Pinal County Arizona Gold Production
The Ray (or Mineral Creek) district is in northeastern Pinal County about 17 miles south of Miami. It lies between the Dripping Springs Range to the east and the Tortilla Range to the west. Copper is the major commodity of this district; gold is a byproduct.
The district was organized by silver prospectors, probably before 1873, and the first locations were made about 1880 (Arizona Bureau of Mines, 1938, p. 80-81). The first copper company was organized in 1883, but attempts at exploitation over the next 23 years failed, owing to the generally low grade of the ore. In 1906 some high-grade copper ore was mined. In 1907 the Ray Consolidated Copper Co. was organized, and extensive surface drilling and underground exploration revealed enormous copper ore bodies which were mined on a large scale in the spring of 1911 (Ransome, 1919, p. 17-19). Ray Consolidated soon became the largest producer in the district. The property continued to be an important source of copper, though ownership was changed to Ray Division of Kennecott Copper Corp.
The Ray district has produced a surprisingly small amount of gold, considering the large production of copper. Total gold production through 1959 was about 35,250 ounces.
The rocks exposed in the Ray district are similar to those of the Globe-Miami district. The oldest rocks are granitic intrusives and Pinal Schist of Precambrian age. Unconformably overlying them are altered sedimentary rocks of the Apache Group and the Troy Quartzite of late Precambrian age. Great sills of diabase were intruded into the Apache Group and the older rocks (A. F. Shride, oral com-mun., 1962). In the eastern part of the district lower Paleozoic sedimentary rocks are exposed in a few fault blocks. Dikes, sills, and irregular bodies of quartz diorite, quartz monzonite, and granite, of probable early or middle Tertiary age intrude the Precambrian and Paleozoic rocks. Conglomerate and a dacite flow of late Tertiary age and the Gila Conglomerate of Tertiary and Quaternary age discordantly overlap the older rocks (Ransome, 1919, p. 123-126). The rocks in the eastern part of the district are displaced by a mosaic of normal faults. West of Mineral Creek, which is in general parallel to the Ray fault (the major structural element in the district), Precambrian and Tertiary rocks are exposed and are considerably less faulted than the rocks east of Mineral Creek (Ransome, 1919, p. 127, 128).
The ore deposits consist of disseminated chalcocite of secondary origin associated with primary pyrite and are chiefly in the Pinal Schist and in diabase adjacent to quartz monzonite intrusives and in the intrusives themselves. The primary deposits, which underlie the chalcocite ore, contain pyrite and chalcopyrite. The chalcocite ore is generally overlain by a leached capping of variable thickness which locally is rich in chrysocolla and malachite. The ore bodies are undulate, flat-lying masses of irregular outline and thickness (Ransome, 1919, p. 12).