MICRO-PIXE ANALYSIS OF SILICATE REFERENCE STANDARDS FOR TRACE NI, CO,ZN, GA, GA, AS, RB, SR, Y, ZR, NB, MO AND PB, WITH EMPHASIS ON NI FORAPPLICATION OF THE NI-IN-GARNET GEOTHERMOMETER

Trace-element analysis is a powerful tool for studying numerous proces ses of research interest in the Earth Sciences; as well, it has import ant applications of interest to the mineral exploration community. Her e, we present the results of a comprehensive study of five internation ally recognized silicate reference standards (BHVO-1, GXR-5, GSR-5, MA G-1 and GSD-50) utilizing micro-PIXE analysis. Results of trace analys es for Ni, Cu, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Nb, Mo and Pb are presen ted. Measured data for the five standards exhibit agreement within +/- 10%, and commonly better, with recommended levels of concentration in the 50-400 ppm range. Detection limits (for a typical 3- to 4-minute a nalysis of an accumulated charge of 2.5 microCoulombs) are in the rang e of 2-10 ppm, with precisions of 1-10%. A detailed study of the X-ray spectra in the vicinity of the Fe, Ni and Co lines illustrates that t he GUPIX software is able to correctly fit the complex spectra and thu s provide accurate Ni concentrations. Further tests on Ni in garnet ar e reported, in the context of current application of the Ni-in-garnet geothermometer in diamond exploration; it appears important to resolve the difference between the two published calibrations of this importa nt geothermometer.