Study On The Geological And Geochemical Characteristics And Genesis Of The Hongshuihe Iron Ore Deposit,Dulan,Qinghai Province,China

The Hongshuihe iron ore district is located in Dulan,Qinghai Province.Its geotectonic location is located in the north-middle part of the eastern Kunlun orogenic belt on the northern margin of the Qinghai-Tibet Plateau,which is the north of the Middle Kunlun fault,adjacent to the Qaidam Basin in the north and the subduction collision complex rock belt in the south of the East Kunlun Mountains,controlled by the fault structures as a whole.In this paper,we take the Hongshuihe iron deposit as the main research object to identify its geological and geochemical characteristics.The strata in the iron ore district includes Jinshuikou Group and Langyashan Formation.The ore bodies are layered or layered similarly in the Langyashan Formation.The faults in the iron ore district are widely distributed,the NWW-SEE tectonic lines with the same regional structures are produced by the affect of Middle Kunlun fault.The iron ore district is a wing of the regional folds,which mainly shows the monoclinic stratum.The magma rocks in the iron ore district and its surroundings are widely developed,their lithology are mainly neutral-acidic intrusive rocks,such as mainly NW-distributed Early-Middle Triassic Quartz diorite and Granite,which was previously considered as the Hercynian period.The mineralization is divided into sedimentary period,metamorphic period,hydrothermal period and oxidation period.Ore types include massive ore,strip ore and hydrothermal superimposed ore.The lithology of ores are magnetite quartzites,the ore minerals are mainly magnetite and hematite,followed by pyrite,and the gangue mineral is mainly quartz.The ore texture is mainly semi-self-other shaped grain texture,followed by self-semi shaped grain texture.The ore structure is mainly strip-shaped structure,blocky structure,vein-shaped structure.The ore-hosting surrounding rock is chlorite phyllite,which is from residual muddy texture to scale crystal texture,phyllite structure,rich in minerals such as chlorite,epidote,sericite,calcite,quartz,and its original rock is sandy sedimentary rocks.The detrital zircons of the phyllite show the magma texture.The ages are mainly concentrated from 699Ma to 1914Ma,and there are four main peaks:788Ma,1118Ma,1557Ma and 1831Ma,respectively.We speculate the earliest sedimentary age is788±9Ma,limiting the formation age of the deposit to the Neoproterozoic.The?_Hf?t?values of these detrital zircons from the phyllite vary from-30.4 to 8.3,indicating that the Hf isotope sources have highly heterogeneity,with two-stage model ages of1448-3596Ma and the positive and negative?_Hf?t?values,which indicate that the source rocks of these zircons include both newborn crust material and reconstructed ancient crust material.The newborn crust might be from Mesoproterozoic and the reconstructed crust from Archean.Through discussing on the classification of zircon ages and comparing the ages of some old sedimentary strata and intrusive rocks of the adjacent areas,it is inferred that the basement of Archean,Baishahe Formation,Xiaomiao Formation,Wanbaogou Group and the intermediate-acid rocks formed in the eastern Kunlun in the late period of Mesoproterozoic are possible provenances.Main trace element test results show that the ores are rich in SiO₂ and TFe₂O₃,the contents of Al₂O₃ and TiO₂ are higher than surrounding rocks,which indicates the presence of terrigenous substances in the formation of ore bodies.The contents of MgO,CaO,MnO,Na₂O,K₂O and P₂O₅ are lower;the SiO₂ contents of the surrounding rock phyllite are high,the TFe₂O₃ contents are obviously lower than the ores,and the remaining major elements are equivalent to the ores.The contents of large ion lithophile elements Rb,Sr,Ba and V,Cr,Y in the samples of ores and surrounding rocks are high and vary greatly.The contents of Nb,Ta,Zr and other elements in the surrounding rocks are basically normal,and in the ores are relatively low.The REE distribution map of the surrounding rocks is relatively flat,indicating that the sedimentary environment is consistent,???REE?is?58.5²28.1?×10^-6,??LREE?is?46.82²03.16?×10^-6,LREE/HREE is 4.03⁸.14,K₂O/Na₂O is 0.11⁴4.00,the average value is 8.38,Eu/Eu*value ranges from 0.87 to 1.16,showing the characteristics of the sedimentary environment of the passive continental margin;The REE distribution map of the ores show that LREE are relatively depleted,HREE are relatively enriched,and Y/Ho values are medium,it is basically consistent with the high temperature seabed hydrothermal and seawater mixing curves,but only the Eu anomalies are different,indicating that the sedimentary environment is more inclined to the mixed environment of low temperature hydrothermal fluid and seawater.The Hongli skarn-type Pb-Zn deposit is located in the northeast of the Hongshuihe iron ore belt,we use the geochemical dataw of the deposit to confirm whether the formation of quartz-sulfide veins in the Hongshuihe hydrothermal superimposed ore is related to the skarn deposit.After testing and analysis,the?³⁴S_V-CDT-CDT values of the skarn deposit vary from-2.44‰to 3.34‰,with an average value of 1.67‰,which are consistent with the characteristics of cellar source sulfur in the magma;the?³⁴S_V-CDT-CDT values of the sulfides of hydrothermal superimposed iron ores vary from 6.36‰to6.47‰,which is obviously higher than that of the former,suggesting that there is neither genetic relationship.The?³⁴S values of these samples are slightly higher than those of the magma hydrothermal sulfur,indicating that the sulfur sources are contaminated by the crust material.Lead isotope test results show that the former sulfides ²⁰⁶Pb/²⁰⁴Pb,²⁰⁷Pb/²⁰⁴Pb,²⁰⁸Pb/²⁰⁴Pb range from 18.3756 to 18.4109,15.2615 to15.6239,38.4032 to 38.4269,and the latter ²⁰⁶Pb/²⁰⁴Pb,²⁰⁷Pb/²⁰⁴Pb,²⁰⁸Pb/²⁰⁴Pb range from 18.4300 to 18.7832,15.6893 to 15.7439,38.6340 to 38.7932,respectively.The difference in lead isotope composition indicates that there is neither genetic relationship.The late hydrothermal fluid may originate from the deep part,and the surrounding rocks are extracted during the upwelling process,so that it has the characteristics of mixed contamination of the crust source material.The H-O isotope test results show that the quartz?¹⁸O values in the quartz-sulfide veins of the Hongshuihe iron deposit are 18.0‰and 14.6‰,and the estimated fluid?¹⁸O_H2O2O values are 11.1‰and 7.7‰;the fluid inclusions hydrogen isotope?D values are-105.5‰and-93.5‰.We believe that the hydrothermal source of quartz-sulfide veins in the late Hongshuihe BIF iron deposit is mainly the primary magma hydrothermal fluid.Finally,we conclude that the genetic type of the Hongshuihe iron deposit is consistent with the Rapitan-type BIF,and its metallogenic model is sedimentary metamorphism-hydrothermal superimposed,The ore bodies and their surrounding rocks are the same sedimentary products,and the sedimentary environment is the passive continental margin.The hydrothermal fluid formed by the hot water jet interacts with seawater to extract Fe and Si in the oceanic crust,entering the interglacial period after the end of the Sturtian glacial period,changes in the redox environment of seawater lead to precipitation and enrichment of Fe and Si substances,accompanied by the incorporation of terrigenous materials into the sedimentary process.Due to the convective circulation of seawater,the iron siliceous layer is alternately precipitated to form a rhythmic sedimentary form,the deposit experienced metamorphism and hydrothermal superposition in later period.