Abstract
Sir: We are delighted to respond to the comments of Reed and Wallace on our paper on the origin of breccia-hosted base-metal mineralization in the Irish ore field (Lee and Wilkinson, 2002). Reed and Wallace’s thesis is that the mineralized breccias we have described within the Mississippian Waulsortian Limestone Formation at Cooleen are not of sedimentary origin and therefore, by extension, that synsedimen-tary breccias do not exist elsewhere in the ore field. If correct, one of a number of lines of evidence that have been used to infer a near–sea-floor origin for at least a component of sulfide mineralization in Ireland—that of reworked clasts of sulfide within sedimentary breccias—would be invalidated. Contrary to the suggestion of Reed and Wallace, the existence of sedimentary breccias spatially associated with mineralization in the Waulsortian is universally accepted in the literature. Mine-based investigations that include underground observations as well as drill core data and sedimentological studies have concluded that the stratiform, wedge-shaped breccia bodies commonly developed within the Waulsortian Limestone facies are sedimentary debris flows of Courceyan age (Boyce et al., 1983; Taylor, 1984; Andrew, 1986; Clifford et al., 1986; Somerville et al., 1992). Submarine fault scarp sedimentary breccias are common in sediment-hosted Zn-Pb deposits (e.g., Goodfellow et al., 1993) and display the same characteristics as the breccias at Cooleen. Hitzman and Beaty (1996, p. 125) also recognized that synsedimentary breccias are present within the Waulsortian at both Silvermines and Lisheen but went on to state that textural and field relationships clearly show that the principal episode of brecciation postdated regional burial dolomiti-zation, inferring a hydrothermal origin for the ore-hosting breccias. While we would not agree with this conclusion, particularly in relation to the Silvermines area, we accept that the ore-hosting breccias at Lisheen, Galmoy, and Silvermines have been …
Published Version
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