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2021, Volume 28 Issue 6
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Metallogenic models of potassium ore deposits in China and demonstration of deep exploration technology ZHANG Yongsheng, ZHENG Mianping 2021, 28(6): 1-9.  DOI: 10.13745/j.esf.sf.2021.1.37 Abstract ( 525 )   HTML ( 20 )   PDF (1512KB) ( 280 )   This research project is a key component of the Special Projects for Exploration and Exploitation of Deep Earth Resources launched in 2017 and supported by the national 13th“Five-Year”Key Research and Development Plan. It is led by the Institute of Mineral Resources, Chinese Academy of Geological Sciences and China Geological Survey involving 10 major research centers from the Ministry of Natural Resources, Chinese Academy of Sciences, Ministry of Education and large state-owned oil companies, as well as several research groups, for collaborative innovation research that fully reflects the close integration of production, research, learning and application. This research focuses on the key scientific issues of potassium formation in Mesozoic (Triassic, Jurassic) marine environments and late stage transformation in the eastern Tethys, and the ‘migration-differentiation-convergence’ mineralization mechanism of deep potassium-rich brines in Qaidam Basin, northern Qinghai-Tibetan Plateau. The key technical problems of the project are the ‘dual complexity’ high-precision seismic imaging technology for deep potassic salt deposit and the logging identification and seismic prediction technologies for deep potassium ore bed (potassium-rich brine layer). Taking the major potassium-bearing areas of western Qaidam Basin and northeastern Sichuan Basin as the foothold of the ore base, and also considering other potassium-bearing basins, the research program is designed to establish the 3D geological and metallogenic models, improve the theory of potassium formation in both marine and continental environments, and establish a complete technical system for the exploration of potassium deposits no deeper than 3000 meters. So far, comprehensive evaluation of deep potassium resources potential and anomalous verification drilling have been carried out, which led to the discovery of a large potassium resource base and 3-4 favorable target areas for potassium deposits. We have finally made the breakthrough in deep potassium ore prospecting and improved the prospects for greater potassium reserves. It is worth emphasizing that only by focusing on domestic exploration, and breaking through in marine environment to find large-scale soluble solid potassium salt deposits in ancient marine evaporite strata in large and medium-sized superposed basins in central and western China, can we fundamentally reverse severe shortage of potassium resources in China. It is gratifying to see a series of new metallogenic theories and prospecting discoveries have been made for marine potassium salt deposits in China after nearly 10 years of hard work. The innovative ‘two-storey’ potassium formation model put forth in southwest Yunnan points to a new direction for the exploration of Jurassic marine potassium salt deposits, and the discovery of a new type of Triassic marine soluble polyhalite potassium ore in Xuanhan area, northeastern Sichuan, leads to a new research field and direction for the exploration of potassium deposits in the Sichuan basin. In the Kuqa area of Xinjiang, a sylvine ore bed with a depth of more than 5000 m has been discovered to show substantial progress in the marine potassium deposit prospecting in this area. And in northern Shaanxi, the ‘W-type double bottom pot’ potassium formation model contributed to the discovery of a thick sylvine mineralization section in the Ordovician marine salt basin, a new important progress in exploring potassium salt deposits formed in the ancient epicontinental sea. Presently, we are at the dawn of breakthroughs in ore prospecting for marine soluble potassium salt deposits in China. The main direction for exploration of potash salts deposits in China in the 14th “Five-Year” and beyond will be to achieve substantial breakthroughs in this field thus to build several large marine potassium salt resource bases, through greater investment and more in-depth research on the basis of the aforementioned new discoveries. References | Related Articles | Metrics

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Research progress and new views on the potash deposits in the Simao and Khorat Basins YAN Maodu, ZHANG Dawen, LI Minghui 2021, 28(6): 10-28.  DOI: 10.13745/j.esf.sf.2021.1.40 Abstract ( 244 )   HTML ( 12 )   PDF (5767KB) ( 217 )   The Simao and Khorat Basins belong to the same tectonic zone of the Tethys. The potash deposits in the two basins share similarities in regional distribution, sedimentary characteristics, potassic salt horizon, mineral assemblage and brine source. Therefore, the Simao Basin is believed to be one of the important areas with high exploration potential for marine potash exploration in China. Although significant progress has been made in understanding the formation mechanism of the potash deposits, the relationship between the two basins and the metallogenic model/pattern of potash deposits are still highly debatable. This paper summarized the recent achievements in the tectonic features, stratigraphic chronology, paleoclimate environment and provenance of potash deposits in the two basins to provide a better understanding for future potash metallogenic regularity study and facilitate breakthroughs in potash exploration in the Simao Basin. We believe: (1) The Simao and Indochina terranes might have been a unified terrane in the subtropical high-pressure belt during the Mesozoic, where the Late Triassic, Middle-Late Jurassic and Late Cretaceous were under favorable tectono-climatic conditions for potash formation. (2) The two basins may share similar potential provenance areas, including the Yangtze, Songpan-Ganzi, Hoh Xil, Yidun and North and South Qiangtang terranes. (3) The principal source materials mainly came from a terrestrial water source, with some seawater and deep hydrothermal fluid recharges. (4) The depositional ages of the potash-bearing strata in the two basins only partially overlap rather than contemporaneous. (5) The potash mines in the Simao and Khorat basins might have deposited in different periods. Together with other tectono-climatic evidence, the formation time of the Khorat potash deposit, i.e, ~85.0 Ma, would be another potentially important period to explore for potash deposits in the Simao Basin. References | Related Articles | Metrics

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Non-traditional stable isotopes in evaporite system: A research review XIA Zhiguang, HU Zhongya, LIU Chuan, WEI Haizhen, LI Weiqiang 2021, 28(6): 29-45.  DOI: 10.13745/j.esf.sf.2021.1.38 Abstract ( 332 )   HTML ( 18 )   PDF (2795KB) ( 210 )   Evaporites are the product of seawater/brine concentration by evaporation. Evaporites of various types are deposited in different hydrochemical environments and distributed in different geological periods. They are important proxies for paleo-seawater and paleoenvironment. The key issues in evaporites studies include the source and formation age of evaporates, the evolutionary history of evaporative basin/brine, and environmental changes recorded by the evaporite minerals. Mineralogical and geochemical criteria (such as elemental ratio and isotopic composition) have been used to resolve these issues. Among the methods used, stable isotopes play an important role in tracing the source and formation processes of evaporites. In the past 20 years non-traditional stable isotope geochemistry has developed rapidly and been successfully applied in evaporites research. These isotope systems consist of anionic elements B, Cl, and Br, and cationic elements Mg, K, and Ca. This paper reviews the advances of several non-traditional stable isotopes in evaporites research, mainly on stable isotope fractionation between evaporite minerals and brine, reconstruction of isotopic composition of paleo-seawater, and use of isotopic information in tracing genesis and formation age of evaporites. References | Related Articles | Metrics

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Revisiting the crystallization field of polyhalite in the Na+, K+, Mg2+, Ca2+//Cl-, SO42--H2O hexary system LI Dongdong, GAO Dandan, BIAN Shaoju, LI Wu, DONG Yaping 2021, 28(6): 46-55.  DOI: 10.13745/j.esf.sf.2021.1.53 Abstract ( 238 )   HTML ( 14 )   PDF (2055KB) ( 126 )   Studying the crystallization field of polyhalite in the Na+, K+, Mg2+, Ca2+∥Cl-, $SO_{4}^{2-}$-H2O hexary seawater system is essential for understanding the origin of polyhalite evaporites. It is also helpful for developing potassium extraction techniques for polyhalite resources utilization. However, the phase equilibrium relations between polyhalite and the more generally CaSO4-based salts (e.g., gypsum, anhydrite, hemihydrates, syngenite, gorgeyite, glauberite and hydroglauberite) are far from clear in terms of both experimental evidence and thermodynamic models. The lack of reliable equilibrium data between polyhalite and multicomponent brines has created huge obstacle to constraining the polyhalite origin conditions and utilizing polyhalite resources. In this study, we re-examined the crystallization field of polyhalite in the Na+, K+, Mg2+, Ca2+∥Cl-, $SO_{4}^{2-}$-H2O hexary system at 25 ℃, both experimentally and by thermodynamic simulation. Our new experimental results using long equilibration time indicate the thermodynamically stable crystallization field of polyhalite is very large even at 25 ℃ and several times larger than the widely adopted experimental results. Moreover, our experimental results well support the predictions by the temperature dependent thermodynamic models. These more reliable phase equilibrium data provided solid physiochemical constrains to the origin of polyhalite evaporites, indicating a diverse stable mineral assemblage of polyhalite in the evaporite basin. Moreover, the potassium/magnesium concentration needed for polyhalite formation is not as high as previously suggested based on phase diagram. The improved knowledge implies that polyhalite is more likely to be an indicator for potassium-rich brines unsaturated with sylvine, rather than for large-scale soluble potassium salts (e.g., sylvine, carnallite, kainite and picromerite). References | Related Articles | Metrics

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Geochemical characteristics and distribution patterns of subsurface brines in the Qianjiang Depression, Jianghan Basin NIU Xinsheng, HUANG Hua, ZHENG Mianping 2021, 28(6): 56-65.  DOI: 10.13745/j.esf.sf.2021.1.42 Abstract ( 322 )   HTML ( 8 )   PDF (3404KB) ( 153 )   Subsurface brines of the Qianjiang Formation, Qianjiang Depression, Jianghan Basin are one type of strategic resource besides oil and gas for their economic values. However, chronic flooding in oilfield has certain influence to subsurface brines. In order to further assess this influence and investigate the distribution of trace elements in subsurface brines, brine samples from the 1st-4th brine beds were analyzed to study their geochemical characteristics and distribution patterns. The subsurface brines of the Qianjiang Formation are apparently affected by chronic flooding in oilfield. Although desalination occurred in general, subsurface brines still have high TDS contents, and the influence of desalination is limited. In the first to the fourth brine bed, arranged from top to bottom of brine reservoir, carbonate content and sodium sulfate subtype brine gradually decreased while chloride content gradually increased with increasing depth. Despite the influence of flooding on subsurface brines, the Li, B and Br contents in brines are still high, mostly reaching or exceeding the industrial grade threshold, with the grades highest in the second and third brine beds and decreasing from the fourth to the first. The nNa+/nCl- ratio of subsurface brines are close to 1, exhibiting the characteristics of lixiviation brine found in continental strata. The ρCl-/ρBr-ratio of brines revealed that the local subsurface brines are the mixing of lixiviation and sedimentary brines. The desulfurization coefficient and calcium/magnesium coefficient of brines revealed that the reservoir space sealing capacity is rather poor, and it improves from the first to the third brine bed, then worsen slightly in the fourth. Horizontally, Li, B and Br showed similar distribution characteristics. In the depression, the brine concentration centre showed obvious bottom-to-top migration characteristics. The area enclosed by Zhongshi, Haozikou, Wangchang and Zhouji Districts is the centre of high-concentration brines, whose distribution is obviously controlled by the distribution of brine reservoir. References | Related Articles | Metrics

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Characteristics of in situ elemental composition of rock salt from the Simao Basin: New metallogenic insights SHAO Chunjing, HU Huan, YIN Hongwei, MIAO Zhongying, ZHANG Xuefei, LI Weiqiang, XIA Zhiguang 2021, 28(6): 66-78.  DOI: 10.13745/j.esf.sf.2021.1.41 Abstract ( 205 )   HTML ( 5 )   PDF (5425KB) ( 103 )   The “two-storey” potash deposit model has led to significant progress in the exploration of Jurassic potassium resources in the Mengyejing area, Jiangcheng salt belt, Simao Basin. However, studies of other salt belts in the basin are lacking. In this paper, salt rock samples from the Lower Cretaceous Mengyejing Formation (K1m) in well L2 in the Mohei area, Zhengdong salt belt were analyzed through microscopic observation, scanning electron microscope and energy dispersive X-ray spectroscopic analysis (SEM-EDS), as well as in situ elemental analysis of rock salt by electron probe microanalysis (EPMA) to study their petrography, mineralogy and elemental content in detail. Meanwhile, the rock salt samples from the Middle Jurassic Huakaizuo Formation (J2h) in well MK-1 in the Mengyejing area, Jiangcheng salt belt were also studied. The K and Br trace elemental contents and 103Br/Cl (mass fraction) ratios in these samples were compared between the two wells in the context of geological evolution of the study area. In the K1m formation in well L2, there are two types of rock salt in the mud-gravel salt rocks. The main type is cement-like detrital halite particles with plastic rheological characteristics, the other is clastic halite precipitate wrapped in detritus of salt or clay minerals. The characteristics of both rock salt types indicate secondary origins. The EPMA results show that the maximum K contents were 0.09% in the main and 0.18% in the inclusion types of rock salt from the K1m formation in well L2 and 0.13% in the potassium-bearing rock salt in the J2h formation in well MK-1; while the Br contents were 60×10-6 at most, (70-410)×10-6 and (70-500)×10-6, respectively, and the 103Br/Cl (mass fraction) ratios were 0.10 at most, 0.12-0.71 and 0.12-0.85, respectively, in the three types of rock salt. The main type, with significantly lower mineral contents compared to the other two types, corresponds to terrestrial source, sea-continent mixed source or recrystallized halite. The other two types, similar in mineral contents, correspond mostly to marine halite, with minor potassium and carnallite crystallized from seawater. It is inferred that the detritus-wrapped halite is an evidence of salt diapir associated with ancient saline sediment. A metallogenic model is proposed on the basis of the above analyses as follows: After Middle Jurassic deep marine sediment migrated to the K1m formation via salt diapirism, one part—modified via leaching, melting and mixing by a combination of Middle Jurassic residual seawater migrated from the inner basin, continental source water flew from the basin margin and deep hydrothermal fluid—formed new brine, while the other part remained as ancient salt gravel. In the late Early Cretaceous during evaporation of the new brine, ancient salt gravel became enwrapped by newly crystallized salt and terrigenous clastic minerals. In the later period, cement-like halite deposit was formed via brine evaporation. This metallogenic model epitomizes the application of the “two-storey” metallogenic model in the Zhengdong salt belt. References | Related Articles | Metrics

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Metallogenic model for the coexistence of potassium-rich brine and natural gas in the same strata: An example from the Middle Triassic Leikoupo Formation in the Moxi Anticline, Central Sichuan Basin, Southwest China CHEN Xiao'er, ZHANG Bing, FAN Kun, YANG Kai, ZHANG Saimin 2021, 28(6): 79-94.  DOI: 10.13745/j.esf.sf.2021.1.43 Abstract ( 188 )   HTML ( 1 )   PDF (6438KB) ( 81 )   Various types of Middle Triassic potash developed in the Leikoupo Formation in the Sichuan Basin, a key target strata for potassium prospecting in China. Brine from the Leikoupo Formation in the Moxi gas field is rich in K, Li, Br and B and has been classified as high-quality industrial grade saline solution, with its contents of minerals including KCl, LiCl, Br- and B2O3 exceeding the grade standards. The brine deposit in Leikoupo Formation shows great prospects for potash exploration. The seismic data interpretation results show that the top-boundary of the Leikoupo Formation appears as a complete anticline with few faults. Potassium-rich brine occurs in the wings of the anticline, while natural gas occupies the upper part of the anticline, both are stored together in the shoal dolomite with dissolved pores in the first member of the Leikoupo Formation, constituting a combined resources of nature gas and potassium-rich brine. Analogous to the concept of petroleum systems, we summarized the key factors affecting the formation, accumulation and preservation of potassium-rich brine into six key elements, namely the source of potassium, reservoir, sealing and trap conditions, transportation, and storage conditions. According to the collocation of these elements in time and space, we performed dynamic analysis of the formations of gas and brine in the same strata of the Leikoupo Formation. Hydrocarbons and halides are unusual substances found in groundwater. Controlled by groundwater dynamics, brine in the Leikoupo Formation continues to move towards the inherited palaeo-uplift upper part—the Moxi Anticline. Under the combined effects of formation water migration and gas reservoir pressure, the initial potassium-rich formation water, formed by gypsum dehydration and ancient seawater evaporation, continuously captures the potassium ions released by the underlying ‘green bean rock’, producing a secondary K+ enrichment, and finally forms the gas-potassium combined resources in the Moxi Anticline. The long-term inherited paleo-uplift is a favorable site not only for hydrocarbon accumulation, but also for secondary migration and accumulation of potassium-rich brine. The result of this research represents a novel approach for “simultaneous exploration of gas and potassium” in the Sichuan Basin and other basins alike. References | Related Articles | Metrics

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Sedimentary evolution of deep marine potassium/lithium-rich brine reservoirs in the Sichuan Basin and a comprehensive response model for the brine storage layer YANG Hongyu, ZHANG Bing, FANG Chaohe, YANG Kai, CAO Qian, ZHANG Saimin, LIN Xiaoyang 2021, 28(6): 95-104.  DOI: 10.13745/j.esf.sf.2021.1.45 Abstract ( 268 )   HTML ( 12 )   PDF (5497KB) ( 131 )   With the increasing demand for potassium/lithium salt, the technology for shallow salt lake brine exploration and development is maturing and the deep brine resources have become the next exploration goal. In the Sichuan Basin, a wide, ultra-thick layer of Triassic evaporites has developed with abundance of high-quality potassium-rich brine reservoirs. In this paper, taking on the issue of ‘lacking saltiness’ in lithofacies paleogeography, we analyzed the distribution pattern of evaporites, the characteristics of lithofacies paleogeography, and the sedimentary evolution in the Sichuan Basin. We demonstrated the formation of a gypsum-salt basin is multi-stage and multi-zoned and determined the scale, distribution, and migration law of gypsum-salt basins in the key salt-forming period T1j4-T2l3 in the Triassic. In a parallel investigation based on the geological and logging data, we determined the geological and logging response characteristics of brine reservoirs in the Sichuan Basin. We consider the quality of potassium/lithium-rich brine reservoirs is controlled by horizon, facies belt and pore type as implied by the coupled logging response characteristics, such as medium-high gamma, low resistivity, high acoustic transit time, and low density. Results from this study can be used to guide deep marine strata explorations for potassium/lithium-rich brine reservoirs at home and abroad. References | Related Articles | Metrics

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Homogenization temperature of fluid inclusions in Early-Middle Pleistocene halite from Liang Hole ZK02 in Dalangtan area, Qaidam Basin and its constraints on potash mineralization FAN Fu, HOU Xianhua, ZHENG Mianping, MENG Fanwei, YANG Zhenjing, MIAO Qing 2021, 28(6): 105-114.  DOI: 10.13745/j.esf.sf.2021.1.44 Abstract ( 254 )   HTML ( 8 )   PDF (2963KB) ( 205 )   Using the cryogenic nucleation method we obtained 158 homogenization temperature measurements of fluid inclusions (pure liquid) in Early to Middle Pleistocene rock salt samples from Liang Hole ZK02 in Dalangtan area, Qaidam Basin. Micromorphological examination revealed inverted cubic fluid inclusions in chevron salt crystals, and no significant correlation was observed between the measured homogenization temperature and inclusion size. The results indicated the samples under investigation contained primary rock salt and fluid inclusions, and the maximum homogenization temperature can represent ancient summer temperatures. Subsequent testing suggested the maximum homogenization temperature in the Early Pleistocene ranged between 25-30 ℃, while high mud and sand contents in the salt rock implied the climate was mild with abundant fresh water injection in the early stage. In the late stage the salt content increased, reflecting intense drought; and at times when summer temperatures were higher than 40 ℃, high temperature and drought were evident. In the Middle Pleistocene, the temperature ranged largely between 30-35 ℃, and the highest temperature reached 50.6 ℃. Together, the range of maximum homogenization temperature and high salinity are indicative of high temperature and drought. Compared to the Early Pleistocene, the Middle Pleistocene saw increasing ambient temperature, salt content and drought severity, with aggravated temperature fluctuation, indicating a more unstable climate consistent with the general climate characteristics of the Middle Pleistocene worldwide. The salt distribution showed the climate instability in the Dalangtan area began to appear since the late Early Pleistocene. The metallogenic model of potassium-bearing brine from the pore of sandstone conglomerate in the Altun Mountain can be revised using the paleotemperature of fluid inclusions obtained from this study: In the mild, humid environment of the Early Pleistocene, weathered salt and N22 ancient salt were dissolved and filtered together to form brine in the sandstone pores, and high temperature evaporation in the Middle Pleistocene eventually led to the formation of brine deposit of the KCl sandstone conglomerate pore reservoir. References | Related Articles | Metrics

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Paleotemperature during the Mid-Pleistocene Transition in western Qaidam Basin: Evidence from fluid inclusions in halite from drill hole SG-1 NI Yanhua, LI Minghui, FANG Xiaomin, MENG Fanwei, YAN Maodu, LIU Yingxin 2021, 28(6): 115-124.  DOI: 10.13745/j.esf.sf.2021.1.39 Abstract ( 296 )   HTML ( 15 )   PDF (2248KB) ( 98 )   The Mid-Pleistocene Transition (MPT) is a global cold event and also recorded in the Qaidam Basin, but the paleotemperature data is rather lacking. Halite is generally formed in shallow water environment, and the homogenization temperature (Th) of primary fluid inclusions in halite can directly reflect the brine temperature at halite crystallization and can be used to reconstruct paleotemperature of brine. This study selected primary halite samples from the 1.22-0.88 Ma section of drill hole SG-1 in the western Qaidam Basin and collected data on 390 fluid inclusions. The maximum and minimum homogenization temperatures were 50 ℃ and 6.8 ℃, respectively, with temperature fluctuations mostly (>90%) within 10 ℃; there is no obvious linear correlation between the size of fluid inclusions in halite and the homogenization temperature. This result indicates that fluid inclusions in halite from hole SG-1 have not been modified by the later hydrothermal solution and the Th data can directly relate to paleotemperature at halite deposition. The reconstructed paleotemperature in this study may be the brine temperature in warm season as halite generally deposits in warm season, while the maximum value of Th may be affected by hydrothermal solution and climate. During the MPT period, the homogenization temperature of palaeo-water (mean value, Th,med) is similar to the average temperature in present-day July in the Qaidam Basin or the surface water temperature in the Mediterranean Sea during the same period, but it is much higher than the annual temperature in the Qaidam Basin or the global average temperature during MPT. The average homogenization temperature (Th,avg) is higher than all the above temperatures. The coldest climate in the Qaidam Basin during MPT occurred at ~1.165-1.0 Ma. References | Related Articles | Metrics

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Seismic identification and attribute prediction of polyhalite in the 4th and 5th members of the Jialingjiang Formation in Northeast Sichuan REN Ruijun, MIAO Yongkang, WANG Yanguang 2021, 28(6): 125-133.  DOI: 10.13745/j.esf.sf.2021.1.46 Abstract ( 214 )   HTML ( 4 )   PDF (5825KB) ( 187 )   Polyhalite, an important source of potassic mineral, is widely distributed in the 4th and 5th members of Lower Triassic Jialingjiang Formation (T1j4-5) in Northeast Sichuan. But T1j4-5 is deeply buried and the lateral distribution of polyhalite is unstable. Therefore, it is necessary to use seismic technology to predict the distribution of polyhalite. However, the polyhalite is mixed in the interbedded strata of low-velocity salt-gypsum and high-velocity gypsodolomite rocks, and the single layer is generally thin with weak response in seismic section, hindering seismic identification. In this paper, well-seismic tie comparison and seismic forward modeling were used to analyze the seismic response characteristics of polyhalite. We observed that polyhalite generally lies in the upper part of thick salt-gypsum layer due to particularities in its formation mechanism; as a result, its seismic response spectrum featured high-frequency and low-amplitude wave on the background of low-frequency, high-amplitude wave trough. More specifically, polyhalite corresponds to low-frequency, high-amplitude wave trough in low-frequency seismic section, and to high-frequency, low-amplitude crest in high-frequency seismic section. On the basis of this differential seismic response of polyhalite and further analysis of the limitations and constraints of traditional layer attributes in polyhalite prediction, we proposed a new method to predict the distribution of polyhalite through volume attribute computation and obtained a better prediction result. It showed that polyhalite is mainly developed in the upper part of the second cyclic gypsum-salt layer of T1j4-5 in the longitudinal direction; on the plane and mainly in areas thickened by plastic deformation, polyhalite is enriched in banded distribution. Our study provided a reference for seismic identification and prediction of polyhalite elsewhere. References | Related Articles | Metrics

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Seismic response characteristics of the Heibei Concave-Dalangtan potassium-rich deep brine reservoir in western Qaidam Basin HOU Xianhua, WANG Wei, ZHENG Mianping, FAN Fu, LI Hongpu, GAO Xuefeng 2021, 28(6): 134-145.  DOI: 10.13745/j.esf.sf.2021.1.49 Abstract ( 376 )   HTML ( 12 )   PDF (9286KB) ( 131 )   The deep brine type potash in western Qaidam Basin is a newly discovered sodium chloride subtype potash deposit with gravel layers as the storage media. In particular, a great deal of in-depth research has been done in the Heibei Concave (or Heibei'aodi)-Dalangtan secondary salt lake depression, where ~350 million tons of KCl resource of this subtype has been obtained. By dissecting this type of ore-forming system one can provide reference for the exploration of potash deposits in the area. The Heibei'aodi-Dalangtan area is the main distribution area of brine reservoir, a piedmont proluvial fan type pore brine reservoir in northeastern Qaidam Basin. In this study, we collected drill, logging and seismic-prospecting data according to the actual production needs. Through seismic reflection profile interpretation and attribute analysis, as well as drill data comparison revealing the reservoir lithology characteristics and distribution, we obtained the seismic response characteristics of the medium-deep pore brine reservoir in the study area. High amplitude in-phase reflections appeared at the bottom of the reservoir, with good local continuity; medium to high amplitude in-phase reflections were observed at top of the reservoir; at the lumpy middle part low amplitude reflections were recorded. The instantaneous frequencies were mainly medium to low frequencies. Larger “sweet spots” were observed at the bottom and top of the reservoir compared to the middle part with a low sweetness value. The envelope attribute was characterized by abnormal high peak values at the top and bottom and low peak values at the middle part of the reservoir. Through seismic profile and borehole data analyses, geophysical indicators for potash deposits were established, which provided a basis for predicting the distribution range of medium-deep reservoir and optimizing hydrogeological survey for borehole drilling. References | Related Articles | Metrics

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Key technology application in high resolution seismic data processing for deep potash deposits: An example from Lop Nur WANG Wei, HOU Xianhua, ZHENG Mianping, GAO Xing, FAN Fu, LIU Qing 2021, 28(6): 146-154.  DOI: 10.13745/j.esf.sf.2021.1.50 Abstract ( 288 )   HTML ( 4 )   PDF (6105KB) ( 183 )   Lop Nur is an important potash exploration area in China. However, the loose ground surface in the area causes low seismic excitation/reception and strong noise interference, resulting in poor-quality seismic data with low signal-to-noise ratio. To solve this problem we used two crossed seismic lines passing through well LDK01. Noise reduction technology using frequency and time dividers was adopted first to effectively suppress outlier low-frequency noise, then the cone-shaped FK filter was used to suppress the strong surface wave interference. Next, space variant surface-consistent deconvolution using varying time intervals was performed to narrow the energy difference in the received near surface excitation signals. Finally, wavelet deconvolution developed by Yu et al. was used to improve the vertical resolution. By using a combination of different high-resolution noise reduction technologies, the dynamic characteristics such as amplitude, frequency, phase and waveform were relatively maintained during data processing, and the quality of profile imaging was improved. Referencing to the geological data from well LUOXI 1, six sets of interfaces—Jurassic, Cretaceous, Paleogene, upper Paleogene, Neogene and upper Neogene bottom boundaries—have been clearly identified, which provides a basis for further improving the Lop Nur deep reservoir formation theory. References | Related Articles | Metrics

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Identification of Triassic polyhalite in Northeast Sichuan by AI-based seismic inversion SHEN Guoqiang, WANG Yumei, ZHANG Fanchang, ZHANG Hong, WANG Xiping, CHEN Songli 2021, 28(6): 155-161.  DOI: 10.13745/j.esf.sf.2021.1.51 Abstract ( 177 )   HTML ( 5 )   PDF (2463KB) ( 71 )   As one of the main sources of potash fertilizer, polyhalite resource is in huge demand. Polyhalite deposits are well developed in the Triassic marine beds of Northeast Sichuan. However, these polyhalite deposits are very difficult to identify since they are deeply buried and scattered. To cut down the cost, seismic data are extremely useful in identifying well locations in pre-drilling exploration. Considering the complex relation between polyhalite deposits and seismic reflection in this area, it is impossible to directly predict potassium-rich salt layers solely by traditional impedance inversion method, herein an artificial intelligence (AI) approach is introduced. First, sensitive attributes suitable for characterizing potassium-rich layers are extracted using a fuzzy rough optimization algorithm. Then, on the basis of nonlinear mapping of the extracted sensitive seismic attributes onto the potassium-content well log, a polyhalite layer prediction method is established by using extreme learning machine. Using this method the polyhalite distribution in Northeast Sichuan was successfully identified. The AI-based seismic inversion methodology provides an alternative approach for the exploration of polyhalite layers in this area. References | Related Articles | Metrics

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Logging response characteristics and distribution of potash salt in Aryskum Depression, South Turgay Basin WANG Binwei, Aini MAIMAITI, LU Zhiming, MA Chongyao, CHEN Kegui 2021, 28(6): 162-170.  DOI: 10.13745/j.esf.sf.2021.1.52 Abstract ( 320 )   HTML ( 6 )   PDF (3143KB) ( 87 )   As a strategic resource, potash salt has an important value in agriculture, industry, and other areas of national interests. Most of the solid potassium resources of the world were discovered in the process of large-scale petroleum exploration. It is particularly important to make full use of various types of petroleum geological and geophysical data in carrying out potash salt exploration. The South Turgay Basin in Kazakhstan has simple geological structure as well as great potential for resource exploration, and we chose the Aryskum Depression of the basin as the study area. Taking into account the sedimentary geological characteristics of the depression, combining with conventional logging data and results obtained in the study area by previous researchers, we performed comprehensive analysis of logging response by examining the abnormal changes in response curves, including natural electric potential curve, natural gamma ray curve, neutron curve, and resistivity curve. The potassium layers have abnormally high GR intensity while the effects of uranium and thorium were eliminated using “uranium free gamma ray” curve. Influenced by drilling fluid, dissolved potash salt causes drill hole to enlarge, which resulted in higher neutron level, slightly higher resistivity, and change of natural electric potential anomaly from negative to positive in sandstone layer. The density value was between 2.25-2.45 g/cm3, and the acoustic value ranged between 270-350 μs/m. These characteristics were used in the comprehensive logging curve analysis, logging curve superposition, and cross-plot analysis to identify potash salts in the study area. Soluble potassium were found in more than 30 wells. They are mainly distributed at depths of 1020.36-1055.85 m. The potassium layers were stable at the bottom of sublayers M-Ⅱ-2 and M-Ⅱ-3, mainly in M-Ⅱ-3. Measurements of the overall thickness of potassium-bearing layers of each well show that the overall thickness does not change significantly over the mostly thin stratum, from 0.76 m to 2.16 m, averaging at 1.23 m. Finally, by analyzing the distribution of potassium layers in the transverse and longitudinal directions by stratigraphic correlation analysis, we obtained the isopach map, which allowed us to delineate the favorable areas for finding potash salt. Thus, we expand the application of logging data to potassium prospecting in the Aryskum Depression and provide future directions for potash exploration. One of the target areas is likely in the northwestern part of the depression. It has good potassium formation, relatively thick potassium salt deposit, favorable evaporation environment, and strong salt formation, making it a potential area for potassium exploration. References | Related Articles | Metrics

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Potassium extraction from potassium-rich brine in Puguang region, northeastern Sichuan, China BIAN Shaoju, LIU Xin, LI Dongdong, DONG Yaping, LI Wu 2021, 28(6): 171-178.  DOI: 10.13745/j.esf.sf.2021.1.54 Abstract ( 218 )   HTML ( 4 )   PDF (1462KB) ( 104 )   The underground brine resources in northeastern Sichuan are abundant, especially in the Puguang region where underground brines are rich in high-quality potassium resource. In this work, computational simulation and experimental verification were carried out to investigate the crystallization stages and features of NaCl, KCl, KCl·MgCl2·6H2O, and H3BO3 under high temperature evaporation. The results showed that ~85% of NaCl crystallized when the rate of water loss was about 80% and KCl saturation was reached; under continuing evaporation, sylvite was produced. As the rate of water loss reached 94%-95%, almost 80% of potassium (KCl) precipitated and the KCl concentration in the precipitant could be as high as ~45% (mass fraction). Subsequently, as the resulting brine cooled down to room temperature, NaCl, KCl, KCl·MgCl2·6H2O, and H3BO3 co-crystallized, including ~80% of boron. Notably, after 80% of water evaporated and most of NaCl precipitated, directly cooling of brine could yield sylvite of grade up to 70%, with 50% of KCl crystallized. Finally, two potassium extraction processes were suggested, one focuses on the production of KCl and H3BO3, the other on high-quality KCl. References | Related Articles | Metrics

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Density prediction for the Na-K-Ca-Mg-Cl-H2O system using the Pitzer model LU Miao, LI Dongdong, LI Wu, DONG Yaping, HU Bin 2021, 28(6): 179-186.  DOI: 10.13745/j.esf.sf.2021.1.55 Abstract ( 222 )   HTML ( 4 )   PDF (957KB) ( 74 )   PVTx properties of natural water are widely used in geochemistry and salt lake industry. By establishing the correlation between density, composition, temperature and pressure of potassium-rich brine, one can better understand the enrichment and migration of potassium in complex brine systems. In order to construct a prediction model for brine density based on the Pitzer model, densities of KCl and CaCl2 aqueous solutions and their mixtures were measured by vibrating-tube densitometry. The concentrations of single solute solutions were near saturation, and ionic strengths of aqueous mixtures were from 1.8 to 11.8 mol·kg-1. The Pitzer single electrolyte parameters and Pitzer mixing parameters at various temperatures between 283-323 K were obtained by Pitzer ion interaction model fitting using the measured densities, and the Pitzer volumetric parameters were obtained by fitting the volumetric Pitzer model to the experimental data. Densities of the Na-K-Ca-Mg-Cl-H2O hexary system over the temperature range of 293-313 K were calculated. The calculated density was in good agreement with the experimental results, with the relative error within 0.25%. The results show that ionic interactions had a significant effect on the density of the hexary system. The Pitzer parameters obtained in this paper reflect the interactions between these ions and can be used to make density predictions for complex brines containing K, Ca and Cl ions. References | Related Articles | Metrics

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Spectral and photodegradation properties of dissolved organic matter in brines YANG Keli, DONG Yaping, LI Wu, PENG Jiaoyu, LIU Haining 2021, 28(6): 187-195.  DOI: 10.13745/j.esf.sf.2021.1.56 Abstract ( 367 )   HTML ( 2 )   PDF (1943KB) ( 60 )   Dissolved organic matter (DOM) in brines has adverse effects on solar pond performance and evaporite product quality, such as slowing down evaporation rate, reducing evaporation level, and causing pungent smell and heavy coloration in evaporate products. Therefore, characterization of DOM in brines in terms of utilization values is essential to guide DOM removal and new technologies development for better mineral extraction. Here, DOM from salt lake (SLDOM) and oilfield (OFDOM) were size-fractionated into high (MW>1 kDa) and low (MW≤1 kDa) molecular weight fractions and analyzed through dissolved organic carbon (DOC) analysis, absorption spectroscopy, fluorescence parallel factor (PARAFAC) analysis to determine their spectral and photodegradation properties. DOC analysis and fluorescence indexes indicated that SLDOM and OFSDOM had comparable organic carbon contents and BIX (biological index), and they both had higher FIX (fermentation index) than DOM from natural water. Compared to OFDOM, SLDOM had higher HIX and HMW DOM. SUVA254 and carbohydrates measurements revealed that aromatic compounds and carbohydrates were mainly in the HMW fraction regardless of sample types. Fluorescence spectra showed that SLDOM mainly consisted of humic-substance, while OFDOM mainly protein-like substances. As for MW fractionation, for SLDDOM, fulvic acids were mainly in HMW DOM while humic acids in LMW DOM; for OFDOM, aromatic amino acids were abundant in HMW DOM. Photodegradation experiment indicated that DOC content in SLDOM and OFDOM decreased by 29.32% and 15.11%, respectively, with increasing light radiation. Further analysis showed that decreasing carbohydrate content and preferential degradation of LMW DOM occurred for both sample types. Moreover, during light irradiation, aromatic content increased and humification status remained stable in SLDOM, whereas in OFDOM aromatics decreased and humification increased. PARAFAC analysis showed that fluorescence intensities of PARAFAC components were enhanced for SLDOM, but reduced for OFDOM. References | Related Articles | Metrics

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The key question of the Aral Sea evolution important for understanding its economic, social and ecological values S.K.KRIVONOGOV, T.I.KENSHINBAY, R.Kh.KURMANBAEV, B.S.KARIMOVA 2021, 28(6): 196-204.  DOI: 10.13745/j.esf.sf.2021.9.36 Abstract ( 333 )   HTML ( 13 )   PDF (831KB) ( 103 )   The paper reviews the up-to-date knowledge on the changes of the Aral Sea level to make it useful for decision makers in social and economic projects. We propose a new vision of the ecological standard for the Aral Sea: small to medium size lake instead of huge one as it was before 1960, when modern human-induced shrinking started. Change of the vision may turn many expensive initiatives based on extreme scenarios to be more realistic. The conclusion is based on the multiproxy data obtained from geological, archaeological, historiographical and hydrological studies. These results gave a quite reliable scheme of the changes during about 20 thousand-year history of the Aral, which experienced multiple abrupt transgressions and regressions. However, understanding of the reasons for these changes, except for the modern one, is still not complete and requires special investigation. In this paper, we discuss approaches for correlating the water level changes with climate change and variations of the Aral Basin water supply from its feeding—the Syr Darya and Amu Darya rivers. References | Related Articles | Metrics

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Subduction reversal in the accretion complex drives the exhumation of deep subducted mélange in southern Qiangtang, Tibet: Insights from the Mao'ershan detachment fault LI Dian, WANG Genhou, LIU Zhengyong, LI Pengsheng, FENG Yipeng, TANG Yu, LI Chao, LI Yang 2021, 28(6): 205-226.  DOI: 10.13745/j.esf.sf.2021.11.12 Abstract ( 277 )   HTML ( 10 )   PDF (12737KB) ( 155 )   The subduction and accretion of oceanic lithosphere may be accompanied by a complex slab motion in depth, and HP rocks are certainly a good proxy to reflect this deep process. Recent studies show that subduction reversal can occur, in particular, in a divergent double subduction zone when a slab pull of one slab exceeds that of a shorter slab, the shorter slab then experiences a net upward pull. This study prompted us to pay attention to this ‘abnormal’ plate movement during oceanic subduction and accretion in objective and comprehensive analysis of collisional orogen belt. Most of the current mechanisms of the exhumation of HP rocks emphasize a single rapid exhumation process, except the ‘corner flow’ model. It can be expected that the exhumation process should be different in the case of subduction reversal. Exhumation of a single HP rock is still a rapid process; but exhumation of an entire HP rock belt must occur during the entire subduction reversal period, so the exhumation process lasts longer. Research on the exhumation related upper crustal structural deformation has the potential to unveil the above process.|||This subduction reversal hypothesis is first proposed for Triassic HP rocks exposed in the southern Qiangtang mélange belt in central Tibet. Therefore, we chose to study the Mao'ershan accretionary complex located in the northernmost part of the Qiangtang mélange belt. We analyzed its crustal structural characteristics, geometric structure, movement style and active period related to subduction reversal, based on geological mapping and structural and chronological studies. The field geological mapping results show that the Mao'ershan complex has similar characteristics as the metamorphic core complex. Subduction-accretion complex forms its core that is surrounded by Late Paleozoic strata from the top, with a detachment fault system separating the two. Beneath the brittle detachment fault, a shear zone develops southward from the top of the subduction-accretion complex. Three-dimensional strain and kinematic vorticity results indicate that the strain type in the Mao'ershan shear zone is elongate strain, dominated by simple shear strain. Mineral deformation analysis and fractal dimension measurements show that the shear temperature is associated with low greenschist and lower amphibolite facies. Based on the new 40Ar-39Ar geochronology data, we conclude that the Mao'ershan shear zone was active at ~260 Ma. Based on the above study and combined with the geological features of the central Qiangtang mélange belt, we believe that the Mao'ershan complex was exhumed during the early stage of the subduction reversal. We thus infer that the movement rate of subduction reversal is about 3.5 mm/a, which is similar to the exhumation rate of HP rocks in central Qiangtang mélange belt. Our research may provide a new perspective on the exhumation mechanism for other HP rocks around the world. References | Related Articles | Metrics

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Application of distributed acoustic sensing in structural investigation of Lake Yigong in Tibet ZHANG Heng, XU Tuanwei, PEI Shunping, ZHAO Junmeng 2021, 28(6): 227-234.  DOI: 10.13745/j.esf.sf.2021.11.10 Abstract ( 199 )   HTML ( 5 )   PDF (3160KB) ( 103 )   Seismic data are essential for seismological detection of underground structures. However, it is difficult to obtain long-term, high-density continuous seismic data using traditional instruments in extreme environments such as underwater or a plateau. Compared with instrument manufacturers abroad, the development of DAS in China is relatively late. Since 2016, domestic DAS has been gradually applied to petroleum logging and underground structure detection in urban areas. However, there is much less DAS application in extremely harsh environments. After years of collaboration among the Institute of Semiconductors, Chinese Academy of Sciences (CAS) and Institute of Tibetan Plateau Research, scientists from CAS deployed the self-developed DAS in April 2021 for collecting field data in the Tibetan Plateau. During testing, an armored optical cable (deployed both in the water and above ground) was used to record continuous ambient noise data and active source signals. In this study, the ambient noise tomography was applied to DAS data, and a near-surface (less than 70 m deep) S-wave velocity structure along a two-dimensional survey line was obtained in the Yigong Lake in southeastern Tibetan Plateau. This study provided both theoretical and experimental evidence for high-density data collection and underground structure detection in harsh environments. References | Related Articles | Metrics

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Basement structure of the Junggar Basin Xiaojun WANG, Yong SONG, Baoli BIAN, Junmeng ZHAO, Heng ZHANG, Maodu YAN, Shunping PEI, Qiang XU, Shuaijun WANG, Hongbing LIU, Changhui JU 2021, 28(6): 235-255.  DOI: 10.13745/j.esf.sf.2021.11.13 Abstract ( 493 )   HTML ( 17 )   PDF (3904KB) ( 339 )   Five comprehensive geophysical profiles, I-I, II-II, III-III, IV-IV and Emin-Hami, have been completed across the Junggar Basin and surrounding areas. A preliminary understanding of the geodynamic problems in the greater Junggar Basin is achieved through comprehensive research. The basement of the Junggar Basin is composed of the Wulungu Terrane in the north and the Manas Terrane in the south. The boundary between the two is the Dishuiquan-Sangequan suture in the NWW direction. It is connected to the NE-trending Dalbutte suture in the west and the NW-trending Cranamary suture zone in the east. The basement of the Wulungu Terrane in the northern Junggar Basin has a double-layered structure, where the upper layer is a folded basement composed of Devonian and Lower Carboniferous rocks, generally thick (3-5 km) in the north and thin (1-2 km) in the south. The Manasi Terrane south of the suture line has a single layer basement, namely the crystallization basement of the middle to upper Proterozoic. The crust in the Junggar Basin, 44-52 km thick, is thin in the north and thick in the south, while the crust in the surrounding mountainous area is thicker compared to the basin area. The crust in the basin area is divided into upper, middle (generally thinner) and lower layers and contains several deep faults. Six major deep faults are in the north-south direction: Hongche, Delunshan, Shixi, Hutubi, Cainan and Fukang. These faults have large dips, extending upward to the lower part of the upper crust and cutting down through the basement interface of the crust. The horizontal structure and structural plane of the crust have no obvious vertical fault or seem to have the feature of “open fault”. These faults are good channels for the upper mantle material squeezing into the Earth's crust. In addition, there are two main transverse deep faults, one is the Dishuiquan-Sangequan deep fault with an NWW strike. It dips to the south and has the property of reverse fault, and it may break the Dishuiquan-Sangequan suture. The other is the near EW Changji-Manas deep fault dipping to the south. It is mainly developed in the middle and lower crust and resembles a reverse fault. These deep faults play a role in controlling the development of basin structure. The Moho interface in the western Junggar Basin extends to the deeper Moho interface in the Tianshan Mountains, while the Moho interface in the eastern part of the basin is not connected to but underneath the one in the Bogda Mountains, indicating crustal subduction. This observation helps to explain the tectonogeomorphologic phenomenon in the eastern part of the Tianshan Mountains, where the tectonic activity is relatively weakened but the Bogda Mountains are uplifted to the north. The surrounding Junggar Basin is characterized by a compression basin-mountain tectonic coupling pattern, especially the Bogda-Zhundong basin-mountain tectonic coupling in the eastern part of the southern margin. The Bogda Mountains, which now separate the Junggar Basin from the Tuha Basin, are a young and still rising mountain range. The uplift of the Bogda Mountain is a reflection of multiple nappe orogeny since the Indo-China Movement, and its present appearance is the result of neotectonic movement since the Neogene. In the Junggar Basin the cap rock developed in three stages: the Permian-Triassic foreland basin stage associated with the formations of the Tianshan and Songpan-Ganzi orogenic belts; the Jurassic-early Eocene intracontinental depression stage when the regional compression was weak; and the Neogene rejuvenated foreland-basin stage related to the uplift of Tianshan. References | Related Articles | Metrics

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Classification and characterization of China national territorial spaces WU Qiang, CUI Fangpeng, XIONG Chen, HUANG Yinzhou, SUN Chen 2021, 28(6): 256-262.  DOI: 10.13745/j.esf.sf.2021.7.7 Abstract ( 284 )   HTML ( 10 )   PDF (935KB) ( 196 )   Comprehensive classification of national territorial spaces is fundamental to territorial planning, development and protection. First, based on the types and present classification needs of territorial spaces, a set of base classifiers, including spatial dimension and property, space usage type, value of mineral resource and scales of underground mining space and other underground spaces, are proposed for the comprehensive classification system. Next, based on the proposed base classifiers, a comprehensive classification scheme is presented, which includes 29 types and 45 subtypes of territorial land and ocean spaces. Finally, the main characteristics of and development planning for the classified territorial spaces are illustrated. The comprehensive classification system provides an important basis for the subsequent territorial space planning, development, utilization and protection. References | Related Articles | Metrics

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Earth system science research on earthquake mechanisms: Theory and validation of a new model ZENG Zuoxun, CHEN Zhigeng, LU Chengdong, YANG Yu, CHEN Kangli, XIANG Shimin, DAI Qingqin, ZHANG Jun, DENG Yanting, FU Yan, DU Qiujiao, LIU Lilin, YANG Weiran 2021, 28(6): 263-282.  DOI: 10.13745/j.esf.sf.2021.9.5 Abstract ( 425 )   HTML ( 12 )   PDF (5449KB) ( 269 )   A combined model of seismic source cavity and latching fault for earthquake mechanism is proposed. Deep seismic source cavities are formed by the anomaly gravity flow and forced vibration of the high temperature, high pressure asthenosphere materials in the complex phase transition space of the temperature field. It is common that the mantle fluids, driven by temperature and pressure differences, are transferred from mantle to crust to form source cavities for shallow earthquakes. Due to the temperature rise, the continuous partial and/or full melting of the wallrocks cause the cavity to expand, increasing the pressure inside the cavity. When the effective pressure (i.e., the difference between the internal pressure and the pressure of overlying crust) inside the cavity reaches the failure strength of wall rock at the edge or top of the cavity where wall rock is connected to the relatively brittle active fault(s), the cavity comes to a crucial state. When the asthenosphere continues to supply energy to the cavity, or when the cavity is triggered by earth tide resulted from the alignment of the celestial bodies to the source region, cryptoexplosion occurs to release the energy accumulated in the cavity plus the strain energy accumulated from regional tectonic stress field acting on the latching active fault(s). In this model, the intracavity energy released from cryptoexplosion is positively correlated with the cavity size, while the released strain energy is related to the size and asperity of the fault(s) as well as to the intensity of the regional tectonic stress field. The junction between the source cavity and the relatively brittle active fault(s) is a potential hypocenter of the impending earthquake. Source cavities generally develop in 1 to 13 days, averaging 7 days, from entering the crucial state to cryptoexplosion. After long-term observations we theorize that the abnormal phenomena, such as drought, temperature rise, sea surface temperature rise and water vapor release, often occur in the potential earthquake area before the earthquake. Direct evidence for the seismic source cavity cryptoexplosion are also introduced.|||Based on long-term observations and the seismic source cavity model, we give full affirmation to seismic clouds which have long been denied by seismological and meteorological circles. We consider that the gravitational wave generated by the cavity oscillation in the air, and the magnetic field induced by the eddy flow of fluid in the cavity acting on water vapor, are the physical mechanism of the formation of seismic clouds. Here we show the satellite images of releasing aqueous vapour prior to the M 7.0 Haiti earthquake on January 13, 2010, the M 8.2 Gorkha (Nepal) earthquake on April 25, 2015, and the M 7.0 Jiuzhaigou earthquake on August 8, 2017. By use of seismic tomography technique, the shape and size of the seismic source cavity for the M 8.0 Wenchuan giant earthquake (May 12, 2008) were determined. We found that the hypocenter of the Wenchuan earthquake lies at the junction between the top of the source cavity and the Longmenshan brittle active faults. We performed statistical analysis on the gravity disturbance data of the Jiuzhaigou earthquake area and its vicinity, collected during the 12 years since January 1, 2002, and on the catalogue of the area's earthquakes equal or above M 3.0. The results show that the equivalent elevation amplitude change attributable to gravity anomaly was 3.9 cm before the M 6 earthquake, and the magnitude of earthquake was proportional to the magnitude of elevation oscillation by statistical comparison. Based on the tectonic stress field obtained from 108 fault plane solutions for the Bohai Bay and its periphery, we found that there are abnormal stress fields above and to the northeast side of the source cavities in both the Tangshan and Haicheng earthquakes. This points to the effect of high pressure in the source cavity on regional tectonic stress field.|||By using the abnormal sea surface temperature, ZENG Zuoxun successfully predicted the epicenter location of the M 6.7 earthquake on May 1, 2021 off the coast of Honshu Island, Japan. Using drought and temperature anomalies, he correctly predicted two days in advance the epicenter location of the M 4.8 Chuxiong earthquake on June 24, 2021 in Yunnan Province.|||Based on the frequency characteristics of the geoelectric field generated by the eddy flow of ions in the crucial state of the cavity, we developed a DD108 geoelectric instrument. With the single station observation we can predict (within 1-13 days after the occurrence of the anomaly, averaging 7 days) the occurring time and the magnitude of a coming earthquake. Some examples are shown in the paper, including the M 7.0 Jiuzhaigou earthquake in 2017, and the M 7.4 Qinghai Maduo and M 7.1 Mexico earthquakes in 2021. 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Multi-index monitoring and comprehensive early warning of landslides in response to rainfall: An example of the Luo'ao landslide in southern Jiangxi Province LI Gao, TAN Jianmin, WANG Shimei, LIN Xu, CHEN Yong, WANG Li, GUO Fei 2021, 28(6): 283-294.  DOI: 10.13745/j.esf.sf.2021.7.17 Abstract ( 382 )   HTML ( 10 )   PDF (3304KB) ( 133 )   Rainfall and displacement are currently the two most commonly used indicators for rain-induced landslide monitoring and warning. However, the rainfall and displacement measurements can only reflect the effect of rainfall on landslide deformation, but they cannot reveal historic landslides in response to rainfall as determined by the inherent physical and mechanical properties of these slides. Therefore, in addition to rainfall and displacement monitoring, one can establish a monitoring system that includes indicators such as water content and matric suction to monitor the dynamic evolution of historical landslides. Such a monitoring system will certainly become the most effective means to grasp the inherent trends in landslide evolution and to develop more accurate criteria for comprehensive early warning of landslides. In this paper, we conducted a demonstrative study on the multi-indicator monitoring and comprehensive early warning for a typical rainfall-type landslide, the Luo'ao landslide in southern Jiangxi Province. The results are: (1) Multiple indicators such as the moisture level, matric suction and temperature in the surface soil produced regular dynamic response to rainfall. (2) With the continuation of rainfall, the volumetric water content and matric suction strength changed after a significant delay since the onset of rainfall. (3) The rate of changes of both volumetric water content and matric suction strength showed significant positive correlation with slip displacement. (4) The soil temperature distribution pattern was influenced by both atmospheric temperature and volumetric water content. Based on the analysis of the measured landslide slope stability, a multi-indicator early warning method was established on the basis of correlating actual rainfall infiltration depth and landslide slope stability. The key indicators are daily rainfall, rate of volumetric water content increase, rate of matric suction strength decrease and displacement velocity. Furthermore, a comprehensive early warning system with defined warning thresholds for key indicators is proposed, aiming to provide a new model for accurate early warning of rainfall-induced landslides. References | Related Articles | Metrics

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Ca. 1.90-1.80 Ga continent-continent collision in southeastern North China Craton: Evidence from the granite-greenstone belt in the Jiaobei Terrane SHI Kangxing, WANG Changming, DU Bin, CHEN Qi, ZHU Jiaxuan, RAO Shicheng, DUAN Hongyu 2021, 28(6): 295-317.  DOI: 10.13745/j.esf.sf.2021.1.59 Abstract ( 188 )   HTML ( 7 )   PDF (7105KB) ( 199 )   The Jiaobei Terrane is located in the southeastern part of the North China Craton (NCC), and its Archean-Paleoproterozoic lithological assemblage, including amphibolite, TTG gneiss, granodiorite, schist and supracrustal rocks, suggests a typical granite-greenstone succession. This succession offers a significant insight into the history of Precambrian tectonic evolution of the NCC and the collision-amalgamation process of microcontinents. Here we investigated a suite of amphibolite, TTG gneiss and granodiorite from the Jiaobei Terrane to understand their genesis. Detailed LA-ICP-MS U-Pd dating of zircons from the magmatic grains yielded ages of 1881±18 Ma for amphibolite, 1852±16 Ma for TTG gneiss and 1840±9 Ma for granodiorite. The inherited ages of 2332±32 Ma, 2244±25 Ma, 1935±21 Ma and the metamorphic age of 1796±17 Ma were also recorded for these zircons. The zircon Lu-Hf isotope show the εHf(t) values ranging from -4.7 to 3.9 and the crustal model ages (TDMc) in a range of 2784-2289 Ma. The results suggest that the formation of the Paleoproterozoic granite-greenstone succession in the Jiaobei Terrane is partly contaminated by the continental crust. The geochemical features of amphibolite are similar to within-plate basalt, with low SiO2, high FeOT, weak differentiation between light (LREE) and heavy REEs (HREE) and absence of obvious Ce and Eu anomalies, negative Nb and Ta anomalies and positive Rb, Pb and K anomalies. The TTG gneiss and granodiorite show enrichment of LREE and absence of obvious Ce anomaly, negative Nb, Ta, Ti and P anomalies and positive Rb, Pb, Zr and Hf anomalies. They display transitional features from post-collisional granite to within-plate granite. The parent magma of the Paleoproterozoic granite-greenstone succession in the Jiaobei Terrane is generated from the partial melts of basalts. Based on the previous studies, this paper supplements geochronological, isotopic and geochemical data of the related rocks, and proposes a ca. 1.90-1.80 Ga continent-continent collision process in the Jiaobei Terrane. Our results are consistent with the continent-continent collision model of the NCC, and they provide further insights into the Paleoproterozoic tectonic history of the Craton. References | Related Articles | Metrics

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Characteristics of S, C, O and Sr isotopes and genesis of the Luiswishi Cu-Co deposit in Katanga, Democratic Republic of Gongo WANG Wuming, SHENG Tao, WANG Lijuan, DONG Shaobo 2021, 28(6): 318-330.  DOI: 10.13745/j.esf.sf.2021.7.21 Abstract ( 314 )   HTML ( 5 )   PDF (4074KB) ( 158 )   The Luiswishi deposit is one of the stratiform-hosted Cu-Co deposits in Katanga (DRC), the northern part of the Central African Copperbelt and in the peripheral of the Lufilian Orogenic Belt. The ore types in the Luswishi mine are classified as oxidized ore in oxidization zone and sulfide ore in depth based on the field survey and literature review. The mineralization stage consists of early diagentic, syn-orogenic and oxidation periods. Chalcopyrite, bornite, carrollite and chalcocite are the main Cu-Co sulfides; while malachite, chrysocolla and heterogenite are the most valuable oxidized ore. The isotope features of sulfides indicate that bacterial and thermochemical sulfate reductions mainly occurred during the diagenetic and syn-orogenic periods, respectively. From the analysis of isotopic characteristics it can be concluded that the main source of diagenetic mineralization might be leached from basement and the resulting minerals remobilized to provide source in the syn-orogenic period. Carbonate and organic matter in the Roan Group provided favorable conditions for the Cu2+ reduction in oxidized solution and precipitation in the carbonate strata. The supergene mineralization enriched the Luiswishi copper-cobalt deposit. References | Related Articles | Metrics

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Distribution characteristics of cobalt-rich ferromanganese crust on the Weijia Guyot: Constraints from the human-occupied vehicle “Jiaolong submersible” near-bottom observation data YAO Huiqiang, LIU Yonggang, ZHANG Huodai, LIANG Donghong, REN Jiangbo, YU Miao, DENG Xiguang, HE Gaowen 2021, 28(6): 331-342.  DOI: 10.13745/j.esf.sf.2021.1.61 Abstract ( 183 )   HTML ( 6 )   PDF (3487KB) ( 79 )   In this paper we analyzed the near-bottom observation video data obtained from the human-occupied vehicle “Jiaolong submersible” that has the high-precision underwater positioning capability. We report for the first time the distribution characteristics of cobalt-rich ferromanganese crusts (CFC) in the raised areas of the mountaintop platform, the transition zone from the mountaintop platform to the summit of the mountainous terrane, and the upper part of the mountain slope in the Weijia Guyot. These findings have great significance in the exploration and exploitation of CFC resources in China and are summarized below. (1) There is obvious difference in the distribution characteristics of CFCs in different topographic units. (2) The raised areas of the mountaintop platform have an continuous CFC distribution and can be used as the key exploration target area. (3) CFCs also distribute widely in the transition zone and in the upper part of the mountain slope, but are often fragmented by corrugated white sediments. (4) Cobalt nodules are less developed in the transition zone, in contrast to the flat top seamounts in the Marcus-Wake Seamounts. References | Related Articles | Metrics