Abstract

Calibrated equilibria are presented which document the responses of silicate-oxide-sulfide assemblages to variations in temperature, pressure, f (sub O 2 ) , f (sub S 2 ) , and f (sub H 2 O) in and around metamorphosed ore deposits in pelitic and felsic volcanic terrains. Using equations developed in Part I and calibrations based largely on published experimental results, a FeO -a (sub Al 2 SiO 5 ) , f (sub O 2 ) -X Fe , and AFM diagrams were produced for temperature and pressure conditions of 500 degrees C, 4 kb; 600 degrees C, 2, 4, and 6 kb; and 700 degrees C, 4 kb with X (sub H 2 O) = 1.0. Results of the calculations indicate that with increasing f (sub O 2 ) and/or f (sub S 2 ) values near ore deposits there is a general trend for staurolite and garnet to disappear and chlorite, (sub Al 2 SiO 5 ) , and cordieritc to become more common. Superimposed on these changes in assemblages are steadily declining X Fe values for Fe-bearing silicates. Also correlated with these changes are various transitions in oxide-sulfide assemblages and declining X FeS contents in sphalerite and pyrrhotite. Variations in volatile equilibria due to the presence of ore deposits during metamorphism consist of decreasing fugacity values for H 2 and H 2 S in vicinity of the ore and increasing values for SO 2 . Comparisons with published field studies of metamorphosed deposits indicate good agreement between predicted and observed patterns in silicate-oxide-sulfide assemblages and mineral chemistries.

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