New Mexico Mineral Symposium — Abstracts

In August of 1872 a prospecting party from Silver City, New Mexico, discovered the mines around Clifton, Arizona. The first mining district was organized under the name of the Copper Mountain district. At that time there were only 18-20 men in the district, including Stevens and Bob Metcalf. Among the first claims to be located were the Arizona Central, Copper Mountain, Montezuma, and the Yankie. Conditions were not encouraging at that time. The nearest railroad was 700 miles away in La Junta, Colorado, no roads had been built, and the Apaches made frequent raids until around 1885. The Lezinsky brothers of Las Cruces, New Mexico, acquired an interest in the mines from Bob Metcalf and soon after gained nearly full ownership of the group. In 1873 an adobe furnace was erected at the Longfellow mine with a 1-ton per day capacity. In 1874 the first water-jacket furnaces were built on the San Francisco River near Clifton. In 1879 the Lezinsky brothers built a baby gage (20-inch) railroad connecting Metcalf to Clifton. In 1881 the Southern Pacific Railroad was completed making larger operations possible and lowering the cost of operations.

About 1893 the great low-grade sulphide bodies of Copper Mountain were discovered. This led to larger concentrators and furnaces being built. By 1901 production reached 38 million pounds. The Detroit Copper Company was formed around 1875. They began smelting rich ore around 1882 at a smelter on the San Francisco River. In 1884 the smelter location was changed to Morenci. Around 1895 the holdings and plant were transferred to Dodge, Phelps and Company.

Mining was conducted with overhand stoping with square sets, the stopes being back filled as far as possible afterwards. Miners wages at the time were $3.00 per day for Americans, $2.50 for Mexicans, and $1.00 to $2.00 a day for common laborers. Timbering was the most expensive cost after labor. The timber was shipped in from California and Oregon. Mining costs varied from $1.50 to $2.00 per ton. The ore was rough sorted to smelting ore, 8% and above, and concentrating ore. Concentrating ore consisted of decomposed porphyry with finely disseminated pyrite and chalcocite. Oxide ore consisted of cuprite, malachite, and azurite. The West Yankie mine was the largest producer. The Manganese Blue mine produced large amounts of high-grade carbonate ore.

The Manganese Blue mine was the mainstay of the Detroit Copper Company for many years before the discovery of the great masses of chalcocite ore below Copper Mountain. It was developed through the Old Blue shaft to a depth of 400 feet. The collar elevation was at 4,853 feet and had four levels at 100, 175, 275, and 375 feet The bulk of the ore was mined out before 1905. The old Manganese Blue workings are where the bulk of our mining for specimens took place.

Geology
The Copper Mountain fault runs along the center line of Copper Mountain and divides the sedimentary beds into two parts. The dip of the fault plane is 63° northeast or north-northeast. The vertical throw is about 225 feet, and the horizontal movement of the northeast block is about 70-90 feet. The rocks are greatly crushed near the fault, and often there are two or three parallel planes within a few feet. The northeast fault block is the Modoc Limestone, which has been altered to a heavy garnet skarn. The southwest side of the fault contains unaltered crystalline limestone. Rock exposed in the Old Blue shaft is as follows: 60 feet of limestone, 60 feet of garnet rock, 50 feet of limestone, and 25 feet of quartzite with more limestone below this.

The oxidization zone is from 400 to 600 feet. To this depth from the surface, the sulphate solutions descended, and along important fissures may have gone somewhat farther. The solutions not only followed fissures, but penetrated the porous, sericitized porphyry with considerable ease. The altered limestones and shales are very compact, non-porous, and impervious. Oxidation through fissures and crack systems here reached 400 feet with no well-defined plane expressing the depth of oxidation.

Ore genesis
Intrusions of stocks and dikes of granite porphyry and quartz monzonite porphyry, which took place in Late Cretaceous or early Tertiary time, produced an important contact metamorphism in shales and limestones of Paleozoic age that happened to adjoin them. This metamorphism resulted in metasomatic development of garnet, epidote, diopside, and other silicates, accompanied by pyrite, magnetite, chalcopyrite, and sphalerite. The sulphides are not later introductions, but contemporaneous with the other contact minerals. The contact zone received substantial amounts of oxides of iron silica, sulfur, copper, and zinc, enough to form good-sized deposits of pure magnetite and low-grade deposits of chalcopyrite and sphalerite, all of which are unknown in the sedimentary series away from the porphyry.

Metamorphosed rocks are manifold and found under many varying conditions. There is only one common factor and that is the presence of the porphyry. It shows that the porphyry magma contained much water, which held in solution various salts, among which were salts of some of the heavy metals. Sodic chloride and ferric oxide probably predominated. It is believed that the magma contained all of the substances mentioned above, and that large quantities of this gaseous solution dissolved in the magma were suddenly released by diminution of pressure as the magma reached higher levels and forced its way through the adjoining sedimentary beds, the purest and coarsely granular limestones suffering the most far-reaching alteration and receiving the greatest additions of substance. It is thought that a direct transfer of material from cooling magma to adjacent sediments took place. The formation of garnet indicates large gains of ferric oxide and silica.

Collecting history
The geologic activity on Copper Mountain created a wonderful environment for the growth of mineral specimens. The Phelps Dodge Corporation has been kind enough to let us work with them in the extraction of these specimens. I have worked there off and on since 1996. In 2005 the last of Copper Mountain was covered with a leach dump, thus ending collecting on that great mountain.