OXIDATION-STATE AND ELECTRONIC CONFIGURATION DETERMINATION OF COPPER IN TETRAHEDRITE GROUP MINERALS BY L-EDGE X-RAY-ABSORPTION SPECTROSCOPY

L-edge X-ray absorption spectroscopy employing a synchrotron radiation source has been used to study the electronic structure and valency of Cu in the chemically and structurally complex tetrahedrite group of m inerals. Mechanical mixtures of Cu2+O and Cu+FeS2 were used to estimat e the relative cross sections of Cu2+ and Cu+; the absorption of Cu2at 931 eV is 25 times greater than that of Cu+ at 945 eV. Using this c alibration, Cu2+/Cu ratios were found to vary from 0.00 to 0.054 in th e tetrahedrite samples studied; the highest proportion of Cu2+ occurs in synthetic tetrahedrites with a composition close to Cu12Sb4S13. Thi s study reveals the utility of the technique for determining the valen ce state of copper in complex minerals, allowing the crystal chemistry to be more fully characterised.