158 ECONOMIC GEOLOGY OF SILVERTON QUADRANGLE. |bull.183. 
The vein filling is solid and shows very little trace of movement sub- 
sequent to the deposition of the ore. It generally lies close against 
the walls of the fissure, with little or no gouge. As in the Silver Lake 
mine, the wall rock does not, as a rule, exhibit any very marked altera- 
tion close to the vein. The microscope shows, however, in the rock 
alongside the vein a thorough recrystallization of the original rock 
constituents into aggregates of quartz and sericite, with some calcite 
and specks of pyrite. A specimen 10 inches from the vein shows 
similar alterations, but with more calcite and abundant chlorite. The 
same general character of alteration is found 2 feet from the vein. At 
50 feet from the vein quartz, chlorite, and calcite make up most of 
the rock, in which traces of the original structure remain, and the 
sericite is confined chiefly to the altered feldspar phenocrysts. 
The Stelzner lode presents the same characteristics in the Iowa mine 
as in the Silver Lake. It is a nearly solid, simple vein, showing as 
much as 8 feet of excellent ore in the stopes. There is usually no 
gouge between the vein filling and the walls. 
The East Iowa vein has not proved of very great importance. It 
has been stoped for a distance of over 100 feet, but presents no features 
of special interest. 
The Melville lode is chiefly notable from the fact that in its south- 
ern portion it dips to the southwest at from 70° to 75°. It carries 
galena, sphalerite, chalcopyrite, and pyrite in a gangue of quartz, 
with a little barite. It varies in width, being in some places as much 
as 4 feet wide. The ore is too poor to work. Northward this vein 
becomes irregular and in places is a nearly vertical fissure Containing 
some gouge, but no quartz. It finally dies out in a few barren string- 
ers. Although in general line with the Black Diamond-Royal lode, it 
is by no means certain that it occupies the same fissure. The low 
grade of its ore and its westerly dip, contrasted with the good ore and 
i steep easterly dip of the Royal, seem rather to indicate that it is an 
overlapping fissure, bearing a similar relation to the Royal that the 
East Iowa does to the Stelzner. 
Regular parallel Assuring of the country rock, the fissures being 
usually filled by stringers of quartz and ore, is even more conspicuous 
in the Iowa than in the Silver Lake mine. As in the latter mine, 
these fissures are apparently minor results of the same forces that 
produced the productive veins of Group II, seeming, in fact, to belong 
to that group. In the Iowa these fissures usually dip very steeply to 
the southwest. 
Generally the lodes in the Iowa are very regular in their productive 
portions, having comparatively few horses. The ore is confined 
within the fissure walls. The disturbance and movement which has 
taken place since the veins were formed is scarcely appreciable. 
Tetrahedrite is reported as occurring in the Iowa workings, but none 
was seen at the time of visit. 
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