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The Dahai Pb-Zn mining area is located in the northwestern Pb-Zn district in northeastern Yunnan Province in the Sichuan-Yunnan-Guizhou Pb-Zn metallogenic triangle (SYGT), east of the Xiaojiang fault. Numerous Pb-Zn deposits (spots) occur in clastic rocks in this area. In this study, the Maliping, Laoyingqing, and Jinniuchang Pb-Zn deposits, representative clastic rocks in the Dahai mining area, were selected as research objects. The results of H-O-S-Sr-Pb isotope analyses show that the three deposits mainly formed through the mixing of a basinal brine with a hydrothermal fluid derived from deep within the underlying (deformed) basement, and brines leached organic matter from wall rocks. The δ34S values range from −2.62–30.30‰. The S isotope results show two different sources of reduced S: one in the Laoyingqing deposit derived from the S reduction generated by the pyrolysis of sulfur-bearing organic matter in the carbonaceous slate of the Kunyang Group, and the second in the Maliping and Jinniuchang deposits derived from the S reduction generated by the thermochemical sulfur reduction (TSR) of seawater sulfate in the Lower Cambrian Yuhucun Formation and Sinian Dengying Formation. The Pb isotope results show that the Pb sources of the three deposits are derived from basement rocks (Kunyang Group) with a small portion derived from Devonian–Permian carbonate rocks and Dengying Formation dolomite, both of which have undergone homogenization during mineralization. The Sr content varied from 0.09629 to 0.2523 × 10−6, and the study shows that the main source of Sr is a mixture of ore-forming fluid flowing through basement rocks (Kunyang Group) and through sedimentary cover. However, most of the Sr in the Maliping deposit is derived from marine carbonate, and in the Laoyingqing deposit, it is provided by basement rocks (Kunyang Group). Based on a comparative study of the deposits, the Pb-Zn deposits in the clastic rocks of the Dahai mining area and the SYGT belong to the same metallogenic system and were formed under the same metallogenic geological background. Finally, a unified metallogenic model of the two types of fluid migration and mixed mineralization of the Pb-Zn deposit in clastic rocks of the Dahai mining area is proposed. The metallogenic model provides a basis for the study of the Pb-Zn metallogenic system and guidance for deep and peripheral prospecting in this area. [ABSTRACT FROM AUTHOR]

The Maliping large-scale Pb-Zn deposit is located in the Sichuan-Yunnan-Guizhou Pb-Zn polymetallic metallogenic triangle area (SYGT), where the Pb-Zn ore body is hosted in the interlayer fracture zone at the interface between siliceous cataclastic dolomite and clastic rocks in the Lower Cambrian Yuhucun Formation and is tectonically driven. Unlike other Pb-Zn deposits hosted in the Sinian and Carboniferous carbonate rocks in the area, the metallogenic mechanism and deep and peripheral ore prospecting prediction research require further exploration. In this study, representative samples of a typical orebody profile were systematically collected, and microthermometry of fluid inclusions and H-O isotopes and metal sulfide trace element analyses were performed. The main findings were as follows: (1) The fluid inclusion study showed that the ore-forming fluids have vapor-rich phase reduction characteristics of medium-low temperature, salinity, and density. (2) H-O isotopic studies showed that the ore-forming fluids are derived from the mixing of deep-source fluids flowing through the deep fold basement (Kunyang Group) and organic containing basin brine. (3) Rare earth element (REE) characteristics indicate that the ore-forming materials were primarily derived from the folded basement (Kunyang Group). (4) The trace element study showed that sphalerite is relatively enriched in Cu, Cd, Ga, and Ge, while depleted in Fe, Mn, Sn, and Co, similar to the typical Huize-type (HZT) Pb-Zn deposit in the area. Therefore, it is suitable to explore the deposit using a large-scale "four step style" ore prospecting method for ore prospecting and prediction. Moreover, the results provide a reference for the study of Pb-Zn metallogenic systems and new ideas for the deep and peripheral prospecting of Pb-Zn deposits in this area. [ABSTRACT FROM AUTHOR]

Located at the intersection of the Tethys and Pacific Rim metallogenic belts, the Laojunshan polymetallic metallogenic province in SE Yunnan Province hosts many large-scale W–Sn and Sn–Zn polymetallic deposits. The newly discovered Caiyuanzi medium-sized Pb–Zn deposit is located in the northern part of this province and has eight sulfide ore bodies. All the ore bodies occur in the siliceous rocks of the Lower Devonian Pojiao Formation (D1p). The ore bodies are conformable with stratigraphy and controlled by a lithologic horizon. The sulfide ores have banded or laminated structures. The ore minerals are mainly pyrite, chalcopyrite, sphalerite, and galena. In this study, in situ sulfur and lead isotopes were used to constrain the origin of the Caiyuanzi Pb–Zn deposit. The results show that the in situ δ34S values of pyrite, chalcopyrite, and sphalerite range from 0.1‰ to 6.0‰, with an average of 4.7‰. This δ34S signature reflects the mixing between magmatic-derived and reduced seawater sulfate sulfur. The in situ Pb isotopes characteristics of pyrite, galena, and sphalerite suggest that the sulfur and lead of ore minerals come from the upper crust. Integrating the data obtained from the studies including regional geology, ore geology, and S–Pb isotope geochemistry, we proposed that the Caiyuanzi Pb–Zn deposit is a hydrothermal deposit formed by sedimentary exhalative and magmatic hydrothermal superimposition. [ABSTRACT FROM AUTHOR]

The Sanjiang Indosinian orogen, located in the eastern part of the Paleo-Tethys tectonic domain, is a critical region to study the Paleo-Tethyan Ocean evolution. Middle Permian–Late Triassic magmatic rocks are widespread in the Deqin–Weixi–Madeng area of southwestern (SW) Sanjiang Indosinian orogen, yet their petrogenesis and tectonic setting remain disputed. In this study, LA-ICP-MS zircon U-Pb age and Hf isotopes, and whole-rock elemental and Sr-Nd isotope geochemistry of Madeng dacite were studied. The Madeng dacite was dated at ca. 241.7 and 243.4 Ma. The samples had high Al2O3 (12.91 to 14.39 wt.%) but low MgO (0.62 to 1.76 wt.%) contents, and were alkali-rich (Na2O + K2O = 6.97 to 8.66 wt.%) with A/CNK > 1.1, strongly resembling peraluminous S-type granites. The rocks were enriched in Rb, K, Th, U and LREE, but depleted in Ba, Sr, Nb, Ta, P and Ti, and showed obvious negative Eu anomalies, suggesting fractionation of Ti-bearing minerals (e.g., rutile and ilmenite) and plagioclase. The dacite had an initial 87Sr/86Sr value of 0.705698 to 0.710277, and negative εNd(t) (−11.28 to −10.64) and εHf(t) (−13.99 to −8.60), indicating a continental meta-sedimentary source. Their average Nb/Ta (12.24) and Th/U (4.65) were also consistent with continental crust. According to the lithological assemblage and geochemical features, we propose that the Deqin–Weixi–Madeng area intermediate-felsic magmatism was generated in a subduction-related tectonic setting. [ABSTRACT FROM AUTHOR]

The Weixi–Qiaohou Fault (WQF) is considered an important zone of the western boundary of the Sichuan–Yunnan block, and its seismicity has attracted much attention after a series of moderate–strong earthquakes, especially the Yangbi Ms6.4 earthquake that occurred on 21 May 2021. In the present research, we investigate major and trace elements, as well as hydrogen and oxygen isotopes, of 10 hot springs sites located along the WQF, which are recharged by infiltrated precipitation from 1.9 to 3.1 km. The hydrochemical types of most analyzed geothermal waters are HCO3SO4-Na, SO4Cl-NaCa, and SO4-Ca, proving that they are composed of immature water and thus are characterized by weak water–rock reactions. The heat storage temperature range was from 44.1 °C to 101.1 °C; the circulation depth was estimated to range between 1.4 and 4.3 km. The results of annual data analysis showed that Na+, Cl−, and SO42− in hot springs decreased by 11.20% to 23.80% north of the Yangbi Ms5.1 earthquake, which occurred on 27 March 2017, but increased by 5.0% to 28.45% to the south; this might be correlated with the difference in seismicity within the fault zone. The results of continuous measurements of NJ (H1) and EYXX (H2) showed irregular variation anomalies 20 days before the Yangbi Ms6.4 earthquake. In addition, Cl− concentration is more sensitive to near-field seismicity with respect to Na+ and SO42−. We finally obtained a conceptual model on the origin of groundwater and the hydrogeochemical cycling process in the WQF. The results suggest that anomalies in the water chemistry of hot spring water can be used as a valid indicator of earthquake precursors. [ABSTRACT FROM AUTHOR]

Evaporites are widely distributed within continental "red beds" in the Lanping–Simao Basin, west Yunnan, China. Sr (Strontium), S (Sulfur), and O (Oxygen) isotope compositions have been measured on 54 sulfate or/and sulfate-bearing samples collected from Lanping, Nuodeng, Jinggu, Mengyejing, Baozang throughout the Lanping–Simao Basin. The 87Sr/86Sr ratios of all samples (0.708081 to 0.710049) are higher than those of contemporaneous seawater, indicating a significant continental contribution to the drainage basin. Sulfates in the Lanping Basin have higher 87Sr/86Sr ratios (0.709406 to 0.710049) than those (0.708081 to 0.709548) in the Simao Basin. Nevertheless, the δ34S values of gypsums (13.4‰ to 17.6‰) in Lanping and Baozang fall within the range of Cretaceous seawater. Gypsums from a single section in Baozang have trends of decreasing δ34S values and increasing 87Sr/86Sr ratios from base to top, indicating continental input played an increasingly significant role with the evaporation of brines. High δ34S values (20.5‰ to 20.7‰) of celestites in Lanping are probably caused by bacterial sulfate reduction (BSR) process in which 34S were enriched in residual sulfates and/or recycling of Triassic evaporites. The reduced δ34S values of gypsums (9.5‰ to 10.4‰) in Nuodeng could have been caused by oxidation of sulfides weathered from Jinding Pb-Zn deposit. The complex O isotope compositions indicate that sulfates in the Lanping–Simao Basin had undergone sulfate reduction, re-oxidation, reservoir effects, etc. In conclusion, the formation of continental evaporites was likely derived from seawater due to marine transgression during the Cretaceous period. Meanwhile, non-marine inflows have contributed to the basin significantly. [ABSTRACT FROM AUTHOR]

The Xi'ao Cu-Sn polymetallic deposit is located in the inner alteration zone of the Laoka granite. The ore bodies extend to 400 m in the granite rock and primarily occur with fluorite and potassic alterations. Two cassiterite samples of altered rock-type ore and one tourmaline vein-type ore in the Xi'ao Cu-Sn polymetallic deposit yielded U-Pb ages of 83.3 ± 2.1 Ma, 84.9 ± 1.7 Ma, and 84.0 ± 5.6 Ma, respectively. The Raman spectrum peak values of A1g were shifted to a lower frequency, possibly due to the substitution of Sn with Nb, Ta, Fe, and Mn. Measured δ18O values of cassiterite samples and calculated δ18OH2O values for the ore-forming fluid indicate that the latter was mostly derived from magma. The high Fe and Mn abundances for cassiterite are consistent with those of hydrothermal origin. The Nb, Ta, and Ti contents indicate that cassiterites in the Xi'ao deposit likely formed in a metallogenic environment that was largely affected by granitic magmatism. Therefore, we conclude that the Xi'ao deposit is a magmatic hydrothermal deposit. [ABSTRACT FROM AUTHOR]