A Mineralogical Investigation on Volatilization of Impurity Elements from Cu-Rich Polymetallic Concentrates During Roasting in Inert Atmosphere

Four different Cu-rich polymetallic concentrates are tested for volatilization of Sb and As during laboratory-scale roasting. The experiments are performed between 200 °C and 700 °C, at intervals of 100 °C and in an inert atmosphere. Sb volatilization is much less (maximum approximately 45 pct) than As volatilization (maximum approximately 95 pct) in these conditions at 700 °C. As volatilization is however limited from the concentrate having As mainly in a tetrahedrite solid solution ((Cu,Ag,Fe,Zn)12(Sb,As)4S13). Sb and As retained in the roasted calcine are found in the low-melting liquid phase, formed at approximately 500 °C. This melt phase gets enlarged and enriched in Sb with an increase in temperature. However, there is noticeable As volatilization from this melt phase with the temperature approaching 700 °C. Furthermore, there is an early and relatively high Sb volatilization from the concentrate having Sb substantially as gudmundite. Micron-scale elemental redistribution in gudmundite in the 350 °C roasted calcine confirms its transformation at this temperature. Other Sb minerals did not undergo any detectable transformation at this temperature, suggesting that the significant Sb volatilization starting between 300 °C and 400 °C was primarily from gudmundite. This benign attribute of gudmundite featured in this work in the context of roasting should also be relevant from the geometallurgical perspective during concentrate production, where concentrates bearing Sb are considered substandard for further Cu extraction irrespective of the Sb mineralogy.

Grain boundary-induced premelting and solid ↔ melt phase transformations: effect of interfacial widths and energies and triple junctions at the nanoscale

Grain boundary-induced transformations between solid, premelt, and melt are studied using a phase field approach. The effect of grain boundary width and energy and triple junction energy is studied.

Experimental observations of TiO2 activity in rutile-undersaturated melts

An estimate of TiO2 activity (aTiO2melt-sat) is necessary for the application of trace-element thermobarometry of magmatic systems where melts are typically undersaturated with respect to rutile/anatase. Experiments were performed in the system SiO2-Na2O-TiO2 to develop two independent methods of estimating aTiO2melt-sat—one based on the commonly applied rutile-saturation technique and another utilizing a novel Ti-in-tridymite thermometer. It is demonstrated that the rutile-saturation model can lead to an overestimate of aTiO2melt-sat relative to TiO2 activity calculated using the solubility of Ti in tridymite (SiO2) coexisting with rutile. Overestimation via the rutile-saturation technique is due to variations in the solubility mechanisms of Ti in the melt phase as a function of Ti content. In natural systems, overestimates of aTiO2melt-sat will lead to an underestimation of crystallization temperatures by Ti-based trace-element thermobarometers. Although this study is not directly applicable to natural systems, it lays the groundwork for future research on natural composition magmas to constrain TiO2 activity in melts.

The architecture of an intrusion in magmatic mush

<p class="western" align="justify"><span lang="en-US">Magmatic reservoirs located in the upper crust have been shown to result from the repeated intrusions of new magmas, and spend most of their dwelling time as cristal-rich mush. Despite advances in our understanding of the physical processes that may occur in a magma reservoir, the architecture of the intrusion into a mush remains poorly constrained. The geometry of such intrusions, however, may greatly affect the thermal and compositional evolution of the magmatic reservoir. We performed numerical simulations coupling computational fluid dynamics with the discrete element method to identify the geometry and emplacement dynamics of an intrusion in a mush, and the relevant physical parameters controlling it. Our results show that the intrusion geometry is to first-order controlled by the density contrast between the melt phases of the intruded and resident materials rather than the bulk density contrast as usually considered. When the melt phase of the intruded materials is denser than that of the host, the intrusion ponds at the base of the mush and is emplaced as a horizontal layer. However, when the intruded melt is lighter, the intrusion rises through the mush forming a Rayleigh–Taylor instability. In the absence of density contrast between the two melts, the intrusion fluidizes the host crystal network and slowly ascends through the mush. The presence of a viscosity contrast between the intruded and resident materials as well as the intrusion injection velocity were found to have less of an influence on the final geometry and intrusion dynamics in mush. In addition, we analyzed the eruptive sequence of well documented eruptions involving an intrusion as a trigger, and found good agreement with our modeling results. This study sheds light on the importance of explicitly considering granular mechanisms and the relative motion between the crystals and the melt phase when studying the physical processes of magmas and mush.</span></p>