Abstract
Sir: The origin of mineralization-associated breccias in the Irish Carboniferous is crucial to an understanding of Irish-type Zn-Pb deposits. One of the key lines of evidence that has been used to support a synsedimentary component to the Irish-type deposits has been the presence of mineralized clasts within the breccias, which were interpreted as being of sedimentary origin (Andrew, 1986; Ashton et al., 1986, 1992). However, if these breccias are, instead, of hydrothermal origin, then arguments for a synsedimentary mineralization component are invalidated (e.g., Peace and Wallace, 2000; Reed and Wallace, 2001). In this context Lee and Wilkinson (2002) have made a timely and important contribution to this problem of breccia origin. Lee and Wilkinson (2002) have advanced a case for mineralized sedimentary breccias at the Cooleen zone, Silvermines, suggesting that the black matrix breccias may have originally been debris flow breccias. We have no disagreement with Lee and Wilkinson’s basic observations, but suggest that these observations better support a hydrothermal origin for the brec-cias, as has previously been suggested for black matrix brec-cias elsewhere in Ireland (e.g., Hitzman et al., 1992). Specifically, we suggest that the breccias are the result of hydrothermal karsting that was directly associated with sulfide mineralization. Hydrothermal breccias are associated with mineralization at many localities throughout the Irish Midlands, and it is important that these breccias are not confused with genuine sedimentary breccias. The morphology and paragenesis of the breccias described by Lee and Wilkinson (2002) have a number of features in common with epigenetic hydrothermal breccias described from elsewhere in the Irish ore field, and from localities outside Ireland. Mineralized breccias from Ireland have been described from Galmoy, Lisheen, Silvermines, and …
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call