Timing of mineralization at the Navan Zn-Pb deposit: A post-Arundian age for Irish mineralization

Navan is the largest of the Irish Zn-Pb deposits and contains some of the m ost important evidence for the inferred early timing of mineralization in I reland (clasts of ore above a middle Carboniferous erosion surface). We hav e examined diagenetic fabrics within the main ore (pale beds) and the overl ying erosion surface (Boulder Conglomerate) in order to determine the timin g of mineralization, This diagenetic analysis (and particularly the presenc e of premineralization dolomite in the Boulder Conglomerate) has revealed t hat all of the mineralization postdates the erosion surface and therefore m ust be post-Arundian (345 Ma) in age. Furthermore, the Navan mineralization must be entirely epigenetic in origin (i,e,, similar to Mississippi Valley -type deposits) and is likely to be Holkerian (343 Ma) in age or younger. T his conclusion disagrees with the previous model of at least partially syng enetic mineralization, and has important implications for the age of other deposits in Ireland and the nature of "Irish-type" deposits in general.