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In order to better constrain the specific depositional age and provenance of the Danzhou Group and understand the geological evolution of the Jiangnan Orogenic Belt, we conducted a combined U-Pb and Hf-isotope analysis of detrital zircons from the Gongdong and Hetong formations of the Danzhou Group in the Longsheng area of the Western Jiangnan Orogenic Belt. Detrital zircons from the Gongdong Formation yield three age populations of 2658–2517 Ma, 2427–1678 Ma and 891–781 Ma, and the youngest ages suggest that the sedimentation began after ca. 783 Ma. U-Pb ages of detrital zircons from the Hetong Formation yield major populations at 2769–2502 Ma, 2492–2100 Ma, and 991–731 Ma, and the youngest ages redefine the maximum depositional age of this unit is 760 Ma, much younger than previously considered. Thus, the upper part of the Hetong Formation in the Longsheng area is newly subdivided into the Sanmenjie Formation, which is characterized by a large amount of 765–761 Ma volcanic rocks. The dominant 991–731 Ma detrital zircons for all samples were likely sourced from the Neoproterozoic igneous rocks of the southeast margin of the Yangtze Block. The subordinate 2494–1678 Ma detrital zircons were probably sourced from the Cathaysia Block. Minor amounts of 2769–2502 Ma detrital zircons may have been sourced from the Yangtze Block. Detrital zircons from the Gongdong Formation have mainly negative εHf (t) values (−1.1 to 21.8, 90%), suggesting that the detritus of the Gongdong Formation is dominated by the recycling of old crustal materials. The εHf (t) values of detrital zircons from the Hetong Formation have a large spread of −22.2 to +9.7, indicating that the source material of the Hetong Formation includes both the juvenile crustal materials and the recycled ancient crustal materials. The above age populations and Hf isotopic characteristics are consistent with the magmatic rocks in the Jiangnan Orogenic Belt and the Southeast Yangtze Block. Taking into account the lithostratigraphic features, provenances, and depositional ages, the Danzhou Group in the Western Jiangnan Orogenic Belt was deposited in a back-arc basin. Full article

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. Full article

Magmatic rocks, deformed structures, and tin–polymetallic deposits are widely distributed in the western Jiangnan Orogenic Belt (JOB) of northern Guangxi Province, China. Magmatism and mineralization are believed to have occurred in the Neoproterozoic stage. Herein, we report the zircon U–Pb dating results of investigations on the Ping’an Pb–Zn–Cu polymetallic veins hosted in gabbro near Ping’an Village. Zircon U–Pb dating of the host gabbro yielded ages of 853.0 ± 7.8, 837.7 ± 7.2, and 450.4 ± 6.7 Ma. The younger age represents the emplacement of gabbros, whereas the older Neoproterozoic age reflects inherited zircons from the wall rocks or source regions. The formation of gabbros (Caledonian) is related to the subduction and collisions of microplates in the western JOB, which are controlled by movements of the Yangtze and Cathaysian plates. We consider that the late Caledonian regional shearing in the western JOB resulted in the fracturing and faulting of rocks (Neoproterozoic and early Caledonian), which provided conduits for the flow of hydrothermal fluids and accommodation for the associated mineralization. Geochemistry investigations show that the Caledonian basic magmatic activity provided a certain material source for the final mineralization. We propose that the tin–polymetallic deposits in the northern Guangx Province, and Neoproterozoic cassiterite crystallization, were subjected to Caledonian shear crushing and hydrothermal transformation with copper, lead, zinc, and other metal elements based on our comprehensive analysis, providing a new ideology for understanding the geology and mineralization in this area. Full article