| Beishan orogenic belt belongs to southern margin of Central Asian orogenic belt.Undergoing multi-phrase geological structures and magmatic activities from Neoproterozoic to Early Mesozoic Era,Beishan orogenic belt has superior ore-forming geological condition and possesses quite abundant mineral resources,so it is one of the important metallogenic belt of China.As a typical iron deposit of Beishan metallogenic belt,the study of deposit type and genesis of Hongshan Iron Deposit is significant to the later prospecting.Through the research of Hongshan Iron Deposit from its geologic structure background,ore morphological feature,features of the ore-bearing rock series and surrounding rocks,geological and geochemical features of the deposit,metallogenic age and deposit type and genesis,the author gets the following knowledge:1.Hongshan Iron Ore belongs to the Sedex type iron deposit,is hot brine sedimentary-metamorphic iron deposit.The ore-bearing layer of the Hongshan Iron Ore is the formation of a set of epimetamorphic clastic rock with carbonate,the mineralization age is the Neoproterozoic Sinian Period,and it is obviously affected by multi-period hydrothermal metamorphism in the early Paleozoic era to Mesozoic,and the age of geothermal event is 429.4-448Ma?364.7-384Ma?237Ma and 126Ma.Among them,364.7-384Ma is the main geothermal event age in this area.2.The content of SiO2 in the Hongshan Iron Ore is 21.5-68.4%?average 43.68%?,the content of Fe2O3T is 27.06-65.16%?average value is 41.77%?,the Al2O3 content is 0.93-3.81%?average 2.2%?,MgO 1.08-8.99%?average 5.6%?,CaO 0.55-14.9%?average 4.7%?,Na2O 0.04-0.57%?average 0.2%?,K2O 0.03-0.83%?average 0.4%?,MnO 0.09-6.19%?average 1.3%?,TiO2 0.07-0.28%?average 0.2%?.Among them,the content of SiO2 and Fe2O3T and is basically the same with the BIF iron ore content originate from the domestic submarine volcano?with some terrigenous debris joining?.The trace elements Ba,Pb,Th,U,Nb and Ta in the Hongshan Iron Ore are relatively rich,and Sr exhibits a strong loss.The total amount of light rare earth elements?LREE?is 9.19×10-6-60.21×10-6,and heavy rare earth elements?HREE?12.57×10-6-38.97×10-6,LREE/HREE is 0.57-2.01,?La/Yb?PASS=0.1-0.5,showing a relative loss of LREE and the relative enrichment of HREE,which is basically the same with the characteristics of Jingtieshan Iron Ore.All of this also indicate that the formation of Hongshan Iron Ore is related to volcanic activity.3.In the Hongshan Iron Ore,thin-layered iron jasper rock,lentoid iron jasper rock and tuff interlayer are found.The source rock is silicoferrite colloidal chemical sedimentary rock,which shows that the formation of the Hongshan Iron Ores is the hydrotherm colloidal deposition related to volcanic activity.The ratio of SiO2/Al2O3 in Hongshan Iron Ore is 7.69-56.53,and the average is 23.34;the Sr/Ba ratio is 0.01-2.66,and the average is 0.44;Eu shows positive anomaly;the average value of Y/Ho is 28.52.All of this show that the ore-forming material of iron ore mainly comes from iron-rich hot brine materials related to volcanism and volcanic hydrotherm.The sulfur,hydrogen and oxygen isotopes of Hongshan Iron Ore show that the ore-forming fluids are mainly derived from magmatic water and metamorphic hydrothermal fluids.The positive anomalies of the U and Th elements and no anomalies of Ce all show that the sedimentary environment of the Hongshan Iron Ore is hypoxic.4.The Hongshan Iron Ore is divided into two stages:?and?.The stage I is the main metallogenic stage: quartz + magnetite + pyrite + chalcopyrite.The stage?is quartz+pyrite stage.The fluid inclusions of this two-stage are mainly liquid H2O inclusions,gas phase H2O inclusions,rich liquid two-phase H2O inclusions and rich gas two-phase H2O inclusions,among which the content of gas-liquid H2O inclusions is the highest.The homogenization temperature of the gas-liquid H2O inclusions is 140-350?;the average is 245?;the salinity is 0.53-19.68% NaCleqv;the average is 10.04% NaCleqv;the fluid density is 0.76-1.05g/cm3;the average is 0.95g/cm3.Characterized by medium-high temperature,medium salt,medium-high density fluid characteristics,it belongs to the H2O-CO2-NaCl system.In the stage?,the homogenization temperature of the gas-liquid H2O inclusions is 80-260?;the average is 170?,salinity 0.53-17.79% NaCleqv,average 9.16% NaCleqv;the fluid density is 0.86-1.05g/cm3,the average value is 0.96g/cm3,with medium-low temperature,medium salt?salinity variation range is smaller than stage I?,medium-high density fluid characteristics,it also belong to H2O-CO2-NaCl system.The metallogenic pressure of stage?is 123.68×105-384.32×105Pa;the average is 254×105Pa,the metallogenic depth is 0.40-1.28km,the average 0.84 km.The metallogenic pressure of stage ? is 22.60×105-311.92×105Pa,and the average is 167.26×105Pa;the metallogenic depth is 0.08-1.04 km,the average 0.56km,all belongs to the hypabyssal metallogenic depth. |
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