by Waldemar Lindgren & Frederick Leslie Ransome
The Dead Pine mine, owned by the Ophir Mining and Milling Company, is situated on the south slope of Battle Mountain, between the Ajax and Gold Coin mines. The workings are confined to the Dead Pine claim, which runs about Northeast 6°, following the general course of the northerly continuation of the Coin lode. In 1894 the Dead Pine was a mere prospect and received only casual mention in Penrose's report.
Between 1894 and 1896, however, an inclined shaft was sunk on the northern part of the claim and some rich ore stoped in the granite near the granite-breccia contact. Later the vertical Oliver shaft was put down and is now the main shaft of the mine.
The Oliver shaft is situated 285 feet from the south end of the claim and is about 900 feet deep. It is connected with levels at 250, 525, 625, 725, and 825 feet below the collar. The old Dead Pine incline, 425 feet from the north end of the claim, follows the contact between the granite and the breccia, which dips 70 ° N.
There are ten levels connected with this incline, approximately 50 feet apart. The old Dead Pine levels 5 and 9 are connected with the main 250-foot and 525-foot levels, respectively.
At the south end of the property is another inclined shaft connecting, with four levels. The second of these is continuous with the 250-foot level of the Oliver shaft and is the only level common to all three shafts.
The main workings have a generally linear plan and extend longitudinally through the claim. Near the old Dead Pine incline, however, are two series of northwest-southeast drifts following short cross pay shoots.
The fissure zone known in the Gold Coin mine as the Coin vein has an average easterly dip at the Gold Coin and Dead Pine line of about 73 °. At the Oliver shaft the average dip is about 82 °. At a point 300 feet north of the Oliver shaft the lode is practically vertical, while north of that point the general dip becomes distinctly westward at an average angle between 80 ° and 90 °.
North of the old Dead Pine incline the fissure zone passes into the breccia, but becomes very small and obscure after leaving the granite.
In addition to this dominant zone of nearly north-south fissuring, there are in the northern part of the mine two zones of cross fissures. The more northerly of these zones has a general strike of N. 48 ° W. The more southerly zone, which intersects the main Dead Pine lode about 125 feet south of the other, has a general strike of N. 26 ° W.
The two zones thus converge toward the Ajax ground. Both fissure zones dip to the southwest - the northern, one at 70 °, the southern one at angles ranging from 35 ° to 80 °, the latter being the usual dip. The southern zone is known as the Montana vein and follows the curved and irregular course of the phonolite dike of the same name.
As the granite-breccia contact, which has locally a nearly east-west trend, dips to the north, while the northern fissure zone dips to the southwest, the two converge upward.. The fissure zone, as a consequence of this convergence, meets the contact in the vicinity of the old level 8.
If it persists above that level it should pass into the breccia, into which, however, it has not been followed. There is no perceptible displacement of the lodes, at the point where the main fissure zone and the cross fissures intersect.
All the ore of the Dead Pine mine occurs in granite or in dikes of phonolite cutting the granite. The contact between the granite and the breccia crosses the northern part of the workings in a nearly east-west direction and dips north at 70 °.
Its position is shown by the old Dead Pine incline, which follows the contact. The latter is fairly sharp and usually accompanied by some pyritization of the neighboring breccia.
A few crosscuts have been run into the breccia without, however, the discovery of anything of value. The long crosscut on the 625-foot level to the northeast corner of the claim passes through breccia into massive latite-phonolite.
The granite of the Dead Pine is the same as that forming the principal country rock of the Gold Coin, Granite, and Strong mines and needs no further description.
The two principal phonolite dikes are the Montana dike and the East-West dike. The former is probably a continuation of the Montana dike of the Gold Coin mine and passes northwestward into the Ajax ground, where it is known as the Apex dike.
It appears to divide as it crosses the Dead Pine and Ajax line, sending off a northerly branch toward the McKay shaft near the northwest corner of the Dead Pine claim. The dike itself is so-irregular, however, in the vicinity of the granite-breccia contact, and there are so many other small intrusions of phonolite in the granite, that it is impossible to trace its exact course without actually drifting on it.
On the old level 8, for example, there is a small curved east-west dike, just south of the incline, which probably joins the Montana dike to the west, and 200 feet southwest of the incline is a nearly north-south dike which probably joins the Montana dike to the south. In the southern half of the Dead Pine claim the Montana dike has not been exposed, though it can not lie very far east of the main drift on the 825-foot level. It probably has here a nearly north-south course.
North of the Oliver shaft it is visible on the 250-foot level in a crosscut 115 feet east of the main lode. From this point it swings northwestward, crossing the line of the main lode and continuing into Ajax ground. Its average dip in this part of its course is about 80 ° SW. The width of the Montana dike varies from 10 to 25 feet.
The East-West dike crosses the Dead Pine claim at the surface about 75 feet north of its south end line. It is usually about 10 feet wider and dips to the north at an angle of 65 °. It is cut on the 250-foot level 170 feet south of the shaft, on the 525-foot level 50 feet south of the shaft, on the 625-foot level at the shaft, on the 725-foot level 65 feet north of the shaft, and on the 825-foot level 125 feet north of the shaft.
There are several other-small phonolite dikes encountered in the mine, but they are less persistent and usually even more irregular than those described.
The principal ore bodies thus far discussed have occurred in the northern part of the mine, near the old incline. One of these pay shoots is in the main fissure zone, between the Montana dike and the granite-breccia contact, and attains its maximum development on the old level 5, or 250-foot level of the Oliver shaft.
This is a narrow sheeted zone in granite similar in character to the short lodes occurring in connection with the large southwest ore body of the Ajax mine.
Another ore body has been stoped on the more northerly of the two cross lodes. This pay shoot begins just above the old level 8 and has been stoped down to the old level 10. On the old level 11, or the present 625-foot level, the ore becomes too narrow to stope. This ore body was rarely over 3 feet wide and probably nowhere more than 50 feet in length.
Between the 250-foot and 725-foot levels bunches of good ore occur on one or both sides of the Montana dike at the intersection of the dike of the main Dead Pine fissure zone (fig. 19). A few small bodies of ore have also been found at other points along the contacts of the Montana dike with the granite, but these have been of little importance.
No pay shoots have yet been found in the Dead Pine lode between the Montana dike and the East-West dike.
Throughout this part of its course the lode is a well defined sheeted zone in granite, occasionally passing through small, irregular dikes of phonolite. Some of these dikes have a general north-south course and are occasionally followed for a hundred feet or more by the fissure zone, as may be seen on the 250-foot level.
On most of the levels the fissuring is rather irregular near the point where the lode changes from an easterly to a westerly dip, but there is nothing to indicate any break in the general continuity of the Dead Pine lode.
South of the East-West dike a few small disconnected bunches of ore have been found in the Dead Pine lode on the 525-foot and 825-foot levels. Near the Gold Coin line the ore has been stoped to a maximum Width of 5 feet and to a height of 40 feet above the 825-foot level.
At this height the fissure zone shows considerable oxidation and no longer contains paying ore. Although the stopes of the Gold Coin come practically up to the Dead Pine line on nearly all levels, there is no sharp change in the character of the ore precisely at the line.
The difference in development in the two mines merely indicates that the Gold Coin mine was able, in connection with its higher-grade ores, to carry its stopes into ore of somewhat lower grade than the Dead Pine mine can profitably handle.
None of the ore formerly mined in the old north workings was seen at the time of visit. It contained tellurides from which the gold had been partly freed by oxidation. In its general character it probably differed in no essential degree from the ore found at the same depth in the granite of the Ajax mine. The ore of the 825-foot level occurs as a telluride - probably calaverite, with quartz and fluorite within the small fractures in the granite which accompany the dominant fissure of the lode.
The vein minerals occur in the usual manner as a drusy incrustation on the walls of the narrow fractures. In the main fissure zone there is usually present a streak an inch or two wide, commonly termed "block quartz," which is used as an indicator in following the lode. This streak is chiefly freely crystalline quartz which apparently owes its dark line to the presence of minute crystals of pyrite. It sometimes has an open or cellular structure and may then contain calaverite, or, if partly oxidized, calaverite and free gold.
Little could be learned at the time of visit of the range in value of the ore stoped in the northern and hitherto most productive part of the mine. Portions of the main lode on the 825-foot level contain as much as 2 ounces of gold to the ton, but the average tenor of the ore now stoped is probably below this. Ore worth less than $12 per ton can not at present be profitably handled.