ASPEN MOUNTAIN. 155 
limestone with no dolomite envelope, but on analysis the ore was found 
to contain 5 or 10 per cent of magnesia, while the limestone around it 
contained none. These facts indicate that dolomization was, in part at 
least, attendant upon the mineralization; that the ore deposition took 
place from solutions circulating along fault fractures, and that they 
deposited their contents by preference at the contact of two or more of 
these fractures. 
The ore in the Durant varies greatly, both in composition and in quality. 
There has been a large amount of oxidized ore taken out, but now a great 
portion of it is sulphide, although most of the existing stopes show more or 
less transition between the sulphide and oxidized conditions. As is the 
case throughout a large part of the camp, the ore is chiefly an argentiferous 
galena, which has replaced the dolomite and limestone to a greater or less 
extent. There is also considerable zinc sulphide and carbonate, and in: 
some of the ore the silver probably occurs in large part as argentite. On 
Pl. XL, B, a cross section through the Durant and down the “Electric 
winze” of the Aspen mine is given, showing the typical structure of the 
Durant and the Aspen mines and the occurrence of the ore bodies. The 
ore figured on this section is that which has actually been taken out, and 
the narrow zone to which it is confined is well shown. There are, however, 
evidences of ore in other parts of the rock, particularly in the faulted region 
in the right-hand or western part of the section. 
 Aspenmine—'T'he Aspen shaft passes through a small quantity of por- 
phyry and Weber shale and through the blue limestone to the Contact 
fault, along which most of the workings are located. The general 
structure shown in the mine is a continuation of that in the Durant. 
Throughout the whole runs the Aspen fault, very nearly vertical and 
with a north-south trend. A short distance east of the Aspen fault, 
between the blue limestone and the dolomite, is the Contact fault. This 
fault has slickensided walls and often a triturated zone, showing its nature. 
In its main course it has a north-south trend, nearly parallel with the 
Aspen fault, but approaching it slightly toward the south, so that finally 
they meet. From the sixth level down the dip of the Contact fault is 
reversed and becomes very steeply east. At the sixth level it is about 
85 degrees, but farther down it approaches 70 degrees. At a certain 
point, which varies, being deeper in the Aspen mine than anywhere else, 
