The origin of hypersaline liquid in the Quaternary Kakkonda granite, sampled from well WD-1a, Kakkonda geothermal system, Japan

Hypersaline metal-rich liquid (ca. 40 wt% total chloride species) was obtai ned from a depth of 3708 m in the Kakkonda geothermal system. Sampling of w ell WD-1a was conducted by reverse circulation after a standing time of abo ut 196 hours (with temperature recovering to > 500 degrees C). Tritium cont ent and the relationship between delta D and delta(18)O showed that the riv er water that was circulated in the well had mixed with an isotopically hea vy fluid during the standing time. Phase separation occurred during tempera ture recovery, concentrating the hypersaline liquid in the bottom of the we ll. This original hypersaline liquid has a salinity of about 55 wt% NaCl eq ., consisting of Na-Fe-K-Mn-Ca chloride, rich in Zn and Pb but poor in Cu, Au and Ag. The fluid originates from the Kakkonda granite and mixed with ci rculating water from the well in a zone of fine fractures induced by therma l stress during drilling. (C) 1998 CNR. Published by Elsevier Science Ltd. All rights reserved.