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Yao T.,China University of Geosciences | Yao T.,Chinese Academy of Geological Sciences | Li H.M.,Chinese Academy of Geological Sciences | Yang X.Q.,Chinese Academy of Geological Sciences | And 5 more authors.
Acta Petrologica Sinica | Year: 2014

The Early Precambrian Banded Iron Formations (BIFs) are the most important iron ore resources type in China, and account for approximately 64 % of the total identified resources. In China, BIFs are mainly distributed in greenstone belts of the North China Craton, such as Anshan-Benxi (in Liaoning Province), Jidong (in Hebei Province)-Miyun (in Beijing), Wutai (in Shanxi Province), Wuyang (in Henan Province), Huoqiu (in Anhui Province), and Luxi (in Shandong Province). Liaoning-eastern Hebei area (including Anshan-Benxi area and eastern Hebei area) is the study area, which accounts for more than 34% of overall iron ore reserves in China. Anshan-Benxi area includes Anshan, Benxi, and Liaoyang and so on, which is composed of the supracrustal rock (about 30%) and granitic rock (about 70%). Archean Anshan Group is the major ore stratum, iron ore mainly occurs in the Middle and Upper Anshan Group. The rocks have undergone greenschist to amphibolite facies metamorphism. Eastern Hebei area includes Zunhua, Qianxi, Kuancheng, Qinglong, Qianan and so on, which is composed of the crystalline basement and sedimentary cover. Iron ore mainly hosted in the Qianxi Group, Zunhua Group, Luanxian Group and Zhuzhangzi Group. The rock have been strongly migmatized, and metamorphosed to the greenschist to granulite facies. Based on field geological and microscopic studies, we found that there are many differences exist on the ore type, degree of metamorphism, ore formation, and mineral combination between the Anshan-Benxi and the eastern Hebei area. In this study, we mainly report rare earth elements of 200 samples of iron ore from 28 iron deposits in Liaoning-eastern Hebei area. The results show that: (1) All samples show very similar characteristics of total contents of REE and Y: the total contents of REE are very low, but Y/Ho ratios are high. After normalized by Post Archean Australian Shale (PAAS), REE and Y patterns display depletion of light REE relative to heavy REE. Most samples have positive La anomalies, distinct positive anomalies of Eu and Y. All of them suggest that the iron ores may be derived from submarine high temperature hydrothermal fluids and sea water in the studied area. Compared to the eastern Hebei area, the Anshan-Benxi area shows more hydrothermal contribution; (2) Although the Ce/Ce ratios were 0. 77 ∼ 1. 09, the lack of true negative Ce anomalies in all samples indicates that BIFs were formed in an anoxic ocean; (3) The contents of REE, Eu anomalies, Y anomalies and Y/Ho ratios vary in a large range, which may be associated with the inputing of detrital material during the BIFs formation. The degree of positive anomalies of Eu and Y from samples in the eastern Hebei area are less than that in the Anshan-Benxi area, and Y/Ho ratios are closer to chondrite meteorites (26 ∼28), which also indicating more detrital material joining.

Yang X.Q.,Chinese Academy of Geological Sciences | Yang X.Q.,Peking University | Li H.M.,Chinese Academy of Geological Sciences | Li L.X.,Chinese Academy of Geological Sciences | And 3 more authors.
Acta Petrologica Sinica | Year: 2014

Liaoning-eastern Hebei area (it mainly includes Anshan-Benxi area and eastern Hebei Province), where plenty of largesuperlarge banded iron formations (BIFs) type iron deposits distributed, is located at the northeastern North China Craton. Anshan-Benxi area and eastern Hebei Province are the two largest iron ore clusters in China. The iron ore reserves of Anshan-Benxi area account for about 24% in China, and the iron ore reserves of eastern Hebei Province account for more than 10%. Although most BIFs which belong to Algoma-type in Liaoning-eastern Hebei area formed in Neoarchean granite-greenstone belt, they may formed at different environment and experienced different late reformations. The BIFs in Anshan-Benxi experienced greenschist to amphibolite facies metamorphism, however the BIFs experienced greenschist to granulite facies metamorphism in eastern Hebei Province, and migmatization is ubiquity in both areas. In this study, we mainly report major elements of 200 iron ore samples from 28 iron deposits in the Liaoning-eastern Hebei area, which offers more information of the formation of the BIFs. The studied BIFs are mostly composed of SiO2 +Fe203 T(the average value of Anshan-Benxi area is 95. 10%, the average value of eastern Hebei Province is 88. 06%). The contents of MgO and CaO are next to SiO2 and Fe 203 T, and the positive correlation also between MgO and CaO in the studied area. The contents of Al203, TiO2, K2O, Na2O, MnO, P2O 5 are very low, all of which indicate that BIFs are typical chemical sedimentary rock, the protolith of BIFs are colloid composed of silicious, iron and small amounts of carbonate mud; Both Al2O3 and TiO2 simultaneously increase in the studied BIFs indicates that these chemical sediments incorporate minor detrital components. In eastern Hebei Province, this correlation is more obvious, and the major elements concentrations are higher than that of Anshan-Benxi area except SiO2 + Fe2O3, all of which represents eastern Hebei Province BIFs forming at wave base, more detrital material input. The average bulk chemistry of BIFs, from greenschist to granulite facies, which formed different mineral composition, the major elements are very similar, these suggest that metamorphic reactionis essentially isochemical. Alkali contents of Anshan-Benxi area BIFs (Na2O ≥ K2O) and eastern Hebei Province (both are higher than Anshan-Benxi area, and Na2O < K2O) are different, combining with field geological characteristics, may indicate that migmatization had more strong influence on eastern Hebei Province than Anshan-Benxi area BIFs.

Li H.-M.,Chinese Academy of Geological Sciences | Yang X.-Q.,Chinese Academy of Geological Sciences | Li L.-X.,Chinese Academy of Geological Sciences | Zhang Z.-C.,China University of Geosciences | And 3 more authors.
Journal of Asian Earth Sciences | Year: 2015

The high-grade magnetite ores related to banded iron formations (BIFs) in the Anshan-Benxi area, Liaoning Province in China, have been widely interpreted as the product of replacement of protore by epigenetic hydrothermal fluids. The high-grade iron ore reserves in the mining area II (164million tons) in the Gongchangling (G2) and Qidashan-Wangjiabuzi (QW) iron deposits (11.45million tons) are the largest deposits in the Anshan-Benxi area. We present a detailed comparison of the geology, geochemical and stable isotopic compositions of the iron ores in the G2 with those in the QW to constrain the role of desilicification and iron activation-reprecipitation in converting the BIFs to high-grade magnetite ores. These two deposits show marked difference in wall-rock alteration, geochemical features, and oxygen and sulfur isotopic compositions. Wall-rock alteration in the G2 is characterized by garnetization, actinolitization, and chloritization, whereas the QW shows chloritization, biotitization and sericitization. The geochemistry of altered rocks in the G2 is characterized by slight REE fractionation, positive Eu and no significant Ce anomalies, whereas the QW is characterized by high σREE contents, strong REE fractionation, and the absence of significant Eu and Ce anomalies. High-grade iron ores in the G2 show similar δ18OV-SMOW values for magnetite, lower δ18OV-SMOW values for quartz and higher δ34SV-CDT values for pyrite when compared to the BIFs, whereas the QW shows lower δ18OV-SMOW values for magnetite, similar δ18OV-SMOW values for quartz and similar δ34SV-CDT values for pyrite. These features indicate that desilicification process by hypogene alkaline-rich hydrothermal fluids were possibly responsible for the formation of high-grade iron ores in the G2 whereas iron activation-reprecipitation process by migmatitic-hydrothermal fluids generated the high-grade iron orebodies in QW. © 2015 Elsevier Ltd.

Li L.-X.,Chinese Academy of Geological Sciences | Li H.-M.,Chinese Academy of Geological Sciences | Xu Y.-X.,Hebei United University | Chen J.,Chinese Academy of Geological Sciences | And 4 more authors.
Journal of Asian Earth Sciences | Year: 2015

Algoma-type BIFs and associated volcanic suites of the Qianxi Group in eastern Hebei Province have undergone high-grade metamorphism and anatexis. The anatectic event is genetically related to high-grade magnetite ores, but the age of the anatectic melting has not been well constrained. We present detailed textural relationship and internal structures of zircon grains and their age data from eight samples of migmatitic rocks representing the different Algoma-type BIF-hosted iron deposits to constrain the formation age of BIF deposition and subsequent anatexis. Six continuous zircon growth stages are distinguished by a series of low-CL and high-CL zones outside from center to edge: inherited magmatic zircon, bright-CL resorption domain, dark-CL recrystallization front, dark-gray-CL diffusion domain, light-gray-CL overgrowth and bright-CL resorption edge. The overgrowths are interpreted as a solid-state diffusion of Zr of primary zircon during interaction with anatectic melt, which resulted in different stages of chemical re-equilibration of primary domains and local re-deposition of newly grown domains on the suitable isostructural substrate of residual magmatic zircon. SHRIMP zircon U-Pb dating of inherited magmatic cores and discrete magmatic grains constrains the peak BIF-deposition age at 2520. Ma, which is different from the peak at 2.75-2.70. Ga for Algoma-type BIFs elsewhere in the world. Zircon U-Pb dating of light-gray-CL rims and newly grown homogeneous grains indicates that the anatectic event lasted from 2511 to 2485. Ma at least, immediately following the BIF deposition. The BIF depositional event is consistent with widespread late Neoarchean magmatism, and the anatectic event is consistent with regional metamorphic events in the eastern part of the North China Craton. © 2015 Elsevier Ltd.

Chen J.,CITIC Construction Co. | Li H.,Chinese Academy of Geological Sciences | Luo D.,CITIC Construction Co. | Li L.,Chinese Academy of Geological Sciences | And 4 more authors.
Geological Bulletin of China | Year: 2015

Eastern Hebei Province is a main BIF concentration area in China. However, previous studies of BIF in this area which had undergone low-grade metamorphism were relatively weak. Zhalanzhangzi BIF occurs in the Zhuzhangzi Group which has generally suffered from green schist to low amphibolite facies metamorphism. The iron ore predominantly consists of magnetite and quartz, with minor tremolite and biotite. The main chemical constituents of iron ores are SiO2, Fe2O3 and FeO. Low content of Al2O3 and extremely low content of TiO2 as well as High Field Strength Element (HFSE) indicate that the contribution of continental detritus was insignificant. The concentration of REE in iron ores is low, and Post Archean Australia Shale (PAAS)-normalized rare earth elements profiles for the iron ores display depletion of light REE relative to high REE. All samples have distinct positive anomalies of Eu and slightly positive anomalies of Y, the ratio of Y/Ho in iron ores is high, and the typical characteristics of the REY (REE+Y) profiles resemble those of the mixture of high-temperature hydrothermal fluid and seawater, suggesting that the ore material might have been derived from submarine high temperature hydrothermal fluids and sea water. SHRIMP zircon U-Pb dating was conducted for the biotite-plagioclase granulites interlayered with orebodies in the Zhalanzhangzi BIF which are mainly prismatic grains with visible internal zonation. The mean Th/U ratio of 17 zircon samples is 1.02, indicating that they are magmatic zircons. Ten concordantly distributed data with a weighted mean 207Pb/206Pb age of 2572±8 Ma (MSWD=5.8) indicates the formation age of the Zhalanzhangzi BIF. A comparison with previous studies of medium or high-grade metamorphic BIFs shows that BIF underwent different grades of metamorphism that originated from the same sources and formed nearly simultaneously in eastern Hebei Province, and metamorphism of BIF was probably connected with mantle plume event in Eastern Block of the North China Craton at 2500Ma. ©, 2015, Science Press. All right reserved.

Chen J.,Chinese Academy of Geological Sciences | Li H.M.,Chinese Academy of Geological Sciences | Li L.X.,Chinese Academy of Geological Sciences | Yang X.Q.,Chinese Academy of Geological Sciences | And 7 more authors.
Acta Petrologica Sinica | Year: 2014

The Sijiaying BIF, the largest iron deposit in the eastern Hebei Province, located in the center part of Eastern Block, North China Craton, is hosted in epidote-amphibolite facies Neoarchean metamorphic rocks. The evolutionary process can be divided into depositional stage, epidote-amphibolite facies metamorphic stage, folding and deformation stage, shearing and hydrothermal alteration stage, uplifting and oxidizing stage. Both striped actinolite-magnetite-quartzite occured in epidote-amphibolite facies metamorphic stage and banded actinolite-magnetite-quartzite, massive magnetite-quartzite, pyrite-quartz veins formed in shearing and hydrothermal alteration stage contain a variety of fluid inclusions. Five types of inclusions are distinguished including primary (I - type) inclusions, pseudosecondary (II-type) inclusions, secondary (III-type) inclusions, daughter mineral-bearing (IV-type) inclusions, CO2-bearing three-phase (V-type) inclusions. The homogenization temperatures of the II-type and III-type fluid inclusions in quartz-1 in striped actinolite-magnetite-quartzite as well as V-type inclusions in quartz-1 in banded actinolite-magnetitequartzite range from 352 ∼ 560°C, with trapping pressure between 0. 11GPa and 0. 20GPa and salinities rang from 0. 4% ∼ 3. 3% NaCleqv. They reflect the temperature and pressure of epidote-amphibolite facies metamorphism. The homogenization temperatures of the II-type and III-type fluid inclusions in quartz-2 in banded actinolite- magnetite-quartzite, massive magnetite-quartzite and pyritequartz veins concentrate in 153-212°C, with salinities between 0. 5% NaCleqv and 22. 6% NaCleqv. The δ18 O values of magnetite-1 from striped actinolite-magnetite-quartzite range from 1.4‰ to 2. 8%‰; While the δ18 O values of magnetite-2 from banded magnetitequartzite and massive magnetite-quartzite range from 1. 1‰ to 6.1‰, these data indicating fluids of shearing and hydrothermal alteration stage may account for leaching Si and concentrating Fe in Sijiaying BIF, hypogene (hypergene) fluids circulated through shear zones and resulted in forming banded actinolite-magnetite-quartzite, massive magnetite-quartzite and pyrite-quartz veins. Moreover, multi-stage fold and deformation activities may also played an important role in forming banded actinolite-magnetite-quartzite. The homogenization temperatures of I-type inclusions in quartzs in all types of ores range from 117-223°C, with salinities mainly between 0.4% NaCleqv and 5.0% NaCleqv, which reflects the characteristics of fluids in the uplifting and oxidizing stage. Relatively low oxidation may be the main reason for which Sijiaying BIF unable formed a large scale of high-grade martite-microplaty ore.

Li H.,Chinese Academy of Geological Sciences | Liu M.,China University of Geosciences | Li L.,Chinese Academy of Geological Sciences | Yang X.,China University of Geosciences | And 4 more authors.
Acta Petrologica Sinica | Year: 2012

In the northwestern part of No. 2 mine of Gongchangling iron deposit, Liaoning Province, the magnetite-bearing dolomitic marbles which are conformitied with banded iron formation are sedimentary carbonate rocks in origin. In this paper, major element, trace element, rare earth element (REE) compositions and carbon, oxygen isotopic data of the marbles and altered rocks are presented. The marbles contain 30. 15% ∼ 34. 32% CaO, 9. 86% ∼ 11. 95% MgO, 6. 76% ∼ 15. 82% total FeO. Compared with Phanerozoic limestones, they are relatively depleted in large iron lithophile elements (LILE) and high strength field elements (HFSE), but enriched in Pb and Mn. In contrast, compared with post Archean Australia sediments (PAAS), they display lower total REE contents, more remarkable positive Eu anomalies but no significant negative Ce anomalies. The δCV-PDB values (-7.0%c ∼ - 6. 0%c) and Y/Ho ratios are either different from seawater or terrigenous clastics. These features indicate that they were formed in an anoxic marine environment, and could be genetically related to submarine exhalative hydrothermal events. The sedimentation of the marbles suggests that the pH value of seawater is neutrality to weak alkaline, which is favorable for the precipitation of iron colloid. The marbles are easily deformed. Actinolitites were thus formed in response for the replacement of SiO2 that is translated when high-grade iron ores were formed from low-grade iron ores. In addition, they provide a basis of Mg for forming garnetite, chloritite and mafic amphibolite.

Li H.M.,Chinese Academy of Geological Sciences | Liu M.J.,Institute of Geological Exploration | Li L.X.,Chinese Academy of Geological Sciences | Yang X.Q.,Chinese Academy of Geological Sciences | And 3 more authors.
Acta Petrologica Sinica | Year: 2014

Global occurrence of BIF-related iron resources are typically represented by high-grade hematite ores (TFe > 50%) formed by supergene leaching. Most of the BIF-related iron deposits in China are low-grade iron ores with TFe grade approximately of 30%. The BIFs in China have experienced intense metamorphism and deformation, which led to the majority of iron oxides transforming into coarse-grained magnetites. Though their ores generally contain only 30% TFe, the BIFs are favorable for industrial exploitation by using magnetic beneficiation. The mining area II of the Gongchangling high-grade iron deposit, the largest high-grade magnetite deposit in China, is referred to a kind of sedimentary metamorphosed deposit. The high-grade iron ores were formed by the superimposition and reformation of banded iron formation (BIF). During the process of the high-grade iron mineralization, the country rocks of the ore bodies were intensely altered into garnet-rich rocks. In BSE images, zircons are observed to be in close association with quartz, ilmenite, cummingtonite and chlorite. The mineral assemblage is distributed along fractures in garnet, indicating that the zircons were formed during the process of retrograde alteration of garnet. Zircons separated from the garnet-rich altered rocks are hypautomorphic-allotriomorphic granular, and display different bright and dark patches in the cathodoluminescence (CL) images and back-scattered electron images and vaguely oscillatory zones in CL images. The inclusions inside the zircons display dark color; long strip and flake shaped euhedral crystal, and are determined as chlorite, gedrite and cummingtonite. In-situ trace element analyses of the zircons by LA-ICP-MS gives Hf from 10672 × 10-6 to 11822 × 10-6, Y from 12. 58 × 10-6 to 19. 41 × 10-6, Ti from 1. 63 × 10-6 to 9. 48 × 10-6, Th from 0. 32 × 10-6 to 1. 48 × 10-6,U from 365 × 10-6 to 663 × 10 -6, Th/U from 0. 001 to 0. 003, Σ REE from 7. 18 × 10-6 to 20.45 × 10-6. Chondrite-normalized REE patterns are MREE and HREE rich and show flat HREE curves and slightly positive Eu anomaly. All of the above suggest that the zircons from the garnet-rich altered rocks are of hydrothermal origin and formed at the same time as the high-grade iron ore and altered rocks. SHRIMP U-Pb dating of the zircons yield an upper intercept age of 1850 ± 16 Ma (MSWD = 2. 1) and a weighted mean age of 1840 ± 7 Ma (MSWD = 1.6). This age represents the metallogenetic age of the high-grade iron deposit, and matches with the uplift of the early metamorphic basement and rift-anorogenic magmatism in North China Craton at ∼ 1. 8Ga. This high-grade magnetite deposit is transformed from BIF by the tectonic thermal event at 1.9 ∼ 1. 8Ga.

Li L.X.,Chinese Academy of Geological Sciences | Li H.M.,Chinese Academy of Geological Sciences | Wang D.Z.,4th Geological Team of Hebei Geology and Mining Bureau | Yang X.Q.,Chinese Academy of Geological Sciences | And 3 more authors.
Acta Petrologica Sinica | Year: 2014

The Chengde area in Hebei Province is the most important magmatic iron ore-concentrated district in North China, with a proven resource reserve of ca. 1 billion tons. The iron mineralization in Chengde area has been lasted from Neoarchean to Paleozoic. The banded iron formations at Neoarchean, the Damiao-type iron deposits at Mesoproterozoic and the Habaqin iron deposit at Late Paleozoic are typical in general. All of them were products related with mafic-ultramafic complexs that formed at tectonic setting of regional extension, and thus providing good examples for metallogenic pedigree study and further exploration. All of the iron-bearing mafic-ultramafic complexes form long linear arrays and occur along the E-W striking Hongshila-Damiao fault. LA-ICP-MS zircon U-Pb ages of three samples of hornblendites in the Habaqin ultramafic complex show that the emplacement age of the ultramafic complex was 406 ±2Ma, which occurred at Devonian, implying that the geodynamic setting of the magmatism had occurred at post-collisional extensional setting after the arc-continental collision between the Bainaimiao arc belt and the northern margin of the North China Craton. As constrained by abundant inherited ages of this study as well as previous studies, the mafic-ultramafic magmatism along the Hongshila-Damiao fault were related to extensional setting and mainly occurred at Paleo-Mesoproterozoic, Devonian, Late Carboniferous-Early Permain, and Late Triassic. As constrained from comparative study of Hf isotope data of zircons, all of the tBm ages of the zircons aged at Neoarchean, Mesoproterozoic and Paleozoic are concentrated within the range from 2. 9Ga to 2. 7Ga. A similar result has been identified in the εht(t)-age diagram, plots of the εht(t) and corresponding zircon U-Pb age values form long linear arrays which coincide with the evolution line at the range of 2. 9 ∼ 2. 7Ga. Therefore, the ore-forming materials of the mineralization of iron in Chengde were initially from a mantle source or mafic lower crust which formed at 2. 9 ∼2. 7Ga.

Liu M.-J.,Institute of Geological Exploration | Liu M.-J.,Chinese Academy of Geological Sciences | Li H.-M.,Chinese Academy of Geological Sciences | Yu S.-X.,Institute of Geological Exploration | And 4 more authors.
Geology in China | Year: 2014

Rhenium and osmium isotopes in a molybdenite sample and ten pyrite samples were used to determine the timing of mineralization by ICP-MS. Re-Os model age of the molybdenite sample is (2376±37) Ma, Re-Os ages of the ten pyrite samples yielded three kinds of ages: (1) (2567±36) Ma - (2540±37) Ma (model age); (2) (2237±112) Ma (model dating); (3) (1572±140) Ma (isochron age). These data suggest that the molybdenite of(2376±37) Ma was formed during early Proterozoic, and was the oldest Re-Os model age of molybdenite, the pyrite of(2237±112) Ma was formed during early Proterozoic, and both of them indicate that the molybdenite and the pyrite were derived from the crust and represented an important hydrothermal activity in 2.3 Ga; the pyrite of (2567±36) Ma - (2540±37) Ma was formed during new Archaeozoic period and yielded the oldest Re-Os model age, which indicates that the pyrite was formed with BIF in 2.5 Ga; the pyrite of(1572±140) Ma was formed during middle Proterozoic, which indicates that pyrite was derived from the crust and represented a hydrothermal activity. The Re-Os isotopic dating result provides a new proof for the existence of hydrothermal activity in iron deposits of the Anshan-Benxi area, and is also important for understanding the ore-forming processes and tectonic evolution in this area.

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