116
FIGURE 21. Geophysical interpretation in the Duncan basin and adjacent areas showing structure and depth to bedrock. Adapted from West (1996) using data from Phelps
Dodge Exploration Inc. and NGDC. Note Clifton-Morenci area is located in the northwest corner of the maps.
A) Simple Bouger gravity anomaly map. Color scheme is based on equal area representation.
B) Aeromagnetic anomaly map. Analytic signal amplitude anomalies are shown using a scheme that emphasizes high amplitudes, or near-surface features
C) Shadow map of the aeromagnetic data. Shaded intensities are based on a ‘sun angle’ inclination of 30 o .
D) Interpretation of gravity and aeromagnetic data. Heavy solid lines represent normal faults interpreted from Phelps Dodge data with an adequate number of gravity stations.
Open double lines represent normal faults interpreted from NGDG gravity data. Thin solid lines represent aeromagnetic lineaments that correlate with outcrops of mid-Tertiary andesite in the southern third, with structure in the middle third, and faulted volcanic rocks under cover in the northern third of the map area. Dotted line represents normal fault based on the edge of shallow magnetic sources in mafic volcanic rocks, where no gravity data is available.

A) B)
117
C) D)
N
Morenci
Open Pit
Arizona New
Mexico
B a sin
D u n ca n
Duncan
Franklin
Day Ranch
Area
Safford
Basin
Fault
Lineament
River, wash
FIGURE 21. Geophysical interpretation in the Duncan basin and adjacent areas.