Occurrence characteristics and enrichment mechanism of cobalt in pyrite from the Han-Xing type skarn iron deposit using laser-ablation inductively-coupled-plasma mass-spectrometry elemental mapping, Taihang Mountain, China

Cobalt is a critical and strategic metal mainly found as associated element in several types of deposits, of which skarn-type deposits are the major sources. Han-Xing type skarn iron deposit, having high grade iron ore and associated cobalt, is a typical skarn-type iron ore in China. But the complete recovery and exploitation of cobalt are restricted because of the lower grade of related cobalt and the dearth of prior research on its occurrence condition and enrichment mechanism. In this paper, pyrite from five typical ore deposits in the Han-Xing area was studied by using electron probe microanalysis (EPMA) and laser-ablation inductively-coupled-plasma mass-spectrometry (LA–ICP–MS) techniques to decipher the occurrence state and enrichment mechanism of associated cobalt in skarn-type iron deposits. The results show that Co²⁺ replaces Fe²⁺ in pyrite through isomorphism. The distribution of cobalt in pyrite from different deposits varies greatly, that is, in the Xishimen iron deposit, the cobalt content is comparatively enriched in the pyrite's core. In contrast, in other deposits, the cobalt content is concentrated in the pyrite's rims, where it can be up to 1000 times higher than in the core. The cobalt mineralization in Han-Xing area can be divided into several stages. The sulphur element of sulphide is mainly derived from evaporite, while cobalt mineralization occurred in the early stage with pyrite formation or in the late stage by metasomatism/cementation of Co-rich ore-forming fluid. The magma assimilated with the Ordovician evaporite not only promoted iron mineralization, but also became the main controlling factor for cobalt enrichment.