Mineralogical changes of bornite by heating in nitrogen atmosphere are studied microscopically. Eornite specimens of about, 3mm diameter, but a few percents of chalcocite. are associated microscopically, are heated for an hour at every temperature between 50°C to 1, 000°C and are observed under the microscope.
The results obtained are as follows:
(1) At.80° ?? 150°C, margin of the chalcocite grains enclosed in bc ?? nite is altered to digenite but above 160°C the mineral is diffused into chalcocite.
(2) Between 190° ?? 650°C, chalcocite diffused into an homogcneous bornite solid solution, bu ?? by slow cooling, chalcocite is reappeared as several inmixing textures.
(3) From 190° to 430°C, minute crystals of chalcopyrite and tetral ?? edrite showing emulsion, wedge-like of globular forms are newly segregated from bornite solid solution. Relation between heating temperatures and segregated amounts of the minerals is shown in Figs. 3 and 4.
As shown in the Table of chemical composition of the sample, the bornite has, some excess chalcopyrite and tetrahedrite components and excess ones are segregated at above temperatures.
(4) A desulphuration curve is. given in Fig. 1-A. As the desulphu ?? ation at 400° ?? 450°C may be explained by that of chalcopyite impurity, the curve of the pure bornite also be considered as Fig. 1-C.
(5) At above. 650°C, some part of the bornite is dissociated to FeS and Cu₂S. Microscopically, two kinds of the texture can be seen as shown in Fig.5 (below 730°C) and Fig. 6 (above 730°C)
(6) Drop-like or veinlet metallic copper is appeared at above 500°C and veinlet pyrrhotite is appeared at above 950°C.