446 GEOLOGY AND GOLD DEPOSITS OF THE CRTPPLE CREEK DISTRICT. 
The great Diamond ore body, which about the year 1896 furnished the bulk of 
the ore from the Portland mine, had a maximum width of fully 50 feet and a length 
of about 100 feet. This ore body extended from a point just above the 600-foot level 
nearly to the 1,000-foot level. Above the 600-foot level the ore ended abruptly at 
the contact of the granite with the overlying breccia. Between the 600- and 700-foot 
levels the ore body w r as divided by a huge horse of granite, on the east side of which 
the bulk of the ore lay. The collapse of this horse, after the removal of the ore ; 
formed a great chamber now well seen from the 700-foot level. 
The body was largest between the 700- and 800-foot levels, and averaged over 
$100 of gold per ton as shot down in the stope, while several carloads of ore mined in 
1899 just above the 600-foot level carried over 30 ounces of gold per ton. On the 
900-foot level the ore was usually less than 10 feet in width and had fallen in value to 
an average of about $25 per ton. Below this level the ore barely paid for extraction, 
and just above the 1,000-foot level ended rather abruptly, in many cases apparently 
at inconspicuous, nearly horizontal joint seams in the granite. On the 1,000-foot 
level the Diamond vein is represented by two sheeted zones in the granite, both 
accompanying phonolite dikes. These zones have a maximum width of about 4 
feet and are approximately 50 feet apart. These fissures are accompanied by pyrite 
disseminated through the sheeted granite, but contain no ore. The phonolite dikes 
visible on the 1,000-foot level are said to have occurred irregularly in the ore body 
above, but the ore itself was always in the granite, never in the phonolite. 
The best example in the mine of an ore body formed by the mineralization of a 
phonolite dike is the original Portland vein. It is essentially a sheeted zone which 
was most productive where it coincided with the dike. At the adit level the general 
country rock is latite-phonolite and the lode is apparently in the same rock down to 
the 220-foot level. On the 350-foot level the Portland dike and vein are in breccia. 
In the present condition of the old stopes no satisfactory study of the lode is practi¬ 
cable. The ore body seems to have been irregular in width and usually to have had 
well-defined walls—those of the phonolite dike. The lode was stoped almost from 
the surface nearly down to the 500-foot level. On this level the lode has left the 
phonolite dike and is in granite. The granite adjacent to the rather indistinct 
fissure zone is metasomatically altered and has the porous texture characteristic of 
granitic ore. It is not, however, of sufficient value to pay for extraction. 
The Bobtail vein, one of the most regular and persistent lodes in the mine, was 
studied only on the 500-foot and lower levels, where it is mainly within the granite, 
southwest of the Burns shaft. It was there seen to be of an entirely different type 
from any of the lodes just described. As a rule the lode shows considerable oxidation 
even down to the 900-foot level and its character is thereby somewhat obscured. It 
strikes nearly northwest and southeast and dips southwest. The Bobtail and 
Portland veins cross without any apparent faulting and most of the Bobtail ore 
occurs on the west side of the Portland vein and within a distance of 100 feet from 
the intersection. Smaller bodies, however, occur in other parts of the lode, as near 
the contact of the granite with the breccia, at about the 500-foot level. The rather 
irregular Assuring of the Bobtail lode follows what at first glance appears to be a 
narrow, irregular dike of some darker rock than the granite. Closer examination of 
the so-called Bobtail dike suggests, however, that it is a breccia containing fragments 
