[H-RE13] 資源地質学

[HRE13-P04] Episodes of Barren to Fertile Porphyry Copper Deposit Magmatism on a Complex Island Arc System: Insights from the Igneous Host Rocks of the Suyoc Epithermal Prospect, Northern Luzon, Philippines

*Karl Dimarucut Jabagat¹、Jillian Aira S. Gabo-Ratio²、Omar B. Soberano³、Karlo L. Queaño⁵、Eric S. Andal⁶、Kotaro Yonezu⁴、Carla B. Dimalanta²、Graciano P Yumul Jr.⁷、Yuan-Hsi Lee¹ (1.Department of Earth and Environmental Sciences, National Chung Cheng University, Taiwan、2.Rushurgent Working Group, National Institute of Geological Sciences, College of Science, University of the Philippines-Diliman、3.Graduate School of International Resource Sciences, Akita University, Akita, Japan、4.Department of Earth Resources Engineering, Faculty of Engineering, Kyushu University, Fukuoka 819-0395, Japan、5.Mines and Geosciences Bureau, Department of Environment and Natural Resources, Quezon City, Philippines,、6.Itogon-Suyoc Resources Incorporated, Itogon Benguet, Philippines、7.Cordillera Exploration Co. Inc., BGC, Taguig City 1630, Philippines)

キーワード：Porphyry Copper Deposit, Fertile magmatism, Baguio-Mankayan Mineral District

Based on new U-Pb zircon ages coupled with whole-rock and in-situ geochemical analyses of igneous host rocks in the Suyoc epithermal prospect, chronologic barren to fertile episodes were identified for the Baguio-Mankayan Mineral District in northern Luzon, Philippines: 1) Late Eocene (36.93 ± 0.62 Ma) barren magmatism associated with a thin, nascent Luzon arc. ; 2) fertile Pliocene (2.87 ± 0.23 Ma and 3.18 ± 0.77 Ma) magmatic event associated with subduction of the Scarborough ridge along the Manila Trench (MT) and 3) Pleistocene (<1 Ma) fertile magmatism associated with slab melting triggered by buoying of the MT subduction angle. The barren Eocene magmatic event, characterized by negative Eu anomalies and lower Sr/Y and V/Sc ratios, is considered as a significant factor in enhancing source and intra-crustal conditions for the onset of younger fertile magmatic events via sub-arc modification and crustal addition/thickening. Furthermore, we consider the fertile (high Sr/Y and V/Sc ratios) Pliocene and Pleistocene magmatism in the Baguio-Mankayan area as two separate events with different petrogenesis. Mafic-silicic interaction in the Pliocene, which is characterized by positive FeO, Al₂O_3, and negative SiO₂ spikes up to 2 wt%, was documented on core-rim analysis of amphiboles from hornblende quartz diorite porphyry samples. On the other hand, slab melt signature in the Pleistocene represented by dacite porphyry samples is characterized by hybrid crust-mantle signature, listric REE pattern, higher Dy/Yb ratios, and a relatively high magmatic H₂O content ranging from 6.3-7.8wt%. Based on the assessment, the shift from barren to fertile signatures in the Baguio-Mankayan Mineral District is intimately linked with arc development and subduction dynamics leading to the formation of fertile magmas.