Sulphide chimneys. East Pacific Rise, 21°N. Pacific Ocean

At 21°N along the spreading axis, zinc-rich chimneys comprise an inner wurtzite-rich core with a copper-iron sulphide-rich margin, whereas copper-rich chimneys have an inner chalcopyrite or iss core (isocubanite) passing out into a copper-iron sulphide rim. Anhydrite, opal, baryte and magnesium silicates are the major non-sulphide components of the 'ores'.

Major Minerals:

Wurtzite, sphalerite, chalcopyrite, pyrite, bornite, chalcocite, isocubanite

Minor Minerals:

Anomalous bornite, covelline, pyrrhotite, marcasite, digenite

Trace Minerals:

Include galena, valleriite, haematite, magnetite, tennantite, lead-silver sulphosalts


Chimneys show mineralogical zoning from core to rim and alteration on their rims. Worm tubes are present. Compositionally zoned wurtzite forms hexagonal crystals with epitaxial chalcopyrite along growth zones. Much wurtzite has inverted to sphalerite. Chalcopyrite is collomorphic to euhedral and is successively replaced by bornite, digenite, chalcocite and covelline. lsocubanite is rimmed by chalcopyrite. Pyrrhotite forms hexagonal crystals or thin laths as part of the 'black smoke'. It is extensively replaced by pyrite and marcasite. Pyrite is collomorphic and intergrown with marcasite or forms discrete euhedral crystals


Hekinian et al. 1980; Oudin, 1981, 1983a; Styrt et al., 1981; Haymon and Kastner, 1981; Goldfarb et al., 1983; Hannington et al., 1986; Caye et al., 1988