This 18-page report by geologist and author Dave Briggs summarizes the long history of mining near Ajo, Arizona.
From Dave's report, "The hostile environment of southwestern Arizona’s
low desert presented many challenges to those who sought to discover and exploit the mineral wealth of the region. Ajo’s remote location combined with hot summer days and scarce water created a number of obstacles that needed to be overcome. Despite these impediments, the district’s wealth was mined by Native Americans long before the arrival of first Spanish explorers, who recognized its potential soon after establishing outposts in this region.
Many years passed before mining professionals with the knowledge, skills and financial backing achieved commercially viable copper operations at Ajo. Application of new technologies and mining practices enabled them to develop Arizona’s first large copper operation to successfully employ open pit methods."
Briggs, D.F., 2017, History of the Ajo Mining District, Pima County, Arizona. Arizona Geological Survey Contributed Report, CR-17-A, 16 p. http://repository.azgs.az.gov/uri_gin/azgs/dlio/1710