Fluid inclusion characteristics and mechanisms of tin mineralisation in the Jialong tin polymetallic deposits, Jiuwandashan-Yuanbaoshan, northern Guangxi, China

• Published in: Australian journal of earth sciences 2024-11, Vol.71 (7), p.988-1004
• Main Authors: Meng, C-L., Bai, L-A., Yue, Z-H., Zhou, S-Y., Dai, Y., Feng, Z-H., Liu, X-J., Zhang, H., Lin, L-Z.
• Format: Article
• Language: English
• Subjects: Boiling; Caledonian Sn mineralisation; Carbon dioxide; China; Decompression; Deformation; fluid inclusion; Fluid inclusions; Fluids; Homogenization; Jialong Sn-polymetallic deposit; Jiangnan orogenic belt; Jiuwandashan-Yuanbaoshan area; Magma; metamorphic hydrothermal fluid; Mineralization; Northern Guangxi; Orogeny; Pressure gradients; Sedimentary rocks; Shear deformation; Shear zone; Tectonics; Tin
• ISSN: 0812-0099; 1440-0952
• DOI: 10.1080/08120099.2024.2427093

The Jiuwandashan-Yuanbaoshan area, which is located in the western Jiangnan orogenic belt, has experienced frequent tectonic and magmatic events, and contains extensive Neoproterozoic Sn-polymetallic deposits. The Jialong Sn-polymetallic deposit is located in the northeastern part of the Neoproterozoic Yuanbaoshan granite and superimposed Sirong ductile shear zone and represents the first Caledonian Sn-polymetallic deposit discovered in this area. In this study, we investigated the mechanisms of Caledonian Sn mineralisation using the numerous types of fluid inclusions that formed during the main mineralisation stage. Liquid-rich inclusions (Wa-type) have a wide range of homogenisation temperatures (180-302 °C) and a bimodal distribution of salinities (8-10 and 21-22 wt% NaCl equiv ). Gas-rich inclusions (Wb-type) have homogenisation temperatures of 379-383 °C and salinities of 4.34-4.49 wt% NaCl equiv . The homogenisation temperatures of CO 2 -rich liquid inclusions (Ca-type) are 222-248 °C, and the salinities are 11.32-13.45 wt% NaCl equiv , indicating the fluid underwent significant boiling. δ 18 O water values vary from 1.1 to 5.3‰ VSMOW, with δD = −65 to −35‰ VSMOW. The ore-forming fluid has the characteristics of a typical metamorphic hydrothermal fluid. There is a significant difference in δ 34 S values between the mafic-ultramafic and granitic rocks in the study area, indicate the ore-forming materials were derived mainly from metamorphosed sedimentary rocks of the Sibao Group. The Jialong Sn-polymetallic deposit is a typical example of Caledonian Sn mineralisation, but there was no coeval magmatism, although the Sirong ductile shear zone was active during the period of Sn mineralisation. During the Caledonian activity of the Sirong ductile shear zone, ductile shear deformation resulted in the generation of metamorphic fluids from distal Neoproterozoic strata. This fluid migrated to the northwest under the influence of a pressure gradient, underwent decompression-driven boiling and precipitated Sn and other elements.