IRON-OXIDE COPPER GOLD (IOCG) ALTERATION AND PETROGENESIS OF LIGHTS CREEK STOCK, PLUMAS COUNTY, CA

Global demand for Cu has increased due to shifts toward more sustainable energy and advancement in technology. Cu is mostly mined from copper porphyry deposits, but can be obtained from other hydrothermal deposits such as iron-oxide±Cu±Au (IOCG) deposits. The Lights Creek Stock (LCS), dated at 184-178 Ma, is a pluton mapped by Juilland in 1970 as 5 distinct units based on the ratio of potassium feldspar to plagioclase feldspar. LCS is in the Plumas Copper Belt (PCB), a historical Cu mining region, and hosts 3 IOCG deposits. It is possible that Juilland’s units represent alteration from the 3 IOCG deposits rather than igneous processes. Common types of IOCG alteration are: sodic(-calcic), potassic, and hydrolytic. Sodic(-calcic) alteration is defined by the addition of Na(-Ca) and yields plagioclase. Potassic alteration is defined by the addition of K and yields K-feldspar. Hydrolytic alteration is defined by the presence of sericite ± chlorite and is associated with upper portions of IOCG deposits. The purpose of this project is to classify alteration types throughout the main “unaltered” body of the LCS and compare alteration patterns to Juilland’s findings. Petrographic data from 38 samples and geochemical data from 20 samples suggest that K and Na(-Ca) alteration assemblages are present in rocks previously described as unaltered. These alteration zones could be used as an exploration tool for undiscovered Cu resources. Future work includes collecting geochemistry from all samples to further define alteration patterns throughout LCS.