STRUCTURAL SETTING AND SYN-PLUTONIC FAULT KINEMATICS OF A CORDILLERAN CU-AU-(MO) PORPHYRY MINERALIZATION SYSTEM, BINGHAM MINING DISTRICT, OQUIRRH MOUNTAINS, UTAH

Cu-Au-Mo porphyry-type and Cu skarn-type mineralization in the Bingham district of Utah are temporally and spatially related to a suite of quartz monzonite and quartz monzonite porphyry intrusions comprising the Bingham complex. Structural control on mineralization at Bingham Canyon mine has been described at the scale of individual large-scale folds and fracture sets but no integrated pattern for the syn-mineralization deformation structures has emerged from earlier research. In this research 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 3d static mine model and the regional context in digital 2d and 3d 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 intrusive rocks of the Bingham district and the associated mineralization system were emplaced during reactivation of a basement-dictated linked system comprising two sets of NW- and NNE-trending strike-slip faults. These faults operated as transfer faults during extensional collapse of the Sevier orogen in Eocene time. Each fault set is characterised by overstep geometries with relay ramps breached by faults reactivated in extension. Strike-slip was accompanied by progressive dilatation of the extensional faults in fault oversteps to permit emplacement of composite stock-like (low aspect ratio) intrusions. The kinematic fault framework identified provides a new structural context for porphyry- and skarn-type mineralization at Bingham Canyon mine, with potential for linking mineralizing fluid flow to 3d structure and the development of that structure through time.