Western Mineral Resources

U.S. Geological Survey
Professional Paper 1733

The Ajo Mining District, Pima County, Arizona—Evidence for Middle Cenozoic Detachment Faulting, Plutonism, Volcanism, and Hydrothermal Alteration

By Dennis P. Cox, Eric R. Force, William H. Wilkinson, Syver W. More, John S. Rivera, and Joseph L. Wooden


View to the west from the Scenic Loop Drive south of the town of Ajo. The hill at right shows pronounced layering in the Oligocene-Miocene Locomotive Fanglomerate. The sharp peak in the distance is North Ajo Peak, formed by units of the Miocene Ajo Volcanics.


The Ajo porphyry copper deposit and surrounding Upper Cretaceous rocks have been separated from their plutonic source and rotated by detachment faulting. Overlying middle Cenozoic sedimentary and volcanic rocks have been tilted and show evidence for two periods of rotation. Following these rotations, a granitic stock (23.7±0.2 Ma) intruded basement rocks west of the Ajo deposit. This stock was uplifted 2.5 km to expose deep-seated Na-Ca alteration.

Download the text for this report as a 53-page PDF file (17.1 MB).

Download the plate for this report as a ~34" x 34" PDF file (3.2 MB).

For questions about the content of this report, contact Dennis Cox

Version history

Download a free copy of the current version of Adobe Reader.

| Help | PDF help | Western reports main page | Western Professional Papers |
| Geologic Division | Western Mineral Resources |

This report is also available in print from:

USGS Information Services, Box 25286,
Federal Center, Denver, CO 80225
telephone: 888 ASK-USGS; e-mail: infoservices@usgs.gov

Accessibility FOIA Privacy Policies and Notices

Take Pride in America home page. FirstGov button U.S. Department of the Interior | U.S. Geological Survey
URL: https://pubs.usgs.gov/pp/pp1733/
Page Contact Information: Michael Diggles
Page Last Modified: June 18, 2008