Sphalerite from transgressive and regressive sediments of the Cambro-Silurian supercycle, Baltic Shield

A sedimentary micro-vent in Lower Cambrian sandstone, and spar filled cephalopod shells in uppermost Wenlockian barite and dolomite carrying silty pelmicrosparite contain well-developed macroscopic ZnS-mineralization and very little pyrite. As controlling factors are suggested, good permeability, availability in underlying sediment of finely dispersed organic matter with sorbed Zn, and low S2- activity in the percolating water. Sedimentation was temporarily rather rapid.