New data concerning Proterozoic volcanic stratigraphy and structure in central Arizona and its importance in massive sulfide exploration

Detailed mapping in the Mayer-Crown King area, Arizona, reveals that Proterozoic volcanism resulted in the accumulation of 3,500 m of basaltic-rhyolitic flows and pyroclastics that are interbedded with chert, limestone, and oxide facies iron-formations. The volcanic rocks were then tilted and unconformably overlain by pelitic sedimentary rocks and intruded by a granodiorite pluton. Subsequent regional deformation has resulted in the isoclinal folding of all stratified rocks about steeply dipping, northeast-striking axial planes. The major reclined structures plunge 60 degrees to 80 degrees in the plane of foliation. This steeply plunging fold geometry has not been previously recognized; as a result the published stratigraphy of the region (Anderson et al., 1971) is in conflict with reconstructions based on this study. New map data reveals that volcanic units trend across regional foliation (030 degrees ) although elongated in that direction; consequently stratified volcanic rocks are oldest in the north and youngest in the south. It is apparent that a revision of the published nomenclature in the Mayer-Crown King area is needed. The recognition of this complicated fold geometry and the resulting complex stratigraphic pattern delineates new areas of exploration for volcanogenic massive sulfide deposits in Arizona.