Quartz Overgrowths in Shales and Sandstones studied by EPMA and SIMS

Cathodoluminescence (CL) offers the ability to measure trace ionic species with relatively short acquisition times enabling large areas to be mapped with detection limits orders of magnitude below elemental detections levels acquired using x-rays under the same conditions. We have applied this technique to the investigation of quartz grains and overgrowths from shale and sandstone samples across Australia with the aim of better constraining the formation conditions of these types of cement. Recent experimental calibration of Ti concentration in quartz [1] provides the basis for a quantitative examination of crystal growth in both hydrothermal and detrital forms. Quartz contains trace element fluctuations at the sub-micron to micron length scale, which are records of the complex interaction between crystals and their host magmas or pore fluids. By combining spectral CL mapping [2, 3], deconvolution and elemental analysis to provide a calibration curve, it is possible to covert a CL intensity map into a trace speciation map for Ti for detrital quartz. Information on the quartz overgrowths will better explain the formation conditions giving rise to them.