Gortdrum, County Tipperary, Ireland

This polymetallic deposit differs from most of the Irish-type deposits as the ores are copper-rich and lead-zinc-poor. It occurs within Dinantian limestones and shales associated with altered basic igneous rocks and close to a major fault. The mineralization is zoned with chalcopyrite and mercury-rich tennantite within bioclastic limestones lying above bornite and chalcocite-rich ore within shaly dolomitized limestones.

Major Minerals:

Bornite, chalcocite, chalcopyrite, Hg-rich tennantite

Minor Minerals:

Pyrite, galena, sphalerite, haematite

Trace Minerals:

Include arsenopyrite, cobaltite, cinnabar, amalgam, wittichenite, stromeyerite, gortdrumite, uraninite, coffinite, digenite, covelline, native copper


Cobaltite is euhedral and zoned. Tennantite is replaced by bornite and chalcocite. Bornite and chalcocite form characteristic symplectite-like intergrowths (myrmekitic or graphic intergrowths) which are probably the result of simultaneous precipitation of the two sulphides at low temperatures. Stromeyerite and wittichenite occur as fine-grained inclusions in chalcocite. Uraninite forms collomorphic bands and is replaced by bornite along the banding


Steed, 1986; Duane, 1988