CHARACTERIZING AMPHIBOLE WITHIN THE LIGHTS CREEK STOCK, PLUMAS COUNTY, CALIFORNIA

The Lights Creek Stock is a pluton located in the Sierra Nevada Mountain range of northern California. The Lights Creek Stock hosts three IOCG deposits, which suggests that the minerals within the host granitoid have likely been altered, since IOCG mineralization is commonly associated with widespread silicate alteration. Calcic alteration commonly alters hornblende to actinolite and potassic alteration commonly alters hornblende to secondary biotite. This study uses the Ridolfi & Renzulli (2011) amphibole geothermometer and several amphibole geobarometers to estimate the conditions of formation of the Lights Creek Stock granitoids and their subsequent alteration.

Analyses of the amphiboles in the LCS granitoids were performed using polished pucks in a scanning electron microscope and electron microprobe. Elemental composition maps were generated on individual amphibole crystals to examine the distribution of elements throughout the crystals, and preliminary data show that these amphiboles exhibit some amount of patchy zoning, with some regions richer in Fe-Al and others richer in Mg-Si. Electron microprobe analyses were then used to determine the chemical composition of the amphibole grains, which were used in calculating temperature and pressure of the observed assemblages.