150 ECONOMIC GEOLOGY OF SILVERTON QUADRANGLE, [bull. 182. 
Round Mountain. In addition, the ITnhy tunnel, run in from the 
southwest side of Arrastra Gulch, cuts the Silver Lake and New York 
City lodes 700 feet below the present main adit level (No. 1). Still a 
third tunnel is being run in a southeasterly direction from a point 
near the Animas River, at the mouth of Blair Gulch, which will, if 
carried through, ultimately tap the Silver Lake lodes at the lowest 
practicable point, over 2,500 feet below the No. 1 level. 
There are no abandoned workings, and the character and relation- 
ships of the lodes may be studied under more than usually advan- 
tageous circumstances. 
The Silver Lake lode as exposed in the mine has a general strike 
of N. 53° W. Its dip is to the northeast and varies from 50° to 70°— 
the flatter dip being more common in the upper workings. The aver- 
age dip is probably a little over 00°. Its croppings are conspicuous 
as a rust-colored zone of oxidation running up the declivity west of 
the lake and passing through the col just south of Round Mountain. 
At this point they have an apparent width of about 40 feet of stained 
and cellular quartz carrying galena, as well as the carbonate and 
sulphate of lead. Northwestward from this saddle the lode, different 
portions of which are known as the Round Mountain, Lowville, and 
Nevada lodes, crosses Whale Basin just above the cliffs of Arrastra 
Gulch, and passes through another saddle into the head of Blair 
Gulch. In its productive portions the Silver Lake lode is from C to 20 
feet in width. Elsewhere it may be represented by a strong clay 
seam or gouge, or less commonly a small tight vein. The filling of^ 
the fissure is quartz, carrying variable amounts of galena, sphalerite, 
chalcopyrite, and pyrite. No regular arrangement of the ore minerals 
within the quartz could be detected. They occur in irregular bunches 
in all portions of the vein, and appear to be the result of a single 
uninterrupted process of deposition. The ore bodies, also, although 
often of considerable size, are without any known regularity in their 
distribution through the lode. The best ore is usually found in the 
more solid portions of the lode, a soft lode with abundant gouge being 
regarded as less favorable. The ore is nearly always separated from 
the walls by more or less gouge. A sheeting of the walls parallel 
with the main fissure is not infrequent, and where it occurs careful 
prospecting is necessary to avoid overlooking considerable masses of 
ore which may be lying behind what appears at the time to be the 
outer wall of the lode. On levels 1 and A the most productive por- 
tion of the Silver Lake lode is divided into two branches by a large 
horse of country rock traversed by stringers of quartz. 
In the levels above No. 1, particularly in level 4, the Silver Lake 
vein is frequently a soft yellowish mass of more or less broken quartz, 
decomposed country rock, clay, cerussite, and other products of alter- 
ation. This portion of the lode thus shows considerable oxidation, 
particularly where there is evidence, in the form of clay seams and 
crushing of the quartz, of movement since the deposition of the ore. 
