New Mexico Mineral Symposium — Abstracts

The Pioneer mining district is in the northeast corner of Pinal County, approximately 65 mi east of Phoenix. It encompasses an area from Silver King to the Belmont mine, from Superior to Gonzales Pass. It is also referred to as the Superior mining district. The Silver King mine was the first one developed in the area, and when the silver ran out, copper became king at the Magma mine (originally located as the Silver Queen). Although not the earliest producer, the longest lived mine in the district is the Magma mine at Superior.

In 1873, while constructing a road over the limestone mountains between Globe and Florence, a soldier (Sullivan) discovered a few lumps of heavy black rock. After leaving the Army, he
mentioned his discovery to residents in the Florence area. Soon thereafter he moved on, and the farmers put together two prospecting expeditions over the next two years. The first discovery, in 1874, was the Silver Queen followed by finally relocating Sullivan's discovery as the Silver King on March 22, 1875.

Mining commenced at the Silver King following the discovery, and profitable operations continued through 1887. Additional, intermittent work continued until 1920 without any real success. The mill for processing the ore was located at Hastings near Picket Post Mountain to be closer to water. Some work was done on the Silver Queen claims, but the silver ore quickly turned to uneconomic black copper mineralization (predominantly chalcocite, which contains 78% copper). Only the most valuable of ores could be mined because all materials and supplies were brought in by mule team from the river port at Yuma, Arizona.

By the turn of the century, the railroad had gotten as far as Florence. As a result, copper economics began to change and more interest was shown in the Silver Queen. William Boyce Thompson (of Newmont Mining Corporation fame) took an option on the property and organized the Magma Copper Company in 1910.

Development of the Magma mine has included the sinking of nine shafts, miles of drifts, the construction of 35 mi of railroad, a concentrator, a smelter, and a townsite. During the last expansion in the early seventies, #9 shaft was sunk a total length of 5,000 ft with a finished diameter of 22 ft. In addition, a haulage adit was driven a total of 7,500 ft with a 12-ft-diameter tunnel-boring machine. Today that is fairly routine but the project was truly innovative in 1969.

The first fifty years of mining extracted ore from the Magma vein and several parallel vein structures. These were generally east-west striking, almost vertical veins. In the 1950s, mining began in manto replacement beds within the Naco, Escabrosa, and Martin limestone units. The replacement bed orebodies were exploited until the mine closed in 1982 because of the poor copper market and high costs experienced at the mine. The Magma mine reopened in 1989 and has continued in production. There have been over 2.5 billion pounds of copper produced from the Magma mine, along with lesser amounts of gold, silver, lead, and zinc.

Other producers in the area include the Lake Superior and Arizona and the Belmont for copper, the Ramsey for gold, the Arizona Hancock for lead and vanadium, and the most famous lapidary locale, "The Apache Tears" pit. Specimen production from mines of the Pioneer district is confined almost exclusively to the Silver King, the Magma, and to a much lesser extent, the Arizona Hancock. The Silver King has produced some of the best native silver from Arizona. The Magma mine has produced world-class examples of barite, pyrite, and calcite. Lesser known minerals include chalcocite, chalcopyrite, groutite, rhodochrosite, and gypsum. For the richness of the orebodies, the copper sulfide minerals are generally poorly crystallized. The Arizona Hancock has produced some fairly nice red vanadinite crystals up to 4.0 mm.