| The Dongbulage porphyry Mo deposit with hydrothermal vein-type lead-zinc deposit is in southern Greater hinggan western slope metallogenic belt,located between Xilamulun River fracture and Hegenshan fracture,belong to the southern Greater hinggan tectonic-magmatic belt.The mineralization features occurred in granite-porphyry,quartz porphyry and Baiyingaolao Formation intermediate-acid pyroclastic rocks near the contact zone.The deposit has a typical porphyry alteration characteristics,mainly potassium,silicon technology,sericitization,and carbonation.The geochemistry of granite in the mine area are characterized by high Si O2,K2O,low Ca O,poor Mg O,Al2O3 and TFe2O3,their geochemical features show the significant positive anomalies in U,La,Hf,Yb,Lu,Rb with negative anomalies in Sr,P,Ti,Ta,Nb,Ba,Eu,the REE patterns shows the typical"right-inclined seagull wing-shaped".The granite belong to the typical A-type granites.The zircon LA-ICP-MS U-Pb dating results show that the granite porphyry,quartz monzonite and quartz porphyry's zircon U-Pb ages are(155.4±1.1)Ma,(157.8±1.6)Ma and(158.7±0.6)Ma,which indicates that they are the same source and synchronous magmatic evolution in different stages,products of magma movement in Late Jurassic.The Re-Os isochron age of six molybdenite samples is(162.1±1.3)Ma.The accurate dating results indicate that the ore-forming and rock-forming process is basically coincide.They are in accordance with the polymetallic metallogenic epoch in the region.The granite porphyry,quartz monzonite and quartz porphyry(87Sr/86Sr)i values range vary from 0.66788 to 0.70912,most?Nd(t)values are greater than 0,minority samples?Nd(t)are less than 0,which has more old of TDM value,the other samples?Nd(t)are greater than 0,and has more young of TDM value.The zircon?Hf(t)values range vary from+2.3 to+10.3,mean value is+8.8,two stages Hf model ages vary from 942Ma to 495Ma.Sr-Nd-Pb-Hf isotopic studies show that magmas were possibly derived from depleted mantle,with ancient crust material varying degrees of mixing characteristics.Fluid inclusions are divided into three categories,homogenization temperature values range vary from 193 to 456?and salinity values range vary from 2.57 to54.51 Na Cleqv,ore-forming temperature and salinity variation range is lager.From the quartz-molybdenite stage to calcite stage lead-zinc ore stage,ore-forming fluid temperatures evolution trend are from high temperature to low temperature,three temperature intervals are 243?375?,231?366?,193?327?.the main components in the inclusion are the gas-liquid H2O,CO2,belong to H2O-CO2-(hydrocarbon)system and the H2O-Na Cl system.Molybdenite phase inclusions with the characteristics of boihng inclusion,decompression boiling are leading CO2 and a lot volatile to escape,which is the main reason for Mo deposition.And temperature reduction is the main reason for Pb-Zn deposition.C-H-O isotope research indicates that mineralization fluid derived from magma,and with the mineralization process mixed with more meteoric waters,metal sulfide S-Pb isotopic studies show that metallogenic material mainly came from magma,and mixed with more rock material in the metallogenic process.The granitoid has the features of post-collision magma activities,according to rock body forming age and petrogeochemistry features,representing they were formed after the closure of Mongol-Okhotsk Ocean with the post orogenic extension period in combination with the regional tectonic evolution,which suggests that research area was in an extensional tectonic setting in Late Jurassic. |
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