Jupiter Mine

Mine Description

The Jupiter property embraces the ground about the extreme southern head of Thaynes Canyon, from the main divide down nearly to the valley bottom. It comprises about a dozen claims, which were located early in the history of the camp and have been worked by a number of different persons. After pioneer prospecting the property was brought to a shipping basis in the early eighties. By the close of 1886 a good vein had been traced continuously down for 200 feet. During the succeeding year 50,000 pounds of high-grade ore was shipped and a deep lower tunnel was started, which was run during the next few years. In 1888 a good shoot of rich carbonate ore was opened, and the next year lessees were working this ground. In 1890 the Jupiter property was incorporated at Council Bluffs with a capitalization of $3,000,000. In 1894 some ore was taken out, and in 1900 the main vein had been opened 300 feet on its dip and yielded excellent ore. It is reliably reported that about five years later, after a period of inactivity, the main tunnel was extended several hundred feet until it crossed the main vein and was then turned and brought back across it toward the south, where a good body of rich lead-silver ore was found. Shipments from this shoot were being made regularly in 1906.

The ground has been opened by an incline sunk from the gap in the main divide at the head of the gully and by a series of tunnels, which enter the canyon wall at different elevations, ranging from one near the top to one near the base of the slope. One incline in the gap appeared to be about 150 feet deep and one is reported to have been sunk 300 feet on a vein. The lower or main recent work tunnel is over 800 feet in length. The tunnels in general extend southeastward and the incline dips steeply in the same direction.

The country rock comprises very highly metamorphosed limestones, shales, and sandstone, which in some places are now marble, slates, and quartzites, respectively. These sediments are so altered as to hide their normal lithologic character and to render identification by fossil remains impracticable. The intense deformation in this area prevents precise stratigraphic correlation with known beds, as a rule. It is probable, however, that the greater part of these metamorphic sediments are members of the Thaynes formation, and some may be younger. East of the gap, along the divide toward Jupiter Hill, is metamorphic shale and a small mass of monzonitic intrusive rock so altered and filled with biotite phenocrysts as roughly to resemble schist. West of the gap are marble and metamorphic shale and limestone, and the tunnels cut metamorphic limestone, black slaty beds, some quartzitic sandstone, and siliceous limestone. In the gap are green shale, gray argillite. quartzite, metamorphic limestone, and ferruginous breccia.

The gap has been eroded along a zone of weakness formed by fracturing and brecciation. The fissures in this general northeast zone range from N. 30° E. to N. 70° E. in trend. The most brecciated and iron-stained zone trends in the gap N. 45° E., and in a tunnel running north below the gap is a strong fissure trending N. 32° E. The prevailing dip is 45°-85° SE., the higher angles being most common. The distribution and truncation of the quartzite, shale, and limestone in the gap indicate considerable complicated faulting.

This zone or particular members of it form the locus of the ore and have been the object of search through the inclines and tunnels. It is understood, though it could not be personally determined owing to the condition of the workings, that the ore occurred as a lode on a northeast fracture zone dipping steeply southeast, which was followed down by inclines for over 300 feet and was cut by the bottom tunnel and certain others.

The ore that was last shipped from the property, that from the lower tunnel, like the ore from the incline at the crest of the divide, is stated to have been a rich silver-bearing lead ore. That from the higher parts of the lode was said to have been a carbonate and that from the lower tunnel a sulphide. From the dump at the mouth of the lower tunnel specimens were taken, which show massive and crystalline pyrite, a little recent azurite and malachite, and probably gray copper, in a gangue of calcite and probably dolomite and much specularite with garnet and quartz.

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

Jupiter Mine MRDS details