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Using LA-ICP-MS technique,the U-Pb isotope determination of zircons in the Emeishan basalts in Tangdian, of eastern Yunnan on the western margin of the Yangtze Plate is carried out. The distribution range of 363 age data is (14.9±0.6)-(3,023±50) Ma, spanning a long geological age, its 11 age peaks are 750~850 Ma, ~450 Ma, ~275 Ma, ~260 Ma, ~247 Ma, ~215 Ma, ~160 Ma, ~120 Ma, ~100 Ma, ~52 Ma and ~35 Ma, respectively, reflecting that Emeishan basalt experienced the contamination of crustal materials in the formation process, and being affected by later tectonic thermal events. The first and second sub-circle of the Emeishan basalt were formed at (259.9±3.2) Ma and (259.2±3.6) Ma, respectively. The zircon ages of the basalts of ~275 Ma may represent the age of the formation age of Emeishan basalt magma chamber and the time when the crust began to uplift due to Emei mantle plume event.After the formation of the Emeishan basalt, the western margin of the Yangtze Plate experienced successively tectonic thermal events of ~247 Ma, ~215 Ma, ~160 Ma, ~120 Ma, ~100 Ma, ~52 Ma, and ~35 Ma. These age data are the time records of the Mesozoic Cenozoic collision orogenic event reaching the peak of temperature and pressure on the western margin of the Yangtze Plate.
Triassic detrital sediments occurring in the northern margin of the Tibetan Plateau, which has been well studied in the Songpan-Ganzi terrane, yet the Triassic basin in the Qilianshan remain poorly understood. In this contribution, we integrated stratigraphy, sedimentology, zircon U-Pb dating on the Triassic sandstones in the Qilianshan to decipher their complex regional tectonic evolution. The results show that the ages of detrital zircons concentrate at four populations in 250-290 Ma,360-460 Ma,1,600-2,000 Ma,and 2,200-2,600 Ma. By comparing with the zircon age spectra in the North China Craton, South China Craton, and the Qinling-Qilian-Kunlun Central Orogenic belt, we suggest that the 1,600-2,000 Ma and 2,200-2,600 Ma zircon age populations were probably sourced from North China Craton, whereas a zircon age population of 360-460 Ma was derived from the North Qilian Orogenic Belt. The 250-290 Ma zircon population may have sourced from the volcanic arc of Eastern Kunlun Orogen in the south. The rare 600-1,000 Ma zircons were probably sourced from the Yangtze Block, since the Triassic North China-Yangtze collision along the Qinling Orogen may have acted as a barrier for the sediments from the Yangtze Block.
To deepen our understanding on the evolution of the Neo-Tethys ocean in Zedang area, Tibet, a study of the petrology, petrochemistry, isotope and geochronology of the Gongguori monzogranite in the Zedang ophiolitic mélange belt is carried out. The result shows that it is small and has similar lithology. LA-ICP-MS zircon U-Pb dating on the pluton yielded Late Cretaceous crystallization age of (90.40±0.68) Ma. The Gongguori monzogranite is rich in Si, Al, and K and Ti-poor, and is metaluminous, calc-alkaline to alkaline. The rocks show LREE enrichments, HREE depletions, and negative Eu anomaly. The monzogranite is also enriched in LILEs (e.g.,Rb, K, Ba, Th, U) and depleted in HSFEs (e.g., Nb, P, Ti). The rocks have (87Sr/86Sr)i=0.705,708 to 0.706,284, (143Nd/144Nd)i=0.512,689 to 0.512,716, and positive εNd(t)=2.00 to 2.51. Based on the geochronological and geochemical characteristics of the Gongguori pluton, this study demonstrates that the Gongguori monzogranite was formed by normal island arc I-type granitic magmatism. The Gongguori monzogranite may have been a partial melting product of the upper crust, which was formed by the Late Cretaceous north-dipping subduction of the Neo-Tethys. The Gongguori monzogranite is unlikely part of the Zedang ophiolite, and the Zedang intra-oceanic arc may have disappeared before 90 Ma.
In this study, we conducted zircon trace element and whole-rock major element analyses on the Shangqimugan granites, and calculated the zircon saturation temperatures and titanium temperatures, which can unravel the temperatures of the source magma, and the formation environment of granite is further analyzed. Our zircon samples present typical igneous zircon REE left-inclining patterns. Besides, LREEs are obviously depleted and HREEs enriched. The samples have distinct negative Eu anomalies and positive Ce anomalies. The results indicate that the zircon saturation temperatures for the Shangqimugan granites are at 772-829 ℃ (average 800 ℃), which belong to high-temperature granite. The minimum Ti-in-zircon average temperature is 614 ℃, the maximum average temperature is 634 ℃, and the zircons were formed at 614-634 ℃ in the granites. Combining with zircon trace elements characteristics, the zircon saturation temperatures and the correlation between titanium temperature with Th/U and 10000/Hf, we suggested that the Shangqimugan granites were formed by delamination of the thickened lower lithosphere led by mantle underplating in the West Kunlun Orogen. During the magma fractionation, zircon has recrystallized and multiphase magma (melts-fluids) replenishment may have occurred. The heat source of magma was probably related to the asthenospheric upwelling (mantle underplating), which occurred during the post-collision intraplate extension at the end of Qiangtang-Tarim plate convergence along the Kangxiwar fault.
The Hailasituwula arfvedsonite-aegitite augite-alkali granite is distributed in southern Chagan’aobao, Sunitezuoqi of Inner Mongolia, an important component of the Erlian-Hegenshan tectonic belt. Through chronological and geochemical studies on it, to explore regional tectonic evolution, LA-ICP-MS zircon U-Pb dating yielded (285.4±1.1) Ma, belonging to the Early Permian, This geochemical study shows that the rocks are featured by being metaluminous, and have relatively high SiO2(76.12%-80.10%) and alkalis (K2O+Na2O=7.62%-9.19%), but low MgO (0.06%-0.10%) and CaO (0.11%-0.20%). The Alkaline index (AI) is 0.98-1.04, and the rocks belong to the alkaline series. The total REE contents of the rocks are relatively low, and the LREEs and HREEs are obviously fractionated. Negative Eu anomalies are distinct (δEu=0.37-0.51), which are coeval with the regional post-orogenic extension. The results indicate that the Erlian-Hegenshan tectonic belt may have entered the post-orogenic stage in the Early Permian.
The Wulanwutai granodiorite in Inner Mongolia is located in the middle part of Xilinhot magmatic arc of an arc-basin system, in the middle part of Xingmeng orogen. To discuss its genetic type and tectonic background, 1:50,000 regional geological survey was conducted and the petrology, mineralogy, geochronology and petrochemistry of the granodiorite were studied. The LA-ICP-MS zircon U-Pb age of (384.8±5.1) Ma indicates a Late Devonian granodiorite emplacement. The rocks mainly contain plagioclase, K-feldspar, quartz, biotite, and amphibole, with accessory zircon, ilmenite, apatite, monazite, and magnetite. The mineral contents resemble typical CPG (cordierite-bearing peraluminous granites) in Barbarin granite classification. In addition, the granodiorite is rich in K2O(3.10%-3.94%) and Al2O3(11.70%-12.89%), and is peraluminous (A/CNK=1.16-1.25). The rocks also contain diorite xenolith. Hence, it is considered that the primary magma of the granodiorite may have derived from partial melting of a crust-mantle mixed source, and formed during the continent-continent collision between the Siberian and North China plates.
The tectonic system is composed of strongly-deformed structural belts and weakly-deformed region. These structural belts and blocks can be expressed in the form of structural planes. Structural plane analysis of the structural system is suitable for the study on the deformation rules, and it facilitates the tracing of structural stress field and evolution. Based on the study of the geological structures and the ore-forming/-controlling elements in the Middle-Lower Yangtze River Valley region, we summarized the distribution features of double-cross planes of the Neo-Cathaysian structural system. The double-cross structures of the Neo-Cathaysian structural system is composed of NNE-trending (25°) compressional fracture and fold belt, NNW-trending (345°, Dayishan-type) tension-torsional fractures, NEE-trending (75°, Taishan-type) compression-torsional structures, and NWW-trending (300°, Yangtze River-type) transverse extension structures. It contains three evolution stages: (1) the NNW 345° to NEE 75°-trending conjugate shear stage, (2) the NNE 25°-trending extrusion stage, and (3) the WWN 300°-trending tensile shear stage. Identification of the double-cross structural style of the Neo-Cathaysian structural system provides an important geological structural basis for the stress-strain genesis study, for the structural system formation and evolution, and for correlating shallow and deep structures. In addition, the structural planes have double-cross distribution features in other types of structural systems.
The structural system is composed of multi-directional, multi-stress-strain properties and different multi-order structures, which have relatively consistent distribution patterns in the stress field. Through geological study of regional metallogenic belts, orefields, and ore deposits, we reveal that the structural plane of the Neo-Cathaysian tectonic system includes three types, i.e., conjugate shear, extrusion, and tensional, forming a double-cross pattern. Using the stress-strain finite element simulation method, the formation of three-stage double-cross pattern is analyzed: the stage-1 conjugate structure developed the NNW 345° (Dayishan-type) tension-torsion fault and NEE 75° (Taishan-type) compression-torsion structure; stage-2 extrusion structure developed the NNE 25° extrusion fracture and fold; stage-3 transverse-tension structure developed the NWW 300° (Yangtze-type) cross-tension fracture. This gives the stress-strain field characteristics favorable of ore control and provides direction for future geological prospecting. The main regional tensile stress is the largest in the stage-1 NNW-trending tectonic belt, followed by the stage-3 NWW-trending “Yangtze” tectonic belt, and then by the stage-2 NNE-trending and stage-1 NEE-trending tectonic belts. The main tensile stress decreases first from the highest to the lowest and then rises again. The maximum compressive stress of the three stages increases from the stage-1 NEE-trending tectonic belt to the largest in the stage-2 NNE-trending tectonic belt, and then decreases to the minimum in the NWW-trending “Yangtze” tectonic belt and the NNW-trending tectonic belt. This shows a trend that increases to the maximum compressive stress and then decreases to the minimum.
The Fen-Wei graben system is located between the Yinshan and Qinling tectonic belts in Eastern China, and comprises (from north to south) over 10 Cenozoic downfaulted basins in the NE syncline, such as the Jining, Huailai, Datong, Yuxian, Xinzhou, Taiyuan, Jinzhong, Fen-Wei, Tianshui, Lixian, Xihe, and Chengxian. This shows that the North China block rotated clockwise in the Cenozoic and caused its rifting, which can be called “S”-type rotation and pull-apart tectonic system. This system had a broad and far-reaching influence on the tectonic framework and development of Eastern China, and strongly modified the tectonic framework of the Qinling-Dabieshan belts and the northern margin of the Jiangnan massif. This may have resulted in the segmentation of the Neo-Cathaysian tectonic system, and initiated the extensional tectonics of the North China Block that reached as far as the Ryukyu trench. Similarly, the Baikal graben system in Russia and Mongolia is composed of Cenozoic rift basins with an inverted-“S”-shaped pattern, and was also developed in ancient crystalline blocks. This represents anti-clockwise rotation of the reversed “S”-type rotation pull-apart tectonic system. Our study shows that they belong to the same tectonic type, and a way of ancient continental block rifting.
The Chaihulanzi gold deposit is located at the intersection of NNE-trending tectonic belt in the Great Hinggan Range and the EW-trending tectonic belt in the northern margin of North China Block. The Chaihulanzi, Lianhuashan, and Honghuagou gold deposits in the area have undergone multistage tectono-magmatic activity. Results of aeromagnetic and remote sensing data interpretation show four tectonic trending features (NNW, NWW, NNE and NEE) in the orefield, which constitute the double-cross-shaped structural pattern that controlled the emplacement of Late Paleozoic magmatic rocks (dikes) and gold mineralization. At Chaihulanzi, structural features of these four directions also form a double-cross-shaped pattern, which controlled the distribution of orebodies (mineralized zones) and geochemical anomaly zones. Both the orefield and ore-deposit tectonic features show the double-cross-shaped distribution characteristics, which demonstrate the magmatic and mineralization controled by different levels of the Neo-cathaysian tectonic system. Our findings provide an important foundation for studying metallogenesis and mineral prediction in the orefields.
Jiaodong is the world’s largest Mesozoic granite-related hydrothermal/metasomatic gold province, and the gold mineralization is related to faulting and alteration. In this paper, the Jiaojia and Zhaoping faults are taken as typical examples to study the geological characteristics of the listric ore-controlling fault distributions, through measuring the deformation and alteration profile and geological mapping. The results revealed that: (1) the fault alteration zone is hundreds of meters to over kilometers wide, instead of meters as previously suggested. The scale and intensity of alteration control the gold mineralization. (2) Orientation for the upper and lower part of the fault is steep and gentle, respectively. Dip angle for the shallow (above -200 m) and deeper (below -400 m) parts of the fault is around 70° and 20°-30°, respectively. The fault morphology is listric. (3) The listric fault indicates motion characteristic of sliding hanging wall, and the stress-strain features show that the mineralization occurred in the regional stress relaxation stage. (4) Dip direction of the fault controls the lateral trend of the mineralized zone. The Jiaojia fault dips to the NW, and the associated mineralization zone trends SW; the Zhaoping fault dips to the SE, and the associated mineralization zone trends NE.
The Middle Permian Zhesi Formation comprises a suite of dark mudstone, gray sandstone, and carbonate in the Songliao Basin, of which the limestone contains marine brachiopod and bivalve fossils. Limited by drilling footage and core data, few previous studies were conducted on the upper Paleozoic strata and sedimentary environment of the basin. Compositions of trace elements (incl. rare earth elements (REEs)) and carbon-oxygen isotopes were measured on the Zhesi Formation dolomitic limestone in the well D101 and D103, and we first presented the element geochemical data of these Middle Permian limestone in the basin. The results show that the δ13CPDB values are generally >0 (mean 1.68‰) and δ18OPDB values < -15‰ (mean -19.98‰), the carbon-oxygen isotope plot indicates positive correlation between the two isotopes, which suggests that dolomitization has obvious effect on the isotopic transformation of limestone. Total $\sum$REE+Y contents of the dolomitic limestone range from 56.88×10-6 to 143.72×10-6 (mean 108.92×10-6). Compared with MREE and HREE, PAAS-normalized LREE depletion was observed with no or negative δEu anomalies (mean 0.94, max 1.57). Negative Ce anomalies are common (mean δCe 0.87, max 1.06). The samples have relatively high Y/Ho ratios (mean 34.59), and the same REE distribution pattern as normal marine facies. The mean trace element contents are relatively high in general, such as Ba (281.55×10-6), Zn (71.91×10-6), Y (17.44×10-6), Zr (117.75×10-6) and Rb (66.84×10-6), and the samples have medium mean ratios of Sr/Ba (2.91), Th/U (2.75), V/Cr (1.45), V/(V+Ni) (0.66). We concluded that the region was a carbonate platform or coastal environment affected by terrigenous debris in the Middle Permian.
Integrating the tectonic evolution and control, and geological characteristics (e.g., structure and thickness) of the sedimentary sequence, the sedimentary facies and environment of the Datong basin are summarized. It is suggested that the Datong basin was formed in the Early Mesozoic (end Late Jurassic to Early Cretaceous), and its tectonic evolution comprises three stages: fault depression formation, half-graben development, and basin formation. This area was not only filled with tectonic layers during the three periods, but also developed faults in the early of Cretaceous, early deposition of Baode Formation and late deposition of Nihewan Formation. Besides five unconformities was showed in the field survey. In the Datong basin and its surrounding areas, EW-trending fold structure likely existed before the Yanshanian movement, and NW-directed compression may have superimposed on the EW-trending structure after the movement. After that, despite strong denudation, the Late Paleozoic and Mesozoic strata remained in the superimposing synclinal nuclei of the EW- and NE-trending folds.
The Yinchuan Basin is located in the junction of the East Asian monsoon and the west wind strip. Sediments in the basin records the climatic environment evolution. In this study, the climatic evolution sequence (MIS6-MIS5 period) in the basin was reconstructed with photoluminescence dating, grain-size analysis, and end-element analysis on sediments from borehole LS01. Four end-members (Em1 to Em4) with specific environmental indications were obtained from the end-element analysis. Em1: weak flow or lacustrine-facies deposits with weak hydrodynamics; Em2: fluvial deposits with strong hydrodynamics; Em3 and Em4: regional tectonic uplift. The climate evolution comprises six stages (1-6): (1) Yinchuan Basin had cold-arid climate with two tectonic uplift events in 150-137 ka (MIS6); (2) The climate was warm and humid as a whole, and there were three warm events at a1 (137-129 ka), a2 (124-120 ka), and a3 (118-111 ka) in 137-110 ka (MIS5); (3) the climate turned to cold and arid in 110-107 ka (MIS5); (4) 107-102 ka (MIS5), cold events b1 (106-104 ka) and b1 (106-104 ka) occurred and the climate was cold and dry in general; (5) 102-87 ka (MIS5), the climate was cold and arid; (6) in 84-75 ka (MIS5), there was a cold event L2 (87-84 ka) but the climate was warm and humid as a whole. The climate change in MIS6-MIS5 phase was mainly driven by solar radiation and precession in summer.
The Hani peat bog is located in the western Changbaishan of Jilin province, Northeast China. The peat records paleoclimate and paleoenvironment change. The record is benefited from the continuous deposition, high deposition rate, and low anthropological influence. In this study, AMS 14C dating was used to determine the age of peat samples, and the magnetic susceptibility was measured to determine its paleoclimatic significance and reconstruct the paleoclimatic evolution since 14 ka B.P.. The results show that magnetic susceptibility of Hani peat is low overall, which indicates that the concentration of magnetic mineral particles in Hani peat is low during most of the Holocene.The magnetic susceptibility of Hani peat records the change of ambient temperature and humidity. Higher magnetic susceptibility indicates warm and humid climate, whereas lower magnetic susceptibility indicates dry and cold climate. The magnetic susceptibility responds strongly to many dry-cold climatic events during the Holocene, including the 0.4-0.6 ka B.P.event ( Little Ice Age), and the events at 2.8 ka B.P., 4.3 ka B.P. and 8.2 ka B.P. Thus, magnetic susceptibility of the Hani peat not only records the climate change since the Holocene, but also responds well to the global climate change.
Establishing Quaternary stratigraphic chronological framework is of great significance to regional stratigraphic correlation and paleogeographic environment reconstruction. According to the sediment colors, structures, and lithological characteristics of borehole S9 in the northern Dachang Depression, together with well-logging, paleomagnetism, 14C and OSL dating, detailed stratigraphic division, sedimentary facies, and stratigraphic chronological framework are established. This work focused on dividing the loose sediments of S9 into four assemblages: (1) diluvial fan deposit; (2) braided river deposit; (3) diluvial fan deposit; (4) flood plain and riverbed deposit. Paleomagnetic data show that the 0-145.3 m interval is Brunhes normal polarity chron, 145.3~212.6 m interval is Matuyama reversed polarity chron, and 212.6-251.8 m interval is Gauss normal polarity chron. Integrating the magnetostratigraphy, lithostratigraphic properties and 14C ages, we divided the Quaternary strata into the Lower Pleistocene, Middle Pleistocene, and Upper Pleistocene series, with depths of 210.9 m, 145.3 m and 24.05 m, respectively.
In response to the request of the Ordovician Branch of the International Commission on Stratigraphy, and to refine the biostratigraphic correlation across the Late Ordovician-Early Silurian Yangtze-Jiangnan region, we systematically studied the Nanba section (Yiyang, Hunan province) in the Jiangnan slope belt, and graptolites from the Parakidograptus acuminatus biozone at the bottom of the Silurian sequence. The Wufeng Formation comprises black shale, which is integrated with the Lower Formation of the Zhoujiaxi Group, and the sedimentation is continuous without interruption. Based on data of the study area and referenced from domestic and international graptolite literature, 6 genera and 8 species of graptolites were identified, including Parakidograptus acuminatus, Normalograptus elegantulus, Nor. mirnyensis, Metabolograptus persculptus, Neodiplograptus parajanus, Neo. guantangyuanensis, Avitograptus acanthocystus, Petalithus hamus, Streptograptus cyclodontus. On the basis of the obtained graptolite specimens, the Metabolograptus persculptus biozone and the Parakidograptus acuminatus biozone was preliminarily identified. Stratigraphic age of this section was determined to be from the Late Ordovician (Hirnantian) to the Early Silurian (Rhuddanian).
The Nanba (Yiyang, Hunan Province) is one of the most complete areas of Tremadocian in China. According to the graptolite specimens from the lower Tremadocian in the study section and the contemporaneous paleontological and stratigraphic data at home and abroad, all graptolites in the study section were measured and statistically identified. Three genera and four species of graptolites were identified, including: Rhabdinopora flabelliforme parabola (Bulman, 1954), Adelograptus tenellus (Linnarsson, 1871), Adelograptus altus Willims & Stevens, 1991, and Ancoragraptus bulmani (Spjeldnaes, 1963), and mainly described and discussed two zone fossils, Rhabdinopora flabelliforme parabola (Bulman, 1954) and Adelograptus tenellus (Linnarsson, 1871). Based on the study of phylogeny, the Rhabdinopora flabelliforme parabola biozone and Adelograptus tenellus biozone were identified from the Yinzhubu Formation, in which, the Rhabdinopora flabelliforme parabola biozone is the lowest Ordovician strata there. Based on the key fossil in the graptolites’ zone, the Rhabdinopora flabelliforme parabola biozone is accurately compared with the coeval domestic and foreign strata.
The Sanjiaoding gold deposit is the only “Linglong-like” gold deposit in intermediate-acid intrusions found in the northern margin of Qaidam Basin, which is very important in regional prospecting. This paper compiled the geological characteristics of the deposit, type of ores, primary features of halos of the ores and rocks, the characteristics of fluid inclusions in the gold-bearing quartz veins, and related regional metallization events, and further investigated the metallogenic characteristics and prospecting significance of the deposit. The gold-bearing quartz veins and gold-bearing silicified mylonites resulted from the combined effects of multi-stage fluid activities with various compositions in the Sanjiaoding area. Fluid inclusions hosted in the gold-bearing quartz veins show features of shallow medium-low temperature and medium-low salinity, and are genetically related to magmatism. The gold-bearing silicified mylonite-type ores are caused by regional dynamic metamorphism. The mineralization depth of the Sanjiaoding gold deposit increases from west to east, and the quartz-vein type in the western ore deposit fields represents the top of the system of this period, forming a dome-like gold mineralization layer. Such dome-like gold mineralization layer of the quartz-vein type in the west segment and the gold-bearing mylonitization zone in the east segment, have great potential targets for further prospecting.
The Tongkuangli molybdenum polymetallic deposit in Qingyang area, Anhui Province is a skarn type Mo polymetallic deposit newly discovered in the Middle-Lower Yangtze River metallogenic belt in recent years. In this paper, the geological characteristics and fluid inclusion characteristics of the deposit are studied in detail, and the origin and evolution of fluids are discussed. Based on the cross-cutting relationship and mineral metasomatism, the mineralization process of the Tongkuangli deposit can be divided into five stages: early skarn, late skarn, quartz molybdenite, quartz polymetallic sulfide and carbonate stages. Microscopic observations show that the types of fluid inclusions in the Tongkuangli deposit are mainly liquid-rich, vapor-rich and daughter-bearing three-phase inclusions. Microthermometric results show that the early ore-forming fluids were high temperature, and medium to high salinity fluids, while the late ore-forming fluids were low temperature and low salinity fluids. This feature, combined with the existing hydrogen and oxygen isotope data, indicates that the early hydrothermal fluids in the Tongkuangli deposit were magmatic water, and that the magmatic water mixed with circulating meteoric water during the late stages. The coexistence of liquid-rich, three-phase and vapor-rich inclusions within quartz of the quartz molybdenite stage, and their similar homogenization temperatures with completely different homogenization way, indicating that fluid boiling may be the main mechanism of molybdenum precipitation in the Tongkuangli deposit.
The central Great Xing’an Range is an important non-ferrous metal province in NE China, such as lead, zinc and silver,and discussion on the ore-forming material source is important for metallogenic prediction and prospecting work in this region. Through extensive geological survey,typical deposits sampling,rock and mineral identification,the whole-rock geochemical compositions and element cluster analysis, the results show that the total REE content of the Hercynian magmatic rocks is low, and the negative Eu anomaly is indistinct, and the LREE/HREE ratio is large,which is positively correlated with the total amount of rare earth and negatively correlated with the δEu value, indicating that the diagenetic material is mainly derived from the mantle. Whereas the Yanshanian magmatic rocks show absolutely contrary characteristics,indicating the characteristic of crustal material. The lead-zinc-silver polymetallic deposit is dominated by zinc. The REE distribution pattern of the lead-zinc ores is basically consistent with that of the mantle-derived differentiated magmatic rocks. Cluster analysis shows that TFeO-Cu-Zn is an independent group, indicating that the TFeO-Cu-Zn material is separated from the magma from late magmatic crystallization. The TFeO-Cu-Zn independent group shows that the sphale-rite in the region is all high-temperature iron sphalerite. The results show that the ore-forming materials of lead-zinc-silver deposits in the region are diorite-derived. The later hydrothermal transformation has certain effects on the lead-silver enrichments. In terms of the ore-forming material source, an intermediate-mafic magmatic-related lead-zinc-silver metallogenic system and a felsic magmatic-related copper molybdenum and copper-tin metallogenic system is presented.
To optimize the prospecting target area in Jinshuikou, Dulan County, Qinghai Province, a 1:50,000 stream sediment survey was carried out based on understanding the geological characteristics of the area. Based on the original measured data, the contents of nine trace elements including Au, As, Sb, Bi, Hg, Co, Cr, Ni, and Zn are statistically analyzed by using the regional concentration coefficient (RCC) and other characteristics parameters. It is concluded that Zn and Au have great metallogenic potential. The R-type cluster analysis, correlation analysis, and R-type factor analysis of nine elements were carried out by using statistical software SPSS25. Four ore element combinations were divided, including F1(Co-Cr-Ni), F2(Au-Bi-Zn),F3(As-Sb), and F4(Hg). The contrast anomaly method is used to calculate the anomaly lower limit of each element and element combination. Surfer15 software is used to compile the element and element combination contrast data into an anomaly map. Combined with the characteristics of element anomaly and metallogenic geological conditions, five prospecting targets are delineated. The abnormality of the No.1 polymetallic minerali-zation in the No.1-1 target area was verified, and the chemical analysis of the picked samples showed that the contents of zinc and total iron reached the lowest industrial grade. The exploration trench project was carried out on the No.2 and No.3 polymetallic mineralization bodies in the No.1-2 target area. After sampling and analysis, it was shown that the contents of some manganese and zinc had reached the boundary grade, and the total iron content was close to the boundary grade, and gold had a certain degree of metallogenic potential indicates that the Jinshuikou area has a large metallogenic potential of zinc, iron, gold and manganese.
The Giant Shuangjianzishan Ag-polymetallic deposit in Inner Mongolia is currently the largest Ag-polymetallic deposit in China and even Asia. Based on the review of the discovery history of the deposit, the geochemical data on the regional geochemical survey are being reprocessed using new methods. A 19 levels of cumulative frequency method is used to map the analyzed 39 elements or major oxides and the results indicate that the major oxides or elements up to 22 items such as MgO, CaO, Fe2O3, Pb, Zn, Ag, V, Cr, Ni, etc. are enriched in the deposit area. The enrichments of major oxides may be resulted from the parent rocks in this area. The seven levels’ classification method on the geochemical anomaly with unfixed backgrounds is adopted to draw the single-element geochemical anomaly map for the 29 trace elements and the results indicate that only 9 elements such as W, Sn, Mo, Bi, Pb, Zn, Ag, As, and Sb have anomalies in or around the deposit area. Therefore, the enrichments of other trace elements in the deposit area may be caused by the parent rocks or their weathering. The recently presented method of geochemical gene is applied in this area and the mineralization similarity of metallogene is used as an integrated index to recognize the geochemical anomalies. The results indicate that the mineralization similarities of gold metallogene and tungsten metallogene all occur anomalies in or around the deposit area which reflects the ore-forming potential in the deposit area. The aforementioned results illustrate the regional geochemical survey is a useful method in the exploration of the Shuangjianzishan Ag-polymetallic deposit.
Taking the soil in Jieyang City as the research object, 1,330 surface soil samples (0-20 cm) and 331 deep soil samples (>150 cm) were collected, and the Pb content in soil was determined. GIS spatial ana-lysis technology, semivariogram fitting and variance analysis were used to study the spatial structure, distribution characteristics and influencing factors of soil Pb content. The results showed that there was no obvious Pb pollution in Jieyang city, and the average Pb content in surface soil was 39.26 mg/kg, which was lower than the background value of Pb in Jieyang City (43.71 mg/kg) and slightly higher than that in Guangdong Province (36.00 mg/kg). Enrichment factors showed that the enrichment degree of Pb in the surface soil of the study area is mainly no enrichment and slight enrichment, accounting for 52.11% and 42.63%, respectively, and Pb enrichment is not significant; The spatial distribution of Pb in the surface soil of the study area showed mode-rate autocorrelation. The Pb high value areas of surface soil are mainly distributed in the eastern and southern parts where human activities have a strong influence. According to the classification statistics of land use, soil parent material, soil type and its physical and chemical properties, the Pb content in surface soil of woodland and unused land is the highest; The Pb content in the soil formed by shale weathering is significantly higher than that of other soil-forming parent materials; Pb content in yellow soil is relatively high; Organic carbon and pH were positively correlated with Pb content in soil.
In order to understand the content, distribution characteristics and health risks of heavy metals in the soil and rice in the typical rice area of Lingchuan County, Guilin City, we selected typical rice fields and collected 10 sets of samples of rice roots, stems, leaves, rice and corresponding root soils. The contents of 8 heavy metals including As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in the soil were determined respectively. The bio-concentration factors (BCF) and transfer factor (TF) of each element were calculated. The enrichment and migration law of heavy metals in different parts of rice were summarized. According to the Risk Control Standard for Soil Contamination of Agricultural Land (GB 15618—2018), the Green Food Environmental Quality for Production Areas (NY/T 391—2013) and Food Hygiene Standards (GB 2762—2017),heavy metal pollution in soils and food health risks were determined. The results show that: (1) The brown rice produced in the research area has no food safety risk, and the heavy metal content in the soil does not exceed the risk control value, but 3 of the 10 sample fields have a Cd content higher than the agricultural land soil pollution risk screening value, and all the sample fields are unable to meet the quality requirements of the green food origin. (2) Comparing the bio-concentration factors of different parts of rice, it is found that the bio-concentration factors of most elements are the largest at the roots and the smallest at the brown rice. The average of bio-concentration factors are 1.13 for roots, 0.26 for stems, 0.20 for leaves and 0.10 for brown rice. (3) Comparing the bio-concentration factors and transfer factor between different elements, it was found that As is relatively easy to accumulate from the soil to the roots, Pb is weak in activity and not easily absorbed by rice, Cu and Zn are relatively easy to transport in rice. In summary, we recommend that local authorities pay attention to the risk of excessive Cd, strengthen land quality monitoring, and take measures such as increasing the application of organic fertilizers and planting rice with low accumulation varieties when necessary to reduce the risk of heavy metals exceeding the standard.
The environmental quality of sediments in inland bay is closely related to the survival of aquatic organisms and human health. Forty-six samples are collected from surface and deep sediments in 23 locations of cross-gulf in the Inland Bay of Shantou City in Guangdong Province. The pH values, the concentration of 7 heavy metal elements, Cd, Hg, As, Pb, Cr, Cu and Zn, and the content of K are analyzed to evaluate the environmental risk of heavy metals in these sediments with reference to soil contamination risk of paddy field in agricultural land. The results show that the pH of sediments in Shantou Inland Bay is between 7.00 and 8.82, with an average value of 7.83. Among 46 samples, 41 samples have pH values greater than 7.5. The contents of 7 heavy metals in the sediments of Inland Bay are obviously lower than their environmental pollution control values, which means there is no need to control the environmental pollution of heavy metals in the sediments. The contents of Cd, As, Pb and Cr are all lower than their screening values of pollution risk, and their pollution risk could be ignored. The concentrations of Hg in 2 surface samples were higher than the screening value of pollution risk, and the contents of Cu and Zn in 18 samples were higher than their screening values of pollution risk. Therefore, it is suggested to monitor the concentrations of Cu, Zn and Hg in these sediments. The content of K is between 0.70% and 2.59%, with an average value of 1.54%. Based on the comparison of elemental contents between surface layer and deep layer sediments it is concluded that the pollution source of Hg in this area should be anthropogenic. However, the pollution sources of Cu and Zn may be anthropogenic or mixed resulted from anthropogenic and natural resources.
Ferromanganese nodules commonly exist in high quantity in karstic soils with high geochemical background and thus play a crucial role in the occurrence and bioavailability of heavy metals. In this study, karstic topsoil (0-20 cm) samples rich in ferromanganese nodules from Qintang District, Guigang city, Guangxi were particularly collected, and ferromanganese nodules of different particle sizes (10-120 mesh) and fine-grained soils (<120 mesh) were screened prior to further chemical analysis. The objectives of this study were to investigate: (1) the distribution of heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn), and composition of iron oxide minerals in the nodules and fine-grained soils, (2) the effect of iron oxide minerals on the accumulation of heavy metals in the nodules and fine-grained soils, and (3) the mechanism of heavy metals occurrence in soils rich in ferromanganese nodules. The results showed that the concentrations of Fe, Mn and heavy metals (e.g., Cd) in ferromanganese nodules increased with the increment of particle sizes, which indicates that heavy metal elements tend to be enriched in the nodules with large size. Quantitatively, about 90% of heavy metals in the topsoil samples occurred in the ferromanganese nodules. It indicates that heavy metals mainly occurred in the form of nodules in the studied soils. The mean contents of hematite and goethite in the topsoil samples containing ferromanganese nodules were 4.94% and 0.61%, respectively. The larger the particle size of nodules, the higher the contents of hematite and goethite. Except for Hg, the concentrations of heavy metals were all significantly and positively correlated with the contents of goethite and hematite, and the correlation with hematite was slightly better than that with goethite. These results indicate that iron oxide minerals are closely related to the enrichment of heavy metals in soils rich in ferromanganese nodules. The presence of ferromanganese nodules can not only promote the enrichment of heavy metals, but also reduce the bioavailability of heavy metals in soils. These results provide a theoretical basis for explaining the high concentrations and low bioavailability of heavy metals in karstic soil with high geochemical background.
Geochemical gene is a new technique presented in recent years. According to the construction steps of a geochemical gene, a new lithogene labelled LG03 was proposed based on trace elements on the sequence of Nb→Ti→Zr→Cr→La→V→Pb→Co→U→Ni→Th with the standardized reference values of 14.5, 4,016, 147, 81, 35, 130, 19, 24, 1.2, 32, and 5.72, respectively in μg/g. The LG03 lithogene along with the LG01 lithogene which was constructed formerly on major oxides and trace elements were tested on 10 weathering profiles including 4 profiles developed over granitic intrusions, 4 profiles formed on basaltic strata, and 2 profiles developed on granodioritic intrusions in Guangdong Province, Hainan Province, Shandong Province, and Beijing City in China. According to the gene similarity value of ≥80% as the criterion to discriminate samples with similar lithogenes, the gene similarity results on 10 weathering profiles indicate that LG03 and LG01 lithogenes all illustrate good steady during rock weathering on the properties of heredity (gene similarity with respect to parent rock) and inheritance (gene similarity with respect to topsoil). Furthermore, according to the acidic similarities (gene similarity with respect to the gene of 10202020202 on LG01 and LG03), samples can be classified into three groups as acidic-like composition with values of ≥80%, intermediate-like composition with values between 75% and 25%, and basic-like composition with values ≤20%. That is to say, LG03 and LG01 have similar effects on composition classification and provenance discrimination. However, LG03 is more stable than LG01 in the properties of heredity and inheritance and the application on provenance discrimination. When the results of compositional classification on LG03 and LG01 are different, the results on LG01 are recommended and the results on LG03 are also helpful for a further constraint. The concentrations of major oxides (such as SiO2, CaO, P2O5, etc.) in geological materials will be changed clearly resulted from the addition of aeolian sands, organisms, etc. during the weathering, transportation, sedimentation processes. Therefore, the LG01 lithogene which was constructed on both major oxides and trace elements may be unstable while the LG03 lithogene constructed only on relative immobile trace elements may illustrate good stability during the geological processes. Hence, the LG03 lithogene may have wider application fields than LG01 lithogene because of the elimination of addition or dilution effects in geological materials.
Recent exploration results of deep volcanic rocks in the western Sichuan Basin indicate that the Permian volcanic rocks in this region have great exploration potential. However, it is still difficult for seismic exploration methods to describe the distribution of volcanic rocks in detail. Therefore, it is necessary to provide more favorable evidence for volcanic exploration through gravity and magnetic methods. This paper takes advantage of the latest gravity and magnetic data to analyze the characteristics of gravity and magnetic properties in the western Sichuan Basin based on existing geological knowledge, and summarizes the gravity and magnetic response characteristics of deep volcanic rocks in this region based on the gravity and magnetic forward simulation results of different models. Through the processing of measured gravity and magnetic data, the distribution characteristics of faults and the distribution law of high magnetic anomalies in the study area are analyzed. The results show that: (1) The forward modeling results show that magnetic anomalies are sensitive to volcanic rocks, and gravity anomalies are sensitive to faulted structures, but not to volcanic rocks. (2) Magnetic anomaly has an outstanding ability to depict volcanic rocks, which can identify the volcanic rocks with a thickness of more than 45 m, but it is difficult to identify the buried depth and lithology changes of volcanic rocks. (3) The fault structures interpreted by gravity anomalies in the study area are in good agreement with the known fault structures in the study area. Meanwhile, the distribution of volcanic rocks described by magnetic anomalies is comparable to the existing understanding. It is concluded that gravity and magnetic exploration plays an important role in volcanic exploration in Sichuan Basin. Gravity exploration can identify the development of deep and large faults that control the distribution of volcanic rocks, and magnetic exploration can identify the plane distribution characteristics of volcanic rocks and quickly delineate the favorable target areas, thus providing favorable gravity and magnetic basis for volcanic exploration.
Located on the Bohai seashore, the Xiaoshan volcano is the direct evidence of crustal activity on the western Bohai seacoast. The area is famous for its typicality, diversity and naturalness. With its unique scienti-fic significance, it is very rare in China. Due to the extensive Quaternary cover on the volcanic rocks, high-precision magnetic measurement was used to delineate the boundary of volcanic relics and to study typical geological structures. In this study, we described the magnetic field distribution characteristics of the Xiaoshan volcanic geological relics protected zone. Distribution range of the magmatic and sedimentary rocks in the zone was identified and their boundaries were delineated, and a number of faults were inferred. This is achieved through analyzing magnetic anomaly of the pole, upward extension, and the search for derivative and other processing methods. Our findings support that the high-precision magnetic method is effective to study the geological characteristics beneath the overburden area. The study of the magnetic field distribution features provides detailed and reliable basic data for the Xiaoshan volcano geological relics, and has important implications for the division of the geological relic landscape and for sensible planning of the protected zone.