Stable oxygen and sulfur isotopes applied to tracing seepage from mine tailings

Abstract

Sulfur and oxygen isotopes in dissolved sulfates were used to trace seepage from a uranium tailings pond into a shallow alluvial aquifer. Twent7-two wells, 2 tailings ponds, and an adjacent stream were sampled on and nearby the Kerr-McGee Nuclear Corporation section 31 millsite at Ambrosia Lake, New Mexico. The isotopic analyses showed significant isotopic differences between acid pond sulfates contributed by the mill process and natural sulfates in the local ground waters. Three distinct groups of waters were identified in the alluvial system at different points downgradient from the millsite, pond leachate, mine discharge, and Tres Hermanos formation waters. This distinct grouping of waters would not have been possible based only on chemical data. Isotope results also provided clues to the types and extent of geochemical interactions occurring as water travels from ponds into an aquifer system.