Abstract: Cu K-edge extended X-ray absorption fine structure (EXAFS) spectra have been obtained for two very dilute solutions of copper in hydrosulfide solutions using beamline ID26 at the ESRF. The concentrations of the solutions (4.4 ppm {69 µm} pH 9.5, 1.2 ppm {19 µm} pH 7.4) are such that the experiments illustrate that, with the advent of third generation synchrotron sources, natural systems can now be studied by EXAFS. Analysis of the data indicates an average environment for the copper of 2.3 S atoms at 2.22 Å in the pH 9.5 solution of 2.5 S atoms at 2.23 Å in the pH 7.4 solution. These results are in accord with the solubility study of Mountain and Seward (1999), who conclude that Cu(HS)₂⁻ and Cu₂(HS)₂S²⁻ are the principal copper species in such solutions.