Irregular Cathodoluminescent Banding in Late Dolomite Cements: Evidence for Complex Faceting and Metalliferous Brines

Irregular cathodoluminescent growth banding occurs in late diagenetic dolomite cements in the Bonneterre Dolomite and Davis Formation (Cambrian), southeastern Missouri. The dolomite cements were precipitated by warm basinal brines and are paragenetically related to the sulfide mineralization of the Viburnum Trend Mississippi Valley-type lead-zinc district. Universal stage microscopy has revealed that the irregular growth bands correspond to complex (non-cleavage rhombohedron) crystal faces that developed during growth of the dolomite cements. During later stages of crystal growth, the cleavage rhombohedron became the dominant morphological form, and the earlier complex faces disappeared. Similar complex faceting has been observed elsewhere, where dolomite and halite occur together. We speculate that metal cations in the chloride-rich, mineralizing brines had a poisoning effect on growing dolomite surfaces which allowed the complex crystal faces to develop