Thermal studies on the lattice intergrowth of chalcopyrite in bornite from Akyama Mine, Yamagata Pref. (1)

Abstract

The fine beautiful lattce-intergrowth of chalcopyrite in bornite from the Akayama Mine occurs in the epithermal quartz veins, filling up the fissures in the Tertiary liparite and its tuff. Under the microscope, chalcopyrite lamellae, oriented crystallographically, are always found in bornite. The texture is interpreted as due to exsolution of a solid solution. Bornite often associates also with brecciated pyrite, massive chalcopyrite and with secondary covelline and chalcocite penetrating bornite and chalcopyrite along irregular cracks. Writers have made thermal studies on these bornite under the guidance of Prof. M. Watanabe of the Tohoku University, and obtained the results as follows; 1) Chalcopyrite lamallae in bornite disappear at 350°C, 400°C, 430°C and 460°C during 60, 6, 3 and 1 hour respectively, but partly remain at 300°C for 157 hours. 2) Bornite-chalcopyrite solution obtained by heating at 470°C for 1 hour shows the unmixing phenomena by reheating at various constant temperatures from 150°C to 400°C for 6 hours or more. The chalcopyrite then appears in various forms in lattice, cell, emulsion, graphic, lens, drop-like, wedge-like, worm-like, dendritic or as skelton crystal types under the conditions given in Table II and III. 3) The lattice structures appear conspicuously at temperatures of about 200°C for 6 hours to 24 hours, often with lens and drop-like crystals. 4) Dendritic, graphic and cell structures are generally found in some higher temperatures or after longer heating. From the results, shown above, bornite-chalcopyrite inter growth from the Akayama Mine may be said to have been formed at temperatures of about 200°C by breaking down of a solid solution.