ART. 15. MINERALOGY OF GOUGE CLAYS—-SHANNON, 5 
identity with muscovite has been sufficiently demonstrated, there are 
in the literature very few records of thorough chemical investigation 
of material from metalliferous veins, especially upon samples of 
demonstrated homogeneity and freedom from extraneous impurities. 
Some specimens of very excellent and typical material of this sort 
from a gold vein in the Boise Basin recently having been received 
at the Museum, the writer undertook to examine the mineral es- 
pecially to secure data for incorporation in his manuscript on the 
minerals of Idaho which isin preparation. The results seem worthy 
of detailed presentation here. Grateful acknowledgment is due Mr. 
Clarence S. Ross, of the United States Geological Survey, for assist- 
ance in determining the optical properties of the mineral, proving the 
homogeneity of the analyzed material by optical methods, and in 
devising a method for freeing the mineral from contaminating impu- 
rities. 
Occurrence.—The specimen came in a series collected by Edward 
L. Jones, jr., of the United States Geological Survey. Jones’‘ de- 
scription of the deposit gives such an excellent idea of the occurrence 
of the mineral that it may advantageously be quoted entire, as follows: 
The Carroll-Driscoll group comprises 14 claims which extend in a northeasterly 
direction from the end lines of the Gold Hill group to Garden Valley Pass. The 
property was worked in the early days and many thousand dollars’ worth of gold 
was produced from surface workings and by sluicing disintegrated veins on the 
Ivanhoe and Capital claims at the head of California Gulch. The principal develop- 
ment work on this group consists of two tunnels, 178 feet apart, on the Ivanhoe 
claim. The upper tunnel, which is several hundred feet long, is now partly caved. 
It isa shallow drift on the vein, which strikes N. 30° E. and dips steeply east. Con- 
siderable ore has been produced but the amount is not definitely known. The ore 
consists of veinlets of massive pyrite and a little quartz which carry free gold. The 
country rock is granite. 
The lower tunnel is driven on a course N. 60° W. for 1,450 feet. It intersects a 
shear zone 135 feet wide, which contains several sulphide veins in zones of more 
intense shearing. These veins trend from N. 30° E. to north and dip steeply east. 
The largest vein is near the hanging wall of the main shear zone, and its width 
ranges from 3 to 12 feet. The zone is further explored by a drift on its hanging 
wall and by short crosscuts driven to the main vein. The shear zone carries an 
abundant flow of water, which, with the softness of the vein matter, renders mining 
somewhat difficult. 
The vein matter is composed largely of a soft white gouge which incloses the 
sulphides. The gouge is sericite, a secondary mica derived from the alteration 
of feldspars. Pyrite in well developed crystal aggregates or individuals, is the 
dominant sulphide in the gouge, but here and there are fragments of older vein 
material in which quartz, calcite, pyrite, galena, sphalerite, and tetrahedrite were 
recognized. These sulphides, however, have largely been ground up and incorpo- 
rated in the gouge. It is evident that there have been two general periods of 
sulphide deposition and that extensive alteration and movement have occurred in 
the vein pubsequent to the first period. Pyrite is the latest mineral in the seri- 
4 Edward L. Jones, jr., Lode Mining in the Quartzburg and Grimes Pass Porphyry Belt, Boise Basin, 
Idaho, U.S. Geol. Survey, Bull. 640, p. 104 ,1916. 
