Thermobarometry of three skarns in the Ludwig area, Nevada, based on Raman spectroscopy and elastic modeling of mineral inclusions in garnet

We report Raman spectroscopic analyses and elastic modeling of mineral inclusions from three skarns in the Ludwig area, Yerington District, Nevada. Raman spectroscopy shows that at ambient conditions, apatite inclusions in garnet from the shallowest skarn, Casting Copper, retain tensile pressures of -75 + or - 30 MPa (2sigma ; n = 33). Apatite inclusions in garnet from the intermediate-depth Douglas Hill deposit retain pressures of -162 + or - 24 MPa (2sigma ; n = 15). Apatite inclusions in garnet from the deepest skarn, Hill 5923, retain pressures of -177 + or - 21 MPa (2sigma ; n = 20). Quartz inclusions in garnet retain pressures of -111 + or - 31 MPa (2sigma ; n = 7) and -152 + or - 86 MPa (2sigma ; n = 10) for the Douglas Hill and Hill 5923 deposits, respectively. Quartz inclusions in garnet from Hill 5923 retain pressures of -152 + or - 86 MPa (2sigma ; n = 10). The higher tensile stress within inclusions from the deeper skarns is related primarily to the higher formation temperatures of these deeper skarns. Elastic modeling of apatite-in-garnet and quartz-in-garnet from the three deposits is in good agreement with stratigraphic paleodepth estimates and corroborates higher formation temperatures for the deeper skarns. Fluid inclusions from these skarns show a bimodal temperature distribution, with inclusions interpreted as primary showing homogenization by critical phenomena at approximately 400 degrees C, whereas lower-temperature liquid-rich inclusions are interpreted as secondary. Isochore modeling of the critical-density inclusions is in good agreement with the results from quartz and apatite inclusions in garnet. Overall, these results indicate that mineral inclusion thermobarometry is an effective method of estimating formation pressures of otherwise inscrutable metasomatic rocks.