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Abstract

This study has focused on a series of quartz ± carbonate ± base metal mineralized veins from Cornwall, southwest England. These extensional veins are characterized by multiple phases of incremental quartz growth and there are a variety of quartz textures presen t. The dominant texture is of prismatic, growth-zoned crystals, although fine-grained, cloudy quartz, sometimes with an unusual lath-like morphology, spherulites of cryptocrystalline silica and quartz cement micro-breccias can also be seen. Desktop cathodoluminescence (CL) studies of these veins show that the prismatic quartz has a short-lived blue-green luminescence and displays growth zoning at a range of scales. This CL zonation can also be seen on a smaller scale (down to <20microns) using a Jeol 8900 electron microprobe equipped with a cathodoluminescence (CL) detector. This zonation appears to be strongly linked to the Al concentrations of the quartz. CL light bands have Al contents ranging from 400ppm to <200ppm, whereas CL-dark bands have between 1000ppm to over 8000ppm. Fourier Transform Infra-Red studies of the veins confirms that that the prismatic quartz contains appreciable quantities of Al balanced hydroxyl groups as structural defects in the crystal lattice.