An experimental study on cubanite irreversibility: implications for natural chalcopyrite-cubanite intergrowths
Pruseth, Kamal L.; Mishra, Biswajit; Bernhardt, Heinz -J.
European Journal of Mineralogy Volume 11 Number 3 (1999), p. 471 - 476
published: May 25, 1999
manuscript accepted: Jan 7, 1999
manuscript received: Aug 24, 1998
ArtNo. ESP147051103006, Price: 29.00 €
Abstract Isocubanite, CuFe2S3, was synthesized at 700°C by reacting the component sulfides and sulfur in evacuated silica tubes. The phase was characterized by optical and X-ray diffraction methods. Microprobe analyses revealed a nearly stoichiometric composition. Annealing experiments on isocubanite were conducted at 185°C for 4, 8, 12, 24, and 32 days. Chalcopyrite lamellae and spindles were observed distributed parallel to (111) and (110) planes within the isocubanite matrix. Formation of pyrrhotite indicates that chalcopyrite is not produced due to simple exsolution, but due to the breakdown reaction: CuFe2S3 = CuFeS2 + FeS (pyrrhotite). Repeated homogenization and annealing resulted in thicker chalcopyrite lamellae. A possible mechanism for deriving the intergrowth of orthorhombic cubanite within chalcopyrite, characteristic of ancient hydrothermal deposits, from the intergrowth of chalcopyrite within isocubanite that is exclusively encountered in modern sea floor hydrothermal deposits, is discussed.