The Laowan deposit is a typical gold deposit in the Qinling-Dabie metallogenic belt, which produces the most gold resources in Central China. After being explored for decades, follow-up exploration requires additional theoretical support. In this study, the factor analysis (FA) and spectrum–area (S–A) multifractal model were used to process multi-element geochemical data from 369 samples collected in the study area for identifying the geochemical anomalies associated with gold mineralization. The results showed that: (1) the mean Au content in this region is up to 1000 times higher than the Au background values of the upper crust of the South Qinling unit; (2) the factor analysis revealed that Au, Ag, Cu, As, Sb, and S can be used as direct ore-prospecting criteria; (3) the observed elemental zonation is consistent with the zonation of metallic elements in the magmatic–hydrothermal system. This supports the magmatic–hydrothermal origin of the Laowan deposit; (4) the spectrum–area fractal model can help to decompose the geochemical patterns in a complex geological setting. The decomposed geochemical anomaly map obtained by the S–A multifractal model indicated that highly anomalous areas have a great relationship with the Au occurrence and can be a guidance for further exploration in the study area.

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Mesozoic lode-gold deposits in the Qinling orogen are important gold reservoirs in China. The Laowan gold deposit is one of the largest one in this region. The ore bodies are fault-controlled, sulfide-rich lodes and disseminations that hosted in amphibolite and mica schist of the Guishan Formation intruded by a Cretaceous pluton at ca. 120 Ma. Long-standing controversies are whether the Guishan Formation provided ore-forming materials or just create a favorable setting for gold deposition. Here, we discussed the mineralogy and geochemistry of this rock formation to pinpoint its contributions to gold mineralization. Studies on metamorphic petrographic and whole-rock geochemical characteristics of the Guishan Formation were carried out to reveal the classification and the tectonic environment of metamorphic protolith. In-situ race element and sulfur-lead isotopic geochemical characteristics of pyrites from the ore samples are compared with those of the Guishan Formation to explore their relationships. Results shows that the amphibolite has tholeiite-like major and trace element compositions with a continental affinity, and the mica schist has geochemical characteristics similar to sedimentary rocks deposited in active continental forearc margin. Significantly enrichment of Au (avg.13 and 22 ppb), Ag (0.14 and 0.17), As (7.81 and 9.26), and Sb (0.47 and 0.39) contents (in ppm) in amphibolites and mica schists of the Guishan Formation suggests they might be a potential ore-forming material source of the gold deposit. The high Ni content (avg. 103 and 38.6 ppm), low Co/Ni ratios (0.41 and 0.5) and δ 34 S values (0.73-2.05‰ and 1.83-2.98‰) in pyrites from the pre-ore and early main-ore stages resemble those from the Guishan Formation (Ni=283 ppm, Co/Ni=0.4, δ 34 S=-0.1-+2.67‰). The similar Pb isotopic composition between the Guishan Formation and pyrite from the early stage of the gold mineralization also suggests a genetic relationship between the two. With the late mineralization stage, magmatic hydrothermal fluids dominated the gold mineralization.