IANSOME.] 
METAMOEPHISM OF THE COUNTRY ROCK. 
129 
lenotes practical constancy of the alumina during the change which 
ms taken place in the rock. 
The notable features of the alteration are the introduction of silica, 
rater, and sulphur, the total removal of iron (except that combined 
vith sulphur to form pyrite), magnesia, and carbon dioxide, and the 
ilmost entire abstraction of lime and alkalies. The formation of 
liaspore brings this alteration close to thai described at the Polar Star 
nine, the original rocks in both cases being of similar chemical com- 
position, while the addition of silica and the formation of kaolin, 
lsually without sericite, is characteristic of the Red Mountain mines. 
Ignoring the small amount of the unknown isotropic mineral, the 
nineralogical composition of the altered rock may be roughly calcu- 
atc(| from the chemical and microscopical data as follows: 
Nineralogical composition of altered m>>ir.(,,iili<- porphyry from National Belle 
mine. 
Constitunr 
Per cent. 
< lonstituent. 
Per <-<'iit. 
juartz , 
60.9 
•.v, .; 
5. ti 
.1-. 
Apatite 
Rutile 
.6 
.6 
kaolin in> 
'yrite 
>i;is]x>r. 
98 4 
Bricite 
<i Dhe diaspore of this rock was also isolated with hydrofluoric acid. It appeared to be fully as 
bundant in the residue ;i- in the similar residue from the Polar Star rock, described on im^e 
El, and the above calculation may be low. 
• 
This is a very different alteration from thai normally brought about 
>y waters carrying alkaline carbonates, which, as Lindgren ' lias shown, 
end to form sericite and carbonates in the wall rock. It is believed 
o be due to the acl ion of acid waters. 
It is unfortunate thai the study of the metamorphism connected 
rith the Red Mountain ore bodies is at the present time practically 
ontined to the surface. However, as far as can be judged from the 
nine dumps, metamorphism of the character described accompanied 
he ore bodies to the greatest depth explored. 
On Anvil Mountain, which forms the southern end of what has been 
ailed for convenience the Red Mountain Range, the bleached rocks, 
rhen critically examined, are found to present some variations in 
omposition. Thus the country rock of the Brobdignag claim, prob- 
bly originally andesitic, is converted into a fine-granular aggregate 
f quartz and barite, with a little sericite. It is impregnated with 
►yrite and is traversed by some veinlets of sericite or kaolin. At the 
Sun] mine the country rock, which was evidently an andesiteor latite, 
Las been recrystallized near the ore body to a mass of quartz, sericite, 
aolin, and barite, with a little epidote in small grains. Some rutile 
1 The gold-quartz veins of Nevada City and Grass Valley districts, California: Seventeenth 
nn. Rept. U. S. Geol. Survey. Pt. II. 1S9G, p. 172. 
Bull. 182—01- 
