Sulfide geochemistry and gold occurrence in the Yu'erya deposit, Eastern Hebei, China: Implications for mineralization and metallurgy

Abstract

The Yu'erya gold deposit is located in eastern Hebei along the northern margin of the North China Craton, which is one of the typical gold deposits associated with Mesozoic granitic intrusions in the region. A systematic characterization on the gold occurrence and sulfide geochemistry are critical for understanding the mineralization process and guiding recovery strategy. However, such information is still lacking for Yu'erya. In this study, the automated mineralogy mapping using TESCAN Integrated Mineral Analyzer (TIMA) and sulfide compositional determination using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) have been conducted to investigate the gold occurrence and the coupled substitution behavior of Au with other trace elements in pyrite. The results indicate that embedded features of visible gold can be classified as fracture-hosted gold, included gold, and intergranular gold, with fracture-hosted gold being the dominant type, accounting for 57.32 % of the total. Based on the spatial distribution, visible gold is further classified into free gold (spatially independent) and intergrown gold (associated with other minerals), with free gold being the predominant type (67.78 %). In terms of grain size, visible gold can be further divided into four categories: micro-grained gold (1–5 μm), fine-grained gold (5–10 μm), medium-grained gold (10–20 μm), and coarse-grained gold (20–50 μm). Their proportions in terms of area are 8.10 %, 36.45 %, 37.21 %, and 18.24 %, respectively, and by quantity, the corresponding proportions are 38.91 %, 43.52 %, 15.06 %, and 2.51 %. The invisible gold primarily occurs as solid solutions or mineral inclusions, with its content varying among different sulfide minerals. The average concentrations are 0.92 ppm in pyrite, 1.11 ppm in chalcopyrite, and 0.49 ppm in sphalerite. Notably, tetrahedrite exhibits the highest average value (4.17 ppm), occurring exclusively as solid solutions. The Au content shows strong positive correlations with chalcophile elements (Ag, Bi, Cu, Pb, Sb, and Te) in pyrite, strongly indicating that Au-Cu-Sb-Ag-Bi complexes are incorporated into the pyrite lattice through coupled substitution of Fe²⁺ ions or as micro-mineral inclusions. These findings provide key insights into gold mineralization mechanisms and offer essential mineralogical constraints for ore beneficiation and metallurgical processing.