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The Qianjiadian deposit is a typical sandstone‐hosted uranium deposit that is hosted mainly in sandstone and siltstone of the Lower Cretaceous Yaojia Formation, located within the transition between the Kailu Depression and Jiamatu Uplift in the Songliao Basin, northeastern China. We studied the geological characteristics of this deposit, and analysed the mineralized sandstone by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) to identify the host minerals of fluid inclusions associated with uranium mineralization and describe their petrographic characteristics. In addition, this research investigated the origin of ore‐forming fluids and the relationship between petroleum fluids and uranium mineralization, based on the following findings. (1) EPMA and SEM data show that uranium minerals are hosted mainly in hydrothermal quartz (HQ) within sandstone cement, which indicates that uranium minerals co‐precipitated with HQ. (2) The fluid inclusions in the HQ show low homogenization temperatures (102.5–169.5°C) and low salinities (1.7–6.1 wt%). In contrast, aqueous inclusions in quartz overgrowths show lower temperatures (60.5–117°C) and higher salinities (4.2–8.7 wt%). (3) Petroleum fluids trapped in HQ homogenize fluid and those along healed microfractures in quartz overgrowth or plagioclase overgrowths at ~70–80°C, those trapped in present‐day organic inclusions at ~85–95°C, and at the boundary of detrital mineral grains show higher homogenization temperatures (~135–145°C). These results indicate that the hydrothermal quartz cement is associated with uranium mineralization, and the ore‐forming fluid of Qianjiadian sandstone‐hosted uranium deposit are characterized by low‐temperature, low‐salinity hydrothermal fluids, and the changes of temperature and salinity of hydrothermal fluids may not be intimately associated with uranium mineralization. [ABSTRACT FROM AUTHOR]

The Chaobuleng skarn deposit, located in the Erlian–East Ujimqin region, Northeast China, is a medium-sized Fe Zn polymetallic deposit. Iron-polymetallic mineralization occurs mainly as stratiform, lenticular, and vein types hosted in the contact zone between the Chaobuleng syenogranite and the Devonian Taerbagete Formation. The Chaobuleng deposit is a calcic skarn deposit dominated by a grossular-rhodonite-allanite-epidote assemblage. The ore minerals mainly consist of magnetite, pyrite, sphalerite, chalcopyrite, and bismuthinite, with lesser amounts of molybdenite, arsenopyrite, and pyrrhotine. Four mineralization stages have been identified: (I) a prograde skarn stage; (II) a retrograde skarn stage; (III) a quartz-minor calcite-polymetallic sulfide stage; and (IV) a quartz-calcite-minor pyrite stage. Three types of fluid inclusions (FIs) in garnet, quartz and calcite were classified: vapor-rich two-phase FIs (V-type), liquid-rich two-phase FIs (L-type), and daughter mineral-bearing three-phase FIs (S-type). The homogenization temperatures of FIs from stages I, II, III, and IV are 446–547, 411–519, 279–415, and 147–217 °C, respectively, with corresponding salinities of 0.87–59.47, 0.52–51.52, 0.70–13.25, and 3.05–7.85 wt% NaCl equiv., respectively. The results suggest that mineralization in the Chaobuleng deposit occurred at a depth of 1.0–2.8 km, with fluid boiling and mixing with meteoric water likely being responsible for ore precipitation. The C O isotope data suggest the early ore-forming fluids were mainly related to felsic rocks and were accompanied by intense water/rock reactions during the fluid migration. The S Pb isotopic compositions indicate that ore materials were derived from the mixing between magma and wall rocks. Zircon U Pb dating yields a weighted mean 206Pb/238U age of 135.9 ± 0.8 Ma (MSWD = 1.03), which represents the crystallization time of the syenogranite. Together, these data suggest that the Chaobuleng deposit is a skarn ore system that is spatially, temporally, and genetically related to syenogranite and formed in an extensional environment resulted from the roll back of the subducted Paleo-Pacific Plate. [Display omitted] • The Chaobuleng deposit is a typical skarn Fe Zn deposit, formed in the Early Cretaceous. • The fluids evolved from a high-temperature, intermediate-salinity NaCl–H 2 O system of magmatic water. • Ore-forming materials had a mixed source of the granitic pluton and Taerbagete Formation. [ABSTRACT FROM AUTHOR]