ANso.MK.I PARAGENESIS OF LODE AND STOCK ORES. 131 
adoubtedly involved rocks of various kinds, reducing them all to 
ight-colored secondary aggregates of similar appearance. Andesites, 
itites, monzonite-porphyry, and rhyolite have been altered to prod- 
Cts which often give Little indication of the nature of the original 
6ck. But in many portions of the quadrangle the rhyolitic rocks 
how certain characteristic phases of metamorphism in connection 
ith ore deposition which seem to merit some special notice. This 
ock, when acted upon by ore-bearing solutions, is particularly sus- 
eptible to recrystallization into secondary aggregates of quartz and 
3ricite, quartz and kaolin, or quartz, sericite, and kaolin. As a 
eneral rule such metasomatic alteration is accompanied by more or 
ss replacement of the rock by ore, as may be seen in the Tom Moore 
i- Silver Ledge mines. 
No favorable opportunity was presented for studying in detail the 
ictasomat ic processes which accompanied t he deposit ion of ore in the 
onzonitic stocks, such as Sultan Mountain. l>nt so far as observed 
e alterat ion is not conspicuous. 
PARAGENESIS OF THE LODE AND STOCK ORES. 
By paragenesis is here meant the association of the various ore and 
mgue minerals with special reference to the order and mode of their 
►rmat ion. 
Beyond the common and well-known derivation of certain second- 
ly minerals in the zone of oxidation, as, for example, anglesite or 
ad sulphate from galena, the directly observable paragenesis of the 
's offers few points which can be embodied in any general statement 
regular association. As a general rule the ore minerals which are 
>und together in any one deposit have formed contemporaneously, 
id cases are rare in which a definite and constant succession of dif- 
rent ore minerals can he recognized. In the Tom Moore lode 
lalcopyrite appears to have formed later than tetrahedrite. The 
bine relation was observed in the Dives lode, where masses of tetra- 
'drite are surrounded by an envelope of chalcopyrite from which 
diate still younger quartz crystals. But in many other lodes these 
\o minerals occur in such irregular relations as to point to practically 
mteniporaneons crystallization. In the Empire- Victoria lode, on 
Ian Mountain, hiihnerite and fluorite have been formed since the 
•e was deposited. Native copper, wherever seen, was plainly of 
ler origin than the sulphide ores with which it was associated, 
ative silver was seen only in detached specimens of ore, but it occurs 
laracteristically in the upper portions of the deposits and is undoubt- 
lly of secondary origin. Quartz of at least two generations is com- 
on, as shown by the relatively barren stringers of this mineral, 
tiich can be found traversing the ore in many of the deposits. 
Free gold occurs usually embedded in quartz and associated with 
'rite or chalcopyrite. In the Sunnyside, Sunnyside Extension, and 
