CATHODOLUMINESCENCE AT LOW FE AND MN CONCENTRATIONS - A SIMS STUDY OFZONES OF NATURAL CALCITES

Point analyses of natural calcite cements by SIMS confirm the earlier suggestions that approximate to 20 ppm Mn is required to activate lumi nescence, whereas Fe concentrations in excess of approximate to 1400 p pm quench it partly, independently of the Mn content. Below this Fe th reshold, luminescence is bright at Mn concentrations in excess of appr oximate to 225 ppm. In the range 20-225 Mn, all types of luminescence- dull, luminescent, and nonlumines cent-can occur. This undifferentiate d domain is evident also from a compilation of literature data. The ty pe of luminescence is not a simple function of Fe and Mn concentration s; other parameters influence CL. Since most diagenetic calcite cement s have Fe and Mn concentrations that place them within the field of mi xed cathodoluminescence, these results force reassessment of models th at equate the type of luminescence with the redox state of the diagene tic environment.