A study of the literature on the centers of major mineralization in western United States reveals that in the preponderant number of those of the mesothermal and hypothermal environments the mineralizing fractures strike northeasterly; that in some of these centers the mineralization and the igneous masses with which it is genetically related are confined to a relatively narrow zone that trends northeasterly in general parallel to the strike pattern of the mineralizing fractures; and that the contained dikes usually parallel the zone, and often the larger igneous masses are elongated in that direction. Furthermore, the centers of the three main metallogenic epochs of the region--Precambrian, Nevadan-Laramide, and late Tertiary--are aligned in belts that also trend northeasterly, closely paralleling the trends in the centers.It is proposed that the belts of mineralization reflect zones of deep rupture in the earth's crust all of which formed simultaneously in response to a common regional stress, and that there is a genetic relationship between the zones of rupture and the magma reservoirs from which the mineralizing solutions were derived.

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