Abstract The Fengjia barite–fluorite deposit in southeast Sichuan is a stratabound ore deposit which occurs mainly in Lower Ordovician carbonate rocks. Here we present results from fluid inclusion and oxygen and hydrogen isotope studies to determine the nature and origin of the hydrothermal fluids that generated the deposit. The temperature of the ore‐forming fluid shows a range of 86 to 302 °C. Our detailed microthermometric data show that the temperature during mineralization of the fluorite and barite in the early ore‐forming stage was higher than that during the formation of the calcite in the late ore‐forming stage. The salinity varied substantially from 0.18% to 21.19% NaCl eqv., whereas the density was around 1.00 g/cm 3 . The fluid composition was mainly H 2 O (>91.33%), followed by CO 2 , CH 4 and traces of C 2 H 6 , CO, Ar, and H 2 S. The dominant cation was Na + and the dominant anion Cl ‐ , followed by Ca 2+ , SO 4 2‐ , K + , and Mg 2+ , indicating a mid–low‐temperature, mid‐low‐salinity, low‐density NaCl–H 2 O system. Our results demonstrate that the temperature decreased during the ore‐forming process and the fluid system changed from a closed reducing environment to an open oxidizing environment. The hydrogen and oxygen isotope data demonstrate that the hydrothermal fluids in the study area had multiple sources, primarily formation water, as well as meteoric water and metamorphic water. Combined with the geological setting and mineralization features we infer that the stratabound barite–fluorite deposits originated from mid–low‐temperature hydrothermal fluids and formed vein filling in the fault zone.
The southern Jiangxi Province is an important part of the fluorite mineralization belt in South China. Fluorite ore bodies are primarily in the contact zone between the Devonian Huitong granitic complex and the Late Cretaceous Ganzhou Formation, controlled by the NE‐trending faults. Zircon U–Pb dating of the Huitong granitic complex yields emplacement ages of 410.7 ± 1.4 Ma and 400.7 ± 4.6 Ma, while the Sm–Nd dating of the fluorite yields an isochron age of 94 ± 2 Ma, suggesting that the Huitong granitic complex is the host rock. Fluid inclusions in the fluorite show low homogenization temperatures (136–207°C), salinities (1.23–3.87 wt% NaCl), and densities (0.87–0.95 g/cm 3 ), suggesting that the ore‐forming fluid is an NaCl‐H 2 O system of low temperature, salinity, and density. Raman spectroscopy showed that the fluid phase is dominated by water. The δD VSMOW values of the fluid inclusions in the Tongda fluorite ranged between −59.5 and −55.2‰, while the δ 18 O VSMOW values of the fluorite ranged from −7.2 to −5.6‰. Collectively, the ore‐forming fluid is dominated by meteoric water, possibly with a minor contribution of hydrothermal fluid. Both the interaction with host rocks and the cooling of hydrothermal fluids are the likely mechanisms of underlaying fluorite precipitation at low temperatures. The mineralization occurred in extensional faults during the Late Cretaceous related to the subduction of the Palaeo‐Pacific Oceanic Plate.
The Baishan Mo deposit in the eastern Tianshan Mountains is representative of the local metallogenic Triassic Mo belt. In this study, the geological characteristics, petrography, and geochemistry of the granite porphyry and the Mo deposit were examined using zircon U–Pb dating, molybdenite Re–Os isotope dating, whole‐rock geochemistry, and fluid inclusions. Results show that the crystallisation age of the Baishan granite porphyry is 229.8 ± 1.4 Ma and the Re–Os age of molybdenite in the ore body quartz vein is 225.0 ± 1.2 Ma. Therefore, the ore formed basically at the same time as diagenesis in the Late Triassic. The Baishan granite porphyry has high levels of Si, Al, and alkalis (K 2 O + Na 2 O = 5.72–8.88%) and low levels of Mg. The differentiation index is high (81.68–91.20), while the aluminium saturation index is low, indicating that the pluton belongs to metaluminous–weak peraluminous highly fractionated I‐type granite. The rock is also enriched in light rare earth elements (LREE) and large‐ion lithophile elements but depleted in heavy rare earth elements (HREE) and high‐field‐strength elements, with a distinct differentiation between LREEs and HREEs. δEu is weakly negative. The high Sr/Y and La/Yb ratios indicate geochemical characteristics similar to adakite rocks. The formation of the deposit is closely related to Mo‐rich, low‐salinity (1.23‐ to 9.73‐wt.% NaCl eqv.), and medium‐ to low‐temperature (91–280°C) magmatic fluid in the plate extension setting. The magma was derived from partial melting of thickened lower crust and possibly mixed with intrusive mantle‐derived magma. The ore‐forming fluids were uplifted, transported, mixed with meteoric water, and precipitated to form the Mo ore.
The Liaodong Bay area in north‐east China has abundant hydrocarbon resources. The study area (referred to as D‐1) is located in the south‐east portion of the Liaodong Graben, a tectonic unit of Liaodong Bay, where the focus for exploration is on sandstone units in the Palaeogene Shahejie Formation. Here, hydrocarbons with an oil production capacity of 629 m 3 /day have been discovered in well D‐1‐2SA. The reservoir facies have been analysed by combining the cuttings, logging, seismic data, sedimentary facies, and sequence stratigraphy. In the sequence stratigraphic study, the second member from the base of the formation is divided into one third‐ and four fourth‐order depositional sequences. The sedimentary facies include fan deltaic, braided river deltaic, and lagoonal systems. Seismic attribute inversion of the sequence framework, depositional models, and sediment distribution has been conducted for each system tract. The reservoirs facies in the D‐1 area are characterized by medium to low porosity, and medium to low permeability. The development of reservoirs facies is related to the subaqueous depositional channels of the fan deltaic system with the best quality for hydrocarbon storage. These channels have strong root mean square amplitudes used for seismic attribute identification for reservoir targets. The formations of the source‐to‐sink system with granitic and metamorphic source rocks and relative distant transportation are considered to have the best potential for hydrocarbon reservoirs.
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