Epidote-Bearing Veins in the State 2-14 Drill Hole: Implications for Hydrothermal Fluid Composition

摘要: Epidote-bearing veins in State 2–14 drill core from 900 to 2960 m depth were examined using backscattered electron microscopy and probe microanalysis characterize the mineralogy, parageneses, texture, composition of vein minerals. In order decreasing abundance, minerals epidote-bearing are pyrite, calcite, K-feldspar, quartz, anhydrite, hematite, chlorite, Fe-Cu-Zn sulfides, actinolite, titanite, allanite. The downhole distribution (+ pyrite quartz) varies as a function includes: (1) calcite above ∼2000 m, (2) K-feldspar between 1700 2745 (3) anhydrite 2195 (4) hematite ± sulfides 2773 (5) actinolite below ∼2890 m. Where present, was first mineral precipitate followed by epidote. all other veins, epidote earliest form. Calcite, paragenetically later. Compositional zoning, common most epidotes, is typically symmetric with Al-rich cores Fe3+ -rich rims. minimum mole fraction Ca2Fe3Si3O12(OH) (XPs) epidotes decreases systematically increasing ∼0.33 at 906 ∼0.21 2900 maximum XPs any given greater than 0.33. Thermodynamic analyses phase relations among vein-filling aqueous solutions depths near 1867 300°C indicate that modern reservoir fluid Salton Sea geothermal system equilibrium + quartz (XPs = 0.33) anhydrite. predicted fugacity CO2 (∼14 bars) for brine close agreement calculated value fCO2 production fluid. Theoretical diagrams CaO-K2O-Fe2O3-Al2O3-SiO2-H2O-O2-S2-CO2 demonstrate mineralogies parageneses recorded hi observed variations Al-Fe3+ content may result only minor changes CO2, O2, S2