Copper and other mineralization in the upper Palaeozoic strata of South-West Cork, Ireland, and related areas.

Small scattered disseminations of metalliferous minerals, primarily copper bearing sulphides and secondary malachite, are widespread in the Upper Devonian sedimentary rocks of South-West Cork. This mineralization is spatially associated with the development of 'red beds'. Typically the host rocks are the sandstone and comstone fractions of green-grey coloured strata. In the 'red bed' sequence such greon-grey strata are present as thin concordant bands. An upward stratigraphic zoning of the sulphides from those rich in copper to those relatively rich in iron occurs. In addition the sulphides show evidence of having been deformed together with the enclosing host rocks during the Ilercynian orogeny. The copper abundances in unmineralized portions of the succession are apparently abnormally lev. Similar though less richly mineralised cupriferous strata occur in the Devonian succession elsewhere in Southern Ireland and in the Anglo-Welsh area. The disseminated mineralisation is considered to have formed as a result of diagenetic processes active within the coinpacting sedimentary column. The position of the water table, the presence of sulphate-reducing) bacteria, the movement of 'waters of compaction', variations in sediment permeability and the presence both of 'red beds' and of the adjacent Variscan marine eeosynclinal basin are considered to have bean important factors in effecting metal concentration. In South-West Cork the subsequent Hercynian orogeny produced small quartz-sulphide veins by lccal renobilization of cupriferous country rock. Larger vein deposit of quartz, of baryte, and of manganese and iron oxides also occur. Where quarts forms a major constituent, metalliferous (chiefly Cu-Pb) mineralization is common. It is suggested that in the main such metalliferous mineralization vas emplaced during the Hercynian orogeny from remnant connate fluids channelled through fractures after the surrounding strata were rendered impermeable. The baryte and the manganese and iron oxides may have been deposited at a much later stage from ground waters circulating in the pre-existing Eercynian fractures. Various microscopic sulphide textures present in the mineralization of the South-West Cork area are, in addition, described and their modes of formation discussed.