Genesis of Kupferschiefer Cu-Ag Deposits by Convective Flow of

Extensive and rich Cu-Ag sulfide mineralization occurs in Poland across the contact between the Upper Permian Zechstein restricted marine sequence and the Lower Permian Rotliegende continental volcanic and clastic sequence. Geologic evidence suggests that the mineralization was formed during late diagenesis when metalliferous brines migrated through the Rotliegende, leaching metals from the volcanic detritus, and up the flanks of basement highs, possibly along fracture porosity, to the pyritic Kupferschiefer and Zechstein limestone above. Thick evaporites in the lower Zechstein preclude a vertical flow-through model, but metal zoning attitudes suggest that the brines overturned where the Rotliegende pinched out against he highs and moved laterally along the base of the Zechstein toward the basin centers, presumably to sink back down into the Rotliegende, completing a convection cell. A Middle Triassic palcomagnetic age for the metal zoning and Kimmerian attitudes of dilatant sulfide veinlets indicate that the mineralizing event coincided with continental rifting associated with the opening of the Tethys ocean. Slow unicellular convection may be commonplace in sandstone basins where small latera