| The Longgouhe rock mass is located in Mohe County,Daxinganling region,northeastern Heilongjiang Province.The type of rock produced by this rock mass is biotite diordiorite.There is a placer gold mine near the rock mass that has been mined for many years.The physical and chemical conditions of the formation of the rock mass and the origin of the rock are unknown,and the mineralization potential is unclear.In view of this,this article studies the chronology,geochemistry,and biotite hornblende composition characteristics of this rock mass.The rock formation and mineralization significance of the body are analyzed.The results show that the contents of U and Th in the zircon samples are 711×10-6-2255×10-6and 225×10-6-2313×10-6,respectively,and the Th/U ratio is 0.4-1.0?Th/U>0.1?,with typical magmatic zircon characteristics.The weighted average age of zircon 206Pb/238U was 129.77±0.99Ma?MSWD=0.16?,and the value of?Hf?t?in zircon varies from-0.59 to-4.81,indicating that the rock zircon is a remelting crust source material products.The Si O2content of the Longgouhe rock mass is between 61.37%and 66.59%,which is mainly a medium acid intrusive rock.The rock is characterized by high Al?Al2O3 content between 15.61%-16.37%?and high Mg#index?between 52-56?.The characteristics of rare earth elements are mainly light rare earth enrichment and strong depletion of heavy rare earth elements.The content of Yb is 0.48-0.71 ?g/g,which is lower than 1.90?g/g,and?Eu is between 0.74 and 0.87,showing a weak negative anomaly.The rock mass is rich in lithophilic elements?Rb,Ba,Th,U,K,and Sr?.The Sr content is between 1082-1396?g/g,and the Y content is between 6.82-9.62?g/g.Between133-162.The sample Sr is positively anomalous;Nb and Ta are low,showing strong Nb,Ta and weak Ti deficiencies on the trace element spider diagram.The geochemical characteristics are similar to those of Adakite.By testing the Sr-Nd-Pb isotope of the sample,the?value of lead isotope is between 9.53-9.55,and the 87Sr/86Sr ratio is 0.709,indicating that it is from crust-mantle mixed source material.The chemical composition of hornblende in biotite diordiol shows that hornblende is calcium-rich w?Ca O??11.24%-11.79%?,magnesium-rich w?Mg O??11.78%-15.11%?,belong to magnesia,with a crystallization temperature of 748.86?-861.87?,an average temperature of 814.93?,and a pressure of 65.53MPa-195.83 MPa,corresponding to magma emplacement depth of 2.5km-7.4km,magma oxygen fugacity during crystallization is?NNO+1.19,water content is w?H2O?=4.70%,reflecting the high temperature,high oxygen fugacity,Characteristics of rich water content and medium and shallow emplacement.Biotite's Fe2+/(Fe2++Mg)ratio is relatively uniform.Biotite composition of biotite II diordiorite rock shows that biotite is rich in magnesium w?Mg O??12.40%-12.98%?,belong to magnesia biotite.Biotite crystallization temperature is 680?-700?;pressure is 198.08-204.10MPa,corresponding to magma emplacement depth is 6.54-6.73km;magma oxygen fugacity during crystallization is 10-13-10-15;magma source is crust-mantle mixture source.Therefore,it can be considered that the diordiorite in the Longgouhe rock mass has the characteristics of medium and high temperature,high oxygen fugacity and water content,crust-mantle mixed source material,and shallow emplacement.In summary,the Longgouhe rock It has the potential to form large gold deposits. |
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