Resistivity imaging over porphyry copper systems in the Red Mountain district, southwest Colorado, USA

The Red Mountain district in southwestern Colorado produced base and precious metals hosted in breccia pipes and vein structures related to an extensive lithocap that overlies pervasive quartz-sericite-pyrite alteration. A helicopter-borne time-domain electromagnetic survey flown over the district yielded resistivity values that range from tens to thousand or more ohm-m, with lesser resistivity values in the lithocap and greater resistivity values in the rocks with propylitic alteration. A 60 m-thick, low resistivity zone subparallel to topography characterizes the magmatic-hydrothermal breccia pipes. A broad zone of low resistivity that may envelope epithermal deposits spans multiple flight lines and occurs beneath rocks with argillic alteration. A 50 m-thick low resistivity zone occurs beneath quartz-sericite-pyrite alteration and may indicate porphyry deposit at depth.