Table of Content

29 January 2016, Volume 30 Issue 1

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Engineering Geology and Environmental Geology

Main Uranium Mineralization Types and Their Comparison of Geochemical Characteristics in Xiangshan Orefield, Jiangxi

2016, 30(1):  1-16. 

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Nearly 30 uranium deposits found in Xiangshan orefield of Jiangxi Province, whose uranium mineralization are closely related to hypabyssal or super hypabyssal intrusive rock (subvolcanic rock). Whether porphyry or volcanic rock type is hydrothermal uranium deposits. Analyzing from the metallogenic tectonic characteristics of the hydrothermal deposits in the orefield, there are two kinds of uranium mineralization, namely, cryptoexplosion clastic rock type and alteration rock type, the latter mainly includes hydromica altered rock type and albitization altered rock type. In this paper, by collecting data, combining with the data of relevant topics, a comparative study of geochemical characteristics of various uranium mineralization was carried out. Results show that, the ore grade of cryptoexplosion clastic rock type is higher, and mostly content of U is more than 1%. There is lower SiO₂ and Na₂O and higher P₂O₅ , and the ratio of K₂O and Na₂O is 11.51 on average, and the main associated elements are Hf, Sb, Cu, Pb, Zn, Zr, etc.; K₂O/Na₂O of hydromica altered rock type is 4.83 on average, and associated elements are W, Pb, Mo, Th, Sb, etc.; K₂O/Na₂O of albitization altered rock type is 0.19 on average, U has a close relationship with CaO and P₂O₅, and associated elements are Sr, Zr and Hf, Sc, W, etc. From the albitization altered rock type, to hydromica altered rock type, to the cryptoexplosion clastic rock type, with the increasing of U grade, REE distribution curve appears a regular change from right to left lean.

Characteristics of Fluid Inclusions of the Liangshan Molybdenum Deposit in Central Jiangxi Province and Their Geological Implications

2016, 30(1):  17-28. 

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The Liangshan molybdenum is one of molybdenum deposits recently discovered in central Jiangxi Province. Its major molybdenite ore bodies are situated within the tectonic fissures of Nanhua system low-grade metamorphic rocks, and molybdenite-quartz veins are the main mineralization types.Fluid inclusions in quartz veins suggest that these inclusions are distributed in groups or scattered stars randomly with long axes of 2-15 microns.There are four types of fluid inclusions, including pure liquid inclusions, gas-rich two-phase inclusions, liquid-rich two-phase inclusions and liquid phase CO₂-bearing three-phase inclusions. Liquid-rich two-phase inclusions are the main type of fluid inclusions.The homogenization temperatures range from 136 to 298 ℃, the salinities range from 1.22% to 10.11% NaCleqv and the density range from 0.78 to 0.99 g/cm³, indicating medium-low temperature, low salinity and lower density.The ore-forming pressure is estimated at 13 to 70 MPa, and the depth is about 0.5 to 2.6 km. The inclusions in gas and liquid ingredients all are mainly composed of H₂O with a small amount of CO₂ and CO in gases by the test of Laser Raman spectroscopy. The hydrogen and oxygen isotopic compositions of the ore-forming fluids show that δD values of the ore-forming fluid are between -61‰ and -57.9‰, and δ¹⁸OH₂O are between -3.32‰ and -0.52‰, which indicates that the ore-forming fluids were derived from the mixing of magmatic water and meteoric water.The sulfur isotope compositions of ore-forming fluid show that δ³⁴S values of the ore-forming fluid are between -1.8‰  and +1.9‰, which indicates that the sulfur of ore-forming fluid has the characteristics of the sulfur of magma source. Our comprehensive studies suggest that the ore-forming fluid of the Liangshan molybdenum deposit is related with the Yanshannian magmatic activities, the mixing of magma fluid with the meteoric water and later potassic alternation are two main factors to ore-forming material enrichment and precipitation. Therefore, it is proposed that the Liangshan molybdenum deposit is a typical hydrothermal filling quartz vein type deposit related with magmatic activities.

A Preliminary Discussion on Genesis and Ore-forming Fluid Characteristics of the Xinping Gold Deposit in Pingnan County, Guangxi,China

2016, 30(1):  29-35. 

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 The Xinping gold deposit is located in the Liucen ore field in Dayaoshan polymetallic mineralization belt. The ore bodies, hosted in the sandstone and mudstone of Cambrian Huangdongkou Formation, are related to the Xinping complicated anticline and fracture zone of EW-trending faults.Fluid inclusions in quartz suggest that ore-forming fluids are moderate temperature, low salinity, low density and contain CO₂. The cations in fluids are Na⁺, Ca²⁺, Mg²⁺ and K⁺, while main anion is Cl^-. The data of hydrogen and oxygen isotopes indicate that the ore-forming fluids are probably derived from magmatic fluids, and superimposed by metamorphic fluids and meteoric water also involved. The sulfur isotope values in sulfides are narrowly ranged negative not far from zero,which infers that sulfur in ore is a mixture of sulfur from deep source and strata. Our study combined with previous research show that Au has multisources, it mainly sourced from Cambrian strata, but the deep magmatic rocks in the region may also provide some Au. Based on above study, we conclude that the Xinping gold deposit was superimposed mineralization of metamorphism and magmatic-hydrothermal fluids.

Dating for Ore-hosting Rock of the Gangcha Gold Deposit in Western Qinling Mountains and Its Geological Significance

2016, 30(1):  36-49. 

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Gangcha gold deposit is a new medium-sized gold deposit which was found in the northern margin along western segments of Western Qinling Mountains, and it is expected to be a larger scale. There are five ore veins in the deposit, which are limited by the fault zones. The shallow part of host rocks are the volcanic and volcanic clastic rock group. The sets of the volcanic rock groups have been identified as Lower Jurassic Langmusi Formation for a long time before. In fact, those are confirmed as Triassic with the age of (245±2) Ma by zircon U-Pb dating method applied to the tuffs in the group this time. Also, there are two kinds of intruded rocks which are granodiorites and quartz diorites in the deposit, and the both ages are confirmed as (242±2) Ma and (246±3) Ma by zircon U-Pb dating method, respectively. That means that those intrusive bodies and ore-hosting volcanic rock group are same magmatic activity products in Indo-Chinese epoch. Above results limited that the Gangcha gold deposit was formed under magmatic hydrothermal activities after tectonic magmatic activity of Early Triassic period. The study conclusion can provide new facts for advancing gold deposit genesis research and clearing exploration direction.

Alteration and Mineralization of the Guihuachong Porphyry Copper Deposit,Tongling Area, Anhui Province

2016, 30(1):  50-58. 

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Guihuachong copper deposit is a porphyry copper deposit newly discovered in the Tongling area, Anhui Province. Lithology of host intrusion is granodiorite porphyry, belonging to metaluminous high potassium calc-alkali granite. Wall rock alteration and mineralization study is an important porphyry deposit mineralization study on migration conducted alteration zone rock for geochemical composition of elements, which is based on the analysis of hydrothermal alteration processes. Wall rock alteration is strong in the Guihuachong mining area, and mainly consists of potassic alteration, sericitization, silicification, chloritization, and carbonatization. Alteration zoning is obvious, occurring potassic alteration, sericitization-silicification, and argillation-propylitization belts in outward succession. Major orebodies occur in the sericitization-silicification belt. Alteration and mineralization process of the hydrothermal stage from early to late is divided into four stages, i.e., potassic alteration, sericitization-silicification, quartz-polymetallic sulfide and carbonate stages. Mineralization took place mainly in the quartz-chalcopyrite sulfide stage. The results of migration quality of components in different alteration zones showed that variation of migration quality in the alteration process is high for the major elements except TiO₂, MnO, MgO and low for the trace elements except Cr and Cu, and rare earth elements are loss in strong mineralization area and enrichment in the zone of mineralization.low for the rare earth elements. The similar chondrite-normalized REE patterns of the intrusion and the altered rocks from the Guihuachong deposit show close connection of the intrusion with mineralization of the deposit and it is the result of continuous action of magmatic fluids.

Relationship Between Granophyre and Molybdenum Ore of Wangwu Mining District in North Wuyi Region: Evidences from Zircon U-Pb and Molybdenite Re-Os Dating

2016, 30(1):  59-68. 

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 The Wangwu Mo-Cu deposit is one that has been explorating and has the potential of large or super-large scale in recent years in North Wuyi region. Based on the study of geological feature, with LA-ICP-MS zircon U-Pb dating, the granophyre vein weighted mean age is (127.5±1.8) Ma(MSWD=1.4).It is shown that the deposit formed in Early Cretaceous Epoch. Using molybdenite Re-Os dating, the isochron age is (153.7±3.2) Ma(MSWD=3.9). It indicates that metallogenesis of Mo occurred in Late Jurassic Epoch. The diagenesis age of granophyre vein is much later than that of Mo deposit, which shows that there is no relationship between them. Comparing the neighbor deposit mineralization feature and analyzing the existed information, it infers that the rock of molybdenum is acidic granite porphyry or biotite granite, which is located in the deep area of southeastern part of the ore district. The major metallogenesis age of Mo is Early-Late Jurassic Epoch (155 Ma±) and Early Cretaceous Epoch(135 Ma±) in North Wuyi area. During this period, the formation of Mo and Cu deposits are related to magmation caused by paleopacific plate subducting.

Geochemical Characteristics and Tectonic Implication of Rilang Formation Basalt in the South Tibet, Zhongba County, Tibet, China

2016, 30(1):  69-77. 

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Lower Cretaceous volcaniclastic litharentites are widely distributed in the Tethyan Himalaya, while less research was reported about the provenance of these volcaniclastic litharentites. In this paper, we report sedimentray and geochemical characteristics of basalts in Rilang Formation of central-western Tethayan Himalaya. Major and trace element compositions show that these basalts belong to alkaline basalt. They are enriched in LREE relative to HREE, similar geochemically to Ocean Island Basalt (OIB) and intra-plate basalt. The contents of Nb fall between the upper crust and lower crust. These basalts have a relatively low content of Th than that of lower crust and relatively high Th/Nb ratio, low Ce/Pb ratio,which indicates that these basalts suffered variable crustal contamination. Sedimentary and geochemical characteristics of these basalts are apparently different from seamounts basalt in the Yarlung-Zangbo ophiolitic mélange belt. The tectonic setting discrimination diagrams based on trace elements suggest that basalts of the Rilang Formation formed in intracontinental rift environment. Combining the petrology and depositional environments of sedimentary rocks, we conclude that these basalts maybe the one of the provenance of volcaniclastic litharentites of the Rilang Formation.

Geochemical Characteristics and Tectonic Implication of Basalt in Lower-Middle Jurassic Sewa Formation in Renacuo Area of Gaize, Tibet, China

2016, 30(1):  78-86. 

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The trachy basalt was discovered in Lower-Middle Jurassic Sewa Formation in Renacuo area of Gaize, Tibet. The contents of SiO₂, Al₂O₃, Na₂O and K₂O are 45.62%-48.46%, 14.09%-16.51%, 2.68%-4.12%, 1.35%-4.73%, respectively, and the ratio of K₂O to Na₂O (K₂O/Na₂O) is 0.34-1.77. The rocks are rich in LREE, and poor in HREE with a weak positive Eu anomaly, as well as an enrichment of elements such as Rb, Ba, U and a depletion of elements like Sr, Yb, Th, Y as a whole. The geochemical characteristics indicate that they are generated in oceanic island environment within the oceanic slab, and that the magma is derived from enriched mantle without or with a little contamination of crust materials and sub-continental lithosphere. The oceanic island rock combination consists of basalt, basaltic gravel and limestone. Combined with the idea that Sewa Formation is seafloor fan sedimentary environment, it can be inferred that the Bangong-cuo-Nujiang ocean was mature oceanic crust in Early-Middle Jurassic.

Geochemistry Characteristics and Provenance Rock of the Upper Triassic Atasi Formation Detrital Rocks in the Southern Qilian Basin

2016, 30(1):  87-96. 

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The Southern Qilian Basin deposits of the continental facies with the development of the detrital rocks in the Upper Triassic Atasi Formation. The lithology and lithofacies characteristics of Triassic sandstone is very similar to Permian sandstone, but the tectonic setting, material composition and the source area of Triassic source rock is different from Permian source rock in Southern Qilian Basin. According to the analysis results of major elements and trace elements of the sandstones,the source rocks of Upper Triassic Atasi Formation belong to an active tectonic setting, mostly like the continental island arc and active continental margin. The material composition of the source rock is mainly the felsic volcanic rock. The source area of the deposition of the Upper Triassic Period in Southern Qilian Basin is most possibly the metamorphic crystalline rock series and granite of the Presinian System and Lower Paleozoic from Middle Qilian integrated with the regional tectonic setting.

Study on Thrust Nappe and Sliding Nappe Structures of Mesozoic-Cenozoic in the Nancheng Area, Jiangxi

2016, 30(1):  97-109. 

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Based on geological surveying and drilling verification of stratum contact relations both between Jurassic Linshan Group and underlying Pre-Jurassic metamorphic strata and between Cretaceous and Pre-Cretaceous strata, this study has newly found the Xiejia structural window, Zhuyouxincun structural window, Shangwushi structural window and Wangtianshi klippe, and moreover, has determined the Yanshanian glide and Himalayan thrust nappe structures in Nancheng area, Jiangxi. The Yanshanian glide structure occurred in the end of Middle Jurassic along the expanding surface from unconformity surfaces between D-T₂/T₃-K₁ (gliding nappe) and lower strata (underlying strata). The dynamics of glide structures maybe relate to the subduction of Pacific plate from southeast toward northwest. The large-scale Himalayan thrust nappe structure had thoroughly altered the former strata sequence and formed present tectonic framework. This framework is composed of multiple imbricated thrust and stacking faults (bedding and crossbedding) and behaves a feature of lateral zonation and vertical stratification. The allochthon Pre-Cretaceous mass thrusts from southeast toward northwest and stacks on the autochthon Cretaceous strata. The autochthon Cretaceous strata exhibit some windows around by Pre-Cretaceous. The dynamics of Himalayan thrust nappe structure is complicated and maybe relate to the distant effect of the collision between the Eurasian plate and the Indian plate.

Pop-up Structure in Fold-and-thrust Belt and Its Implications: An Insight from Analogue Sandbox Models of Thrust Wedge

2016, 30(1):  110-121. 

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Pop-up structure is widely developed in fold-and-thrust belt and strike-slip tectonic setting, and has been paid much attention for its great significance in petroleum exploration. Analogue sandbox modeling has proved to be a powerful visual tool for simulating such complex structures in various tectonic settings. This study conducted a series of sandbox modeling to unravel the difference in structural geometry of pop-up structure during the development of fold-and-thrust belt, based on the same initial condition with various shortening velocities (0.3 mm/s, 0.1 mm/s, 0.005 mm/s). From the modeling results, two types of pop-up structures, i.e. superimposed and simple pop-up structures, would be developed in thrust wedge depending on different shortening velocities. In particular, there is a significant difference between superimposed structure and simple pop-up structure. The wedge shows simple deformation styles characterized by simple pop-up structures and increasing deformation while propagating continuously towards foreland. The propagation way of analogue sandbox models of thrust wedge has a significant control on the types of pop-up structure. Forward-breaking propagation took place in the foreland, mainly developed from simple pop-up structure; back-breaking propagation occurs in hinderland, mainly developed from superimposed pop-up structure.

Study on the Evaluation Method of Fault Sealing and Its Application: An Example of Neogene Layer in Enping Sag, Pearl River Mouth Basin

2016, 30(1):  122-129. 

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Taking the Neogene layers of the Enping sag as an example, a new way to evaluate fault sealing of structural closure is introduced under the current exploration practice to calibrate critical values, that is, obtaining clay content in fault zone, shale smear value and normal pressure of fault surface from sealing rules of faulted reservoir. The results show that the threshold values of shale smear factor in drilled faulted reservoirs gradually increases with depth. Development of shale and its content of fault zone are prerequisites for fault sealing, and the evaluation of fault sealing is affected by structure map accuracy, structural adjustment and fault activity. The risk of fault sealing, including faults vertical and lateral sealing, could be analyzed by the evaluation method, so as to improve the success ratio of fault traps exploration. And the evaluation method could be applied to the new exploration area with the similar tectonic genesis and sedimentary background as Enping sag, which is an effective methods to evaluate fault sealing during the early exploration periods.

Sedimentary Sequence and Environment of Shuangqiaoshan Group from the Adjacent Area Between Anhui and Jiangxi

2016, 30(1):  130-143. 

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The adjacent area between Anhui and Jiangxi is located in the northern margin of the eastern section of Jiangnan orogenic belt, in which Shuangqiaoshan Group is widely distributed in a large-thickness and low-grade greenschist-facies metamorphic flysch formation which is given priority to with argillaceous-arenaceous metamorphosed fine clastic rocks and contains a small amount of volcanic rocks. Synthesizing analysis of rock assemblages and sedimentary structures shows that Shuangqiaoshan Group may be formed in a set of volcanic-terrigenous clastic rocks which can be divided into four stages of sedimentary facies about the bathyal-shelf margin slope, neritic shelf, shelf slope and shelf slope-shelf facies under tectonic background of continental margin island arc, indicating the shrinking-closing stage of the basin evolution during the period. The proximal source region and discontinuous incomplete Bouma sequence of Hengyong Formation and Anlelin Formation, mainly generated by turbidity current and few by sandy debris flow, respectively formed during the northward limited subduction process of the lithospheric fault block in South China with oceanic crustal sea areas, and after that under ocean-basin thinning regressive environment in Neoproterozoic. From the perspective of volcanism with sedimentation co-evolution on the relationship between the sedimentation and tectonic analysis, the volcanic activity resulted from oceanic crust subduction may be started from southwest of the study area. This study provides the important evidence for the geotectonic evolution of the Neoproterozoic in the adjacent area between Anhui and Jiangxi from the aspect of the sedimentary stratigraphy.

Fracture Characteristics and Main Controlling Factors of Shales of the Second Member of Kongdian Formation in Cangdong Sag, Huanghua Depression

2016, 30(1):  144-154. 

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The shale in the second member of Kongdian Formation(Ek₂) in Cangdong Sag with large thickness, high values and excellent types of organic abundance, is one of the important intervals for dense petroleum exploration. Based on the detail observation and description of cores, this paper studied lithologic characteristics, fracture types and development characteristics(including length, opening,angle and filling)of shales in Ek₂ in Cangdong Sag of Huanghua Depression by the observation of polarizing microscope and fluorescence microscope and laser scanning confocal microscope together with analysis of X-ray diffraction and rock pyrolysis. Furthermore, it analyzed the main controlling factors of fracture development. The shales of Ek₂ in Cangdong Sag are mainly composed of felsic, carbonate and clay minerals; the main lithologies are dolomitic shale, silty mudstone, argillaceous dolostone, sandy dolomite and dolomite, etc; the main types of sedimentary structures include massive structure, lamellar structure, laminated structure and lenticular structure, etc.Four sorts of fractures develop in Ek₂, i.e. structural fracture, interlayer lamellation crack, vertical-difference load fracture and overpressure-breaking fracture, among which the structural fracture is the most, followed by the interlayer lamellation crack and vertical-difference load fracture, and the overpressure-breaking fracture is the least. The main fillings in fractures are pyrite, analcime, calcite and asphalt. The results show that tectonism, lithology, mineral composition, sedimentary structure, diagenesis and organic matter abundance(TOC) are the main controlling factors for the development of fractures in shales of Ek₂ in Cangdong Sag.

Formation Mechanism and Characteristics of Non-tectonic Fractures in Shales

2016, 30(1):  155-162. 

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Non-tectonic cracks are commonly observed in shale and some of them are greatly significant for the evaluation of shale gas accumulation and preservation. On the basis of the previous research and considering the inherent characteristics of shale, a category scheme of shale fractures has been put forward, and the forming mechanisms of the non-tectonic shale cracks has been summarized. According to the core and field observations, we briefly depicted the characteristics of the non-tectonic shale cracks. Among the non-tectonic cracks of shale, those bedding cracks formed in the diagenesis and those overpressure fractures induced by undercompaction or hydrocarbon generation have close relationship with shale gas accumulation and preservation.

Micro/Nano Pore Heterogeneity and Main Controlling Factors of the High-Maturity Longmaxi Formation Shale in Southeastern Chongqing

2016, 30(1):  163-171. 

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Studying shale pores is the key to understand the mechanism of shale gas occurrence and accumulation. But there is little effective means to quantitatively depict micro/nano pore heterogeneity characteristics of high-maturity shales. This article quantitatively analyzed micro/nano pore heterogeneity and main controlling factors of the high-maturity Longmaxi Formation Shale in southeastern Chongqing through the low pressure N2 adsorption/desorption, high-pressure mercury injection (MIP), and field emission scanning electron microscopy (FE-SEM) experiment together with the use of the fractal dimension. The results show that micro/nano pores develop very well in high-maturity shale. Mesopores are mainly slit-shaped clay interparticle pores and ink-bottle-shaped organic pores. Fractal dimensions of pores between 2.0 nm and 4.5 nm in diameter have an average value of 2.853,4, while fractal dimensions of pores between 4.5 nm and 50.0 nm in diameter have an average value of 2.736,7. The strong heterogeneity is mainly controlled by organic matters. When total organic carbon (TOC) content is less than 0.9%, the pores provided by minerals play dominant role, while the TOC content is larger than 1.7%, organic pores play dominant role. In addition, the increase of clay mineral content will increase the mesopores heterogeneity in a certain extent. Macropores are mainly composed of slit-shaped interparticle pores and a small amount of ink-bottle-shaped organic pores. Fractal dimensions of macropores have an average value of 2.844,1, which show strong heterogeneity, indicating the pore structure is complex. The heterogeneity of macropores is mainly controlled by quartz and carbonate minerals. With the increase of carbonate minerals content, the degree of heterogeneity increases. As organic pores size is relatively small, they have no obvious influence on shale macropore heterogeneity.

Pore Characteristics and the Controlling Factor of the Paleozoic Shale in the South Anhui

2016, 30(1):  172-180. 

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In order to assess the property of the Paleozoic shale gas reservoir in the south Anhui of Yangtze region, based on the scanning electron microscopy, high pressure mercury-injection, N₂ and CO₂ gas adsorption methods, the pore characteristics and structures of shale samples from the Paleozoic shales in the South Anhui were studied, and the controlling factors of pores development were discussed. The results show that the porosity and permeability of shale samples are low, and the microscopic pores mainly include inter-grain pores, floe pores, dissolution pores, matrix intergranular pores and organic pores, and the micro-nano scale pores are well developed in these shales. The main pore types in the Paleozoic shales are micropores and mesopores, which account for over 50%. The pore structure of shale is dominated by the parallel-plate pore, cylinder pore and mixed pore, and the average size is about 4.17-12.06 nm. The pore volume and specific surface area increase with the increasing of total organic carbon content (TOC). The porosity of shale reduces as the vitrinite reflectance (R_o) increases. The pore volume increases with the increasing of clay mineral content, but decreases with the increasing of brittle mineral content.

Shale Gas Accumulation Condition and Resource Potential Analysis of Devonian in Dian-Qian-Gui Basin

2016, 30(1):  181-191. 

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Based on the outcrop observation, profile survey and sample analysis of Devonian dark shale, this paper studied the accumulation condition of Devonian shale gas in Dian-Qian-Gui Basin. The results show that two sets of dark shales of intraplatform depression facies were deposited in Dian-Qian-Gui Basin during the Early to Middle Devonian, and the single layer thickness of Devonian shale is 10-55 m; the accumulative thickness is generally between 100 m and 450 m. The TOC values are mainly in the range of 1.0% to 2.5%, and the organic matter type is Ⅰ-Ⅱ₁, and the vitrinite reflectance values indicate high to over mature thermal evolution stages. As an effective reservoir, the porosity and permeability of Devonian shale in Dian-Qian-Gui Basin are similar to those of Jiulaodong Formation in well Wei-201, and various reservoir space types well developed in the shale, and the content of brittle minerals is averagely up to 67%. The gas preservation conditions of southwestern Qiannan Depression and middle-west Guizhong Depression are relatively better because of the relative flat strata, low fault density and erosion thickness, and thrusting and transpressional faults. Overall considering of the dark shale thickness, buried depth, organic matter content, thermal evolution degree and preservation condition, it can be predicted that the favorable intervals of Devonian shale gas are Tangding Formation and Luofu Formation, and the favorable areas mainly distribute in Tian’e-Nandan-Hechi area and Luzhai-Laibin-Heshan-Dahua area of middle Guizhong Depression. By using the analogy method of geological resource abundance, it can be calculated that the geological resources of Devonian shale gas is 0.66×10¹² m³ to 1.09×10¹² m³ .

Division of Hydrocarbon Plays and Resources Evaluation in the North Ustyurt Basin, Central Asia

2016, 30(1):  192-199. 

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Based on the integrated analysis of the basic geological features and oil and gas fields distribution, and cored by reservoirs, seven hydrocarbon plays are divided in the Eocene, Lower Cretaceous, Middle and Lower Jurassic, and Carboniferous reservoirs in the North Ustyurt basin. The undiscovered recoverable petroleum resources of the plays have also been reevaluated by the Monte Carlo method. The result reveals that the total amount of the undiscovered resources is about 2 102 MMboe, of which oil is 1 201 MMbbl and gas is 5 406 Bcf. Geological risks evaluation of key elements including reservoirs, traps, migration and preservation have also been completed. Then, the seven hydrocarbon plays are ranked by the double factors method of resources-risks. According to the classification criterion, there are one Ⅰ-class play, one Ⅱb-class play, two Ⅲ-class plays, two Ⅳa-class plays and one Ⅳc-class play in the North Ustyurt basin. The most favorable exploration objectives in the Mesozoic should be faulted anticlinal traps in the northern slope and on the top of the North Buzachi uplift, where the Paleozoic Bashkirian and Asselian carbonate reservoirs may also have potentials. In addition, it is hopeful to find oil and gas reserves in the local Eocene and Middle Jurassic sandstone and the Carboni-ferous Visean carbonate reservoirs in the eastern basin.

Controlling Factors on the Miocene Channel in Baiyun Sag, Pearl River Mouth Basin

2016, 30(1):  200-208. 

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During 21-18.5 Ma, 13.8-12.5 Ma and 10.5-8.5 Ma of Miocene, the channels developed in Baiyun Sag. In these three stages, the shape and architecture of the channels were different. During 21-18.5 Ma, the architecture of the channel was simple, the channel extended a long distance and the sediment was deposited in the distal end. In 13.8-12.5 Ma, the channel migrated northward. During the early of 13.8-12.5 Ma, the channel only developed in the south, then developed upstream. The channel in 10.5-8.5 Ma became deeper and narrower, and had the convergent feature. These changes of these channels’ migration and shape feature were due to different controlling factors in these stages. In 21-18.5 Ma, the channel was related to the abundant sediment supply from the shelf margin delta. In 13.8-12.5 Ma, the channel was affected by the significant sea-level decline in 13.8 Ma. In 10.5-8.5 Ma, Dongsha Movement led to the Baiyun Sag uplift and the paleo-topography determined the channel development. The analysis of the controlling factors in different stages provided new information to the research of the channel shape and evolution in each stage.

Diagenesis, Pore Fluid and Controlling Factors of Reservoir Quality in the Basalt Area of Laibei Slope Zone, Huanghekou Sag

2016, 30(1):  209-219. 

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In order to explore the influence of basalt eruption on reservoir diagenesis in Huanghekou sag, clay mineral, zeolite and trace elements in the Laibei slope zone were studied to make it clear that the pore fluid changes in different formation of Paleogene and then to establish the reservoir diagenesis and pore evolution model in igneous rocks area. In the period of the first and second members of the Shahejie Formation, under the influence of alkaline water medium formed in the small-scale basalt eruption environment and arid-semiarid climate, albitization and carbonate cementation developed universally and dolomite coat grew on grain surface, also we can see the phenomena of quartz dissolution. In the third member of the Dongying Formation, the delta reservoir was influenced by the brine precipitation in dark mudstones of the first member of Shahejie Formation and terrestrial freshwater input, also late rich mafic pore water mixing effect, so the main diagenesis are zeolite dissolution, clay mineral transformation and albitization in alkalescence water medium conditions. In the period of the first and second members of the Dongying Formation, it is characterized by extensive eruption basalt, strong hydrolysis of minerals rich in iron and magnesium element which led to the pore fluid rich in mafic, and the precipitation and dissolution of low silica zeolite. The local precipitate and dissolution of zeolite and “I-shaped” framework associated with basalt eruption is in favour of sandstone pore preservation of Dongying Formation. During the deposition of the first and second members of Shahejie Formation, pectinate dolomite coat which inhibited the quartz overgrowth under the alkaline water medium and the phenomena of quartz dissolution is beneficial to the preservation of the sandstone pore.

Simulation of Secondary Hydrocarbon Migration Direction and Prediction of Favorable Zones：An Example from the Second Member of Shahejie Formation of West Slope, Shulu Sag

2016, 30(1):  220-229. 

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The Shulu sag in the south of Jizhong depression is a typical rift basin. Paleogene formation develops many sets of source-reservoir-cap assemblage, showing good exploration prospects. In order to seek the breakthrough in oil and gas exploration and to clarify the main exploration direction and zones, it’s urgent to deepen the understanding of the secondary hydrocarbon migration of the study area.Taking the Second Member of Shahejie Formation as an example, based on the Arcgis software platform, we could manage the various geological information, such as source kitchen, conducting system, structural features, fluid potential, etc. After then, we simulate the direction of the secondary hydrocarbon migration with fluid potential model under the large scale conditions. The simulation results reveal that the secondary hydrocarbon migration is dominated by nose-structural belt under the restraint of development status of sandbody, and the oil and gas gather in its spine. Finally, four nose-structural belts are selected to be the favorable accumulation zones based on the understanding of simulation results and reservoirforming conditions.

3D Metallogenic Prediction Based on Minerogenetic Series: A Case Study in Tongling Mineral District of Anhui

2016, 30(1):  230-238. 

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In order to quantitatively predict the underlying mineral resources in Tongling mineral district and implement mixed genesis prediction according to the different deposit types, 3D metallogenic prediction based on minerogenic series is imperative. In this paper, we summarized two minerogenic series on the basis of previous studies, including the minerogenic series related to the Yanshanian magmatism and the sedimentary-reformation(metamorphic) minerogenic series. In addition, we summarized the porphyry-skarn-hydrothermal metallogenic model in the study area. Using 3D visualization technology, the 3D digital mine is modeled. After that,by implementing “cubic predicting model”prospecting method, we carried out a three-dimensional metallogenic prediction in the study area, and delineated 14 predicted targets according to the value of information and geolo-gical condition. Our research combines the traditional two-dimensional regional metallogenic prediction methods with advanced visualization technologies successfully, and extends the prediction of mineral resources within the region to three-dimensional space, makes it more conducive to concealed ore delineation work within the region, and also provides a reference for future three-dimensional prediction.

An Improved Lithological Classification Method for Thermal Infrared Hyperspectral Data Based on Spectral Matching

2016, 30(1):  239-246. 

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Feature spectral characteristics are the base of hyperspectral remote sensing technology. Based on rock spectral characteristics, for the purpose of classifying lithology by using Thermal Infrared Airborne Hyperspectral Imager (TASI) data, an improved lithological classification algorithm-spectral divergence energy-level matching (SDEM)-is presented in this paper. SDEM can identify tiny differences between any two different spectra. Also, this method takes both spectral band intensity and spectral waveform into account, and can effectively reduce the impact of image noises. Compared with the traditional lithological classification method-high spectral angle mapping (SAM), the improved algorithm can distinguish those similar but different spectra more precisely, and can identify those easily confused lithology. This method is also good at distinguishing the lithology known as “different features with similar spectra”. Using the TASI data of Liuyuan region in Gansu Province, we compared the lithological classification results of SDEM and SAM methods, and found that the SDEM method can identify the lithology that SAM can’t identify or wrongly identified. Based on our field validation work, the classification result by SDEM is more accordant with the actual distribution of rock, and is also more detailed.