Geochemical characteristics of ores and prospecting implications for the Chaliangzi iron-cobalt polymetallic deposit, Weining Beishan, Ningxia

The Chaliangzi Fe-Co polymetallic deposit is located in the Weining Beishan area of Ningxia and represents one of the important prospecting areas for cobalt polymetallic mineralization in the eastern segment of the North Qilian Orogenic Belt. To investigate the occurrence characteristics and enrichment mechanisms of cobalt, this study conducted whole-rock trace element geochemical analyses of ores, based on a systematic review of the regional geological background and deposit geological features. The results indicate that the Fe-Co mineralized alteration zones are controlled by faults and mainly hosted in tectonic breccias, fault gouges, and lenticular quartz sandstones, characterized by pervasive limonitization, psilomelane mineralization, and intense supergene oxidation alteration. The ores in the mining area can be broadly classified into limonite ores, limonite-psilomelane cobalt-bearing ores, and psilomelane cobalt-bearing ores. The mineral assemblage is dominated by quartz, Fe-rich minerals (mainly limonite), and clay minerals, with minor Mn-bearing minerals and sulfides, reflecting a multi-stage mineralization process characterized by a transition from reducing to oxidizing conditions, overprinted by supergene weathering-leaching and hydrothermal alteration. The total rare earth element (REE) contents and distribution patterns vary significantly among ores with different alteration intensities. Light and heavy REEs exhibit pronounced fractionation, whereas the internal distribution of heavy REEs remains relatively stable. Most samples display distinct negative Eu and Ce anomalies, indicating mineral fractionation and a relatively oxidizing metallogenic environment. Primitive mantle-normalized trace element patterns show that the samples are generally depleted in high field strength elements (HFSEs) such as Nb and Ta, and commonly exhibit decoupling of Zr and Hf anomalies, suggesting that the mineralization system was open and influenced by multi-stage fluid processes. Transition metal element characteristics and correlation analyses reveal significant positive correlations between Co and Ni as well as Zn, whereas correlations between Co and Cu, Cr, V, and Sc are weak. The Co-Ni correlation mainly reflects the primary mineralization background, while the Co-Zn correlation is more likely related to supergene enrichment controlled by Mn oxides. Comprehensive analysis indicates that the Chaliangzi Fe-Co mineralization system experienced a multi-stage evolutionary process. Cobalt mainly occurs as isomorphic substitutions or in finely dispersed forms within Fe-rich carrier minerals, and its enrichment is jointly controlled by redox conditions, the evolution of carrier minerals, and element redistribution processes. Based on REE fractionation, HFSE decoupling, and Co-Ni-Zn correlations, this study constrains the multi-stage mineralization processes and enrichment mechanisms of Fe-Co polymetallic deposits in the Weining Beishan area, and further highlights a mineralization model characterized by structural control and multi-stage superimposed modification, providing practical geochemical criteria for ore prospecting and target delineation.