Thermal studies on bornite in melted sulphur

Abstract

In this paper, the experimental data on behaviour of bornite in melted sulphur are described. When bornite is sealed in pyrex tubes with sulphur powder and then heated in an electric furnace, the following process is observed. 1) At temperatures higher than 120°C, bornite reacts to form covellite with melted sulphur (Figs. 1A, 6). When cracks are found in bornite, the covellite is produced also in veinlets or as network along them, similar to those of supergen origin (Fig. 1B). 2) At temperatures from 140°C to about 450°C, chalcopyrite appears in bornite in the forms of lattice, emulsion, lens, semi-cell, droplike and worm-like crystals. The lattice pattern is formed at temperatures from 140°C to 320°C in bornite only near covellite, while the drop-like crystals appear in the inner part of bornite at temperatures higher than the former. The lenticular granules often appear in pairs when heated for one hour at temperatures from 250°C to 350°C (Figs. 4, 6), and they change into drop-like crystals when heated at higher temperatures or for longer times. These various forms of chalcopyrite are thought to be an unmixing product from a solid solution, formed in association with covellite. 3) At temperatures higher than 300°C, a reddish brown mineral is formed in bands or patches in bornite, adjacent to covellite (Figs. 6B, 9B). This mineral resembles bornite, but is anisotropic very strongly. 4) At higher temperatures than 360°C, fine granular pyrite newly appears in bornite and also in massive chalcopyrite, originally existed. From these results, the wirier infers that: a) It is probable that some ore minerals are formed by thermal dissociation in solid state, as mentioned above. b) The unmixing phenomena from a solid solution, formed by mechanism of a), can be expected in geological process.