To determine the range of the isotopic composition of mercury (Hg) from the Idrija mine, samples from the mine itself and from the Mercury Heritage Management Centre geological collection were analyzed. Samples from various geological periods, genesis types, ore types, formations, and excavation fields and levels were analyzed. Both Hg concentration and isotopic composition were measured. The δ²⁰²Hg ranged from −1.35‰ to 0.46‰, and the Δ¹⁹⁹Hg ranged from −0.18‰ to 0.16‰. A relatively homogenous ore fingerprint was obtained from one of the excavation fields; otherwise, the isotopic fingerprint of the Idrija mine seems to be heterogenous. This study presents the first statistically robust constraints on the isotopic composition of Hg from the Idrija mine, which may help in further studies of the isotopic composition of similar ore bodies or the potential tracing of Hg from the mine to the environment in the vicinity or downstream of the mine. Full article

Pure marine chemical sediments are archives of geochemical proxies for the composition of seawater and may provide information about the ancient hydrosphere–atmosphere system. The early stage of the Emeishan large igneous province (ELIP) was characterized by the subaqueous eruption of mafic igneous rocks around the J. altudaensis zone of the Capitanian Stage that has been proposed to have contributed to the Guadalupian mass extinction. However, detailed mechanisms and the impact of the eruption on the Guadalupian marine environment have yet to be assessed. Here, to examine the Guadalupian marine environment, we studied major and trace element concentrations, particularly rare earth element and yttrium data, along with high-precision Sr-Nd isotope ratios, of three types of Mn ores (i.e., clastic, massive, and oolitic) and siliceous limestones from the Zunyi Mn deposit in South China formed following the early-stage eruption of the ELIP. Our results indicate that the clastic Mn ores contain notable detrital mafic aluminosilicates. In contrast, the massive and oolitic Mn ores and siliceous limestones preserved the pristine geochemical signatures of the Middle–Late Permian seawater characterized by distinctly low (⁸⁷Sr/⁸⁶Sr)_i and high ε_Nd(t) values. These data indicate a strong impact of the early-stage submarine eruptions of the ELIP on the marine environment in South China and worldwide, likely through intensive seawater–rock interaction. Full article

The Jiaodong Peninsula is located on the junction of the North China Craton (NCC) and South China Block (SCB), where Mesozoic igneous rocks are widespread. However, the petrogenesis and tectonic settings for these Mesozoic igneous rocks are still controversial. In this study, we present detailed geochronological and geochemical analyses of quartz monzonite, monzogranite, syenogranite, and alkali feldspar granite in the Qingdao area, east of the Jiaodong Peninsula, to constrain their petrogenesis and tectonic setting. Zircon U–Pb dating shows that they mainly formed in the Early Cretaceous (120.5–113.1 Ma). Quartz monzonite exhibits adakitic geochemical features (e.g., low Y and high Sr/Y). Combined with its Sr–Nd–Hf isotopic features, we suggest that quartz monzonite may have been produced by the partial melting of phengite-bearing eclogites at the base of the thickened continental crust of the NCC. In contrast, monzogranite and syenogranite exhibit I-type granite affinities, whereas alkali feldspar granite exhibits features consistent with A-type granite. The strongly negative ε_Hf(t) and ε_Nd(t) values of the I-type rocks indicate that they were most likely produced through partial melting of granitic gneisses from the NCC, whereas A-type magmas may be formed through fractional crystallization from the non-adakitic granitic magma. Combined with previous studies, we suggest that these granitoids were formed in a lithospheric extensional setting via the rollback of the subducted Paleo-Pacific slab, which resulted in the reworking of the deep crust beneath the Sulu ultrahigh-pressure metamorphic belt. Full article

In depth of the Simao Basin (2390 to 2650 m depth interval), many gray mudstone or carbonate rocks are developed in the red salt-related strata, and pyrite crystals are found in the fissure and matrix. In this study, petrology, mineralogy, element geochemistry, and LA-MC-ICP-MS in situ sulfur isotope analysis were used to constrain the genesis of pyrite, and the influence of relevant geological activities on potash mineralization was discussed. The results show that: (1) In the upper part of the salt layer, particle size of the pyrite ranges from 50 to 300 μm. The crystal morphology is mainly pentagonal-dodecahedral and irregularly granular, with a small amount of cuboidal pyrite. In the interlayer between rock salt, particle size of the pyrite is from 50 to 100 μm, and the crystals are mainly octahedral. (2) The S/Fe value of pentagonal-dodecahedral pyrite is significantly greater than 2; the S/Fe value of octahedral and cubic pyrite is less than 2; and the S/Fe value of irregular granular pyrite is close to 2. (3) The δ³⁴S_V-CDT values of pyrite in the upper salt-related strata range from −15.65‰ to 11.81‰, and the average δ³⁴S_V-CDT values of all samples range from 0.79‰ to 8.20‰. The δ³⁴S_V-CDT values of pyrite interlayer between rock salt range from −15.02‰ to −6.36‰, with an average value of −10.66‰. The above results indicate that the pyrite in the upper part of the rock salt layer was formed in a medium-low temperature hydrothermal environment, and the ore-forming sulfur elements have hydrothermal sources, bacterial sulfate reduction (BSR) sources, and thermochemical sulfate reduction (TSR) contributions. The pyrite between the rock salt layers is of sedimentary origin, and the ore-forming sulfur element comes from BSR. At present, there is no evidence of the influence of hydrothermal activities on deep potash-rich salt bodies, and the influence on the Mengyejing potash deposit has continued since the metallogenic period. Full article

The Gacun deposit is a typical Volcanic Hosted Massive Sulfide (VHMS) associated with Late Triassic seafloor calc-alkaline felsic volcanics. Studies of zircon ages, petrology, major and trace element geochemistry, and Sr-Nd-Hf isotope geochemistry of volcanic rocks from the Northern Yidun arc were undertaken in this paper. We reshaped the Gacun magmatic system activity time, defined the origin of magma evolution, and proposed a metallogenic model of the deposit. Whole-rock major element compositions of the magmatic rocks in the Northern Yidun island arc indicate that they are a complete basalt–andesite–dacite–rhyolite assemblage, showing three obvious stages of composition evolution. They are enriched in large-ion lithophile and light rare earth elements, but depleted in high field-strength and heavy rare earth elements, with weak-to-negligible Eu anomalies (obvious in rhyolite). These geochemical features indicate that the Northern Yidun island arc is a magmatic arc based on ancient continental crust. The Ganzi–Litang oceanic subduction induced mantle melting and produced calc-alkaline basaltic magma, while the MASH processes at the bottom of the crust produced andesitic magma. Part of the andesite magma erupted to form andesite lava. The remaining part was mixed with magma produced via anatexis of ancient crust (approximately 20%–40% of the ancient crustal component), forming the ore-bearing rhyolite. Zircon U-Pb age data defines Gacun magmatic–hydrothermal mineralization sequence of events: At 238 Ma, arc magmatism led to the formation of andesite in the eastern part of the deposit. At 233 Ma, in the arc zone (the western part of Gacun deposit), a large-scale bimodal magmatism formed the main ore-bearing rock series of Gacun deposit, rhyolitic volcanic rocks. At 221 Ma, volcanic eruptions tended to end and sub-volcanic intrusion occurred, forming a lava dome, which was located under the ore-bearing rhyolitic volcanic rocks. The lava dome acted as a thermal engine and promoted hydrothermal circulation. The hydrothermal activity reached a peak at 217 ± 1 Ma, and the Gacun VHMS deposit was formed. Full article

The Sijiaying iron deposit is located in the Eastern Hebei area of the southern section of the northern margin of the North China Craton (NCC) and is the largest single iron deposit in China. The deposit contains many banded iron formations (BIFs) and was proven to have more than 3 million tons of high-grade iron ore resources. This study carried out geochemistry and zircon U–Pb analysis of normal-grade iron ore, high-grade iron ore, and wall rock (biotite–leptynite, chlorite–sericite schist) in the Sijiaying deposit and discussed the genesis and metallogenic age of high-grade iron ore. BIFs have low concentrations of Al₂O₃ and TiO₂ and high field strength element (HFSE) depletion, indicating almost no contamination via terrestrial debris. The standardized post-Archean Australian shale (PAAS) rare earth element (REE) distribution pattern indicates that the iron formation exhibits positive Eu, Y, and heavy rare earth element (HREE) anomalies and lacks negative Ce anomalies, indicating that the Sijiaying BIF was enriched with iron sources via high-temperature hydrothermal fluids from the seabed and deposited in an anoxic ancient marine environment. In addition, geological field work identified two types of high-grade iron ore in the mining area: primitive sedimentary and hydrothermally altered high-grade iron ore. Further ore geochemical research showed that the primitive sedimentary-type iron ore is similar in geochemistry to the BIF. In addition to low Eu/Eu* values, the hydrothermally altered high-grade iron ore shows geochemical characteristics similar to those of the BIF, suggesting that they share the same iron source but did not form at the same time. The total large ion lithophile element (LILE) (Sr, Ba, Pb) contents in primitive sedimentary-type high-grade iron ore are higher than those in hydrothermally altered high-grade iron ore, indicating that LILEs are carried away via fluids during the hydrothermal alteration process in normal-grade iron ore. The geochemical characteristics of biotite–leptynite and chlorite–sericite schist include high contents of SiO₂ and Al₂O₃, light rare earth elements (LREEs), LILE enrichment (Rb, Ba, Sr, Zr), and HFSE depletion (Nb, Ta, P, Ti), characteristics that are similar to island arc volcanic rocks. The reconstruction of the original rock indicates that the wall rock is a product of volcanic sedimentary cycles in an island arc setting. Zircon cathodoluminescence images and LA–ICP–MS zircon U–Pb dating can be divided into four age groups (3283 Ma, 2547 Ma, 2500 Ma, and 2407 Ma), which correspond to the earliest volcanic activity in eastern Hebei, the main mineralization age of the Sijiaying BIF (the mineralization age of primitive sedimentary high-grade iron ore), a regional tectonic–metamorphic event, and the occurrence of migmatization (the mineralization age of hydrothermally altered high-grade iron ore), respectively. Therefore, the Sijiaying BIF and primitive sedimentary high-grade iron ores were deposited and mineralized at 2547 Ma, and the iron orebody was later altered via the hydrothermal solution at 2407 Ma, forming large-scale high-grade iron ores. Full article