Abstract:From the different distribution areas of the Sijizhuang Formation at the bottom of the Hutuo Group, one sample of orthoclase granite-porphyry and one sample of porphyritic monzogranite gravels were selected, along with one sample of orthoclase granite-porphyry intruded into the Sijizhuang Formation in Jiangcun area. Zircon U-Pb-Hf isotope analysis was conducted. The weighted average ages of the orthoclase granite-porphyry and the porphyritic monzogranite gravel were determined to be 2 507±14 Ma and 2 519±35 Ma, respectively, indicating that the sources of the granite gravels were likely the late Neoarchean Ekou granite and Lanzhishan granite. The zircon ²⁰⁷Pb/²⁰⁶Pb age of the orthoclase granite-porphyry intruded into the Sijizhuang Formation was determined to be 2 157±15 Ma. Combining the ages of the Sijizhuang Formation and the Gaofan Group volcanic rocks in the Wutai area, and the geological events in the North China Craton from 2.2 to 2.0 Ga, it is inferred that the lower boundary of the Hutuo Group is likely to be 2.2 to 2.18 Ga, and its upper boundary age is approximately 2.0 Ga. The depo- sition process represents a period of intense intracontinental rift setting. The Hf isotope results of the Neoarchean granite gravel and the Paleoproterozoic granite zircons indicate that there was strong crustal growth in the early Neoarchean and crustal growth also existed in the late Neoarchean in the Wutai area.

Abstract:The Qujia gold deposit is located in the central part of the Jiaojia gold metallogenic belt, which is an important concentrated area of altered-type gold deposits in China. The elevation of the deposit ranges from -726 m to -1 334 m. To study the evolution of pyrite and its indicative role in gold mineralization processes, in-situ trace element analysis of pyrite was conducted using LA-ICP-MS. The pyrites were categorized through petrographic observation and cluster analysis. It is revealed that trace elements such as Co, Ni, and As in pyrite mainly in the form of isomorphism, while elements such as Au, Ag, Cu, Zn, Pb, and Bi predominantly exist as mineral inclusions at the nano- and micron-scale. Pyrite is classified into five main types: Co-rich Py1, Ni-rich Py2, Au- and As-rich Py3, Au-, Ag-, Pb-, and Bi-rich Py4, and "clean" Py5. The trace element characteristics of pyrite indicate that ore-forming materials may have primarily originated from Precambrian metamorphic basement rocks and Mesozoic magmatic rocks, with a lesser contribution from the mantle. Ore-forming hydrothermal fluids likely resulted from a complex mix of metamorphic hydrothermal fluids, magmatic hydrothermal fluids, and shallow atmospheric precipitation. The different types of pyrite reflect the evolution of ore-forming hydrothermal fluids from Co- and Ni-rich to As- and Au-rich, and finally to Pb-, Bi-, Au-, and Ag-rich compositions. After the formation of Py1 and Py2, intense tectonic activities caused significant disturbance and enhanced the adsorption of gold complex compounds onto fracture surfaces, promoting gold precipitation within the fractures. This process likely played an important role in gold enrichment and mineralization. Pyrite with low Co and Ni contents but high fragmentation levels, as well as elevated concentrations of Au, Ag, As, Pb, and Bi, is closely associated with mineralization. In addition, the content of Co and Ni in pyrite is high, the crushing is strong, and the content of ore-forming elements is high, which is the characteristics of pyrite formed in the early stage and transformed by the later mineralization.

Abstract:Shamai tungsten deposit is a medium sized magmatic hydrothermal deposit located in Dong Ujimqin Banner of Inner Mongolia. The ore bodies mainly occur in biotite monzonite granite and biotite monzonite granite porphyry. In this study, the petrography, LA-ICP-MS zircon U-Pb chronology and petrogeochemistry of biotite monzonite granite and biotite monzonite granite porphyry are studied in order to clarify the genesis and age of the two rocks and provide further data for regional prospecting. The results show that the LA-ICP-MS zircon U-Pb ages of biotite monzogranite are 135.6±1.6 Ma and 136.3±1.8 Ma, and the biotite monzonite granite porphyry is 138.6±1.1 Ma. The main elements show they are peraluminous high potassium calc alkaline granite which are characterized by high SiO₂ (73.73%~78.23%), Na₂O+K₂O (7.56%~8.89%)and low MgO (0.09%~0.20%), CaO (0.51%~0.89%), TiO₂ (0.03%~0.12%). They are enriched in Rb, K, Th, U, and depleted in Sr, Ba, Nb, P, Ti, with strong negative Eu anomaly and high FeO^T content, FeO^T/MgO and FeO^T/(FeO^T+MgO) ratio indicating the characteristics of A-type granite. The zircon U-Pb age of the Shamai granite is consistent with the age range of the large-scale metallogenesis in eastern China. The tectonic environment discrimination diagrams indicate that it was formed in the extensional tectonics environment after the continental collision in the Yanshanian period, which is related to the lithospheric thinning of northern margin of the North China Craton.

Abstract:On the basis of field profile and core observation, multiple methods such as thin section identification, scanning electron microscopy, and electron probe were used to conduct a detailed analysis of the occurrence characteristics and formation mechanism of authigenic chlorite in sandstone reservoir of the Qigu Formation in the Fudong slope area, providing the adjustment direction for the search for oil and gas reservoirs and development plans. The results indicate that the authigenic chlorite in the sandstone of the Qigu Formation reservoir in the study area exhibits three occurrence states under the microscope: liner-type, membrane-type, and filling-type, with liner-type being the main occurrence, and the corresponding reservoir properties are good; Authigenic chlorite is iron-rich chlorite, and the dissolution of tuffaceous debris and feldspar minerals, the transformation between clay minerals, and the flocculent precipitation formed by Fe dissolved in rivers are the important material basis for the formation of authigenic chlorite; Sandstones with large grain size and well sorting have high content of authigenic chlorites, which is helpful for forming and protecting of authigenic chlorite; Strong fluid dynamic is also an important controlling factor of authigenic chlorite formation; The occurrence states of chlorite in the Qigu Formation are similar, and different content of authigenic chlorite have a certain affection on the reservoir property and sensitivity.

Abstract:The Triassic Baikouquan Formation in the the Junggar Basin has huge oil and gas exploration potential, but the reservoir sand body has poor physical properties and strong heterogeneity. The reason for the formation of high-quality reservoirs is not yet clear, and the understanding of diagenetic characteristics is vague, which limits the exploration and development of oil and gas in this area. Based on the core observation,thin section analysis, scanning electron microscopy and physical property analysis, the diagenesis and pore evolution of the reservoir from the Baikouquan Formation are analyzed in detail. The results indicate that the rock type of the Baikouquan Formation in the study area is mainly sandy conglomerate, and the reservoir can be divided into reservoir supported by sand and gravel and supported only by sand. The overall reservoir space is mainly composed of primary intergranular pores with poor physical property, belonging to the low porosity and low permeability type. The diagenetic stage of the reservoir is the middle diagenetic stage B. Based on quantitative analysis, it was found that compaction and cementation have a significant impact on the physical properties of the reservoir. The pore increasing ability of dissolution is controlled by the type of rock support, and has a significant impact on the pore increasing of reservoir rocks supported by sand and gravel, while it has a relatively poor impact on the pore increasing of reservoir rocks supported by sandy particles.

Abstract:The Longtan Formation in the Dafang area of Northwest Guizhou is characterized by alternated shale, coal seams, and sandstones, with typical characteristics of marine-terrestrial transitional facies. On the basis of profile measurement and sample collection, combined with XRD analysis of whole rock and clay minerals, determination of total organic carbon (TOC) measurement, rock pyrolysis, kerogen macerals, and vitrinite reflectance (R_O) analysis, the development characteristics of hydrocarbon source rocks of the Longtan Formation in the study area are studied and evaluated. The results indicate that: ① The minerals in the rocks of the Longtan Formation are mainly clay minerals with strong adsorption capacity, but there is a significant negative correlation between clay mineral content and quartz content (R>0.8), especially the clay content of over 70% in shale and the lower brittleness index, which is very unfavorable for fracturing development; ② The abundance of organic matter in the Longtan Formation is significantly controlled by lithology. The coal seam has the highest TOC content (average 42.9%) and hydrocarbon generation potential (average 2.68 mg/g), indicating strong hydrocarbon generation potential of coalbed methane; The hydrocarbon generation potential of shale is less than 2 mg/g, but about 80% of the samples have TOC content exceeding 2%, and the shale gas resource potential is less than that of coalbed methane; Silty sandstone has the worst hydrocarbon generation potential, with an average hydrocarbon generation potential of 0.13 mg/g and a TOC content of 1.4%~5.6%, indicating a certain degree of tight gas potential; ③ The macerals of the Longtan Formation kerogen are mainly composed of liptinite and vitrinite, with type Ⅲ kerogen being the main type and type Ⅱ₂ being the auxiliary type. They have a high degree of thermal evolution and are in the stage of high-over mature dry-gas generation; ④ The middle section of the Longtan Formation, where coal seams are more developed, is a favorable zone for joint exploration of coalbed methane, shale gas, and tight sandstone gas in the Dafang area.

Abstract:Strontium isotopes have become one of the effective tools for studying and comparing global geological events such as global sea level changes, orogeny, paleoclimate, and paleoenvironment. This article takes the field profiles and drilled cores of Early and Middle Triassic evaporites in the eastern region of Sichuan Basin as the main research objects, tests the strontium isotope compositions of carbonate rocks, sulfate rocks, and halite rocks, and establishes the corresponding strontium isotope evolution curves. The results show that the average ⁸⁷Sr/⁸⁶Sr value of carbonate rocks is 0.707 895, the average ⁸⁷Sr/⁸⁶Sr value of anhydrite rocks is 0.708 174, and the average ⁸⁷Sr/⁸⁶Sr value of halite rocks is 0.708 177, and the ⁸⁷Sr/⁸⁶Sr value of carbonate rocks increased rapidly from 0.707 413 in the Early Triassic to 0.708 515 in the early Middle Triassic, and then showed a downward trend. Overall, the ⁸⁷Sr/⁸⁶Sr values are close to the published global ⁸⁷Sr/⁸⁶Sr data of the same period in the Early and Middle Triassic, indicating that the material source of the Early and Middle Triassic potassium salt in the eastern region of the Sichuan Basin is mostly seawater and deposited in a marine sedimentary environment. At the same time, the greenhouse effect caused by volcanic activity also provides climatic conditions for potassium salt deposition.

Abstract:Volcanoes are a window for humans to explore deep magma systems. From a global perspective, crystal-poor and melt-rich volcanic rocks (especially basalt and rhyolite) are mainly exposed all over the earth, while crystal-rich felsic volcanic rocks exposed around many calderas. The felsic crystal-rich volcanic rocks can be mainly divided into two types: one type is the volcanic rocks with homogenous composition and crystal contents; the other type is the volcanic rocks with zoned composition and crystal contents. The crystal-rich volcanic rocks erupted due to the cold stored crystal mush was remelted, reactivated, and remobilized after being repeatedly recharged by hot magma. The composition of the preexisting materials in the reservoir constrained the type of crystal-rich volcanic rocks formed by reactivation. The existence of crystal-rich volcanic rocks can well explain the contradictory phenomenon that the magma reservoir has a long life, but the process of magma accumulation and crystallization is rapid. Although the research of felsic crystal-rich volcanic rocks has made obvious progress in recent years, there are still many problems to be solved, such as the origin of porphyritic lava, how to reveal the reactivation of crystal mush, the relationship between crystal mush reactivation and volcanic eruption, the time scale of magma recharge and crystal mush reactivation, etc. Further research on crystal-rich volcanic rocks will promote the understanding of the mechanisms of melt evolution, migration, and shallow accumulation and eruption, providing more information for establishing a more comprehensive model of felsic magma evolution.

Abstract:By segmenting the sand sample image into single particles and identifying its components, the accuracy and efficiency of sand sample lithology analysis can be significantly improved. The existing methods for sand sample image segmentation mainly rely on traditional watershed algorithms and convolutional neural networks, but due to insufficient extraction of details from single particle rock debris contours, the mis-segmentation rate is high. Therefore, this paper proposes a single particle image segmentation and extraction method that combines convolutional neural networks and watershed algorithms, using image fusion algorithms as a bridge. Firstly, an improved Mask R-CNN network is used to quickly segment the original sand sample image and obtain its initial segmented image; Then, the initial segmented image is fused with the original sand sample image, and an improved watershed algorithm is used to segment the fusion results; Finally, using the coordinate point matching method of the original sand sample image, the resulting image obtained from watershed segmentation is corrected to complete the extraction of single particle rock debris images. The experimental results show that the accuracy of the single particle automatic segmentation and extraction method proposed in this paper is as high as 96.77%, and the model is lightweight and precise, providing a feasible and effective method for rock debris image segmentation, which can meet the needs of effectively calculating structural changes in oil reservoirs, searching for potential sediment sources, and dynamic changes of reservoirs.

Abstract:TESCAN Integrated Mineral Analyzer (TIMA) is an analysis system based on a scanning electron microscope that incorporates multiple X-ray spectrometers and other detectors. It could automatically identify minerals and produce images. TIMA has been widely applied in earth sciences, including petrology, mineralogy, geochemistry, petroleum, and paleontology, particularly in the rapid analysis of some geological samples with complex mineral composition and structure and small grain size, and a large number of repetitive samples to obtain statistical data for research purposes. In order to achieve the goals of analysis and save costs, it is crucial to select the optimal analytical conditions, but this aspect is often overlooked. This article takes sample of gold-bearing pyrite-sericite-quartz altered rock from the Huachanggou gold deposit in Lueyang County, Shaanxi Province, as an example. Using TIMA, the samples were analyzed under different scanning modes, analysis types, and various experimental parameter settings. The study compared the mineral phase composition data, image quality of mineral phase maps and elemental distribution maps in a small field, as well as statistical data such as mineral grain size. The results indicate that the main factors influencing the quality of TIMA analysis are the backscattered electron (BSE) pixel spacing, energy-dispersive X-ray spectroscopy (EDS) test dot spacing, and X-ray acquisition counts. The selection of analytical conditions primarily depends on the mineral composition, mineral grain size, and the purpose of the analysis.