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 most important evidence for the inferred early timing of mineralization in Ireland (clasts of ore above a middle Carboniferous erosion surface). We have examined diagenetic fabrics within the main ore (pale beds) and the overlying erosion surface (Boulder Conglomerate) in order to determine the timing of mineralization. This diagenetic analysis (and particularly the presence of premineralization dolomite in the Boulder Conglomerate) has revealed that all of the mineralization postdates the erosion surface and therefore must 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. This conclusion disagrees with the previous model of at least partially syngenetic mineralization, and has important implications for the age of other deposits in Ireland and the nature of "Irish-type" deposits in general.