MICRO-PIXE ANALYSIS OF SILICATE REFERENCE-STANDARDS

The accuracy and precision of the University of Guelph proton microprobe have been evaluated through trace-element analysis of well-characterized silicate glasses and minerals, including BHVO-1 glass, Kakanui augite and hornblende, and ten other natural samples of volcanic glass, amphibole, pyroxene, and garnet. Using the 2.39 wt% Mo in a NIST steel as the standard, excellent precision and agreement between reported and analyzed abundances were obtained for Fe, Ni, Cu, Zn, Ga, Rb, Sr, Y, Zr, and Nb; all materials were analyzed at least twice by obtaining three to ten individual spot analyses. For BHVO-1 and Kakanui hornblende, the precision of individual point analyses was evaluated by five replicate measurements at a single location. For Kakanui hornblende, the precision of these analyses expressed as relative percent [(standard deviation/mean) x 100] is Fe, < 1; Ni, 10; Zn, 5; Ga, 5; Rb, 12; Sr, 1; Y, 12; Zr, 6; Nb, 4; and Ba, 33. This precision of individual analyses is sufficiently high that studies of trace-element zoning and diffusion are feasible. Count rates were stable for the five replicate measurements, indicating that higher precision could be obtained simply by repeatedly analyzing the same spot. It is our hope that this demonstration of the ease, accuracy, and precision of in situ trace-element analysis by proton microprobe will lead to greater appreciation and application of the micro-PIXE technique by the geologic community.