STRUCTURE OF THE GOLD DEPOSITS. 
163 
Fig. 10.—Section of part of Blue 
Bird Vein, level 13, showing 
massive vein of quartz and 
fluorite between phonolite and 
breccia. 1. Breccia. 2. Mas¬ 
sive quartz and fluorite. 3. 
Fragment of breccia. 4. Dolo¬ 
mite veinlet. 5. Phonolite. 
in a few places is 5 inches wide, and veinlets of 2 inches in width are common in 
nearly all the large mines. 
Although the prevailing narrowness of the productive fissures is one of the most 
characteristic features of the district, there are not lacking numerous examples of 
fissures which opened to considerable width. The Blue Bird 
lode in some places contains a vein, 3 feet wide, of solid fluorite 
and quartz inclosing fragments of breccia (figs. 10 and 11). 
Parts of the Work vein, or Black vein, as it is called, in the 
Mary McKinney mine, consist of a foot of fluorite or vuggy 
quartz between well-defined walls, accompanied by parallel 
sheeting. The Howard flat vein, as exposed in the Ophelia 
tunnel, shows bj r its large vuggy cavities that it must origi¬ 
nally have been a sheeted zone with occasional openings 2 
or 3 feet wide. The cross veins of the Last Dollar mine are 
apparently not wery persistent, yet one of them on level 12 
showed a local gaping of the fissure walls to a width of 2 
feet. The cross lode on level 11 of the Findley mine has a 
middle vein of compact fluorite and quartz up to 15 inches 
wide, with a few small parallel seams on each side. The 
middle fissure of the Buena Vista lode contains in places a 
similar vein up to 6 inches wide. Portions of the Doctor- 
Jackpot lode and the Lead vein of the Moon-Anchor mine fill 
fissures which 'opened to widths of 6 inches or more. In 
some cases these wide fissures occur merely in portions of a lode which elsewhere 
shows close parallel sheeting. In other cases, such as the work vein, the presence 
of a fairly thick plate of quartz and fluorite, or of 
other vein filling, is characteristic of the lode. 
In the upper parts of some of the lodes, the 
original structure is obscured by oxidation, 
whereby the sheeted structure is often lost and 
the vein forms a clayey streak sometimes several 
feet wide. Within this zone may occur veinlets 
of kaolin or alunite up to a foot wide. The most 
conspicuous example of this alteration is the Wild 
Horse vein, which is entirely oxidized in its 
productive portion to a depth of 1,000 feet. It 
is a structureless clayey mass, up to 25 feet wide, 
with two or more well-defined but curved and 
irregular walls. These walls are not continuous, 
but die out in places and are succeeded by others. 
Although most of the veins show by their 
structure and by their failure to dislocate the 
various dikes and intrusive sheets which they 
cross that the opening of their fissures was not 
accompanied by noticeable faulting, there are a few lodes, such as the Bobtail vein 
in the Portland mine, the Mary McKinney vein, the Doctor-Jackpot vein, and the 
Gold Coin vein, which have a somewhat different character. 
3 -Ft. 
Fig. 11.—Structure of Blue Bird vein, level 9, 
showing filled fluorite vein in middle. 
