Crucial questions regarding the mineralizing processes involved in the formation of disseminated gold mineralization remain unresolved, which complicates our understanding of metal precipitation processes in these systems and impedes effective exploration. This study integrates petrographic and geochemical analyses of chlorite within barren and ore-bearing marble, granite, and granofels units from the Guocheng gold deposit in Jiaodong, China. The petrographic analysis of these samples indicates that ripidolite is the primary chlorite phase within altered wall rocks, replacing biotite, hornblende, and plagioclase via dissolution-crystallization. In contrast, ore-associated chlorite is dominated by brunsvigite and pyrochlore, forming by dissolution-migration-crystallization. The mineral chemistry of this chlorite indicates that ore-related chlorite has lower Fe2+/(Fe2+ + Mg2+) ratios and higher Fe3+ concentrations than chlorite within altered wall rock areas. This indicates relatively lower amounts of ion substitution and suggests relatively higher oxygen fugacity conditions in the ore-forming environment. Furthermore, chlorite formed during mineralization exhibits elevated Mn but decreased Ti, Ni, Co, and Rb concentrations compared to altered wall rock-hosted chlorite, coupled with lower Rb/Sr ratios. These geochemical signatures indicate that the low-salinity H2O-CO2-NaCl ± CH4 ore-forming fluids mobilized only limited quantities of these elements during transport. These data indicate that ore-forming fluids interacted with ferreous minerals in the high-oxygen-fugacity wall rocks under high water-rock ratio condition, which elevated the oxygen fugacity of this part of the system by the precipitation of Fe-rich carbonates and magnetite. The resultant decrease in Au(HS)2– complex stability enabled efficient gold precipitation. These data also provide insights into variations in chlorite Fe2+/(Fe2+ + Mg2+) and Rb/Sr ratios, as well as concentrations of Mn, Ti, Ni, Co, and Rb, and ion exchange intensities, further discriminating mineralized and barren regions in the same host rocks within the Guocheng gold deposit. The findings enhance understanding of hydrothermal alteration linked to gold precipitation and highlight chlorite’s potential as a fertility discriminator in the Guocheng gold deposit.

The Sanchahe iron-gold deposit in western Shandong province is located in the southeast of the North China Craton. The skarn type of iron-gold deposit (without copper) is located in the contact belt between pyroxene diorites and Ordovician limestone xenoliths. The zircon U-Pb age of pyroxene diorites is 138.4 ± 1.2 Ma belonging to the Early Cretaceous. Pyroxene diorites (Rittmann index σ = 2.2~2.5) belong to the calc-alkaline series and the SiO₂ content is 55~59%. Furthermore, pyroxene diorites are characterized by high Mg and Na contents and high contents of Sc, Cr, Co, and Ni, indicating that it has a geochemical affinity with mantle-derived magma. All of the samples are enriched in light rare earth elements (LREEs) and depleted in heavy rare earth elements (HREEs), with a weak Eu-negative anomaly. They are also enriched in Cs, Ba and Sr and depleted in high field strength elements (HFSEs) (Nb, Ta, Zr), indicating the involvement of some crustal materials. The whole-rock (⁸⁷Sr/⁸⁶Sr)_I values are 0.70824~0.70891, and the ε_Nd(_t) values are from −8.1 to −12.5. Two-stage model ages of T_DM2 are 1591~1928 Ma. The εHf(t) values range from −7.0 to −17.4, and the two-stage model ages of T_DM2 range from 1629 to 2297 Ma, indicating that the magma was derived from Mesoproterozoic to Neoarchean crusts. Combined with Pb isotopic characteristics, pyroxene diorites may be generated by the partial melting of the enriched lithospheric mantle, which had been metasomatized by the ancient lower crust materials of the North China Craton and formed in the strong extensional tectonic setting linked with lithospheric thinning, which may be caused by the rollback of the Pacific plate after subduction.

The northeastern Jiaolai Basin of China hosts significant gold resources (223 t contained Au) and has substantial exploration potential for the identification of new gold mineralization. However, the mineralization in this area differs from most deposits elsewhere in the Jiaodong gold province in terms of mineral assemblages and host rocks, meaning that the genetic processes that formed the Jiaolai Basin mineralization remain controversial. Here, we integrate field observations, petrography, in situ monazite U-Pb and sericite Rb-Sr dating, mineral chemistry, sulfur isotope analysis, and thermodynamic modeling of the Tudui, Longkou, and Houkuang deposits to develop a genetic model for the gold mineralization located within the Jiaolai Basin. The deposits in this area are hosted within Paleoproterozoic metamorphic rocks and granites and are dominated by disseminated sulfide-hosted Au mineralization controlled by NE-SW–striking faults. Monazite U-Pb and sericite Rb-Sr dating constrain the timing of mineralization to the Early Cretaceous (ca. 120 Ma), synchronous with regional gold mineralization elsewhere within the Jiaodong gold province. The mineralization contains two generations of pyrite: Pyrite-I is medium- to coarse-grained, euhedral to subhedral, and is present as large individual crystals that are commonly replaced by magnetite. Pyrite-II is anhedral to subhedral and coexists with pyrrhotite, chalcopyrite, magnetite, and gold. In situ sulfur isotope analysis indicates that δ34S values decrease from Py-I to Py-II (Longkou: 10.6‰ to 8.4‰; Houkuang: 9.5‰ to 6.3‰; Tudui: 7.4‰ to 6.3‰), indicating an increase in oxygen fugacity (fO2) of the ore-forming fluid. Thermodynamic modeling indicates that this increase in fO2, along with the formation of alteration minerals, reduced the solubility of Au(HS)2− complexes within the ore-forming hydrothermal fluid by ~75%, leading to efficient gold precipitation. The overall heavy sulfur isotope values (6‰–12‰) combined with previously published lead isotope data that yielded values similar to those obtained for gold deposits elsewhere within the Jiaodong region suggest that the mineralization in the study area involved metals and sulfur derived from a subduction-modified region of the lithospheric mantle. These data demonstrate that gold mineralization in the northeastern Jiaolai Basin was contemporaneous with regional ore-forming events and that all of the deposits in this area derived metals and sulfur from similar sources and record identical metal precipitation processes. All of this indicates that the gold mineralization in the northeastern Jiaolai Basin is genetically linked to the regional-scale Early Cretaceous ore-forming system in the wider Jiaodong region.

Table S1: Major element composition of gold. Table S2: Major element composition of chlorite. Table S3: Results of the in situ LA-ICP-MS U-Pb dating of hydrothermal monazite in the Tudui deposit. Table S4: Results of the in situ LA-ICP-MS Rb-Sr dating of hydrothermal sericite in the Longkou deposit. Table S5: Trace element data for pyrite formed during different stages of mineralization in the Tudui, Longkou, and Houkuang deposits. Table S6: Sulfur isotopic data for pyrite formed during different stages of mineralization in the Tudui, Longkou, and Houkuang deposits.

Table S1: Major element composition of gold. Table S2: Major element composition of chlorite. Table S3: Results of the in situ LA-ICP-MS U-Pb dating of hydrothermal monazite in the Tudui deposit. Table S4: Results of the in situ LA-ICP-MS Rb-Sr dating of hydrothermal sericite in the Longkou deposit. Table S5: Trace element data for pyrite formed during different stages of mineralization in the Tudui, Longkou, and Houkuang deposits. Table S6: Sulfur isotopic data for pyrite formed during different stages of mineralization in the Tudui, Longkou, and Houkuang deposits.

Whether the genesis of gold deposits in the Northeastern Jiaolai Basin is consistent with that in the Northwestern Jiaodong area remains controversial. This study presents in situ Rb-Sr dating of sericite, along with in situ trace element and sulfur isotope analyses of pyrite in the Longkou gold deposit. The sericite Rb-Sr inverse isochron yields an age of 120.9 ± 2.4 Ma, indicating that gold mineralization occurred in the Early Cretaceous. Two generations of pyrite, Py1 and Py2, were identified. Py1 is anhedral and hosted in relatively low-grade, weakly altered marble wall rock. Py2 is euhedral to subhedral and hosted in relatively high-grade, strongly altered marble ore. The δ³⁴S value of Py1 is 7.38‰, whereas that of Py2 is 6.79‰. The decrease in δ³⁴S values from Py1 to Py2 reflects an increase in the oxygen fugacity of the ore-forming system. These features suggest that fluid–rock interaction led to an increase in oxygen fugacity, thereby triggering gold precipitation. The mineralization age and precipitation mechanism of the Longkou gold deposit are consistent with those of the Northwestern Jiaodong area. The Longkou gold deposit is best classified as a Jiaodong-type gold deposit.