The phase relations in the central portion of the Cu-Fe-S "dry" system have been studied at 100 degrees C and 600 degrees C. The 600 degrees C isothermal section is presented and low-temperature phase relations based on synthetic and natural assemblages are discussed.At low temperatures, the minerals chalcopyrite (CuFeS 2 ), cubanite (CuFe 2 S 3 ), talnakhite (Cu 9 Fe 8 S 16 ), mooihoekite (Cu 9 Fe 9 S 16 ), and haycockite (Cu 4 Fe 5 S 8 ) are stable phases. Chalcopyrite, talnakhite, and mooihoekite have been synthesized, while attempts to synthesize cubanite and haycockite have been unsuccessful.Synthetic talnakhite (beta -phase), on heating, shows transformations at approximately 186 degrees C and at approximately 230 degrees C to intermediate high-temperature phases, I and II, and finally transforms at 520 to 525 degrees C to a face-centered cubic (fcc) sphalerite-like structure (iss). None of these phases are quenchable. Synthetic mooihoekite (gamma -phase) transforms to intermediate high-temperature phase A at approximately 167 degrees C, and this phase changes at approximately 236 degrees C to the fcc sphalerite-like structure (iss). Both high-temperature forms of mooihoekite are unquenchable.For the haycockite composition, an unquenchable high-temperature phase is formed between 20 and 200 degrees C which appears isostructural with fcc high-temperature mooihoekite and iss. On quenching, this phase changes to a structure which can be indexed as having a primitive cubic cell with a nearly equal 5.32Aa.Cubanite transforms to a fcc phase at 200 to 210 degrees C which appears isostructural with high-temperature mooihoekite (and iss). This reaction has not been reversed in the laboratory; annealing experiments below the transition produce chalcopyrite exsolutions in a high-temperature cubanite matrix.