Analysing hornblende textures within the Engel Deposit at Lights Creek Stock, Plumas County California

The Lights Creek Stock (LCS), located in Plumas County, CA, is an intrusive unit composed of gabbro, quartz diorite, diorite, quartz monzonite, which hosts three iron oxide copper-gold (IOCG) deposits. The Engels IOCG deposit is hosted within a gabbro unit of the LCS. The magmatic history of the LCS gabbro is poorly understood, and past research has only focused on the IOCG mineralization processes. This research will evaluate the magmatic history of the gabbro using whole-rock geochemical data, single mineral analysis, petrographic, and lithologic descriptions. Integration of petrography and geochemical analyses of individual hornblende crystals will give insights into the processes through which the gabbro formed . Petrographic analysis reveals: hornblende oikocrysts replacing pyroxene; unzoned crystals; and three distinct types of zoning: (1) simple zoning characterized by a homogeneous core and an abrupt change within the rim, commonly seen with embayment, that is seen in euhedral and subhedral crystals (less than 400 microns); (2) Patchy zoning seen in tabular subhedral and acicular hornblende crystals; (3) zig-zag zoning that is apparent in oikocryst and subhedral acicular crystals. Analyzing textural changes within the hornblende can give insight into the petrogenesis of the gabbro and further expand our knowledge on hornblende rich gabbro.