By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Cochise County, third among the gold-producing counties of Arizona, produced approximately 2,-723,000 ounces of gold from the beginning of mining in the county in about 1879 to the end of 1959. Of this amount, about $24,275,000 (1,174,408 ounces) was a byproduct of copper ores, mainly from the Bisbee district (Wilson and others, 1934, p. 117), and about 950 ounces was from placers. Other districts that have produced more than 10,000 ounces of gold are the Turquoise (Courtland, Gleeson), Dos Cabezas, and Tombstone.
The Bisbee (or Warren) district is in the southeastern Mule Mountains, in the southern part of the county, immediately north of the Mexican border. Although the Bisbee district was the largest gold producer in Arizona in 1959, most of its gold was a byproduct of copper ore.
Though lead carbonate ore was discovered in the district about 1876, there was little activity in the area until after 1880 when rail connections, generally favorable business conditions, and copper prices encouraged prospecting. The Copper Queen ore body, found in 1877, was developed in 1880. In subsequent years the Copper Queen Mining Co., under the control of Phelps, Dodge, & Co., acquired other properties in the district and became the leading producer (Ransome, 1904, p. 13-15). In 1900 the Calumet and Arizona Co., another major producer, was organized. In 1902 a custom smelter was erected at Douglas, and some of the smaller mining companies, among them the Shattuck and Denn, were started. At the end of 1931 the two largest companies, the Copper Queen and the Calumet and Arizona, were consolidated as the Phelps Dodge Corp., Copper Queen Branch (J. B. Tenney, in International Geological Congress, 1935, p. 222). In 1947 the Denn mine was sold to the Phelps Dodge Corp., and in 1949 the custom mill of the Shattuck Denn Mining Corp. was closed, leaving the Phelps Dodge Corp. as the only large producer in the district. Phelps Dodge maintained large-scale operations through 1959.
The gold production of the Bisbee district before 1895 was not ascertained. From 1895 through 1929 the district produced 1,110,058 ounces of gold (J. B. Tenney, in International Geological Congress, 1935, p. 222) and from 1930 to 1959, a total of 1,082,765 ounces was produced. Total gold production through 1959 was about 2,193,000 ounces.
The oldest rocks in the Bisbee district are the Pinal Schist and a granite of Precambrian age. These are unconformably overlain by about 5,250 feet of Paleozoic rocks which in turn are unconformably overlain by about 4,750 feet of Cretaceous sedimentary rocks. The Paleozoic rocks consist of about 430 feet of Cambrian quartzite, succeeded by about 4,800 feet of limestones of Cambrian, Devonian, and Carboniferous age. In pre-Cretaceous time, folding and faulting occurred, and in post-Cretaceous time the rocks were warped and dislocated by thrusts and normal faults of moderate throw (Ransome, 1904, p. 24-73, 106-108). Dikes, sills, and stocks of granite porphyry intrude the Paleozoic rocks, but their relation to the Cretaceous rocks is not clearly revealed (Tenney, in Ransome and others, 1932, p. 46-47; O. N. Rove, in New-house, 1942, p. 211-212). The main stock of granite porphyry is exposed on Sacramento Hill, the principal and most productive center of mineralization. The stock was intruded in the plane of the east-trending Dividend fault, a dominant structural feature of the district. Surrounding the intrusive mass is a zone, ranging from a few feet to 1,000 feet in thickness, of contact breccia composed of rounded and angular fragments of the intruded rocks. The border of the porphyry, the contact breccia, and the adjacent limestone are all silicified. Surrounding this silicified zone is a chloritized zone that grades outward into a marbleized zone in the limestone.
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