88 
ECONOMIC GEOLOGY OF SILVERTON QUADRANGLE, [bull. 183. 
pyrite, aud other minerals are all crystallized irregularly in the fissures 
without external crystal form and without definite arrangement. As 
a rule the constituent minerals appear to have crystallized practically 
simultaneously. 
This structure is exceedingly "common and is the characteristic one 
of the quadrangle. It is typically exhibited by the ores of the Silver 
Lake, Royal, Stelzner, New York City, Iowa, and East Iowa lodes of the 
Silver Lake Basin (PI. XI, B). The quartz sometimes incloses empty 
spaces, either as minute interstices between interlocking quartz prisms 
or as small vugs lined with quartz crystals. Occasionally, instead of 
being perfectly massive, the ore exhibits indistinct traces of the struc- 
ture next to be described. The two are connected by intermediate 
forms. 
2. Banded structure by deposition. — The ore and gangue minerals 
have been deposited in more or less parallel sheets, distinguishable 
I 
1 \ 
* i 
Fig. 7.— Cross section of No-Name lode, Sunnyside mine, a, country rock; 6, ore, chiefly galena 
with quartz gangue; c, rhodonite. 
from each other by the fact that they contain the constituent vein- 
forming minerals in different proportions. 
This is far less common than the preceding, but it is found in many 
small and unproductive veins and in some of the more important 
lodes, such as the Gold King, where the pyrite has been deposited in 
bands alternating with white quartz. On the large scale it is perhaps 
exemplified in the Sunnyside lode, where the ore streaks, themselves 
of massive structure, consisting of galena, sphalerite, chalcopyrite, 
pyrite, tetrahedrite, and free gold in a gangue of quartz, rhodonite, 
and a little fluorite, are separated by plates or lenses of relatively 
barren rhodonite. This structure is illustrated by fig. 7, which is a 
section of the No-Name vein in the Sunnyside ground. 
In the smaller veins and stringers carrying galena and quartz the 
galena frequently fills the medial suture formed by the opposing 
pyramidal ends of the quartz crystals which have' grown out from the 
walls of the fissure. This is well seen in some of the veinlets of the 
Silver Lake Basin. Even the larger lodes, with prevailingly massive 
