Abstract: Geologists used the Mohr-Coulomb criterion and Becker's strain ellipsoid to explain brittle fractures and plastic deformation, respectively, in traditional structural geology, and considered that formation of ductile shear zones was parallel to the circular sections of a strain ellipsoid. However, they failed to explain the stable angle ~110° facing contraction direction between conjugate ductile shear zones due to deformation localization. In fact, deformation localization is an independent deformation category controlled by MEM-criterion besides brittle fracturing and plastic deformation. The concept of deformation partitioning put forward at the end of twentieth century got rid of the bondage of continuum mechanics, and successfully explained the widespread phenomenon, strike-slip faults parallel to subduction zones or fold-and-thrust belts. The establishment of inhomogeneous and discontinuous medium mechanics opens up a new prospect for the combination of geology and mechanics.
Abstract: The Yeba Group, located in the southern margin of Gangdese, is a typical structural transition zone with complex multistage structural deformations. Previous evidence has shown that these complex structural deformations are related to the Qulong and Jiama deposits developed in the Yeba Group. Kinks therein are a representative of structural deformation in the brittle-ductile structural transition zone. Their deformation and distribution characteristics, kinematic features and temperature environment are the focus of this study, so as to explore the tectonic background. The results from the chlorite thermometer and calcite e-twins characteristics show that the temperature is between 170℃~299℃ for the formation of the kinks in the study area, indicating a tectonic uplift during the formation process. According to the kinematic analysis of the kinks based on field outcrops and BSE-based images, it is inferred that the principal compressive stress is top-down (vertically downward), which is consistent with the principal compressive stress of the large-scale NS-trending gliding nappes in the southern margin of Gangdese during that period. Combined with the results of the relative chronological analysis, we believe that the kinks developed in the Yeba Group are the product of brittle-ductile deformation under the extension of the southern Lhasa terrane since 25 Ma.
Abstract: The Wuwei Basin at the eastern end of the Hexi Corridor, between the North Qilian Mountain and the Longshou Mountain in the northeastern margin of the Tibetan Plateau, was in a NE-trending compressional environment during the Holocene. Our field survey results indicate that there are two groups of near-vertical normal faults, namely the NWW-trending and NE-trending faults. The OSL dating results show that the two groups of normal faults experienced two periods of tectonic activity in 0.70 ka and 0.49~0.18 ka. The analysis concludes that the NWW-trending normal faults were formed by the differential stress perpendicular to the stratigraphy, which was produced by the continuous uplift of the Fenmenshan uplift in the Wuwei Basin. The NE-trending normal faults could be the extensional rupture (T rupture) produced by the nearly EW-trending sinistral strike-slip faults on both sides of the Wuwei Basin, or be formed by the extension vertical to the NE-trending compression of the Tibetan Plateau. Therefore, the tectonic deformation in the Wuwei Basin was controlled by the tectonic activities in the northeastern margin of the Tibetan Plateau during the late Holocene.
Abstract: The Changjiang uranium ore field, located in Renhua county of Guangdong province, is the most important granite-type uranium ore field in southern China. There developed the NNW-trending (nearly SN-trending) ore-bearing fault structures, NEE-trending Mianhuakeng fault and NWW-trending Youdong fault. Understanding the characteristics of the Mianhuakeng fault and the Youdong fault and their relation to uranium mineralization is conducive to the building of ore-controlling structure system and further prospecting for uranium deposits. We carried out detailed field investigations, and focused on the analysis of the correlation between the Mianhuakeng fault, Youdong fault and NNW-trending (nearly SN-trending) ore-bearing faults, especially the development characteristics of fault structures and their combination with each other. Our key findings are as follows. (ⅰ) The Mianhuakeng fault is a brittle fracture belt, characterized by uncemented tectonic breccia and fault gouge containing well-rounded granite rubbles. It has obvious linear structures and negative geomorphic features, belonging to a post-mineralization compresso-shear fault, and it dislocates uranium ore body and uranium mineralization zone with small displacement; (ⅱ) The Youdong fault is a brittle fracture zone with linear structures and negative landforms. It is a tensional-torsional fault associated with NNW-trending (nearly SN-trending) ore-controlling structure and partially filled by subsequent mafic dikes. It is not a high degree ore-controlling fault and only plays a role of local ore-bearing structure; (ⅲ) There are several small ductile deformations near the Youdong fault, not that they formed a continuous ductile deformation belt resulting from the Youdong fault, but that they are ductile deformations inner the Youdong granite body with small scale, different strike and sporadic occurrence. (ⅳ) Based on the distribution of NNW-trending (nearly SN-trending) ore-bearing fault structures, the further prospecting for uranium deposits should be not along the Meihuakeng fault and Youdong fault, but along the NNW-trending (nearly SN-trending) fault belt, concentrated on the strike extending area and dipping deep area. In the meantime, there is a good chance for concealed ore zone at the surface and shallow parts of the vacancy for prospecting between existing ore zones.
Abstract: The north of Kunlun River area, which is close to the central Kunlun Fault Zone, has experienced multi-stage magmatic activities of early Paleozoic and Paleozoic-Mesozoic. A number of gold deposits (occurrences) have been discovered successively in this area for the past few years from west to east, such as Heihaibei, Lalingzaohuo, Suhaitu, Jiazutashixi, Xiangyanggou, Jiazutashidong, Dazaohuo and Heicigou, forming a metallogenic belt with an EW-length of nearly 150 km. In consideration of the basic characteristics of gold deposits in the belt, the ore-hosting wall rocks from the Heihaibei and Jiazutashidong gold deposits were selected to carry out zircon U-Pb dating in this study. The results show the silicified monzonitic granites from the Heihaibei deposit yield zircon weighted mean 206Pb/238U age of 443±8 Ma, which should be formed under the stretching environment after the collision of the Proto-Tethys Ocean to the Qaidam block. The diorite dikes from the Jiazutashidong deposit, which bears more inherited zircon, yield the zircon weighted mean 206Pb/238U age of 250±1 Ma and 420±2 Ma for primary zircon and inherited zircon, respectively, indicating a continental arc tectonic setting under the northward subduction of the Paleo-Tethys Ocean during the emplacement of diorites. Overall, it is believed that the gold mineralization in the northern Kunlun River area is more closely related to the Early Mesozoic Triassic magmatic activity, but opinions vary about the deposit types on whether it belongs to the orogenic or magmatic hydrothermal. Soil geochemical anomalies, low-resistance and high-polarization IP anomalies, and altered fracture zones formed by secondary faults can be used as the main ore prospecting markers in the northern of Kunlun River. It is considered that this metallogenic belt has good prospects for gold deposits.
Abstract: The Naqiong Sb-Au deposit is a newly discovered Au-polymetallic deposit in Longzi county, Tibet. Recent years of regional geological surveys reveal that its mineralized zone is controlled by fault structure. In view of the relatively low research degree of this deposit, specialized and systematic research on its metallogenic geologic conditions, geologic characteristics and prospecting potentials will lay a foundation for further prospecting and exploration work of this deposit. The geologic characteristics, geophysical and geochemical anomaly characteristics, and inclusion geochemical characteristics are analyzed based on the regional metallogenic geological background. The analysis results in combination with the remote sensing geologic characteristics and anomaly verification work show that the ore bodies mainly occur in the Nieru formation of the upper Triassic and are controlled by the EW-trending secondary fault structural belt. Three fractured alteration zones have been found. Through the soil geochemical profile survey, Sb, Au, As, Bi and Cu are selected as the indicator elements for Sb and polymetallic mineralization. Altogether there are ten single element anomalies, showing good match with each other. Two polarization bodies and three apparent polarizability anomalies are defined by induced polarization intermediate gradient measurement. The fluid inclusions related to mineralization are mainly liquid-rich inclusions. It is inferred that the fluid in the mining area belongs to a medium-low temperature and low salinity NaCl-H2O hydrothermal system containing traces of CO2 and N2. Overall, the available data support the notion that the Naqiong Sb-Au mining area has superior metallogenic conditions for Au-polymetallic deposits.
Abstract: The Pingguo area in Guangxi Province has considerable reserves of sedimentary bauxite of the Upper Permian Heshan Formation which are characterized by the occurrence of associated dispersed element Ga (gallium). It is of great significance to study the geochemical characteristics and depositional environment of the sedimentary bauxite and their correlation with Ga in the deposit on the basis of major and trace element analyses. This research helps to improve the comprehensive recovery and utilization of bauxite, and also to increase the economic values of the deposit. The contents of major and trace elements, including the Ga concentrations, were measured in 18 different types of ores and bauxite samples which were collected in the study area. The results calculated by statistical method and analyzed by correlation diagram show that the average content of Ga in the samples reaches the industrial grade (0.002×10-2), but the enrichment degree of Ga in different ore types accords with the regular rule of oolitic bauxite>dense massive bauxite>aluminous rock. Ga shows a significantly positive lower correlation with Al2O3, but a significantly negative correlation with SiO2, In addition, the Ga concentrations show a slightly positive lower correlation with V and Zr, and no significant correlation with rare earth elements. Based on the analyses of the paleo-geographic environment, Sr/Ba ratios, Ga enrichment and LREE/HREE ratios of different types of samples, this study suggests a costal to shallow marine facies with a relatively stable, acidic and humid climatic condition during the main metallogenic period of the sedimentary bauxite in the Pingguo area. Moreover, an oxidation environment of the coastal facies during the early deposition of the Upper Permian Heshan Formation was gradually transformed into a reducing, shallow marine facies during the late deposition of the Upper Permian Heshan Formation. Correspondingly, the ore type changed from the purplish red, dense massive mineralization to lime gray to grayish dark, oolitic mineralization.
Abstract: The Daliangzi deposit in southwestern Sichuan is a representative epigenetic hydrothermal Pb-Zn deposit hosted by carbonate rocks of Sinian Dengying Formation in the Sichuan-Yunnan-Guizhou area. The mineralization-alteration zoning law of this deposit is still unclear. A mineralization-alteration petrographic mapping is carried out at a scale of 1:200 in the middle sections of 1884 m, 1944 m, 2004 m and 2064 m in the mining area. The alteration type, intensity and altered rock fabric are carefully studied, and the mineralization-alteration intensity variation, mineral paragenesis, element compositional zoning characteristics are summarized. The results reveal the variation law of characteristic element contents in different mineralization-alteration zones, following the mineralization-alteration zoning pattern from the center of Pb-Zn ore body to host rock: medium silicification+dolomitization brecciated Pb-Zn ore facies belt (I)→medium silicification+dolomitization and stockwork Pb-Zn mineralization facies belt (Ⅱ)→strong silicification+dolomitization+calcitization+veined to star shaped pyritization facies belt (Ⅲ)→calcitization+carbonaceous+pyritization facies belt (IV). The variation characteristics of metallogenic elements, characteristic element compositions and element ratios show that the mineralization indicator elements follow the horizontal zoning law of Pb-Zn-Cd→Pb-Zn-Ag-Cu(Sb)→Ag-Cu-As-Sb→As-Sb in different alteration zones, and the variation trend of mineralization indicating elements is summarized. This study provides a reference to the deep prospecting and exploration in this deposit and studies on mineralization-alteration zoning of the same type of deposit.
Abstract: The Jiadi gold deposit, located in southwestern Guizhou Province, is a newly discovered large-scale basalt-hosted and fine-grained disseminated gold deposit. This article focuses on the characteristics of ore-forming fluid in order to discuss the ore-forming mechanism by the fluid inclusion analyses from different mineralization stages of the deposit. Based on the field observations and laboratory analyses, the hydrothermal ore-forming processes of the deposit can be divided into three stages: the pyritization forming-stage (1st stage), the smoky-gray quartz forming-stage (2nd stage) and the sulfide forming-stage (3rd stage), among which the smoky-gray quartz forming-stage is the primary stage. The fluid inclusions are mainly composed of NaCl-H2O and CO2-NaCl-H2O type, and CO2-rich inclusions are frequently observed in the first stage minerals, with homogenization temperature (Th) ranging from 211 to 231℃, and salinity (wt) from 2.10 to 7.60 (%NaCl equiv). There are a lot of NaCl-H2O and CO2-NaCl-H2O type of inclusions in the second stage, with the homogenization temperature (Th) changing from 182 to 218℃, and the salinity (wt) from 1.40 to 5.90 (%NaCl equiv). The homogenization temperature (Th) of the third stage is generally lower than 183℃, with the salinity (wt) varying from 0.90 to 5.30 (%NaCl equiv). The results of laser Raman spectroscopy show that the inclusions generally contain CO2, CH4, N2, SO2 and other gas-phase components. As the homogeneous temperature, salinity and density of the ore-forming fluid continue to decrease, the component types in the inclusions tend to reduce. By calculating the ρ, P, pH, Eh, and ƒO2, the ore-forming environment is characterized by low to moderate temperatures, low salinity, low density, near neutrality, relative reducibility and low oxygen fugacity. The change in fluid inclusion assemblage (FIA) indicates that the mineralization occurred as the fluid CO2 content continued to decrease. The fluid mixing in the main ore-forming stage and the regional extensional structure caused strong fluid boiling, and a large number of metal components (pyrite, natural gold, etc.) were rapidly precipitated to form gold ore bodies.
Abstract: The Lanmugou gold deposit is located in Xunyang County, Shaanxi Province, produced in the Indosinian Shiquan-Shenhe thrust nappe of the South Qinling, and controlled by the Heihumiao brittle-ductile shear zone. In this paper, via the analysis of the mineralization background, ore-controlling structure features and geochemical characteristics of the deposit, the preliminary conclusions on the geological characteristics and metallogenesis of the Lanmugou gold deposit have been obtained. Co content of pyrite in strata varies from 67.6×10-6 to 208×10-6, Ni content from 108×10-6 to 585×10-6, and the total amount of rare earth elements from 2.16×10-6 to 22.9×10-6. Simultaneously, Co content in hydrothermal pyrite varies from 317×10-6 to 751×10-6, Ni content from 82.8×10-6 to 304×10-6, and the total amount of rare earth elements from 4.04×10-6 to 51.74×10-6. δ34S value in hydrothermal pyrite ranges from 9.9‰ to 12.1‰, with the average value of 11.27‰. 206Pb/204Pb value of hydrothermal pyrite ranges from 18.560 to 20.206, 207Pb/204Pb value from 15.668 to 15.708, 208Pb/204Pb value from 38.257 to 38.860; 206Pb/204Pb value of pyrite in the strata ranges from 18.502 to 20.086, 207Pb/204Pb value from 15.644 to 15.788 and 208Pb/204Pb value from 38.475 to 38.907. δ18OV-SMOW value of quartz in ore ranges from 13.5‰ to 15.9‰, with the average value of 14.7‰, and the δDV-SMOW value ranges from -77.8‰ to -71.3‰, with the average value of -74.55‰. Re-Os isochron age of pyrite in the ore is 202±12 Ma. From the comprehensive studies, it is concluded that the source of ore-forming materials of the Lanmugou gold deposit is from the interlayer of volcanic rocks in strata, and the ore-forming fluids are multiple-sourced (basically metamorphic water derived from interlayer water, atmospheric precipitation). The inference of metallogenesis is that the ore-forming hydrothermal fluids filled the lamellae of brittle-ductile shear zone and the minerals were precipitated and enriched in the extension stage after the collision of the Qinling orogenic belt at the end of the late Triassic-early Jurassic. The metallogenic characteristics show that the Lanmugou deposit is an orogenic gold deposit.
Abstract: Controlled by the dual dynamic background, the superposition of Paleogene extension and strike-slip is obvious in the Xianhe mining area, Dongying sag, Bohai Bay Basin. It is of great significance for oil and gas exploration to clarify the superposition of the fault system. This paper is based on high-precision seismic data and drilling data. We conducted in-depth research on the fracture types and combination styles, fracture superposition, fracture activity and evolution, and regional dynamics background by using an integrated interpretation of well-log and seismic data, structural style identification, quantitative characterization of faulting and balanced profile recovery. The results show that two fracture systems, extensional and extensional–strike-slip, are developed in the Paleocene of the Xianhe mining area, and the extensional–strike-slip fractures are formed by the superposition of the previous extensional fractures with slip action. Regional faulting reached two peaks in the Paleogene, one is in the middle of Member 3 of the Shahejie Formation and the other is in the early Dongying Formation. Under the superposition of extensional and strike-slip stress, the faults in the Xianhe mining area experienced five major evolution stages: initial extensional stage (Ek–Es4), intensely extensional stage (Es3x–Es2x), strike-slip stage and weak extensional stage (Es2s–Es1), reactivation and extensional stage (Ed), and stabilization stage (N–Q).
Abstract: In this article, low-maturity source rocks of different kerogen types from the Laizhou Bay Sag are selected to study the correlation of activation energy with kerogen type, organic sulfur content in kerogen, soluble organic matter and clay minerals. The correlation analyses show that activation energy of TypeⅡ1 and TypeⅠ kerogens cover a wide distribution range, while TypeⅡ2 and Type Ⅲ a narrow one, and the average activation energy of kergens follows that Type Ⅲ>TypeⅡ2>TypeⅠ>TypeⅡ1; As the content of organic sulfur in kerogen increases, the average activation energy decreases, and organic sulfur of kerogen plays a catalytic role in hydrocarbon generation; Soluble organic matter affects the size and distribution characteristics of the average activation energy, and it distributes in the interval of low activation energy. It also plays a catalytic role in hydrocarbon generation. The content of Aemon mixed layer in clay minerals of source rock is positively correlated with the average activation energy, while illite shows a negative correlation with the average activation energy, working as a catalyst for hydrocarbon generation as well.
Supervisor： China Geological Survey
Sponsor： Institute of Geomechanics, Chinese Academy of Geological Sciences