History of the Copper Mountain (Morenci) Mining District, Greenlee County, Arizona


The Arizona Geological Survey has just published a well-written history of the Morenci, Arizona, mining district. The report was written by geologist David F. Briggs and was published as AGS Contributed report Cr-16-C. The 79-page report is available for free download:

The Copper Mountain (Morenci) mining district is located approximately 115 miles northeast of Tucson, Arizona.

Mining began in 1873. This district has produced more than 36 billion pounds of copper from 1873 to 2015. Since 1985 is has been America’s largest domestic copper producer.

The discovery of copper at Morenci during the turbulent years of the American Civil War brought new opportunities for many, but foreshadowed the end of a way of life for Native Americans, who had lived in the region for millennia. A diverse cast of characters has played a role in Morenci’s history, including veterans who ventured west after the war, as well as immigrants eager to make a new life in America.

Briggs provides an interesting narrative of the development of the district as different companies gradually consolidated the mines. Briggs breaks the history into five phases of development as the owner(s) dealt with different types of ore, changing technology, new discoveries, and the sometimes volatile copper market.

Phelps Dodge Corporation operated the district beginning in 1917. Freeport-McMoRan Copper and Gold, Inc. (renamed Freeport-McMoRan, Inc. in July 2014) acquired an 85% interest in the Morenci project through its merger with the Phelps Dodge Corporation in March 2007, and has been operating the mine since then.

The report contains many maps and both current and historical photographs. This report is an interesting read and its story is one that was similar to that of many mines in the West.



 More reports from AZGS:

AZGS field guides to Arizona Geology

A guide to the geology of the Sedona & Oak Creek Canyon area of Arizona

A Guide to the Geology of the Santa Catalina Mountains

A Guide to the Geology of Organ Pipe Cactus National Monument and the Pinacate Biosphere Reserve

A Guide to the Geology of the Flagstaff Area

A Guide to Geology of Petrified Forest National Park

A Guide to Oak Creek-Mormon Lake Graben

AZGS Guides to Northern Arizona Geology

History of the Copper Mountain (Morenci) Mining District, Greenlee County, Arizona

Earthquakes shake Morenci, Arizona area

During October, six earthquakes, ranging from 2.5- to 4.1-magnitude, occurred about 25 miles north-northeast of Morenci in Greenlee County, east-central Arizona. These earthquakes were recorded by several seismographs around Arizona, including one in Tucson. In addition, there have been swarms of lesser magnitude earthquakes in the area according to the Arizona Geological Survey (AZGS). AZGS has a short article on these recent earthquakes here. The article includes maps and seismograph records.

According to Wallace (1989) “The background seismicity level for southern Arizona is quite low, especially compared to California. The two most seismically active regions in southern Arizona are the southeastern corner of the State, extending north from Douglas along the New Mexico border to the Clifton-Morenci area, and the southwestern corner south of Yuma along the Mexico-Arizona border.”

Just why earthquakes occur in the Morenci area is subject to speculation. No faults have been positively identified, but the topography suggests that a fault exists in the area. The Morenci area has long been seismically active. In May of 2010, 12 earthquakes ranging from Md 2.0 to 3.5, and 5 events below Md 2.0 occurred near the area of recent earthquakes.

Arizona is divided into two main physiographic provinces. In the northeast is the high-elevation Colorado Plateau characterized by mainly flat-lying sediments. The southwest part of the state is the Basin & Range province, lower in elevation, and characterized by long, thin mountains ranges separated by fault-bounded valleys. The Basin & Range topography is the result of crustal stretching during the past 20 million years.

Separating the Colorado Plateau from the Basin & Range, is the so-called Transition Zone which runs diagonally through Arizona from the northwest corner to the southeast corner. This area is characterized by faults and marks the boundary between the zone of crustal extension and the more stable plateau. The Morenci area earthquakes occur in this transition zone and may reflect continued crustal adjustment to the on-going extension.

UPDATE: A magnitude 3.4 earthquake hit just before 1a.m.  this morning, November 1, about 22 miles NNE of Morenci, in eastern Arizona.