Yaojia Formation Research Articles

Research on an Intelligent Sedimentary Microfacies Recognition Method Based on Convolutional Neural Networks Within the Sequence Stratigraphy of Well Logging Curve Image Groups

Sedimentary facies identification constitutes a cornerstone of reservoir engineering. Traditional facies interpretation methods, reliant on manual log-response parameter analysis, are constrained by interpreter subjectivity, reservoir heterogeneity, and inefficiencies in resolving thin interbedded sequences and concealed fluvial sand bodies—issues marked by high interpretive ambiguity, prolonged cycles, and elevated costs. This study focuses on the Lower Cretaceous Yaojia Formation Member 1 (K2y1) in the satellite oilfield of the Songliao Basin, integrating sequence stratigraphy into a machine learning framework to propose an innovative convolutional neural network (CNN)-based facies recognition method using log-curve image groups by graphically transforming five log curves and establishing a CNN model that correlates log responses with microfacies. Results demonstrate the model’s capability to identify six microfacies types (e.g., subaqueous distributary channels, estuary bars, sheet sands) with 83% accuracy, significantly surpassing conventional log facies analysis. This breakthrough in interpreting complex heterogeneous reservoir lithofacies establishes a novel technical avenue for intelligent exploration of subtle hydrocarbon reservoirs.

Epigenetic Alteration of the Hailijin Sandstone-Hosted Uranium Deposit and Its Indications on Uranium Metallogenesis in the Songliao Basin, NE China

This study focuses on the Hailijing sandstone-hosted uranium deposit in the Songliao Basin. Through a combination of petrographic analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), and geochemical analysis, the epigenetic alteration of the deposit was systematically investigated, and the alteration zonation was delineated. On this basis, the metallogenic mechanisms were further explored. The results indicate that six major types of alteration can be identified in the ore-bearing strata of the Hailijing uranium deposit: hematitization, limonitization, carbonatization, pyritization, clay mineralization (including kaolinite, illite, and illite-smectite mixed-layer), and baritization. The mineral assemblages at different stages of alteration vary: during the sedimentary diagenetic stage, the assemblage consists of “hematite + clay minerals + II-type pyrite (framboidal pyrite) + III-type pyrite (euhedral granular pyrite)”; during the uranium mineralization stage, it transitions to “ankerite + barite + I-type pyrite (colloidal pyrite) + minor kaolinite”; and in the post-ore stage, alteration is characterized by calcite cementation in red sandstones. Based on petrological, mineralogical, and geochemical characteristics, as well as the spatial distribution of the host gray sandstones, it is inferred that during uranium mineralization stage, the ore-bearing strata underwent reduction by uranium-rich reducing fluids sourced from the Lower Cretaceous Jiufotang Formation. The primary red sandstones of the Lower Yaojia Formation, formed under arid to semi-arid conditions, experienced varying degrees of reduction, resulting in a color transition from light red, brownish red, and yellowish brown to grayish-yellow and gray. Accordingly, four alteration zones are distinguished in the Hailijing uranium deposit: the primary red zone, weakly reduced pink zone, moderately reduced grayish-yellow zone, and strongly reduced gray zone. Furthermore, as the uranium-rich reducing fluids migrated from a high-temperature, high-pressure deep system to the low-temperature, low-pressure ore-bearing sandstone strata near the surface, uranium was unloaded, precipitated, and enriched, ultimately forming multi-layered and tabular-shaped uranium orebodies within the gray sandstone. This study elucidates the epigenetic alteration processes and metallogenic mechanisms of the Hailijing uranium deposit, providing a critical theoretical basis for further uranium exploration in the southern Songliao Basin.

Discovery of Trogtalite (CoSe2) in the Qianjiadian Sandstone‐Type Uranium Deposit in China

ABSTRACTCobalt (Co), selenium (Se) and uranium (U) are strategic and critical elements with significant global demand. Typically, cobalt is mainly recovered as a by‐product from sulfide and sulfoarsenide minerals associated with copper, nickel, and iron, while its occurrence as independent minerals, particularly trogtalite (cubic CoSe2), is rare. This study reports the presence of trogtalite in a sandstone‐type uranium deposit in China. It was identified in the Qianjiadian deposit in the southwestern Songliao Basin, through electron probe microanalysis (EPMA) and Raman spectroscopy analysis (wavenumber 188 cm−1). The trogtalite occurs as cubic or polyhedral microcrystals, distributing as detrital mineral dispersed in the clay matrix or enclosed in detrital quartz or feldspar in uranium‐mineralized sandstones from Upper Cretaceous Yaojia Formation. The sandstone also contains selenides, including clausthalite, ferroselite, and krut'aite, which are typical cobalt mineralization associations found in the deposits in Argentina and Congo. The uranium‐mineralized rocks in the Qianjiadian deposit are enriched in Se, suggesting the co‐enrichment of Se and U during the mineralization. Thus, Se serves as an indicator of uranium mineralization in this deposit.

Paleoclimatic and paleogeographic significance of the early Santonian ice-rafted dropstones in the Songliao Basin, NE China

Paleoclimatic and paleogeographic significance of the early Santonian ice-rafted dropstones in the Songliao Basin, NE China

The behavior of pyrite during in-situ leaching of uranium by CO2 + O2: A case study of the Qianjiadian uranium deposit in the Songliao Basin, northeastern China

The behavior of pyrite during in-situ leaching of uranium by CO2 + O2: A case study of the Qianjiadian uranium deposit in the Songliao Basin, northeastern China

Mineralogical and geochemical studies on the Qianjiadian deposit, Songliao Basin, NE China: Insights into multiple metallogenic processes in the sandstone-type uranium deposit

Mineralogical and geochemical studies on the Qianjiadian deposit, Songliao Basin, NE China: Insights into multiple metallogenic processes in the sandstone-type uranium deposit

Polymorphic transformations of titanium oxides contribute to economic uranium mineralization in sandstone

Abstract Sandstone-hosted uranium (U) deposits provide a significant U resource for nuclear energy worldwide. Driven by redox reactions, tetravalent uranium-bearing minerals are commonly associated with reductants (e.g., pyrite and organic matter). However, numerous observations have revealed that tetravalent uranium-bearing minerals can spatially coexist with chemically stabilized titanium oxides in sandstone-hosted U deposits, requiring a complementary mechanism to interpret these findings. We present a new model based on in situ texture, trace-element content, and titanium isotopic ratio, as well as polymorph type and related transformation for titanium oxides from the Yaojia Formation of the southwestern Songliao Basin in northeast China. Specifically, in our model, abundant nanopores were generated during the spontaneous transformation of anatase to rutile, producing a porous material for hexavalent U adsorption. Facilitated by a U-rich source rock, adsorbed U in porous titanium oxide from the lower Yaojia Formation was up to several thousand parts per million. In order to minimize surface energy, a subsequent decrease in surface area by merging small pores is inevitable. When the evolved surface area was small enough, hexavalent U would be desorbed and subsequently transformed to tetravalent U by local reductants, forming uraninite nanoparticles on the surface of U-rich rutile with relatively large pores. Our newly proposed mechanism not only contributes to a better understanding of economic U mineralization in sandstone, but also suggests that U occurred as uranium oxide instead of brannerite in sandstone-hosted U deposits, providing a nano-mineralogical perspective required for industrial processing.

Tectonic setting and provenance analysis of the Yaojia Formation in the northeastern Songliao Basin, NE China: constraints from sandstone geochemistry, Hf isotopes, and zircon U–Pb chronology

The Songliao Basin is rich in uranium ores, and the Yaojia Formation, which is dominated by gray fine-grained sandstones, contains the main ore-bearing stratum. Rocks in the formation contain high SiO2, Al2O3, and total alkali, with enrichment in Rb, Th, U, K, and light rare earth elements but are depleted in high field strength elements, similar to upper crustal rocks. U–Pb dating of zircon grains from sandstones in the formation yielded four groups of ages, including 99–182, 202–245, 284–365, and 1800–1900 Ma. These ages combined with the Hf isotope composition, geochemical characteristics, and regional history suggest that the Yaojia Formation rocks are associated with passive and active continental margin settings. These clastic rocks originate principally from felsic rocks in the Zhangguangcailing–Xiao Xing'anling area, and these were deposited in oxic freshwater environments.

Uranium pre-concentration in sandstone-hosted U deposits: A case study from the Hailijin ore field, SW Songliao Basin, NE China

Uranium pre-concentration in sandstone-hosted U deposits: A case study from the Hailijin ore field, SW Songliao Basin, NE China

Discovery of water fern megaspore Ghoshispora and new dating for the Upper Cretaceous Yong'ancun Formation in Jiayin, NE China

Discovery of water fern megaspore Ghoshispora and new dating for the Upper Cretaceous Yong'ancun Formation in Jiayin, NE China

Provenance, Sedimentary Environment, Tectonic Setting, and Uranium Mineralization Implications of the Yaojia Formation, SW Songliao Basin, NE China

The SW Songliao Basin is an extremely significant part of the giant sandstone uranium metallogenic belt in northern China. The Yaojia Formation is the most significant ore-bearing layer in the region. However, the poorly constrained sedimentology of the Yaojia Formation has substantially hindered the understanding of the basin and the exploration of uranium deposits within it. To determine the sedimentology, provenance, and tectonic setting of the Yaojia Formation in the study area, we conducted petrography, whole-rock geochemical analysis, and electron probe research. Based on the results of the study, it appears that the Yaojia Formation sandstone is predominantly composed of lithic sandstone and feldspar lithic sandstone. Uranium exists in two forms: as independent minerals and as adsorption uranium. Pitchblende is the most common independent uranium mineral, with small amounts of coffinite also occurring. The ratios of Sr/Ba, V/(V+Ni), V/Cr, Ni/Co, and (Cu+Mo)/Zn of the samples indicate that the Yaojia Formation was deposited in a sub- to oxygen-rich freshwater environment with a moderately stratified bottom water body and smooth circulation. The geochemical characteristics of the Yaojia Formation sandstones imply that they are primarily derived from felsic igneous rocks in the upper continental crust in active continental margin and continental island arc environments. According to geochemistry and previous detrital zircon U-Pb chronology studies, the Mesozoic and Late Paleozoic felsic igneous rocks of the southern Great Xing’an Mountains are the principal sources of the Yaojia Formation in the SW Songliao Basin. Besides providing sediments for the study area, the uranium-rich felsic igneous rocks in the source areas also represent a long-term, stable, and ideal source of uranium, suggesting substantial potential for uranium exploration in the study area.

Geochemical Characteristics of Trace Elements and REEs and their Geological Significance for Uranium Mineralization within the Qianjiadian Sandstone-Hosted Uranium Deposit, Songliao Basin

The Qianjiadian uranium deposit is a typical interstratified oxidized zone sandstone-hosted uranium deposit hosted in the Upper Cretaceous Yaojia Formation of the southern Songliao Basin. Despite its significance, little research has been conducted on the relationship between trace elements, REEs, and uranium mineralization in this deposit. This study presents new geochemical data from sandstones in the oxidation, transition, and reduction zones. The sandstones in the transition zone are highly enriched in U and moderately enriched in Mo, Cd, and V compared to those in the oxidation and reduction zones. They are also weakly enriched in Co, Ni, and Zn. The oxidation and transition zone sandstones have higher ∑LREE and ∑HREE contents than those in the reduction zone. However, the oxidation zone sandstones are characterized by LREE enrichment and flat HRRE distribution, while the transition zone sandstones show HRRE enrichment and flat LREE distribution. These trace element and REE differentiation characteristics within each subzone are closely related to the geological process of interstratified oxygenation. Oxygenated uranium-bearing fluids from southwestern provenance areas carried multiple trace elements and REEs and infiltrated along the oxidation sandstones to reach the Yaojia Formation’s transition zone. During this process, a certain amount of Mo, V, Cd, and LREE from the oxygenated ore-forming fluids was precipitated by Fe-Mn hydroxide adsorption or calcite and siderite cementation. Meanwhile, about 20.33% of preexisting U in the oxidation zone sandstones was continuously extracted and entered into the oxygenated ore-forming fluids. In the transition zone, where dissolved oxygen was exhausted and hydrocarbons were continuously injected, U, Mo, Cd, V, Co, Ni, Zn, and REEs were unloaded and precipitated as uranium minerals, sulfide minerals, or carbonate minerals. The enrichment of Mo, Cd, V, and HREEs in the sandstones can serve as new prospecting indicators for the Qianjiadian uranium deposit.

Petroleum exploration breakthrough and geological significance in Cretaceous Yingcheng and Denglouku formations of Shuangcheng area, northern Songliao Basin, NE China

Petroleum exploration breakthrough and geological significance in Cretaceous Yingcheng and Denglouku formations of Shuangcheng area, northern Songliao Basin, NE China

Organic Geochemistry and Hydrocarbon Generation Characteristics of Shale of the Fourth Member of Yingcheng Formation in the South Shuangcheng Fault Depression, Songliao Basin

In order to evaluate the potential for oil and gas resources in the deep fault depression of the Northern Songliao Basin, shale from the fourth member of the Yingcheng Formation (K1yc4) in the South Shuangcheng Fault Depression was selected as an example. The organic geochemical characteristics such as abundance, type and maturity from experiments on low-maturity source rock samples, the hydrocarbon generation conversion rate, hydrocarbon generation amount and hydrocarbon generation period of the shale from K1yc4 were evaluated via the chemical kinetics method. The hydrocarbon generation threshold of shale from K1yc4 in the South Shuangcheng Fault Depression was analyzed by examining the organic matter (OM) in shale core samples from K1yc4. Based on the thermal simulations to an approximate buried depth of 750 m, the maximum oil-generation stage corresponds to an approximate buried depth of 1380 m. The amounts of generated oil and gas from the shale in K1yc4 are approximately 2.417 × 108 t and 0.546 × 1011 m3, respectively. The shale in K1yc4 generated crude oil mainly during the sedimentary period of the Qingshankou Formation, Yaojia Formation and Nenjiang Formation, and mainly generated natural gas during the sedimentary period of the Nenjiang Formation. In the South Shuangcheng Fault Depression, the high parts of the local structure are the favorable areas for oil and gas exploration of K1yc4 in the sag zone, which could be used for the combined production of shale oil, tight sandstone oil and conventional oil.

Factors controlling reservoir quality of a retreating delta-front in shallow-water lacustrine in the Songliao Basin, Northeast China

Factors controlling reservoir quality of a retreating delta-front in shallow-water lacustrine in the Songliao Basin, Northeast China

Detrital zircon U-Pb ages of the Cretaceous strata in the southern Songliao Basin, NE China: Constraints on basin-and-range evolution

Detrital zircon U-Pb ages of the Cretaceous strata in the southern Songliao Basin, NE China: Constraints on basin-and-range evolution

Diagenetic evolution of the lower Yaojia Formation of Songliao Basin, China: Impact on reservoir quality

Diagenetic evolution of the lower Yaojia Formation of Songliao Basin, China: Impact on reservoir quality

Comparative analysis of the characteristics of the fracture systems of the Yaojia and Quantou Formations in the X Oilfield

With the gradual industrial development of the Fuyu oil formation in the X oilfield and the frequent occurrence of set losses in the stratigraphic parts of the Nengjiang Formation, the importance of the overall characterisation of the fracture system has increased significantly. By establishing an integrated model of the fracture system from the Nengjiang Formation to the Quantui Formation, research work such as batch extraction of fracture elements and comparative analysis of the characteristics of the fracture system in the X Oilfield was carried out. The study shows that the Yaojia Formation to Quantou Formation fault system, vertically, has a multi-phase fault inheritance relationship; when the faults formed at a later stage develop, the faults formed at an earlier stage are revived again and grow together with the later faults, and the development pattern of the present-day faults is the result of multiple phases of tectonic movements and the cumulative development of faults.

Hydrothermal Alteration and Its Superimposed Enrichment for Qianjiadian Tabular-Type Uranium Deposit in Southwestern Songliao Basin

The evolution characteristics of hydrothermal activity and superimposed uranium mineralization in the Qianjiadian ore field in southwestern Songliao Basin are still controversial and lack direct evidence. In this comprehensive study, a detailed identification of dolerite and hydrothermally altered un-mineralized sandstone and sandstone-hosted ore in the Yaojia Formation have been performed through the use of scanning electron microscopy observation, electron probe, carbon-oxygen-sulfur isotope, and fluid inclusion analyses. The results show that the hydrothermal fluid derived from the intermediate-basic magma intrusion is a low-temperature reducing alkaline fluid and rich in CO2, Si, Zr, Ti, Fe, Mg, Mn, and Ca, producing different types of altered mineral assemblages in the rocks, including carbonation, pyritization, sphalerite mineralization, clausthalite mineralization, silicification, and biotitization. Specifically, the carbonate minerals in sandstone are mixed products of deep hydrothermal fluid and meteoric water, with carbon and oxygen isotopes ranging from −5.2‰ to −1.7‰ and −20.4‰ to −11.1‰, respectively. Carbon source of the carbonate minerals in dolerite is mainly inorganic carbon produced at the late stage of intermediate-basic magma evolution, with carbon and oxygen isotopes from −16.1‰ to −7.2‰ and −18.2‰ to −14.5‰, respectively. Various carbonate minerals in the rocks may have been precipitated by the hydrothermal fluid after the magmatic stage, due to the change of its CO2 fugacity, temperature, and cation concentration during the long-term evolution stage. A series of carbonate minerals were generated as calcite, dolomite, ankerite, ferromanganese dolomite, and dawsonite. The precipitation processes and different types of carbonate mineral mixtures identified in this study mainly occur as parallel, gradual transition, interlacing, or inclusion metasomatism in the same vein body, without obvious mineralogical and petrologic characteristics of penetrating relationship. Homogenization temperature of fluid inclusions in calcite is high, in the range of 203–234 °C, with a low salinity of 0.71–4.34% NaCl, and the data range is relatively concentrated. Homogenization temperature of fluid inclusions in ankerite is usually low, ranging from 100 °C to 232 °C, with a high salinity of 4.18–9.98% NaCl. The precipitation processes of carbonate minerals and the results of this study are basically in consistent. Overall, the sandstone-type uranium deposits have a temporal and genetic relationship with hydrothermal activities during Paleogene. (1) Hydrothermal activity was directly involved in uranium mineralization, result in dissolution and reprecipitation of earlier uranium minerals, forming uranium-bearing ankerite and complexes containing uranium, zirconium, silicon, and titanium. (2) Hydrothermal fluid activity provided reducing agent to promote hydrocarbon generation from pyrolysis of carbonaceous fragments and accelerate uranium precipitation rate. (3) Regional water stagnation prolongs reaction time, contributing to huge uranium enrichment. This study provides new petrologic, mineralogical, and geochemical evidence for multi-fluid coupled and superimposed mineralization of sandstone-hosted uranium deposits in the sedimentary basin.

Characteristics of fluid inclusions in the sandstone‐hosted Qianjiadian uranium deposit, southwest Songliao Basin, northeastern China: Implications for the nature and evolution of ore‐forming fluids

Abstract 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.