Cordilleran Section - 115th Annual Meeting - 2019

Paper No. 36-4
Presentation Time: 9:00 AM-3:30 PM


LOPEZ, Alexis R., Dept of Geological & Environmental Sciences, CSU, Chico, 400 West 1st St, Chico, CA 95929, BOURRET, Andre, Geological and Environmental Sciences, CSU Chico, 400 West 1st Street, Chico, CA 95929 and AIRD, Hannah M., Department of Geological and Environmental Science, CSU Chico, 400 W 1st Street, Chico, CA 95929

The Moonlight deposit, located in the Plumas County Copper Belt, California, is an iron oxide-copper-gold (IOCG) deposit associated with the quartz monzonitic Lights Creek Stock. Few studies have focused on the regional geology of the Plumas County Copper Belt and those that centered on the area have primarily focused on the paragenesis of the two other deposits associated with the Lights Creek Stock (Superior and Engels) and neglect to describe the Moonlight deposit. Five of the 21 available drill cores were chosen to describe the paragenetic sequence of the Moonlight deposit, based on historical and incomplete drill logs that specified the length, grade of copper (>0.25 wt.%), and quantity of the remaining core. The five drill cores were logged to compile a detailed lithologic description and petrographically analyzed to fully characterize the alteration and mineralization assemblages. Preliminary results show the mineralization of the deposit was dominated by hypogene alteration and was later overprinted by supergene alteration. Assay data shows lower copper concentrations (<0.25 wt.%) from 0-40ft. and then an increase to (>0.25 wt.%) as depth increases, with intermittent zones of (<0.25 wt.%) at ~60ft-80ft. deep for four of the five holes. Detailed logging also shows variation in mineralogy with depth: pyrite (1-5%) with subordinate chalcopyrite (1-3%) below 44ft., associated with tourmaline and specularite (specular hematite), and pyrite and chalcopyrite are found within quartz veins at 80ft. Characterization of the paragenetic sequence of the Moonlight deposit will expand our understanding of IOCG deposits and the regional tectonic setting that influenced the mineralization and alternation of the deposit.