The rocks of the Globe-Miami district range from lower Precambrian to Recent. The oldest formation, the Pinal schist, comprises several varieties of schist formed by dynamic and thermal metamorphism of shale and feldspathic sandstone during the early Precambrian Mazatzal revolution. During the later stages of this revolution, the schist was intruded by a complex of dioritic rocks and by plutons of granite and quartz monzonite. There were extensive intrusions of a biotite-quartz diorite, known as the Madera diorite, mainly south of the district. In the northern part of the mapped area, the schist was invaded by an extensive mass, the Ruin granite, which is a coarse-grained rock most commonly of quartz monzonitic composition. There are also smaller sill-like masses of slightly gneissic muscovite granite.
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Geology and ore deposits of the Globe-Miami district, Arizona