A deposit that cropped out in the western part of the mineralized area. All outcrops of this vein have long since been obliterated by caving operations of the Inspiration Mine. Development of this vein was begun in 1897. In 1905, the Keystone Copper Co. was organized to continue exploitation of the deposit. Operations ceased in 1907 when the bottom of the silicate ore was reached. Since 1909, the history of this vein is concerned with the exploration and development of the Miami-Inspiration orebody.
The Keystone vein occupied a fissure in the sill-like body of granite porphyry facies of the Schultze granite that overlies the schist in the western segment of the Miami-Inspiration disseminated copper deposit.
Ransome (1903, pp. 160-161), described the ore of this vein as bluish-green, brittle chrysocolla adhering finely to the porphyry walls of the fissures and frequently inclosing fragments of the country rock. The ore contained a little quartz and malachite, the latter as streaks in the chrysocolla. It appeared to fill mechanically formed spaces for the most part, but there was also a little replacement of the wall rocks. The maximum width of the ore was about 18 inches (45 cm). The ore ended at the contact with the underlying schist.
This deposit is credited with production of 427,000 pounds of Cu.
References
Peterson, N.P. (1962), Geology and ore deposits of the Globe-Miami District, Arizona, USGS PP 342: 137.
Mineral List
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