FAST, QUANTITATIVE ROCK MINERALOGY WITH QEMSCAN: THE QUIET REVOLUTION IN ROCK CHARACTERIZATION

Scanning electron microscopes with multiple high-speed energy dispersive detectors capable of collecting hundreds of thousands of energy dispersive spectra per hour on polished thin-sections or epoxy pucks are becoming an indispensible laboratory tool in many fields of geology. Previously only available in laboratories of major mining houses, QEMSCAN Technology is increasingly accessible to the academic community where applications in standard petrographic studies of igneous, metamorphic and sedimentary rocks, ores, soils, precipitates, experimental products, engineered materials, and dusts are in their infancy. Applications in the fields of geophysics, hydrology, atmospheric sciences, and forensics are also emerging.

We present the results of more than a half dozen student projects that illustrate some of the capabilities of the newly installed QEMSCAN systems at the University of Utah (March, 2009). These mini-projects are illustrative studies involving chemical diffusion in metamorphic rocks, petrology of glauconitic sandstones, structural deformation in mylonites, acid-generating potential of tailings, petrology of iron concretions in Navajo Sandstone, petrology of fine-grained gold ores from Carlin-type gold deposits, mineralogical characterization of shale and its associated geophysical properties (electrical), quantitative characterization of copper concentrates and predictive copper recovery, and the mineralogy of iron ores. Point count data on igneous and sedimentary rocks are compared with standard petrographic results, and textural data are presented in the form of high-resolution (down to 1 micron) color “mineral maps” relevant to various applications. The digital images can be processed to quantify any desired aspect of the sample (grain size distribution, mineral associations, grain morphology, etc.).

This tool provides data that are difficult to obtain via traditional methods (such as XRD) or would entail multiple analyses to acquire (such as microprobe, SEM, and optical microscopy). QEMSCAN Technology is ideal for obtaining high-resolution mineral/chemical information on solid samples. QEMSCAN enlarges the geologist/geochemist's analytical toolbox.