MINES OF BULL HILL. 
381 
GEOLOGICAL FEATURES. 
Volcanic breccia in places containing much latite-phonolite occupies the largest 
part of the area; but, as may be seen from the map, the area of massive latite-phono¬ 
lite which covers the surface at the Gold Sovereign, Blue Bird, and Dexter mines 
throws out a wide branch northward on the west side of Bidl Hill, almost reaching its 
summit at the Zenobia mine. This body of intrusive rock rests like a thick sheet on 
breccia, in which are most of the underground workings. A short distance east of 
this latite-phonolite, which may be called the Blue Bird area, appears another which 
is designated as the Altman area. This seems to reach down as far as the under¬ 
ground workings in the Findley mine have penetrated—1,500 feet. Whether the 
Shurtloff No. 1 vein is in breccia or latite-phonolite on level 15 of American Eagle 
has not been ascertained. At any rate, latite-phonolite must begin a short distance 
east of it. 
A very prominent phonolite dike about 25 feet wide traverses the Logan work¬ 
ings with a north-northwest trend; it lies 200 feet west of the shaft and is cut by 
levels 3, 5, 10, and 12. A parallel dike is stated to lie 50 feet west of the shaft. The 
main dike continues through the Dante workings and is probably continued through 
the Blue Bird and possibly into the Colorado City mine. It forms part of the great 
phonolite-dike system of the Portland mine and may be identical with the Rigi dike 
crossing the southern part of the Modoc mine. In the Logan it is not reported 
to carry values. 
Two persistent basic dikes cut through the central part of the properties in the 
Orpha May mine, and one of them at least is traceable on the surface for 2,000 feet. 
The western dike is exposed in the Favorite workings, where it dips steeply east- 
northeast; then in various crosscuts between the Eagle and Logan shafts, and finally 
in the Orpha May workings, where it is very productive and is intersected at an 
acute angle by the Orpha May vein. The other dike lies 200 to 300 feet farther 
northeast and is exposed by long drifts on Orpha May level 13 and Logan level 5. 
This does not seem to carry much ore. 
The Isabella dike of dark trachydolerite is said to be intersected by the Ameri¬ 
can Eagle shaft between levels 2 and 3. 
VEIN SYSTEMS. 
Several important vein systems traverse the property and at least three of them 
appear to converge toward a point from 500 to 800 feet north of the American Eagle 
shaft. Nearly all the veins trend north-northwest to north and stand vertical or 
dip a few degrees to the west. The Zenobia is the only one 6f importance which 
strikes northeast. 
Beginning from the west the productive veins are as follows: 
LOGAN VEIN. 
The Logan vein is exposed on various levels near the shaft and trends north- 
northwest. It is said to have carried ore for 200 feet below the surface. The lower 
workings disclosed many veins in various directions like those of the Dante, but no 
ore shoots of importance are recorded. 
13001—No. 54—06-26 
