Title: Origin of SEDEX-Style Mineralisation in the UDL (Lucan Formation) Hanging Wall Rocks at Navan – a New Lithogeochemical Exploration Tool?
Researchers: Dr Lola Yesares, Dr Julian Menuge
The research is focuses on the SEDEX-style mineralisation that may be an alteration halo of the recently discovered Tara Deep orebody associated with the Navan deposit. As Navan is the only active Zn-Pb mine in Ireland, the mineral exploration and mining community in Ireland is keen to find additional Zn-Pb orebodies. Thus, we are challenged to enhance understanding of how these deposits formed and from this knowledge to research new methods of mineral exploration.
Sedimentary exhalative (SEDEX) ore deposits supply substantial zinc and lead and lesser copper globally, e.g. the Australian McArthur River (HYC) and Mt Isa, and the Alaskan Red Dog deposits, with major unexploited deposits including the Selwyn Basin, Yukon. SEDEX deposits are hosted mainly in clastic sedimentary rocks; in contrast, Irish-type Zn-Pb-(Cu) deposits formed primarily by replacement of Lower Carboniferous limestones and dolomitized limestones.
Seafloor exhalative sulphide deposition nevertheless accompanied formation of some Irish-type deposits, including part of the Conglomerate Group Ore (CGO) and the lower part of the overlying Upper Dark Limestone (UDL) at Navan. These CGO and UDL environments share many features in common with classic SEDEX deposits: they include carbonaceous, clastic host rocks deposited in euxinic environments; base metal sulphides formed where bacterially reduced dissolved sulphide mixed with warmer base metal-bearing fluids rising on active and recent extensional faults; metals were hydrothermally scavenged from underlying metasupracrustal rocks. These similarities suggest that economic SEDEX mineralisation may occur in the Irish midlands orefield. Navan UDL-hosted metal precipitation appears to have formed at or just below the seafloor in a euxinic environment. Recent exploration drilling has revealed new sub-economic, halo UDL mineralisation above the Pale Beds-hosted Zn-Pb ore at Gainstown (now called Tara Deep). Here, the basal UDL contains framboidal pyrite of sedimentary or diagenetic origin with replacive sphalerite and the development of siderite and haematite, with chert developed at higher stratigraphic levels.
Main Objetives: 1) Acquire petrographic, sulphide and whole-rock geochemical and S-O-Zn isotopic data for Gainstown (Navan) UDL and Pale Beds-hosted mineralisation. 2) Model the geometry of this mineralisation, and the potential geochemical linkages between the UDL- and Pale Beds-hosted mineralisation. 3) Develop geochemical tools to vector towards potential UDL-hosted SEDEX-style and possibly related Pale Beds-hosted mineralisation.