An occurrence of secondary sulfides from Leg 37 basalts

Two types of secondary sulfides occur on the walls of a vesicle in slightly altered basalt recovered from site 332A of DSDP Leg 37. The first consists of euhedral crystals of pure pyrite, with occasional small partial overgrowths of fibrous chalcopyrite, embedded within smectite (altered glass) which lines the vesicle. The second type occurs as small composite sulfide spherules lightly attached to the surface of the smectite. The spherules are composed of pyrite crystallites arranged in approximate pyritohedral symmetry, with marcasite crystallites decorating the pyritohedron edges. Precession camera photographs and optical studies suggest the marcasite and pyrite grew simultaneously from a pyrite nucleus, with marcasite adopting the pyrite growth habit. These spherules differ sharply from the magmatic sulfide spherules previously described.