Location:

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

Textures:

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

References:

Steed, 1986; Duane, 1988