Structural Setting and Synplutonic Fault Kinematics of a Cordilleran Cu-Au-Mo Porphyry Mineralization System, Bingham Mining District, Utah

摘要

Cu-Au-Mo porphyry-type and Cu skarn-type mineralization in the Bingham mining district of Utah are temporally and spatially related to a suite of monzonite and quartz monzonite porphyry intrusions comprising the Bingham complex. Structural control on mineralization at the Bingham Canyon mine has been described at the scale of individual large-scale folds and fracture sets but no integrated pattern for the synmineralization deformation structures has emerged from earlier research. In the work reported here we have investigated hitherto largely unrecognized components of deformation (translations, rotations, and strains) associated with emplacement of many cubic kilometers of granitic rocks in the intrusions of the Bingham district. We have used both the local three-dimensional static mine model and the regional context in digital kinematic two- and three-dimensional forward and reverse modeling to identify a geometrically valid and admissible fault framework for the Bingham district and a kinematic solution for this framework through time. The results indicate that porphyry intrusions and associated mineralization were emplaced during reactivation of a basement-dictated linked system comprising two sets of northwest- and (north)-northeast-trending strike-slip faults. Both sets operated as transfer faults during extensional collapse of the Sevier orogen in the Eocene. Each fault set is characterized by overstep geometries with relay ramps breached by faults (re)activated in extension. Strike-slip was accompanied by progressive dilation of the extensional faults in fault oversteps to permit emplacement of composite stocklike (low aspect ratio) intrusions. The kinematic fault framework identified provides a new structural context for porphyry- and skarn-type mineralization at the Bingham Canyon mine, with potential for linking mineralizing fluid flow to three-dimensional structure and the development of that structure through time.