In discussion by Schultz (p. 1443-1449) relating to a paper published by Derry et al (for reference, see this Bibliography Vol. 30) the following points of difference are noted: The ore-bearing carbonate sequence contains very little volcanic material. Tectonic folding was significant. The forms and stratigraphic relationships of the sulfide-barite deposits have little in common with the syngenetic ironstones. The sulfide-barite deposits are cavity-fillings and replacements with a complex paragenesis; they show mineral zoning unrelated to stratigraphy, and are not strata-bound. The sulfide-barite deposits are epigenetic, and their proximity to the ironstones is regarded as a coincidence. In reply, Derry points out that the lack of mineralization in beds overlying the ore-bearing 'reef' limestone, together with worldwide association of volcanism and iron-formation, and of iron-formation and base-metal sulfides, supports volcanogenic synsedimentary origin of base-metals at Tynagh.