RELATION OF ORE SHOOTS TO COUNTRY ROCK. 
209 
Between the Findley and Hull City mines the ore shoot leaves breccia and enters 
into latite-phonolite without marked change in composition or value. On the 
other hand, latite-phonolite and syenite are notably unproductive in the Portland 
mine (PI. XXVIII, p. 434). 
The relations of ore shoots to bodies of phonolite are sometimes significant. 
In some places the ore shoots are enriched when entering phonolite, while in other 
cases they are distinctly and markedly impoverished. In the Elkton mine the flat 
ore body corresponds roughly to the outline of a body of phonolite in which it 
occurs between two lines of vertical fissures 120 feet apart. The ore in this case is 
confined to this flat body of phonolite. An interesting case showing the localiza¬ 
tion of an ore shoot by a phonolite sheet is shown in fig. 15 (p. 208), representing a 
pay shoot in the Prince 
Albert mine on Beacon 
Hill. In this case a verti¬ 
cal fissure system inter¬ 
sects a flat dike of phono¬ 
lite in granite. The ore 
has accumulated on the 
upper side of the dike, 
while below it there is only 
a very small quantity. It 
appears very much as if 
the solutions were locally 
descending and as if con¬ 
traction of the fissures in 
the more resistant phono- ^ig. 1(i -— Longitudinal section of the El Paso vein, showing form of ore body at 
.. i i 1 • [intersection with phonolite dike. 
hte prevented the active 
circulation and induced precipitation on its upper side. An instance somewhat 
similar to this, but on a much larger scale, occurred in the Isabella mine; the Chey¬ 
enne ore shoot is suddenly cut off just below level 10, where the fissure leaves 
breccia and enters into a hard, compact phonolite. The richest part of the whole 
shoot was found here, resting immediately on top of the thick sheet of phonolite. 
Similar relations are said to have obtained in the adjoining Victor mine. 
The ore body of the El Paso lode on Beacon Hill has the form of a flattened 
ellipsoid lying against the under side of a phonolite dike, its longest axis pitching 
northeast with the general line of intersection of lode and dike. In this case also 
the dike probably limits the ore shoot by reason of being less permeable to the 
solutions than the surrounding granite. 
RELATION TO INTERSECTIONS. 
The factor which most obviously influences the position and extent of ore 
shoots is the intersection of veins with one another or with “basic” or phonolite 
dikes. That such intersections are favorable to the development of ore shoots 
must be regarded as a well-established law in this district, as well as in many others. 
In some cases it is found that intersections of two veins have an adverse influence 
E/ Paso tunre/ 
