BIOTITE WITHIN THE ENGELS AND SUPERIOR IOCG DEPOSITS, LIGHTS CREEK STOCK, PLUMAS COUNTY, CA

As the development and demand for clean energy grows, resources like copper are being needed now more than ever. This makes studying geological copper formations such as iron-oxide copper-gold (IOCG) deposits crucial for economic profit. The Lights Creek Stock of the Taylorsville District of the Plumas County Copper Belt in CA hosts multiple such IOCG deposits. These deposits have been mined for copper in the past but their formation and origin are still little studied and understood. This study aims to analyze biotite crystals within two different IOCG deposits, Engels and Superior, to understand more about their development. Petrographic and geochemical analyses were conducted on two typical generations of biotite that were found in both deposits. The first is a coarse, subhedral, primary generation of biotite that occasionally contains chlorite replacement. The other is a very-fine, anhedral, secondary generation of biotite. Both have been found associated with feldspar, quartz, magnetite, and sometimes titanium-bearing minerals such as ilmenite or titanite. Geochemical analyses were conducted using a SEM-EDS for closer inspection. The chemical composition between both generations was similar but the primary biotite appeared to have a slightly higher titanium content compared to the secondary biotite. Ti-in-biotite geothermometers were then used to determine a rough estimate of the biotite formation temperature. Preliminary results suggest the primary biotite formed at higher temperatures compared to the secondary biotite.