Hydrogen Isotope Determination of Fluid Inclusion Water From Epithermal Vein Quartz: Do Values Accurately Reflect Water of Deposition

Abstract

Fine-grained quartz and adularia in the Hishikari (Japan) crustiform epithermal veins, contain up to -1 wt.%, excluding adsorbed and fluid inclusion water. Water extracted from the veins is predominantly from sub-micron size fluid inclusions in quartz which are the remnants of water from precursor hydrous silica polymorphs. Quartz-rich parts of veins have total water contents >OS wt.%, and constant 6D values (-75%~~). These 6D values are lower than present day meteoric water (-50%~~). Hydrogen isotope analyses of amorphous silica and water from geothermal power plants and natural springs suggest that a 20 to O%O fractionation occurs between the precursor silica polymorphs and water at epithermal temperatures (15OoC to 200OC). Extraction of water from he-grained epithermal quartz is not consided to be a suitable technique for determining the SD, values of palaeo-geothermal waters.