Apatite Texture, Composition, and O-Sr-Nd Isotope Signatures Record Magmatic and Hydrothermal Fluid Characteristics at the Black Mountain Porphyry Deposit, Philippines

Abstract The trace elemental and isotopic signatures in apatite can be modified during hydrothermal alteration. This study investigates the suitability of as an indicator source, chemistry, evolution magma fluids. In situ textural, elemental, O-Sr-Nd isotope analyses were performed on thin sections, from fresh propylitically altered pre- synmineralized dioritic porphyries Black Mountain porphyry Cu deposit Philippines. All studied crystals have similar subhedral to euhedral shapes are homogeneous grayscale backscattered electron images. cathodoluminescence images, rocks displays yellow yellow-green green brown luminescence, respectively. Apatite has a higher Cl Mn content, lower Fe, Mg, Sr, Pb, calculated XOH-apatite, compared rocks. content F, rare earth elements (REEs), Y, U, Th, Zr, Sr-Nd all grains (87Sr/86Sr = 0.7034–0.7042 vs. 0.7032–0.7043, εNd(t) 5.3–8.0 5.1–8.4). X-ray maps oxygen across individual typically both distinct luminescence colors, coupled with mobile element compositions (Cl, OH, Mn, Pb), indicate modification primary magmatic interaction similarities Sr ratios 0.7032–0.7043) but slight differences O (δ18O 6.0 ± 0.3‰ 6.6 0.3‰) consistent fluids having same source suggest significant phase separation given that 18O preferentially fractionates into residual liquid relative 16O separation. similarity immobile (REE, Zr) contents populations apatite, consistency textures Nd compositions, absence obvious dissolution-reprecipitation features retains some characteristics. zircons sample 5.9 0.3‰), indicating little no fractionation between zircon good proxy for composition magma. Based replacement assuming their equilibrium high-temperature fluid fluid, respectively, early later estimated 6.4 15.1 wt % ~0.25 0.03 %, indicates depletion demonstrates cathodoluminescence, (such Cl, Pb) Sr-O alteration, whereas other components preserved. These used constrain origin, ore-forming