The Silvermines B-Zone 4611 Silver-Rich Pod—An unusual Ag-Ge-Sb-As-Ni assemblage, Co Tipperary, Ireland

The Silvermines Pb-Zn-Ag-Ba orebodies comprise vein, replacement, cross-cutting and stratiform mineralization mostly hosted in Lower Carboniferous limestones in the vicinity of a major ENE and E-W trending normal fault array and represent a classic example of Irish-Type Zn-Pb mineralization. The deposits were exploited historically at various times, but the major limestone-hosted Zn-Pb-Ba mineralization was not discovered until the 1960s. Structurally controlled crosscutting vein and breccia mineralization represent pathways of hydrothermal fluids escaping from the Silvermines fault at depth that exhaled and replaced shallowly buried Waulsortian limestones creating the larger stratiform orebodies such as the Upper G and B Zones. The B Zone, comprising a pre-mining resource of 4.64Mt of 4.53% Zn, 3.58% Pb, 30 g/t Ag has a locally highly variable gangue mineralogy dominated by pyrite, barite, siderite, within dolomitic and limestone breccias with local silica-haematite alteration. A small, highly unusual pod of very high-grade Ag-rich mineralization in the B Zone, the 4611 Pod, discovered in 1978, has not been previously documented. Unpublished mine records, field notes, mineralogical and chemical data from consultant reports have been assimilated to document this interesting and unusual occurrence. The pod, representing an irregular lens of mineralization ca 2m thick and representing 500t occurs within the B Zone orebody and comprises high grade Zn and Pb sulfides with significant patches of proustite-pyrargyrite (ruby silvers) and a host of associated Pb, Ag Sb, As , Cu, Ge sulfide minerals, including significant argyrodite (Ag-Ge sulfide). Although evidence of any distinct feeder below the pod is lacking, the nature of the pod, its unusual mineralogy and its paragenesis suggests that it represents a small, possibly late source of exotic hydrothermal fluid where it entered the B Zone stratiform mineralizing system.