California Mine

Mine Description

The California ground is situated on the west side and near the head of Thaynes Canyon, immediately south and west of the Comstock mine.

This property comprises about eight claims, which have been prospected from time to time. Its history seems to be made up of a number of movements from one part of the property to another, each probably following some new favorable development. Thus in the swinging of the pendulum Thaynes Canyon was the point of prospectors interest in 1881, 1883, 1889, 1893, and 1900. In 1883, it is said, the camp fires in Thaynes Canyon gave the place the appearance of an army encampment. Early in 1893 the California mine was reported to have suspended operations, owing to an excessive flow of water, and to have resumed work in March. In March, 1895, lead ore that carried considerable zinc had been found, and the lower tunnel was started. Enough low-grade ore appears to have been uncovered in the next five years to lead, in June, 1900, to the purchase and remodeling of the old Apex mill, which was running by August of that year. A good body of ore was opened the succeeding year. Subsequently a dispute arose between certain officers of the company and certain interests in it, also, it was understood, between the Comstock and California companies as to the ownership of certain ore under the apex law. During the present examination of the district the property was idle.

The plant includes the small mill obtained from the Apex property, remodeled and with Wilfley tables added, a small shop and an office.

The ground has been explored by two tunnels, the lower or main tunnel near the creek level and the shop tunnel 100 feet above, by an intermediate level between the two, and by a shaft from the hillside to a depth of 185 feet, or 20 feet below the lower tunnel. The intermediate level is connected with the tunnel level by a chute and with the shop level by a 20° inclined stope. Both tunnels extend northwestward, the lower about 500 feet and the upper about 100 feet to the main workings, which comprise an extensive stope, a northeast drift of about 600 feet on the intermediate level, and two roughly parallel northeast drifts of 600 and 400 feet on, the lower level.

The lower part of the slope on the California ground is largely covered with glacial material and the upper part with float, so that bedrock was not observed in the vicinity of any of the workings. On the west limestone of the Thaynes formation outcrops. Dumps at prospect holes indicate that the underlying bedrock is metamorphic limestone of the Thaynes formation with dikes of biotitic porphyry.

Underground the country rock is metamorphic limestone and calcareous sandstone, with a transecting dike of porphyry. The prevailing dip of the sediments is 10°-20° N. 5°-35° W. The width of the dike is about 42 feet; the strike of the east wall where it is cut by the shop tunnel is N. 55° E. and by the lower tunnel N. 40° E., and the dip at these points is toward the southeast at angles of 32° and 60°, respectively.

The country rock is traversed by a great number of fissures, most of which trend N. 45°-60° E. and dip steeply toward the east or stand vertical. The main zone of fracturing is in the footwall of the dike and extends northeastward parallel to it, being over 100 feet wide on the shop and intermediate levels and nearly as wide on the lower level. The dip of a branch, which is followed southwest on the lower level toward the shaft, is 75° SE. and the dip of the foot of the main zone at the northernmost point where it is cut on the bottom level is 85° SW. Beyond this master zone toward the northwest are several strong north-east fissures dipping southeast, and about 100 feet from it lies one that has been followed southwestward for about 400 feet, dipping 60°-75° SE.

No concrete indication of the direction of movement on the master zone was found, though small traces showed movement upward on the west at some points and downward at others. On the whole the strong series of northeast faults dipping eastward against the bedding suggests a force from the east tending to thrust the eastern member up and over the western and relatively dropping the western. Considerable movement also occurred along bedding planes.

Mineralization seems to have taken place either along or adjacent to northeast fissures in a series of thin-bedded shaly limestones. Both true lode deposits and characteristic bedded replacement deposits occur. The principal mass of ore is a lens in the footwall of the main fracture zone, lying along the bedding, dipping northward, and divided into a series of minor lenses adjacent to northeast fissures. These fissures appear not only to have afforded the pathways for the ore-bearing solutions, so that the lens is elongated along them, but they also served for post-mineral fault planes, on which the ore beds appear to have been relatively elevated in progression from east to west, thus stepping the ore. In the western part of the ground a somewhat different type of occurrence was noted, namely, a shoot in the fissure and replacing a certain adjacent inclosing bed, pitching within the fracture zone with the dip of that bed.

The ore is a silver-bearing lead ore, of milling grade with much associated zinc and a generally calcareous gangue. Galena, the common source of the lead, is in large part embedded in a band of brown sphalerite. Cupriferous pyrite, both granular and crystalline, occurs in the same manner, also in veinlets on joints and slip planes and disseminated through metamorphic limestone. Some of the silver may be traced to jamesonite, which occurs sparingly in the form of minute bands and tufts of hairlike crystals in metamorphosed limestone within bands or lamellre of silica. The high proportion of sphalerite is noteworthy.

Source: Geology and Ore Deposits of the Park City District, Utah, 1912 - USGS

California Mine MRDS details