Location:

Galapagos Mound sulphides. Pacific Ocean

Massive sulphide mounds are associated with inactive vents lying along the Galapagos Rift. The sulphides are pyrite-chalcopyrite-dominated, unlike those found along 21'N, and share many similarities with massive sulphide ores found within ophiolite volcanic sequences. Opal and gypsum are the main non-sulphides.

Major Minerals:

Pyrite, chalcopyrite

Minor Minerals:

Marcasite, sphalerite/wurtzite

Trace Minerals:

Include pyrrhotite, haematite, tetrahedrite group minerals, galena, cubanite, covelline, blaubleibender covelline

Textures:

The chimney-like 'ores' have an inner chalcopyrite-rich core and pyrite-rich rim. Collomorphic pyrite is intergrown with marcasite. Euhedral pyrite encloses small chalcopyrite, isocubanite, wurtzite/sphalerite, haematite and galena inclusions along growth zones. Zinc sulphide has the habit of wurtzite and carries chalcopyrite inclusions. Chalcopyrite occurs as void infillings and is altered to covelline. Lamellae of pyrrhotite show extensive alteration to pyrite and marcasite

References:

Schrader et al., 1980; Malahoff, 1982; Oudin, 1982; Skirrow and Coleman, 1982; Malahoff et al., 1983