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The Atlas porphyry Cu–Au deposit is located in central Cebu Island in the Philippines, with a proven mineral reserve of 1420 Mt at 0.45% Cu, 0.24 g/t Au, 0.018 g/t Mo, and 1.8 g/t Ag. It is associated with the Lutopan quartz diorite porphyry stock that was emplaced into the Cretaceous volcano-sedimentary sequences of the Cansi Formation. Two stages of hypogene alteration have been identified at Atlas: stage I quartz–magnetite ± chalcopyrite ± pyrite veins associated with potassic and propylitic alteration and stage II anhydrite–pyrite–chalcopyrite ± specularite veins associated with phyllic alteration. Supergene gypsum veins are also present. Mineralization is mainly associated with the stage I and stage II veins. The Lutopan quartz diorite porphyry yielded a zircon U–Pb age of 108.5 ± 1.6 Ma and is characterized by high Sr/Y (54–69), with the corresponding magma having high oxygen fugacity (avg. ΔFMQ +2.7, avg. Ce4+/Ce3+ of zircon = 439) and H2O concentrations (presence of amphibole and biotite phenocrysts) and low magmatic temperatures (avg. Ti-in-zircon thermometry = 706 °C). The relatively low La/Yb ratios (9–11), listric-shaped normalized REE patterns with weak or absent Eu anomalies, together with zircon εHf(t) values of 3.4 to 10.0, whole-rock ISr values of 0.70373–0.70382, εNd(t) values of 2.4–3.4 and Mg numbers of 49–53 suggest that the Lutopan quartz diorite porphyry was likely derived from partial melting of young lower continental crust or interaction between asthenospheric melts and lower crust melts, that evolved to adakite-like trace element compositions through amphibole fractionation. Stage I veins yielded a pyrite Re–Os isochron age of 110.2 ± 5.6 Ma, making Atlas the only Mesozoic porphyry deposit discovered in the Philippines. [ABSTRACT FROM AUTHOR]

[Display omitted] • Four generations of magnetite (from Mag1 to Mag4) were identified, controlled/modified by the dissolution and reprecipitation, oxy-exsolution, and recrystallization. • The Ti and V variations suggest a decreasing temperature and increasing f O 2 trend from Mag1 to Mag3, and the trend reversed from Mag3 to Mag4. • The high f O 2 and the precipitation of Mag1 to Mag3 may be the key for Stage Id mineralization. • The second pulse fluids may have provided more Fe2+. And the high temperature with decreasing of f O 2 is the indispensable factor to form Stage IIa-mineralization. The Atlas porphyry Cu–Au deposit (PCD) in central Cebu Island (Philippines) has a proven ore reserve of 1420 Mt @ 0.45% Cu, 0.24 g/t Au, 0.018 g/t Mo, and 1.8 g/t Ag. The PCD is characterized by four generations (Mag1 to Mag4) of magnetite, a mineral that can record the chemical evolution of the magmatic-hydrothermal system. The magmatic Mag1 is characterized by being euhedral with ilmenite lamellae formed by the oxy-exsolution process. The well-developed microporosity and 120° triple junction suggest that Mag2 has been modified by recrystallization or dissolution-reprecipitation process. The Mag3 (from the early-ore Stage I) is well-porous with almost no oxy-exsolution ilmenite lamellae. The Mag4 is from the late-ore Stage II in which the Mag4a has distinctive zoning formed by massive cavities, whereas the Mag4b has only a few pores. LA-ICP-MS trace element (esp. Ti and V) compositions indicate that the formation temperatures decrease from Mag1a to Mag3, then increase from Mag3 to Mag4a, and eventually decrease from Mag4a to Mag4b. On the contrary, oxygen fugacity (f O 2) decreases from Mag1a to Mag3 but increases from Mag3 to Mag4, suggesting two magmatic-hydrothermal pulses driven by the Lutopan porphyry intrusion at Atlas. This is consistent with the development of two mineralization styles at Atlas, i.e., high f O 2 magnetite mineralization and the subsequent giant Atlas porphyry Cu–Au mineralization. [ABSTRACT FROM AUTHOR]