INFLOWS OF GEOTHERMAL FLUID CHEMICALS TO THE WAIKATO RIVER CATCHMENT,NEW-ZEALAND

Data collected from two monitoring programmes conducted by Environment Waikato, New Zealand, have been used to estimate the mass flows of Li , B, As, SO4, and Cl from geothermal fluids entering the Waikato River up stream of Lake Whakamaru. Chloride is the major anion in geotherma l waters and is closely related to Li, B, and As. The total river wate r mass flow of Cl is 4600 g s(-1) at the outlet of Lake Whakamaru and of this, 78% originates from geothermal fluids; 13% flows into Lake Ta upo, and 65% enters the river down stream of Lake Taupo. The Wairakei field contributes the largest fraction of 45% and geothermal fluid flo ws which were not directly measured in the monitoring programmes contr ibute 23%. The remaining 10% derives from measured flows from 14 of th e 16 known geothermal fields. The origins of Li, As, and B closely fol low those of Cl. Geothermal SO4 is produced from the oxidation of H2S carried by geothermal steam and the estimates made of the mass flows o riginating from geothermal fluids are less certain than those for Cl.