SULFUR EVOLUTION OF OXIDIZED ARC MAGMAS AS RECORDED IN APATITE FROM APORPHYRY COPPER BATHOLITH

Uniformly sulfur-rich cores abruptly zoned to sulfur-poor rims (simila r to 1 to <0.2 wt% SO3) in apatite from the Yerington batholith, Nevad a, indicate that early magma that is crystal poor, oxidizing, and sulf ate rich evolved to sulfate-poor magma via crystallization of anhydrit e, a mineral observed in magmas from Pinatubo and EI Chichon. We predi ct that the characteristic zonation to sulfur-poor rims of apatite in the Yerington batholith is common in other oxidized, hydrous, calc-alk aline magmas, and can be used to track cryptic anhydrite saturation as well as to monitor sulfur evolution. Sulfate-rich are magmas such as Yerington magmas may crystallize to produce hydrothermal fluids rich i n chlorine, copper, and sulfur and porphyry copper ores.