ran omb.] CLASSIFICATION OF THE ORE DEPOSITS. 43 
ores, the concentration of which is often rendered troublesome by the 
presence of sphalerite and barite, and which almost invariably require 
smelting. 
CLASSIFICATION OF THE ORE DEPOSITS. 
The ore deposits of the Silverton quadrangle may be conveniently 
classified and described under three heads: (1) Lodes, (2) stocks or 
masses, and (3) melasoinalic replacements. To the firsl class belong- 
by far the greater uumber of the deposits that are being worked at 
the present time. To the second class are assigned most of the ore 
oodles formerly worked in the Red .Mountain district, often Locally 
known as "chimneys." In the third class, by far the least important 
in this quadrangle, are placed a few deposits occurring in limestone 
or in rhyolite. 
In the classification of actual ore deposits it is usually found that a 
given ore body presents features common to two or more ideally dis~ 
tinet types. Thus a fissure vein may he accompanied by some replace- 
ment of the adjacent country rock, or it may be found impossible to 
draw any definite line between impregnation 1 ami total metasomatic 
replacement. The present field offers no exception to this general 
difficulty, and the division of the ore deposits here made is not to be 
regarded as in all eases discriminating between totally different 
things. The aim is to group the deposits broadly, under most promi- 
nent characteristics of occurrence, in order that they may be conven- 
iently ami systematically described. 
THE LODE FISSURES. 
DEFINITIONS. 
\\y fissure, as used in this report, there is meant a somewhat exten- 
sive fracture in the rocks. Such a Jissnre is not necessarily accom- 
panied by recognizable faulting, nor by the production of visible 
open spaces, nor by mineralization. According to the classical defi- 
nition of Von Cotta, 2 a vein is the filling of a fissure. As designating 
a simple type, of frequent occurrence, it seems very desirable that in 
accurate description the term vein should retain this significance, 
i. e., a "true vein" or fissure vein. In mining speech, however, 
the word commonly has a broader meaning, and is made to include 
not only the filling of a preexisting fissure, but also, in many cases, 
more or less altered and impregnated country rock alongside the fis- 
sure. Frequently the "vein" of the miner is a sheeted zone, embrac- 
ing several veins in Von Cotta's sense, or it may be a zone of more 
or less irregular ore-bearing stringers. For this reason, lode will be 
1 As used in this report, impregnation is merely a structural term indicating the fine dissemi- 
nation of ore particles through a rock mass. In the majority of cases it involves true metaso- 
matic replacement. 
2 Die Lehre von den Erzlagerstatten, 2d ed., Freiberg, 1859, p. 102. 
