On the Genesis of Chalcopyrite Lattice in Bornite

Abstract

Bornite normally appears homogeneous under a reflexion microscope at the magnification of 1, 000 times. However, upon heating at 100°C to 450°C bornite will show, always, chalcopyrite segregations in the shape of small lattices, lamellae emulsions and lenses or cells. Such microstructures of bornite chalcopyrite intergrowths strongly resemble the sc-called exsolution texture frequently found in natural ores. To shed light on this phenomenon, samples of bornite produced at the mines enumerated in Table 1 were crushed to granules of about 150 cubic millimeter, sealed hermetically in pyrex glass tubes, and heated at a rising temperature rate of 10°C per hour until within the range of 100°C to 500°C, then they were quenched. Upon examination of these heated products, the following observations were made.
(1) The functional relationship observable between the quantity of segregated chalcopyrite and the temperature differed according to the origin of the ores. The differences were in quantity segregated, temperature of segregation, and temperature of disappearance.
(2) The texture of chalcopyrite appearing in the bornite samples from Yakuwa Mine went through the following transitions : a) at about 130°C, fine chalcopyrite lattices began to appear all over the ore particle, b) the lattices decreased in number and increased in size with the rise in temperature, c) the total quantity of segregated chalcopyrite gradually increased and formed lamellar, tense-like and emulsive textures in addition to the lattices, d) at temperatures higher than 320°C, the segregated chalcopyite began to decrease, the texture being reduced to some lenses and emulsions, which also disappeared in the final stage at 450°C. In the bornite from Sangasho and Sakurago Mines only a small quantity of chalcopyrite segregated upon heating, and the change in texture was limited to the formation of some lens-shaped or emulsive segregations.
(3) The results of chemical analyses of the samples used are given in Table 2 (Items (1, 4, 7 and 10)).By subtracting the value for the impurities computed by Rosiwal′ s method from the analytic value the ore samples were found to contain 3, 5, 10 and 15 mol% of chalcopyrite respectively. These values were collated with the quantity of segregated chalcopyite and found to be in an approximately direct ratio with the latter, as illustrated in Figure 4.
(4) X-ray photographs of the samples from Yakuwa and Sakurago Mines showed the following phenomena : a) Debye-Scherer's lines due to chalcopyrite as well as to bornite were presented even when the samples were at room temperature. b.) when the sapmles were heated and the maximum chalcopyrite segregation was effected the lines increased their intensity, c) when the temperature was rised at 400°C to 450°C only Debey-Scherer′s lines due to bornite were observed.