MINES OF BATTLE MOUNTAIN, EAST GROUP. 
439 
be but imperfectly discovered. Some of them, as the dike exposed on the 500-foot 
level east of the Captain veins (PI. XXVIII) were olivine-feldspar basalts, pos¬ 
sibly nepheline bearing, in which the olivine has been alter d to serpentine and 
carbonates and the groundmass is full of calcite. Others, such as the Anna Lee 
dike, which passes through the Anna Lee shaft (PI. XXVIII) and is probably one 
of the dikes cut in the crosscut west of the No. 3 shaft, contained phenocrysts of 
olivine and augite lying in a groundmass rich in augite and magnetite. This 
groundmass, though obscured by calcite, apparently never contained plagioclase, 
and the rock is probably to be lassed as a limburgite. The basaltic dike shown 
on the 500-foot level (PI. XXVIII) just east of the Burns ihaft is also probably a 
limburgite. It contains a little biotite and some kernels of unaltered olivine. The 
groundmass shows abundant calcite and a clear isotropic mineral which is probably 
analcite. 
As a rule the basic dikes as encountered underground are of a dull dark- 
greenish color, so softened by decomposition as to be readily picked down and 
rapidly disintegrating on exposure to the air. The harder, fresher phases are 
nearly black and commonly reveal a regular platy jointing parallel to their walls. 
These fine parallel cracks are frequently filled with white calcite and the structure 
thereby accentuated (PI. XVI, B, p. 166). 
The basic dikes are all later than the phonolite dikes, which they frequently 
cut. Whether the feldspathic basalts are earlier or later than the limburgites is 
not known, though it is probable that both belong to the same general period of 
eruption. 
LODE SYSTEMS. 
The Portland mine contains more productive lodes and presents greater variety 
in the character of its ore bodies than any other mine in the district. By far the 
greater number of the lodes have courses lying between north and N. 35° W. In 
general the more nearly north-south strikes prevail in the southern part of the mine, 
near the Burns shaft, while the more westerly strikes are characteristic of that part 
of the mine lying just north of the No. 2 shaft. The only notable exception to the 
foregoing general statements is that furnished by the Bobtail vein, which strikes 
about N. 60° W. A number of the lodes are practically vertical: others have a 
westerly and some an easterly dip. The dips as a whole are high—rarely under 70°. 
The Bobtail, however, has a southwesterly dip of a little less than 65°. The ground 
which has hitherto proved most productive in the Portland mine lies in two broad 
vertical zones which cross the general strike of the lodes nearly at right angles. One 
of these northeast-southwest zones crosses the lode systems at the Burns shaft, and 
contains the productive portions of the Portland, Bobtail, Diamond No. 2, Rose, 
and Scranton lodes. The width of this zone is not susceptible of accurate meas¬ 
urement, but one boundary may be considered as passing about 300 feet northwest 
of the Burns shaft. The other boundary probably lies between 1,100 and 1,200 feet 
southeast of the Burns shaft and includes the productive ground north of the 
No. 1 shaft of Stratton’s Independence mine, as well as that of the Strong, Dillon, 
and Monument mines. Such lodes as pass from granite into breccia, or vice versa, 
cross the contact between these rocks without noticeable deflection. 
