Regional Geological Survey Research Articles

Effects of human and tectonic activities on groundwater in the upper Yellow River terraces of the loess Plateau

Terraces of the Yellow River are among the most crucial geomorphological landforms pertaining to human survival on the Loess Plateau. After more than half a century of surface flood irrigation, rapid rises in groundwater levels have led to frequent geological disasters, causing a rapid short-term evolution of Yellow River terraces, and an increasingly serious contradiction between this rapid evolution and human survival. However, the process by which water transfers through the thick loess vadose zone and causes a rapid groundwater response within months or years remains controversial. Using the Heitai platform of Yellow River terrace IV as an example, we found, on the basis of regional geological surveys, that at least 112 tectonically-induced cracks have developed in this area. We contend that the superimposed effects of earthquake ground motions from historical and ancient earthquakes since the Late Pleistocene have driven the development of such densely distributed cracks in the loess layer. These cracks, together with a series of fault planes generated by NE-directed extrusive stress at the regional scale, constitute a potential network of preferential channels for water transport within the Heitai platform. Combined with the results of a large-scale in situ ponding test and electrical resistivity tomography, we found that this network of cracks helps to establish catchment areas within the loess layer, thereby increasing soil saturation at a more extensive spatial scale, which may then increase the overall movement velocity of the wetting front. We semi-quantified the efficiency of the crack network in enhancing the recharge of surface water to groundwater, and suggested that the impact of human and tectonic activities substantially shortens the response time of groundwater to surface water, with the reduced time far exceeding one order of magnitude. The results of a field investigation of structural traces and terrace groundwater after the Ms 6.2 Jishishan earthquake on 18 December 2023 further emphasize that a causal mechanism of human and tectonic activities leading to the rapid short-term evolution of groundwater distribution patterns may be universally applicable to all Yellow River terraces on the Loess Plateau. This study mitigates the long-standing controversy concerning the mode of surface water infiltration, including piston flow and preferential flow, and the infiltration medium by which rapid surface water recharge to groundwater occurs in loess areas over short time periods.

Research and application of comprehensive detection methods for geological structural planes in drill and blast tunnels

At present, the detection of geological structural plane that give rise to rockburst is a complex problem. A large number of rockburst cases show that the geological structural plane influence the boundary of rockburst, especially the slip-type rockburst of structural plane. However, there is no set of comprehensive geological prediction methods at home and abroad for the detection of geological structural plane that give rise to rockburst, or low accuracy and high workload. Therefore, a method that can effectively detect geological structural plane is needed. Based on the analysis of regional engineering geological characteristics and geostress, this paper puts forward that based on the characteristics of rockburst cases in high geostress area and the rockburst prone to occur in the position with large geostress difference, the method of “combination of long and short geophysical prospecting method first, drilling and engineering geological analysis combination” is adopted to detect geological structural plane finely. The results show that: (1) Under the background of regional engineering geological survey and geostress inversion, the comprehensive geological prediction is carried out to detect the geological structural plane. The TSP has the detection accuracy of 10 m to meters, the ground penetrating radar has the detection accuracy of meters to decimeters, and the borehole imaging has the observation accuracy of centimeters. The combination of the three can multi-scale clearly reflect the distribution of geological structural plane compared with the previous single geological prediction. (2) Due to the complex distribution of surrounding rock mass interface and geological structural plane, the collapse phenomenon will also appear in the rockburst area on site, and the collapse causes a number of structural plane, which means that these structural plane becomes an important factor in slip-type rockburst of structural plane. In short, accurate detection of geological structural plane has certain reference significance for predicting the boundary of slip-type rockburst of structural plane and collapse.

Baddeleyite U-Pb age and whole-rock geochemical characteristics of ∼ 1670 Ma diabase dyke in the Shennongjia area: Implications for the tectonic setting of northern Yangtze Craton during the late Paleoproterozoic

The Shennongjia Group in the northern margin of the Yangtze Craton consists mainly of thick carbonate rocks interlayered with some intervals of volcanic and terrigenous clastic rocks. With the geochronological achievements in recent years, the depositional age of this group can be constrained into the time span of 1400–1000 Ma at present, belonging to the Mesoproterozoic Ectasian period. It is also a potential candidate interval for the “Undefined System/Period” in the Regional Chronostratigraphic Chart of China. According to the 1:200,000-scale conventional regional geological survey in the ‘1960–1970 s’, at the northwest side of the dominant peak of the Mt. Shennongding, it shows a ring-shaped gabbro-diabase dyke intruded in these Ectasian formations. However, due to the lack of comprehensive studies, there are lots of controversy both about the intrusion time and the tectonic setting of the mafic dyke.In this study, by means of the LA-ICP-MS and SHRIMP method successfully, the baddeleyite from the Banbiyan gabbro-diabase dyke yielded gained the weighted average 207Pb/206Pb age 1668.3 ± 5 Ma (MSWD = 1, N = 53) and 1667.8 ± 7 Ma (MSWD = 0.7, N = 23), respectively. It represents an unambiguous late Paleoproterozoic Statherian Period magmatic event in northern Yangtze Craton. Further, for the first time, it indicates the existence of the geological records prior to ∼ 1.67 Ga in the Shennongjia area.In addition, Banbiyan gabbro-diabase samples have relatively concentrated SiO2 (48.33 % to 49.65 %) and high whole iron content (10.25 % to 12.78 %). They show Na2O + K2O ranging from 2.9 % to 4.64 % and TiO2 from 1.36 % to 1.62 %. All samples are enriched in LILE, e.g., Rb, K, and Ba. The REE pattern shows a moderately right-inclined curve between E-MORB and OIB. These geochemiacal characteristics are agreed with contemporaneous magmatic event in the southwestern Yangtze Craton, indicating a within-plate rifting background and should correspond to the rifting of the Columbia Supercontinent.

Preface

The Iraqi Bulletin of Geology and Mining (IBGM) was first issued in April 2005 and published local research, mostly of the Iraq Geological Survey (State company of geological survey and mining at that time) employees’ research. It was aimed at encouraging geologists of the survey to publish the results of the regional geological survey of Iraq, largely archived within their library. Fortunately, after 20 years, the current issue of volume 20 publishes 9 international articles from various institutes and universities, such as Baghdad, Sulaimani, Babylon, and Salahaddin universities from Iraq in addition to Federation University Australia. These articles cover several geological fields, which microfacies analysis, structure geology, seismology, groundwater, industrial geology, petrology, geochemistry, and engineering geology. The Editorial Board of the bulletin hopes that the articles published in the present issue will provide valuable and accurate information for the scientific community in general. I take the opportunity to tell you that the Editorial Board has taken action to improve the template, reference style, way of citation, website, etc. of the bulletin to be ready for the next achievement by indexing the bulletin within the SCOPUS database. It was important to include a Digital Object Identifier (DOI) for each article. Being within the SCOPUS index is a significant step, where almost all the authors prefer such indexed journals.

RockS2Net: Rock image classification via a spatial localization siamese network

The acquisition of rock property information is at the core of regional geological survey and mineral exploration, but hand-crafted feature-based methods are heavily influenced by human prior knowledge and have limited transferability. End-to-end deep learning techniques, exemplified by convolutional neural networks (CNNs), have attained significant accomplishments in the domain of image classification. However, previous end-to-end CNN-based methods are hard to focus on image critical areas, and they also cannot make full use of global alignment dependency of the rocks. In this paper, rock image classification via a RockS2Net is proposed. The RockS2Net framework adopts a Siamese architecture, characterized by two branches that share parameters, enabling the efficient extraction of both global and local features. This approach facilitates the extraction of global features from entire images and focuses on critical areas to extract local features. The architecture of spatial transformer network (STN) is introduced to transform microscopic images of rock sections to their critical areas. By fusing local features and global features, the properties obtained from microscopic images of rock sections can be more accurately predicted. To test the robust generalizability of the proposed method, the constructed CHN-Rock images dataset is used for experiments and evaluation. Experimental results show that the accuracy of the proposed RockS2Net on the CHN-Rock image dataset is 2–3% higher than that of other rock image classification networks.

A hybrid method of combination probability and machine learning for Chinese geological text segmentation

To address the issues surrounding incomplete coverage of core dictionaries, limited training corpora, and low precision in Chinese geological text segmentation, a knowledge- and data-driven word segmentation method by combining combination probability and machine learning was proposed in this paper. We extracted mathematical feature information from terms in Chinese geological text to construct a Term Combination Probability Model (TCPM) for Chinese word combinations by integrating the combination features of geological terms and the Chinese writing styles under zero-sample conditions. The TCPM was used to extract geological terms with high combination characteristics as a user-defined dictionary, and then a geological corpus was constructed by using a general domain word segmentation method based on this dictionary. After a small amount of manual review and optimization, the geological corpus was trained with a BiLSTM-CRF model to segment Chinese geological text. The proposed method in this paper was tested using a regional geological survey report set in Henan Province, and the precision, recall, and F1-score of the method are 92.65%, 92.53%, and 92.59%, respectively. The experimental results demonstrated that this method, combined with the inherent knowledge features of geological text and the machine learning method, can assist in expanding the core dictionary for Chinese geological text segmentation based on zero-sample, and can improve the segmentation precision of Chinese geological text compared to simple general word segmentation methods or machine learning methods.

A preliminary discussion on a framework for health geological survey and evaluation

While the Healthy China strategy is being implemented, the China Geological Survey has proposed and deployed a health geological survey project, starting a new journey of health geological survey and evaluation to support and serve the construction of Healthy China. However, there are still many urgent problems to be solved in this project, such as the survey vision, the framework of the evaluation indicators, the risk identification method, and the service scopes of the potential achievements. Therefore, in this paper, a framework for health geological survey and evaluation was proposed, which includes regional health geological survey zoning and local ecological risk identification. At regional scale, the framework of indicators, grading standard, score calculation, zoning method of health geological survey, identification of beneficial and harmful health geological factors, and application of achievements were proposed. These contents were presented based on the core evaluation indicators (e.g., the chemical composition, physicochemical properties, topography, and climate of the crustal surface environment caused by geological evolution processes) and the optional evaluation indicators (e.g., sanitary condition, economic level and geo-environment). At local scale, the selection of evaluation area, workflow, risk identification and the application of achievements were proposed to avoid the ecological risks of harmful trace elements and develop beneficial health geological resources.

Modelling and Estimation of Coal Resources Using Circular Method in Beringin Makmur II Area, North Musi Rawas Regency

The Muaraenim Formation is a coal-bearing formation located in the South Sumatra Basin. The research location is in the Beringin Makmur 2 area, North Musi Rawas Regency, which is included in the Airbenakat and Muaraenim Formations. The aim of this research is to do 2-dimensional and/or 3-dimensional modeling in the research area to determine the feasibility of the mining process. The feasibility test of a coal seam body will be used as a study for the next stage, namely resource estimation. The method for calculating coal resources is the USG circularS method based on drill log data. The following data is needed, such as drilling data for 64 drill points, regional geological data and survey data at the research location or mining business permit (IUP) location. Then an analysis will be carried out so that 3D subsurface modeling and calculation of coal resources can be continued. Based on the research results, it was found that there were 3 coal seams with updip in the north direction and downdip in the south direction N1800E - N1820E. In the research area, synclines were found that affected the distribution of coal. Interpretation of the 3D model is obtained from the correlation between drilling data and survey data. The results of the calculation using the USGS circular method, the estimated tonnage of inferred resources is 91,840,000 tons, indicated resources are 55,330,000 tons, measured resources are 235,870,000 tons so that the overall estimate of the coal seams is 383,040,000 million tons/ton.

Innovative understanding in the geological research of China seas and adjacent regions - based on the 1∶1000000 marine regional geological survey

Innovative understanding in the geological research of China seas and adjacent regions - based on the 1∶1000000 marine regional geological survey

Geochemical Characteristics of Crude Oil in Member 7 of Yanchang Formation in Yanchang Oilfield

Oil is an important primary energy for national production and life and national defense, and China is the key to rapid development. It is of great strategic significance to ensure the safe and efficient production of the oil industry. Yanchang Oilfield is located in the main position of oil and gas accumulation in Ordos Basin, China, and the seventh member of the Yanchang Formation is the area with the richest crude oil output at present. Studying the geochemical characteristics of its crude oil exploitation is of great engineering significance for the exploration of oil and gas content in similar terrain and the continuous improvement of oil extraction and refining technology. On the other hand, it also provides first-hand data and important technical references for the exploration and exploitation of oil and gas resources in other areas of the Ordos Basin. Firstly, this paper points out the important strategic significance of the petroleum industry for China’s development, and briefly describes the basic situation of Yanchang Oilfield and the basic characteristics of crude oil. The power and diversion system of the Yanchang Formation in Yanchang Oilfield are studied, and the main factors of formation and flow of deep reservoirs in the Yanchang Formation are explored, as well as the regional geological survey of the Yanchang Formation No. 7 in Yanchang Oilfield. The characteristics of crude oil and its maturity evaluation system are emphatically discussed, and the changes in crude oil characteristics under the action of microorganisms are comparatively studied. In this paper, Yanchang Oilfield, the main reservoir area of the Ordos Basin, is taken as the research object, and the formation mechanism of the oil reservoir and the geochemical characteristics of crude oil in the 7th member of the Yanchang Formation are deeply explored, so as to provide a preliminary theoretical study for the research of crude oil exploitation in reservoirs and other oilfields in the Ordos Basin.

Permian arc magmatism in southern Tibet: Implications for the subduction and accretion of the Zhikong–Sumdo Paleo-Tethys Ocean

The tectonic evolution of the Zhikong–Sumdo Paleo-Tethys Ocean (Hereafter referred to as Zhikong–Sumdo Ocean) in southern Tibet is controversial due to the limited records of arc magmas. Here, the newly discovered Zhangda complex in the Zhikong area of Tibet is selected as the research object. Zircon U–Pb geochronology, zircon Hf isotopes, whole-rock geochemistry and Sr-Nd isotope analyses performed based on field geological surveys show that the Zhangda complex is composed of Early Permian hornblende gabbro (278.3 ± 1.1 Ma), cumulate gabbro (277.4 ± 1.7 Ma), tonalite dike (281.1 ± 1.9 Ma), Middle–Late Permian gabbro diorite (267.8 ± 2.9 Ma, 269.0 ± 3.1 Ma), and tonalite (258.0 ± 2.7 Ma). The Zhangda mafic rocks show weak fractionation of light and heavy rare earth elements, and they are enriched in large ion lithophile elements and depleted in high field strength elements. Meanwhile, the Zhangda tonalites show the characteristics of metaluminous calc-alkaline I-type granite. They are enriched in light rare earth and large ion lithophile elements and are depleted in heavy rare earth and high field strength elements. The ɛHf(t), ɛNd(t) and the initial 87Sr/86Sr values of the mafic rocks are + 9.3–+14.4, +4.2–+5.9 and 0.702803–0.704264, respectively, while the ɛHf(t), ɛNd(t) and initial 87Sr/86Sr values of the tonalites are + 9.8–+16.3, +5.5–+6.1 and 0.703105–0.704071, respectively. Combined with the regional geological survey results, the Permian Zhangda complex was found to be formed in a tectonic setting of subduction north of the Zhikong–Sumdo Ocean. The Zhangda mafic rocks were formed by partial melting of the depleted mantle modified by subducted metasomatic fluids, while the Zhangda tonalites were the products of partial melting of the juvenile crust. During the Zhikong–Sumdo Ocean subduction, mantle-derived magma underplating led to the growth of juvenile crust in southern Tibet.

Initiation and evolution of coarse-grained deposits in the Late Quaternary Lake Chenghai source-to-sink system: From subaqueous colluvial apron (subaqueous fans) to Gilbert-type delta

Investigating the formation and evolution of coarse-grained deposits in modern lakes and the relevant controlling conditions is indispensable to the prediction of reservoir sandbodies, disaster prediction, and limnological research. The source-to-sink system of coarse-grained deposits in Lake Chenghai, a deep, scarped Late Quaternary lake, was investigated in this study based on 62 outcrops, Advanced Land Observing Satellite (ALOS) digital elevation model (DEM) data, and regional geological survey data. The findings include the following: (1) the source areas of coarse-grained deposits in Lake Chenghai were lithologically classified into carbonate source areas, basaltic source areas and siliciclastic source areas, and were geomorphically categorized as scarp type or confluence type. Subaqueous colluvial aprons have formed downstream of the carbonate source areas and scarp-type basaltic source areas, while Gilbert-type deltas have formed downstream of siliciclastic source areas and confluence-type basaltic source areas. (2) The formation and evolution of coarse-grained deposits are controlled by the sediment flux that evolves in synchrony with the geomorphic evolution of the source areas and the sink regimes. Scarps represent the initial landform of the source areas. Source material rolls off or slides down scarps or forms small-scale debris flows before entering the lake. The source material initially formed subaqueous colluvial apron (synonymous with subaqueous fans) where sufficient space was present to accommodate sediments and the basement angle exceeded than the natural angle of repose. As weathering and denudation have progressed, the initial scarps have transformed into confluence-type slopes, and the source material has formed medium- and large-scale debris flows that have entered the lake, resulting in an increase in sediment flux. Consequently, the subaqueous colluvial aprons have rapidly grown and developed subaerial deposits, which have evolved into larger-scale Gilbert-type deltas that overlie the initial aprons. (3) The morphology and distribution of coarse-grained deposits vary in response to differences in quantity and composition of materials from different source areas, which resulting from different rates of weathering and denudation and different sediment input regimes. Firstly, the size and surface slope angle of a subaqueous colluvial apron from a carbonate source are smaller than those of a subaqueous colluvial apron of basaltic origin. Secondly, a Gilbert-type delta from a basaltic source features a greater slope angle and a thicker topset than does a Gilbert-type delta of siliciclastic origin, and the latter exhibits a longer foreset and a thicker bottomset than in the former. Thirdly, the sizes of subaqueous colluvial aprons are not strongly correlated with the sizes of the source areas, while the sizes of Gilbert-type deltas are.

Shear Strength Characteristics of Clay-Gravel Layer and Its Slope Failure Law and Mechanism

The Anqing Formation clay-gravel layer is widely distributed in the Anqing area of the upper reaches of the Wanjiang River. It is a typical soil-rock mixture composed of gravel and clay. The poor engineering properties of the clay-gravel layer are the main factors for the failure of the slope. On the basis of regional geological survey, the clay-gravel threshold, clay mineral composition and cementation characteristics of clay-gravel layer were studied. The in-situ horizontal push-shear tests under different gravel content, water environment and overlying load were designed and carried out, and its shear failure mode and strength were analyzed. The study found that the shear zone was in the shape of a broken line and was controlled by the particle size and distribution of the gravel. The shear strength of the clay-gravel layer is relatively high in the natural state due to the structure of the gravel and the friction and cementation force between the clay and the gravel. Water had the greatest influence on the shear strength of the clay-gravel layer, and the overlying load affected its shear strength within a certain range. The indoor rainfall erosion model test of the clay-gravel slope was carried out, and the failure and instability modes and mechanisms of the slope with different gravel contents were studied. When the gravel content was 30%, the failure of the slope surface was the development of gullies. The erosion damage process was similar to the soil slope. When the gravel content was 50%, affected by the distribution of gravel, the slope failure was manifested as the development of erosion pits, followed by local slumps, and finally the overall sliding in layers. When the gravel content was 70%, the clay particles on the slope were quickly washed away by the water flow, and the gravel skeleton of the slope formed a temporary relatively stable structure. After being disturbed, the gravel layer collapsed as a whole.

Mineralization timing and genesis of the Qukulekedong Au–Sb deposit in the East Kunlun Orogenic Belt, northern tibetan Plateau: Constraints from arsenopyrite Re–Os ages, zircon U–Pb ages, and Lu–Hf isotopes

The Qukulekedong Au–Sb deposit is the first large Au–Sb deposit discovered in the western section of the East Kunlun Orogenic Belt. Even though the significance of the deposit is important, mineralization timing and genesis of the deposit have remained elusive. This study integrated a regional geological survey and the analysis of deposit characteristics with newly acquired geochemical data (Re–Os dating, LA–ICP–MS zircon U–Pb dating, and Lu–Hf isotopes) to gain insights into the chronology and genesis of this deposit. The deposit is closely related to granodiorite and diorite porphyry intrusions in space. The orebody occurs in the inner and outer contact zones of the intrusions and is characterized by disseminated, quartz veins, and breccia type mineralization. The main Au-bearing minerals are pyrite, arsenopyrite, and stibnite. The zircon U–Pb ages of the granodiorite and diorite porphyry are 214.8 ± 1.1 Ma and 211.0 ± 3.7 Ma, respectively. The Re–Os isochron age of Au-bearing arsenopyrite is 209 ± 12 Ma. The εHf(t) values of zircons from the granodiorite range from 4.78 to 9.16, the εHf(t) of zircons from the diorite porphyry range from −1.81 to 7.05, and the initial 187Os/188Os value of Au-bearing arsenopyrite is 0.7851 ± 0.0079, indicating that the magmas of deposit were derived from the lower crust and ore-forming materials were mainly derived from ancient lower crust. These results show that the Qukulekedong Au–Sb deposit was formed in a Late Triassic post-collision extensional background and is an Au–Sb deposit related to the crust-derived magmatic activity. There is still significant prospecting potential in the depth of the deposit.

Petrogenesis and tectonic implications of Maoniushan monzogranites in the western margin of the Yangtze Block, Southwest China: Constraints from geochemistry, zircon U–Pb geochronology, and Hf–Nd–Sr isotopes

The Neoproterozoic granites along the western margin of the Yangtze Block are crucial for understanding the evolution of the Rodinia supercontinent and crust–mantle interaction. Based on a regional geological survey, this study analyses the zircon U–Pb geochronology, Lu–Hf isotope, whole‐rock Sr–Nd isotopes, and geochemistry of the Maoniushan granites along the western margin of the Yangtze Block and discusses the Neoproterozoic tectonic evolution history of the Mianning–Maoniushan belt. The results show that the Maoniushan granites belong to calc‐alkaline weak peraluminous monzogranite. The granites are enriched in large‐ion lithophile elements (i.e., Rb, Sr, Cs, and Ba) but relatively depleted in high‐field‐ strength elements (i.e., Nb, Ta, U, and Th). The zircon saturation temperature (TZr) ranges from 628 to 766°C, and the weighted average 206Pb/238U ages of zircon range from 771 ± 30 to 759 ± 26 Ma. The εHf(t) values range from −2.0 to +7.2, with TDM2 model ages ranging from 1,797 to 1,208 Ma. The whole‐rock Sr–Nd isotopic data show (87Sr/86Sr)i ratios of 0.7039–0.7093, and the εNd(t) values range from +1.25 to +1.76 with TDM2 model ages ranging from 1,303 to 1,344 Ma. These findings indicate the presence of deep Mesoproterozoic crustal materials in the source area. The Maoniushan monzogranites belong to I‐type granite, which is formed by the partial melting of the basic rocks and pelites in the ancient lower crust due to the metasomatism of fluids from the subducted oceanic crust. The Maoniushan monzogranites may be formed in the process of transformation from regional thickening to thinning under the oceanic crust subduction setting.

Paleomagnetic and geochronological results of the Risong Formation in the western Lhasa Terrane: Insights into the Lhasa-Qiangtang collision and stratal age

To constrain the Lhasa-Qiangtang collisional age, a combined paleomagnetic and geochronologic investigation has been performed on the Risong Formation redbeds and volcanic rocks in the Wuma area of the western Lhasa terrane (LT). A U-Pb dating result from the volcanic interlayer at the bottom of the Risong Formation redbeds yields the youngest weighted mean 206 Pb/ 238 U age of 110.6 ± 1.3 Ma, and the two detrital zircon U-Pb chronological results from the Risong Formation redbeds provide the youngest weighted mean 206 Pb/ 238 U age of 106.9 ± 3.3 Ma (the top strata of section A) and 120.5 ± 3.0 Ma (the top strata of section D), respectively. Our new geochronological results suggest that the studied Risong Formation redbeds formed during the Early Cretaceous, rather than during the Late Jurassic as assigned by 1:250,000 scale Wuma regional geological survey report. Characteristic remanent magnetization (ChRM) directions from two different limbs of folds concentrate in two different groups, and both site-mean directions pass positive fold tests. One group including 32 sites yields a tilt-corrected site-mean direction that is D = 356.1°, I = 33.1° with α 95 = 2.3°, corresponding to a paleopole at 75.2°N, 278.1°E with dp/dm = 1.5°/2.6° and a paleolatitude of 18.1° ± 1.5°N for the study area (32.41°N, 83.39°E). The other group including 24 sites provides a tilt-corrected site-mean direction that is D = 60.5°, I = 48.5° with α 9 5 = 2.0°, corresponding to a paleopole at 38.7°N, 159.6°E with dp/dm = 1.7°/2.6° and a paleolatitude of 29.5° ± 1.7°N for the study area (32.41°N, 83.39°E). After syntectonic-sedimentation-correction, the Fisherian site-mean inclination of 41.7° ± 1.6° and corresponding paleolatitude of 24.0° ± 1.2°N obtained from 56 sites of two different limbs are consistent with the inclination-only mean of 39.6 ± 3.1° and corresponding paleolatitude of 22.5° ± 2.2°N deduced from the ChRM directions of all the 56 paleomagnetic sites, suggesting that the observed inclination discrepancy of the Risong Formation redbeds may result from the syntectonic sedimentation. Comparing the Early Cretaceous paleolatitudes observed from the western LT with those from the western Qiangtang terrane shows insignificant paleolatitude difference, supporting that the Lhasa-Qiangtang collision in the western part occurred at or before the Early Cretaceous. • New dating shows the sampled Risong Formation redbeds formed during the Early Cretaceous rather than the Late Jurassic. • The Wuma sampling area was located at ~22.5° ± 2.2°N during ~120.5–106.9 Ma. • The Lhasa-Qiangtang collision occurred before ~120 Ma in the western part.

Intelligent Recognition of Ore‐Forming Anomalies Based on Multisource Data Fusion: A Case Study of the Daqiao Mining Area, Gansu Province, China

AbstractNovel prediction methods using artificial intelligence have been developed to improve the identification, discovery, and utilization of new types of mineral resources at new depths or using new technologies. However, most artificial intelligence methods require large training data sets that are often unavailable for mineralization prediction models, leading to inaccuracies. To address this issue, we developed a semi‐supervised machine‐learning method to identify metallogenic anomalies using the density‐based spatial clustering of applications with noise method and autoencoder. The outputs of this method show irregularity in distributions inferred from geological, geochemical, and hyperspectral remote sensing data that match known mineralization locations. We focus on the Daqiao mining area of Gansu Province in China to show that the model predictions are highly consistent with known deposits of the Yinmahe and Daqiao gold mines, and two new prospecting areas have been highlighted for further field confirmation. The accuracy of this semi‐supervised learning method was verified by an interdisciplinary intelligent analysis, showing that this method could have wide‐reaching applications for improving regional geological surveys.

Geological Characteristics and Distribution of Granite Geothermal Reservoir in Southeast Coastal Areas in China

The southeast coastal areas in China have distributed lots of granite outcrops of different periods. Previous research has shown that granite geothermal reservoirs are also distributed under sedimentary basins in these areas, such as in Zhangzhou basin. Therefore, granites with fractures buried in deep can be used as a potential deep geothermal reservoir in these areas. In order to study geological conditions of the deep granite reservoir and discuss the genesis of the deep granite geothermal system, rock geochemistry and zircon U-Pb chronology from outcrop and parts of the drilling cores of granitic rocks have been analyzed, combined with the anatomy of the deep seismic data and electromagnetic detection data in selected area. Based on the results of geochemistry and zircon U-Pb chronology, most granites in this area are of Yanshanian periods. Based on the seismic data, the thickness of the overlying strata on granite in Huangshadong area of Huizhou City is up to 1.5 km. According to the regional geological survey, multi-stage joints are developed in the granite, and most of hot springs rise from intersection of fracture with different directions to the surface. The heat source in the study area mainly comes from the mantle carried up by the deep NNE-trending faults. There are a large number of thermal springs at the intersection of the surface and the NW-trending fault, and the NW-trending fault provides the drainage conditions for the upwelling of underground thermal springs. There is a huge amount of deep granite geothermal resources in the southeast coastal area. The analysis of deep granite geological conditions and genetic models can provide guidance for the evaluation of deep granite geothermal resources and the further optimization of favorable zones in these areas.

Mesozoic horizontal stress in the East Sichuan Fold-and-thrust Belt, South China: Insights for Lower Paleozoic shale gas retention

The Lower Paleozoic organic-rich shales are the primary targets of shale gas exploration in the East Sichuan Fold-and-thrust Belt (ESFB), South China. Horizontal compression during the Mesozoic orogeny caused the decollement of these shales and further influenced the retention of shale gas. In this study, seven sets of rock samples were recovered from outcrop sites in the ESFB, and the measured occurrences of the exposed strata in the ESFB were extracted from regional geological survey works. Acoustic emission tests under uniaxial compression were conducted on these outcrop samples. Magnitudes of the two principal horizontal effective stresses, SH-eff and Sh-eff, at the seven sampling sites, were acquired based on the Kaiser effect; magnitudes of the Mesozoic SH-eff experienced by the Lower Paleozoic shales in the different tectonic belts were then determined based on previous and newly measured paleo stress magnitudes, as well as their correlation with the measured dip angles of strata. Finally, the maximum depths of decollement (HD-max) of the shales were computed using the inferred paleo stress magnitudes. Measured SH-eff magnitudes of the outcrop samples ranged from 74.7 MPa to 117.0 MPa, and the ratios of SH-eff magnitudes to Sh-eff magnitudes fell between 1.10 and 1.55. The magnitudes of the paleo stress experienced by the Lower Cambrian shale were higher than those of the Lower Silurian shale due to a greater burial depth. The inferred maximum Mesozoic SH-eff magnitudes decreased from 180–200 MPa at the margin of the orogenic belt to 60–80 MPa at the margin of the basin, and the computed HD-max values decreased from more than 10 km to less than 5 km correspondingly. A lower magnitude of the Mesozoic horizontal stress and a shallower decollement contributed to better retention of the Lower Paleozoic shale gas inside the Sichuan Basin.

Organic geochemical characteristics and gas prospectivity of Permian source rocks in western margin of Songliao Basin, northeastern China

The Permian in western margin of Songliao Basin is a strategic potential field of oil and gas resources in northeastern China, but the systematic researches since few boreholes were drilled up to Permian strata, as well as there is a lack of seismic and well-logging data. This paper presents the lithological composition of the Permian Formations on the basis of regional geological survey in western margin of Songliao Basin. A total of 60 mudstones and shales were collected to evaluate the organic geochemical and petrophysical characteristics and gas prospectivity of Permian source rocks. The Permian is composed of Shoushangou, Dashizai, Zhesi and Linxi Formation, which represent large sets of mudstones and shales, which are mainly deposited in a weakly to strongly reducing marine environment. The primary organic matter precursors in Permian were lower aquatic organisms such as zooplankton and algae, while a few samples of Linxi Formation indicate mixed sources of lower aquatic organisms and terrigenous higher plants. The Permian gas–prone source rocks are at over–mature stage with vitrinite reflectance Ro% = 2.01%–3.14% and mainly classified as fair to good quality and type II–III kerogens, and generally have a tricyclic terpane distribution pattern of C21>C23>C20, but Shoushangou Formation and Linxi Formation have subordinate patterns of C21>C20>C23 and C23>C21>C20, respectively. The residual organic matters in Permian source rocks have CH4 yields up to 24.34 mg/g∙TOC at EASY%Ro = 4.45%, which indicate the possibility of secondary gas generation at Ro% = 2.0%–3.5%. The pores and fractures are developed in Permian source rocks with widths of 5.28–18.64 μm, and mean values of porosity and permeability are 2.17% and 0.0043 × 10−3 μm2, respectively. The source–reservoir–cap rock assemblages in Carboniferous–Permian and Mesozoic sedimentary sequences are included in situ and near–source accumulation in Permian, and long–distance migration and accumulation in underlying Carboniferous and overlying Triassic, Jurassic and Cretaceous. The Permian system can be regarded as a potential gas exploration target in the western margin of Songliao Basin.