The origin of the calcites from Pb-Zn veins in the Harz Mountains, Federal Republic of Germany

Studies of the REE distribution in calcites from hydrothermal, banded Pb-Zn mineralizations, as well as in calcites from pelitic and psammitic unmetamorphosed rocks and magmatites, of the Harz Mountains, revealed that the calcite of the banded ores crystallized from hybrid magmatic—metamorphic solutions. These were rather rich in REE3+ Fe3+ and probably Zn2+ and Pb2+ ion concentrations. The absence of any negative Eu anomalies points to oxidizing conditions. The sulphides have crystallized from a different solution. It is suggested that the necessary HS−-rich solutions stem from near-surface hydrothermal convection cells set up by nearby granitic intrusions. The alternating deposition of calcite and sulphide (banded ores) may be explained by assuming that farther away from the intrusions, the HS−-rich solutions were intermittedly admixed with the hybrid fluids. This caused a decrease in temperature, an interruption of calcite deposition and sulphide mineralization. Near the intrusion, continuous mixing of these two fluids became more common and, consequently, banded ores are rather rare.