Iron oxide and associated base metal mineralisation in the Central Midlands Basin, Ireland

Abstract

This study describes and characterises the iron oxide mineralisation (hematite, magnetite, silica) associated with base metal mineralisation in the Irish Central Midlands Basin. The iron oxide mineralisation occurs over a range of styles and sizes from isolated jasper nodules at Silvermines, Lisheen, Galmoy and Navan to thick, stratabound, banded ironstone units at Tynagh and Crinkill. The iron oxide mineralisation formed during the early diagenesis of the Waulsortian Mudbank Complex at Tynagh, Crinkill, Silvermines and Garrycam, that is, during the Courceyan to Chadian in a seafloor to sub-seafloor setting (10s of centimeters to 10s of metres burial). However, massive ironstones and iron oxides occur throughout the entire Courceyan to Chadian carbonate package at Tynagh, from the upper Ballysteen Limestone Formation, throughout the Waulsortian Mudbank Complex and within the lower Grey Calp/Supra-Waulsortian. Hence at Tynagh. the hydrothermal system appears to have been active over significant a period of time (approximately 5Ma).