Critical-Element Deportment in Porphyry and Skarn Copper Ores: Evidence from Three Kazakhstan Deposits

The growing demand for critical metals associated with the global energy transition has increased interest in their potential recovery as by-products of copper processing. This study investigates critical- and associated-element deportment in ores and flotation products from three Kazakhstan deposits representing contrasting ore-system types: the Aktogay and Bozshakol porphyry Cu–Mo deposits and the Severny Samombet Cu-skarn deposit. Bulk geochemistry, optical mineralogy, SEM–EDS observations, and technological mass-balance data were integrated to evaluate mineralogical associations and element recovery into Cu and Mo flotation products. The two porphyry systems show comparatively selective deportment: Re preferentially reports to the Mo concentrates, with recoveries of 4.05% at Aktogay and 19.03% at Bozshakol, whereas Se preferentially reports to the Cu concentrates, reaching 55.35% and 27.18%, respectively. SEM–EDS observations of Aktogay molybdenite provide mineral-scale compositional evidence for Re-bearing molybdenite. In contrast, the Severny Samombet Cu concentrate shows broader multi-element recovery, particularly for Ag (86.00%), In (74.82%), Zn (68.15%), and Cd (55.04%), accompanied by intermediate recovery of Pb, Co, and Bi. Mineralogical observations reveal a heterogeneous sulfide assemblage together with discrete Bi–Pb- and Ag–Te-bearing accessory phases. Ge shows consistently low recovery into the investigated concentrates, including only 1.31% into the Severny Samombet Cu concentrate, indicating that bulk enrichment does not necessarily translate into flotation recovery. These results demonstrate contrasting critical-element deportment patterns among the three investigated deposits and show that evaluation of potential by-products requires integration of mineralogical characteristics with quantitative flotation-product recoveries. The results provide a basis for identifying technological streams warranting further assessment for critical-metal recovery, while quantitative determination of trace-element partitioning among individual mineral hosts requires mineral-specific analytical methods.