Analytical procedures are described for the solid state phase microanalysis of synthetic and natural tin-, arsenic-, and antimony-bearing sulfosalts and sulfides of thallium, tin, lead, and silver. In these procedures, abrasive stripping voltammetry and coulometry of the solid phases are applied. Trace amounts of the sample compounds were transferred onto the surface of a graphite electrode and the electrochemical reduction or oxidation was followed by voltammetric techniques. The most valuable technique for distinguishing different mineral phases is to record the anodic dissolution voltammograms after a preliminary electrolytic reduction of the sulfides or sulfosalts to the elementary metals which are still confined to the electrode surface. For various compounds an approach was developed in which the ratio of charges consumed during reduction and oxidation of the solid phases is used for unambiguous identification. Coulometric measurements are also used for the determination of the quantitative composition of the solid phases.

The phase relations in the Cu-Fe-S, Fe-Ni-S, and Cu-Ni-S systems were investigated by silica-tube quenching, differential thermal analysis, and high-temperature X-ray powder diffraction experiments. In addition, portions of the Cu-Fe-S and Fe-Ni-S systems were studied by gold-tube quenching and differential thermal analysis experiments under high confining pressures. At elevated temperatures extensive liquid immiscibility fields span the sulfur-rich region of each of the three systems, whereas homogeneous liquid fields dominate the phase relations in their central portions. The average composition of the Sudbury Cu-Fe-Ni sulfide ore, when projected onto the Cu-Fe-S plane, is accounted for above 860° C by a mixture of copper containing hexagonal pyrrhotite and copper-rich sulfide liquid. Thus at high temperatures a mechanism exists that may be responsible for certain copper-rich segregations observed in this type of ore. The minerals of the Cu-Ni-S system, with the rare exception of millerite, do not occur in Sudbury-type ores. Knowledge of the phase relations in this system is prerequisite, however, for systematic investigations of the complex Cu-Fe-Ni-S system. Applications of the phase relations in the Cu-Fe-S and Fe-Ni-S systems to typical ore assemblages show that extensive reequilibration took place among the sulfides after their initial deposition. The sulfides in Sudbury-type ores commonly have compositions and crystal structures that can be produced in the laboratory only at low temperatures.

No abstract

No abstract

No abstract