PALEOMAGNETIC DATING OF THE NAVAN ZN-PB DEPOSIT, IRELAND

The genesis of the Navan Zn-Pb deposit has been much debated, in large part because it has not proven amenable to radiometric age dating. The epigenetic ore occurs in platform carbonates of the early Courceyan Navan Group (~351 ± 4 Ma) and in the overlying late Chadian - early Arundian Boulder Conglomerate (~337 ± 1 Ma). Paleomagnetic analyses were done on 282 specimens from 26 sites using AF and thermal demagnetization. Paleomagnetic fold test on mineralization and carbonate host rocks were negative. Conglomerate tests on mineralized and non-mineralized clasts were negative. A contact test using a Tertiary dike cutting mineralization was positive. Thermal step demagnetization and isothermal remanence tests affirm that pseudosingle domain magnetite carries the characteristic remanence in both ore and host rocks. The pole position indicates that mineralization occurred in the late Arundian to early Holkerian (334 ± 3 Ma) following deposition and deformation of the overlying Holkerian Lucan Formation during the waning stages of the Hercynian orogeny in the mine area.