| Abstract |
Except for very high 3He/4He ratios (R/Ra = 6.5-8), noble gas isotopic ratios determined for eleven (11) well samples in Palinpinon approximate those of air. The He ratios are typical for island-arc settings, indicating a definite mantle He source for the Palinpinon geothermal fluid. The close to atmospheric ratios of the other noble gases (Ar, Ne, Kr, Xe), on the other hand, suggest that these are derived mainly from air or air-saturated water. The use of noble gas isotopes to study geothermal fluids as an aid in reservoir management is a relatively new and unexplored field of noble gas geochemistry. Most of the work done on noble gas geochemistry (e.g., Ballantine & Barfod, 2000; Ozima, 1994; Burnard et al., 1997; Moreira et al., 1998, among others) deal with origins and compositions of mantle rare gases relative to atmospheric, cosmic and other noble gas reservoirs. Others workers (e.g., Kennedy et al., 1997; Sorey et al., 1993/1998; Hiyagon and Kennedy, 1992; Clark and Torgersen use changes as Work geothermal a et Christenson Mazor Magro 1992; others). actually rare Kennedy role gas geothermal other investigation. Re-calculated bulk compositions of Palinpinon noble gases can be explained by simple single and multi step boiling models. Dry well samples fit separated steam single step boiling lines, while 2-phase and liquid-dominated well fluids fall on multi-step boiling separated steam curves. There is, however, a systematic increase in Kr and Xe concentrations and normalized ratios, F(X) with decreasing Ne and Ar. This "behaviour" cannot be explained by boiling models, and it is construed that this is due to mixing between three (3) end-members - air saturated water (ASW), the geothermal parent fluid, and reinjection water. |