Spatial and Temporal Relationships between Hydrothermal Alteration Assemblages and Intrusions at the Palinpinon Geothermal Field, Philippines - Implications for Porphyry and Epithermal Ore Deposits

Abstract

Biotite, calc-silicate, propylitic, advanced argillic and illite alteration assemblages at Palmpinon are genetically associated with the Nasuji and Puhagan intrusions. Age determinations of hydrothermal biotite (40Ar/39Ar = 0.7-0.6 Ma) and alunite (IUAr = 0.9-0.8 Ma) demonstrate that biotite and hypogene advanced argillic assemblages formed contemporaneous with the Nasuji Pluton (40Ar/39Ar = 0.7-0.3 Ma). The 'blind' intrusion at Puhagan provides the heat source for present geothermal activity. Magmatic-hydrothermal alteration assemblages (biotite, calc-silicate) have developed above this intrusion with a halo of propylitic alteration. At <2 km, an illite-bearing alteration assemblage is in thermal equilibrium with the present geotheml system. The intimate spatial and temporal relationship between intrusion emplacement and the styles of alteration at Palinpinon are characteristic of deposit styles such as porphyry, skam, HS and LS epithermal. However, mineralized zones have not been detected at Palinpinon, possibly due to poor fiacture permeability, insufficient fluid flux, or a lack of metals in the hydrothermal fluids.