Features of composition measurements of copper sulfides of the Volkovskoye deposit (Middle Urals, Russia)

Abstract

Introduction: the Volkovskoye deposit is an important copper deposit in the Urals those exploitation depends on the degree of ore oxidation. A main source of copper is bornite and the associated minerals, such as chalcopyrite and digenite. The feature of copper sulfides of this deposit is the difference of elements ratio from stoichiometric minerals composition and it is considered that copper in sulfides migrates under the influence of electron beam, which can distort obtained data of minerals compositions. To identify the reliable deviation of element ratios, in the frames of the present study copper sulfides have been studied under energetically different conditions of energy dispersive spectra (EDS) bу excitation.

Methodology: ore samples with bornite, chalcopyrite and digenite have been sampled at the exploited quarry of the North-West section of the Volkovskoye deposit (Middle Urals, Russia). The chemical composition of bornite varieties and associated copper sulfides have been analyzed using microprobe analysis at different electron beam energies, graphs of experimentally obtained compositions have been built and optimal conditions of EDS accumulation have been determined.

Results and discussion: the results of microprobe analysis of bornite chalcopyrite and "digenite" show that the ratio of elements value analyzed by energy-dispersive spectra depends on an excitation energy. The determined optimal conditions for the study of the copper sulfide composition are 17-21 kV (at current 0.315¸0.160 nA) for bornite, 17¸25 kV (0.315¸0.125 nA) for chalcopyrite, and 15-25 kV (0.235¸0.125 nA) for «digenite». A study of the Volkovsky bornite composition under optimal conditions have confirmed a significant copper deficiency. It is revealed that the chemical composition of «digenite» may indicate a new mineral phase.

Conclusion: by using a range of optimal conditions of EDS spectra excitation the correct elements relations in sulfides of the Volkovskoye deposit have been obtained, the significant copper deficiency in bornite has been identified, the pink variety – Cu_4.55Fe_1.01S₄ and the orange variety – Cu_4.57Fe_0.98S₄. During the study the copper sulfide Cu_1.87S has been revealed, which requires additional studies for its phase diagnostics.