A number of sediment-hosted, Carlin-type/-like gold deposits are distributed in the Youjiang basin of SW China. The gold ores are characterized by high As, Hg, and Sb contents but with low base metal contents (Cu+Pb+Zn < 500–1000 ppm). The Nibao deposit is unique among these gold deposits by having tennantite–tetrahedrite-series minerals in its ores. The deposit is also unique in being primarily hosted in the relatively unreactive siliceous pyroclastic rocks, unlike classic Carlin-type gold deposits that are hosted in carbonates or calcareous clastic rocks. In this study, we have identified tennantite-(Zn), tennantite-(Hg), and tetrahedrite-(Zn) from the tennantite–tetrahedrite-series mineral assemblage. The tennantite-(Zn) can be further divided into two sub-types of Tn-(Zn)-I; and Tn-(Zn)-II;. Tn-(Zn)-I; usually occurs in the core of a Tennantite–tetrahedrite composite and appears the darkest under the SEM image, whereas Tn-(Zn)-II overgrows on Tn-(Zn)-I and is overgrown by tetrahedrite-(Zn). Tennantite-(Hg) occasionally occurs as inclusions near the uneven boundary between Tn-(Zn)-I and Tn-(Zn)-II. An appreciable amount of Au (up to 3540 ppm) resides in the tennantite–tetrahedrite-series minerals, indicating that the latter is a major Au host at Nibao. The coexistence of tennantite–tetrahedrite-series minerals and Au-bearing pyrite indicates the Nibao ore fluids were more oxidized than the Carlin-type ore fluids. The tennantite–tetrahedrite series at Nibao evolved from Tn-(Zn)-I through Tn-(Zn)-II to tetrahedrite-(Zn), which is likely caused by Sb accumulation in the ore fluids. This indicates that the Nibao ore fluids may have become more reduced and less acidic during Au precipitation.

The Jiangnan orogenic belt is located between the Yangtze and Cathaysia blocks in South China and is one of the largest W–Sn–Nb–Ta ore belts worldwide. Mineralization occurred from the Proterozoic to Mesozoic, but Caledonian Sn mineralization has rarely been reported. The Jialong cassiterite–sulfide deposit is located in the western Jiangnan orogenic belt. It is hosted by the Sibao Group and in contact with the northeastern part of the Yuanbaoshan granite. The deposit was overprinted by the Sirong ductile shear zone. Here, we present cassiterite U–Pb and mylonitic granite muscovite ⁴⁰Ar/³⁹Ar ages for this deposit. The cassiterite and muscovite yielded concordant U–Pb and ⁴⁰Ar/³⁹Ar ages of 422–420 Ma, indicating that Sn mineralization occurred during the early Paleozoic and was spatially and temporally related to the ductile shear zone. The cassiterite is depleted in Nb (0.51–5.46 ppm), Ta (0.01–1.09 ppm), Ti (32.84–423.15 ppm), Sc (0.02–1.45 ppm), Hf (0–1.11 ppm), and other high-field-strength elements. Elements, such as Pb (0.01–8.11 ppm) and Sb (9.92–56.45 ppm), are relatively enriched in the cassiterite, which indicate the Jialong deposit was not directly related to magmatism. Shearing along the Sirong ductile shear zone occurred at 419.6 ± 3.8 Ma, concurrent with the formation of the Jialong Sn–Cu deposit. Moreover, cassiterite in the deposit exhibits obvious shear and brittle deformation, and dissolution and regrowth, suggesting that Sn mineralization was closely related to ductile shearing. The Sirong ductile shear zone and secondary shear structures had a key role in controlling the Sn orebody. The heat generated during tectonic deformation in the ductile shear zone may have produced the ore-forming hydrothermal fluids, and NW–SE-trending fractures in the strata provided the space for mineralization. Metamorphic hydrothermal fluids generated by Caledonian shear deformation extracted Sn from Sn-rich strata, which then migrated along interlayer fractures produced by shearing. A decrease in pressure and water–rock reactions led to the mineralization of Sn and other elements. This deposit is the first example of Caledonian and shear zone-related Sn mineralization identified in the Jiuwandashan area of northern Guangxi.

The Shabaosi gold field is located in the western Mohe Basin, part of the northern Great Xing’an Range, NE China, and contains multiple gold deposits. However, the sources of the ore-forming materials, the fluid evolution, and the genesis of these gold deposits have been disputed, especially regarding the classification of these deposits as either epithermal or orogenic gold systems. Based on detailed field geological investigations and previous research, we conducted systematic research on the Shabaosi, Sanshierzhan, Laogou, and Balifang gold deposits using fluid inclusion and H-O-S-Pb isotope data, with the aim of constraining the fluid properties, sources, and mineralization processes. Fluid inclusion analyses reveal diverse types, including vapor-rich, vapor–liquid, CO₂-bearing, CO₂-rich, and pure CO₂. Additionally, only a very limited number of daughter mineral-bearing fluid inclusions have been observed exclusively in the Laogou gold deposit. During the early stages, the peak temperature primarily ranged from 240 °C to 280 °C, with salinity concentrations between 6 and 8 wt% NaCl equiv., representing a medium–low temperature, low salinity, and a heterogeneous CO₂-CH₄-H₂O-NaCl system. With the influx of meteoric water, the fluids evolved gradually into a simple NaCl-H₂O system with low temperatures (160–200 °C) and salinities (4–6 wt%). The main mineralization stage exhibited peak temperatures of 220–260 °C and salinities of 5–8 wt% NaCl equiv., corresponding to an estimated formation depth of 1.4–3.3 km. The δD_V-SMOW values (−138.3‰ to −97.0‰) and δ¹⁸O_V-SMOW values (−7.1‰ to 16.2‰) indicate that the magmatic–hydrothermal fluids were progressively diluted by meteoric water during mineralization. The sulfur isotopic compositions (δ³⁴S = −0.9‰ to 1.8‰) and lead isotopic ratios (²⁰⁸Pb/²⁰⁴Pb = 38.398–38.579, ²⁰⁷Pb/²⁰⁴Pb = 15.571–15.636, and ²⁰⁶Pb/²⁰⁴Pb = 18.386–18.477) demonstrate that the gold predominantly originated from deep magmatic systems, with potential crustal contamination. Comparative analyses indicate that the Shabaosi gold field should be classified as a epizonal orogenic gold system, which shows distinct differences from epithermal gold deposits and corresponds to the extensional tectonic setting during the late-stage evolution of the Mongol–Okhotsk orogenic belt.