Geological Features And Ore Genesis Of Gold Metallization In The Walali-Beixili Area,Heilongjiang Province

The Walali-Beixili area is located in the middle-northern Greater xing'an Range where there are a series of gold deposits and ore deposits closely related to Paleozoic magmatic activities.In this paper,take Walali,Heilonggou gold deposit and Fenghuang Mountain ore spot as the main research objects,geochemistry,zircon U-Pb and Lu-Hf isotopes research,petrography of fluid inclusions,microthermometry and compositional analysis are carried out for the metallogenic rocks and ore-forming fluid,so that to investigate the diagenetic and metallogenic epoch,petrogenesis and provenance,ore-forming fluid characteristics and metallogenic dynamics background of gold deposits in the area,moreover,get the following points:The gold ore bodies in the Walali-Beixili area are mostly distributed in the granitoid rocks and the quartz veins located at the contact zone between granites and Xinghua formation.The main metal minerals are pyrite,galena,sphalerite and so on.The ore texture is mainly composed of crushed structure and grain texture,and the ore structure is mainly in vein and honeycomb.The main types of wall rock alteration are silicification,sericitization and a little carbonation.Besides,the main metallogenetic rocks mainly are Late Carboniferous moyite and monzonitic granite.The distribution of ore bodies is controlled by ductile deformation.Late Carboniferous granites of the metallogenic rock bodies are characterized by high K,Si,Al,and calc alkalinity,which also enriched with high field strength elements such as Th,Zr and Hf,and depleted large ion affinity elements such as Sr and Ba,besides,with obvious negative Eu anomaly,the granites have the genetic characteristics of the transition type from I type to A type.The?_Hf?t?values of the moyite and monzonitic granite are+2.6⁺5.5 and-5.4⁺2.3,respectively,with T_DM2 range from972 Ma to 1157Ma and 1180 Ma to 1660Ma,respectively,which indicate that the granite studied can be derived from partial melting of the lower crust in the depleted mantle and is contaminated by ancient crustal materials during emplacement.The zircon U-Pb ages of granites of the metallogenic rock bodies are311.0Ma?FXL-09??312.6 Ma?XJ-05??313.6 Ma?FHS-N1??317.2Ma?P17-1?,which belong to the product of Late Carboniferous magmatism,consistent with magmatic activity in the area.Moreover,the gold bearing quartz veins were formed at the late stage of magmatic evolution,it is presumed that the metallogenic epoch of the gold deposits was the Late Carboniferous.The fluid inclusions in quartz minerals of carrier minerals in the gold deposits are mainly gas liquid two phase inclusions,which are NaCl-H₂O systems.The homogenization temperature of the main metallogenic stage is 159.2²07.1?,the salinity is 0.39¹0.58%NaCl eqv and the density is 0.77⁰.95 g/cm³,which is characterized by low temperature,low salinity and poor CO₂.The granite of the metallogenic rock bodies and the gold deposits were formed in the transitional setting from syn-collisional to post-collisional which was related to Songnen plate subducting and colliding with the Xing'an-Erguna plate in the Late Paleozoic.The genetic type of gold deposits in the area is mainly post-magmatic hydrothermal type.In the Early Carboniferous,with the gradual closure of the Paleo-Asian Ocean,the Paleo-Asian Ocean plate subducted under the Xing'an-Erguna plate.In the Late Carboniferous,the final closure of the ancient Asian Ocean resulted in a collision between the Songnen plate and the Xing'an-Erguna plate and the thickening of the continental crust.The plates subducting down to the Xing'an-Erguna plate subducted and disconnected,causing the convection of the lower asthenosphere,and the region entered the post-collision extension environment.With the lithospheric extension thinning,the high potassium calc alkaline magma was invaded.In the process of emplacement,the gold elements in the strata were activated and moved into magma under the joint action of the heat source provided by the magma and the brittle shear of the region.In the late stage of the evolution of the magma,the gold elements were enriched,forming the ore-forming fluid and eventually filling the mineralization along the fissure.