Wotice of Syenitic Rocks from California. — Turner. 381 
Whether the main mass of the lode can be correctly called porphyry, 
can I think, only be determined by microscopic examination : it may be 
porphyritic quartz having feldspar as a constituent, and what I take to 
be feldspar also occurs in masses, some of it of a greenish tint. The 
characteristic material of the lode is a heavy, hard, highly siliceous, 
dark -gray rock of sub-conchoidal fracture, seamed more or less with 
white quartz and impregnated with pyrites of which there are two 
classes, the one hard, bronze-colored, cubical, striated and not very 
rich in gold, the other softer, brass-yellow and not obviously cubical ; 
this latter kind is rich, and I think there are some tellurets among 
them. Arsenical pyrites also occur. * * * This is or has been a " poor 
man's mine" though also affording an opportunity for large operations, 
and it has been worked in dozens of shallow shafts, and drifts along the 
sides by " xjocket-hunters " many of whom have been richly rewarded 
for their labor. I learn that fully $200,000 in gold has thus been taken 
out, in great part by the aid of hand mortars. The feldspar is auriferous 
where it is permeated by seams of quartz, and the gray rock gives good 
assays, and also shows coarse gold, even where no quartz is visible. 
The Shaw mine lode is shown by Mr. Lindgren on the eco- 
nomic map of the Placerville folio. The specimens, on which 
the writer's notes are based, were received from Mr. Leo Von 
Rosenberg, of New York city. 
One of the specimens (No. 235 Eldorado County coll.) from 
the Orofino or Big Canyon mine lode contains, besides the 
feldspar, much original hornblende; another specimen (No. 
234) contains none. This lode is now thoroughly impregna- 
ted with carbonates and iron di-sulphide and was said to 
carry from $3 to .$4 per ton in gold. 
An examination of the Big Canyon mine was made by Mr. H. 
W. Fairbanks,* who writes : "An examination of this ore body 
shows it to be a very hard, compact and fine-grained mass of 
gray quartz, which is thickly sprinkled with small but regu- 
lar crystals of iron pyrites. Gold occurs both in the free 
state and in combination with the sulphurets. The ore carries 
from 8% to 10% of sulphurets." A twenty-stamp mill and a 
chlorination plant were being operated at the time of Mr. 
Fairbanks' visit. 
During the season of 1895, in the area of the Sonora sheet, 
the writer found abundantly white rocks occurring as dikes 
in various rocks chiefly along the belt of gold quartz mines 
known as the Mother lode. The similarity of these rocks to 
♦Twelfth Report of the State Mineralogist of California, pp. 10:5 and 
480. 
