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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.

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.

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.

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.

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.

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