Lithogeochemistry of hydrothermally-altered host rocks by multiple mineralizations in the Mankayan Mineral District, Philippines

The overprinting episodes of porphyry-type and epithermal-type mineralization in the Mankayan District, northern Luzon, Philippines allow an investigation on variation of geochemical signatures with different alteration assemblages. Due to the multiple hydrothermal activities in Mankayan, some older porphyry-type deposits have been overprinted by acid-sulfate alteration that is commonly associated with high-sulfidation epithermal mineralization. In this study, we analyzed metavolcanic basement rocks and dioritic rocks that host porphyry-type mineralization in the Far Southeast deposit, Honeycomb prospect and Christine prospect, which all have near-neutral pH alteration assemblage of illite/muscovite + chlorite ± quartz. We compared their geochemical data with those of the Fatima porphyry deposit, which was overprinted by quartz + alunite ± kaolinite/dickite alteration. Furthermore, we also compared the geochemical data of the metavolcanic and dioritic rocks in the Carmen and Florence prospects hosting quartz-pyrite-gold and enargite veins which overprinted earlier porphyry-type mineralization. N-MORB-normalized multi-element diagrams show that the host rocks preserve negative anomalies of high field strength elements (HFSEs) that are typical of magmas generated in a supra-subduction zone setting. The non-mineralized metavolcanic and dioritic rocks show variable signature of the large ion lithophiles (LILEs), while the altered metavolcanic and dioritic rocks show a more consistent signature. Negative anomaly of Rb is associated with acid-sulfate alteration, while positive anomaly of Rb was observed in the dioritic rocks that have been altered by near-neutral pH fluids. Furthermore, acid-sulfate alteration significantly added LREEs and depleted HREEs compared to the near-neutral pH alteration.