142 ECONOMIC GEOLOGY OF SILVERTON QUADRANGLE, [bull. 182. 
and that occurring in disseminated particles or in larger masses in 
the metasomatic country rock. The Red Mountain stocks undoubt- 
edly owe their form partly to metasomatic replacement, and might 
almost as well be described under this head. Ore-bearing fissures 
traversing rhyolite rocks are in this region frequently accompanied 
by notable replacement of the wall rock by ore. But there are a few 
deposits where replacement is so conspicuous a feature and where so j 
small a part of the ore occurs within distinct fissure wails that but 
little doubt need arise as to their proper classification. They are, 
however, neither abundant nor relatively important in the Silverton 
quadrangle. 
Direct replacement of limestone by ore occurs on the eastern side 
of Ironton Park, where, for some distance, a thick bed of white 
crystalline limestone, probably of Devonian age, is exposed beneath 
Tertiary volcanic rocks. At the Saratoga mine the ore, consisting in 
its unoxidized state of pyrite, chalcopyrite, and galena, with perhaps 
a little argentite, has replaced the upper portions of this limestone 
to a varying depth. The ore-bearing solutions have been chiefly 
active along the contact between the limestone and an overlying 
andesitic breccia or tuff belonging to the Silverton series. A little 
Telluride conglomerate, consisting largely of limestone pebbles, 
occurs near the adit of the mine, between the limestone and the over- 
lying volcanic series. It has been silieified and probably partly 
replaced by ore, but was not recognized as present in the main work- 
ings. The ore is sometimes associated with rhodonite, which has 
also replaced the limestone and frequently incloses residual kernels 
of the latter. The ore was probably deposited b}^ solutions rising 
through one or more northeast-southwest fissures, although no direct 
connection of the ore with any of the fissures could be made out. In 
the Baltic mine a similar but lower-grade ore occurs, also as a replace- 
ment of the upper portion of the same bed of limestone. This ore, 
however, is directly connected with an ore bod} 7 filling a fault fissure 
(the Mono vein). In the Maud S. claim, which is part of the Baltic 
group, some argentiferous copper ore occurred in bunches in the same 
limestone alongside of a fault fissure. The direct connection between 
the replacement ore bodies of the Baltic group and a system of north- 
east-southwest fault fissures strongly suggests that a similar connec- 
tion does or did formerly exist in the case of the Saratoga ore body. 
In the southern portion of the quadrangle the Devonian limestone 
at the east base of Sultan Mountain carries disseminated particles of 
native silver on the Fairview claim, while in an unknown prospect 
near the King mine a bod} 7 of chalcopyrite occurs partly in a fissure 
and partly as a replacement of the limestone near the fissure. The 
ore in this case makes largely at the underside of the limestone, where 
it rests upon quartzite. 
