214 ECONOMIC GEOLOGY OF SILVERTON QUADRANGLE, [bull. 182. 
Columbia mine. — This property is also on a prominent lode which 
lies southwest of the Argentina, and which is the southeastern con- 
tinuation of the Cimarron vein in the Telluride quadrangle. The 
Columbia mine is at present not extensively or continuously worked. 
The vein as seen underground is much like the Japan, but less regu- 
lar. Its strike is about K 30° W., with a variable dip of 00° to 75° to 
the southwest. The ore is sometimes 2 feet in width, but more often 
about 10 inches. In places it is solid, consisting of quartz, galena, 
sphalerite, and pyrite, with little or no gouge; but often it is crushed 
and pinched by post-mineral movement along the fissure. As in the 
Japan, parallel sheeting of the walls of San Juan breccia is a noticea- 
ble accompaniment of the vein. The stringers of quartz which often 
fill the fissures in the sheeted country rock are practically barren. 
All the ore is concentrated. The best of it carries about 1 ounce of 
gold, 70 ounces of silver, and 30 per cent of lead. 
North Chicago mine. — This property, which has been idle for some 
time, lies in Savage Basin near its head, and is perhaps on the Tomboy 
lode. It was worked through a shaft. 
ORE DEPOSITS OF THE RED MOUNTAIN REGION. 
General. — Under this head will be described the various ore depos- 
its occurring about Ironton Park and Red Mountain. Thej^ include 
ordinary fissure lodes and replacement deposits of more than one kind. 
But the bodies of ore which gave this particular region its fame are 
of a type less commonly met with in other districts. The ore occurs 
in so-called "chimneys" — i. e., nearly vertical bodies of ore roughly 
circular or elliptical in plan. Unfortunately, owing to the idleness of 
these mines, satisfactory study of the ore bodies is not at this time 
possible. In a few cases access was had to the old upper workings, 
but for information in regard to the deeper portions of the deposits 
recourse must be had to a few published descriptions, the annual 
reports made by superintendents to the directors of companies, and 
to information gathered from those who were familiar with the deeper 
mines before they shut down. The latter is sometimes conflicting, 
but hy judiciously weighing its various sources and by making allow- 
ances for different points of view an endeavor has been made to 
supply as nearly as possible the unavoidable lack of observation at 
first hand. 
The country rock in which the Guston, Yankee Girl, and neigh- 
boring mines lie is a part of the Silverton formation. It is an ande- 
sitic breccia, usually somewhat decomposed near the surface, and 
apparently originally of rather homogeneous character. With it are 
associated some flows of massive andesite. Locally the rock has been 
so altered hy thermal action as to obliterate its original features. It 
is changed to a white or yellowish siliceous mass, in which the breccia 
structure is usually obscured or lost. Quartz is abundantly visible 
