins may have been locally enriched by passing through 

 earlier impregnations in schist or old concentrations in the sandstones 

 and conglomerates of the metamorphic series, the gold contents of which 

 have, ho^^ever, only been proved in isolated cases. 



These considerations, though involving many most difficult questions, 

 strengthen the belief that the origin of the gold must be sought below 

 the rocks which now make up the surface of the Sierra Nevada, possibly 

 in granitic masses, underlying the metamorphic series.* 



Summary. 



The auriferous deposits extend through the state of California from 

 north to south in an irregular and broken line. 



The gold-quartz veins occur predominantly in the metamorphic series, 

 while the large granitic areas are nearly barren. The contact of the two 

 formations is not distinguished by rich or frequent deposits. 



The gold-quartz veins are fissure-veins, largely filled by silica along 

 open spaces, and may dip or strike in any direction. 



The gangue is quartz, with a smaller amount of calcite ; the ores are 

 native gold and small amounts of metallic sulphides. Adjoining the 

 veins the wall-rock is usually altered to carbonates and potassium-micas 

 by metasomatic processes. 



The veins are independent of the character of the country-rock, and 

 have been filled by ascending thermal waters, charged with silica, car- 

 bonates and carbon-dioxide. 



Most of the veins have been formed subsequent to the regional meta- 

 morphism which affected the auriferous slates and the older igneous 

 rocks associated with them, and also subsequent to the granitic intru- 

 sions which closed the Mesozoic igneous activity in the Sierra Nevada. 



* Mr Beeker, reasoning from analogy, has some time ago suggested such a derivation : " Quick- 

 silver Deposits," p. 449. Militating against this view is the general absence of compounds of boron 

 and fluorine so often occurring in ore deposits in granitic rocks. 



