GEOLOGICAL STRUCTURE OF THE DISTRICT. 
33 
dicator and Golden Cycle mines. The Battle Mountain syenite and latite-phonolite 
are also facies of a single intrusive mass. 
The latite-phonolite occurs mainly as irregular stock-like bodies or in thick 
sheets. A good example of the former type of occurrence is found in a biotitic 
variety (biotite trachyte) which is exposed over a large part of the northern slope of 
Battle Mountain and in the workings of the Portland and Dead Pine mines. The 
No. 3 shaft of the Portland mine was started in this rock and continued in it to a 
depth of about 1,000 feet. It then passed out of the latite-phonolite into breccia, 
the irregular contact between the two rocks here dipping to the west. A narrow 
tongue of the latite-phonolite passes through the saddle of Battle Mountain, extends 
southward nearly to the granite, and is reached in some of the western workings of 
the Portland mine and in a northeast crosscut in the Dead Pine mine. This intru¬ 
sive body was described by Cross as a mica andesite, but on account of its unsatis¬ 
factory surface exposures was not mapped by him. Underground workings have 
since thrown considerable light upon the shape and extent of this intruded body. 
Another irregular mass of latite-phonolite which sends out a number of dike 
apophyses lies between Battle Mountain and Goldfield. This rock was mapped by 
Cross as augite andesite and was thought to be a remnant of an early surface flow 
that had been partly brecciated by later volcanic explosions. It has not been so 
well exposed underground as the micaceous facies of Battle Mountain, but has been 
cut at a sufficient number of places in the Portland and Independence mines to 
demonstrate its irregular intrusive character. The adit level of the Portland mine 
is in this rock for about 1,000 feet from the portal. Owing to the general eastern dip 
of its western contact, the latite-phonolite lies to the east of the principal Portland 
workings on the 500-foot and lower levels. It occasionally shows syenitic facies. 
The large area of latite-phonolite extending from Bull Ilill to the saddle north 
of Battle Mountain, though connected with dikes, seems to be in the main a thick, 
irregular intrusive sheet. The shaft of the Blue Bird mine penetrates this sheet and 
passes into breccia at a depth of from 300 to 400 feet. The same relation is shown 
in the Dante, Gold Sovereign, and other mines in the vicinity, which at depths of a 
few hundred feet at most pass out of latite-phonolite into breccia. The flat bottom 
of the sheet is exposed also in the Lower Trail tunnel in Arequa Gulch, above Elkton. 
The mass of latite-phonolite reaching from Independence to Altman also lias a nearly 
horizontal under contact near the Shurtloff No. 2 shaft, which is reported to pass 
into breccia at a depth of about 500 feet. On the east side of the mass, however, the 
workings of the Dead wood No. 1 mine show the contact to be nearly vertical for a 
depth of at least 300 feet. 
The shape of the large body of latite-phonolite that underlies the town of Altman 
and extends down through Independence is unknown. The southwest contact of 
the mass with the breccia is very steep at the Findley mine, for on the 900-foot level 
syenite (probably the equivalent of the latite-phonolite on the surface) is reached 
130 feet east of the shaft. 
The contact of the breccia with the latite-phonolite or syenite, between the 
Vindicator and Lillie shafts, is almost vertical for a depth of 1,000 feet. No breccia 
has been found underneath the Vindicator area of syenite. In all of the lower levels 
