EXPERIMENTAL DEFORMATION AND ANNEALING OF SULFIDES AND INTERPRETATION OF ORE TEXTURES

Results of recent annealing and intrusion experiments on copper, lead, zinc, and iron sulfides show that plastic flow occurs very quickly in galena, chalcocite, bornite, pyrrhotite, and chalcopyrite at temperatures within the ranges recognized for the greenschist and amphibolite rock facies and under confining pressures less than 1,700 bars. Under the same conditions sphalerite may adjust by minor twinning or fracture. Pyrite fails by fracture, if at all. At 550 bars confining pressure and temperatures above 400° C galena could be forced to flow plastically into cracks in pyrite, sphalerite, chalcopyrite, and pyrrhotite. Galena, pyrrhotite, and chalcopyrite could penetrate pyrite or sphalerite. With increasing temperature at 550 bars, chalcocite would start to recrystallize at around 465° C, chalcopyrite at 565° C, and pyrrhotite between 525° C and 666° C. Recrystallization, if complete, would wipe out all evidence of plastic flow. At higher pressures below the crushing strength of pyrite, most of the temperatures given would be lowered by modest amounts, but the order of occurrence of the changes would probably be the same. Moderately lower strain rates would probably have similar effects, but at very low strain rates common in rock deformation, the effects on textures cannot be predicted with any certainty at present. Much more careful and detailed investigations are needed before interpretation of textures of ore deposits can be said to be on a reasonably firm foundation. © 1969 Society of Economic Geologists, Inc.