Serpentinization of the Acoje massif, Zambales ophiolite, Philippines: hydrogen and oxygen isotope geochemistry

Oxygen and hydrogen isotope ratios in serpentine (lizardite-chrysotile) from the Acoje chromite mine (Zambales ophiolite, Philippines) and in regional meteoric water from the Zambales and Sierra Madre mountains have been measured to help determine the physical conditions and source of fluids during serpentinization. The measured range of δ¹⁸O in serpentine is + 2.3 to +5.9 and that of δD is -119 to -83. The range of δD in regional meteoric water (including published analyses from the Baguio gold district and the Tongonan, Leyte, geothermal system) is - 75 to -34. The isotopic data for Acoje serpentines are consistent with Serpentinization by regional meteoric water at temperatures between 30 ° and ~ 350 ° C (thermal stability limit of serpentine + brucite). The range of serpentine compositions suggests a Serpentinization process involving: (1) episodic infiltration by isotopically distinct meteoric waters and/or (2) progressive infiltration by a water having constant initial isotopic composition that undergoes isotopic fractionation as a function of reaction progress.