A combination of cathodoluminescence (CL) microscopy with digital image analysis and spectroscopic analysis allows the detailed investigation of the commonly occurring colour shift from initial to final CL-colours in detrital quartz with increasing irradiation. A method for the quantification of the colour shift is presented and applied to different quartz sands: unlithified sands of the Lower Cretaceous Kuhfeld Formation from Ottenstein (W Germany) and Holocene sands from the barrier island of Wangerooge (N Germany). The colour shift depends on the defect structure of the quartz grains. The defect structure is determined by the physico-chemical conditions during crystallization and therefore can help trace the source of quartz grains. A total of 25 different types of quartz grains in the Ottenstein-sands indicates a highly variable southern provenance. Many of the grains have recycled quartz cement overgrowths indicating an at least second cycle origin. In contrast, only 16 different quartz types have been observed in the Wangerooge-sands reflecting a less varied plutonic to metamorphic Scandinavian provenance. The study demonstrates the potential of quantified CL initial colour and colour shift in assessing the provenance of quartz-rich sands and sandstones.