Ore-forming Geological Features And Ore-prospecting Direction Of Bishui Pb-Zn Deposit In Northern Great Xing'an Range

The Bishui lead-zinc deposit is situated in the northern part of the Great Xing'an Range,the north of the Derbugan fault and south of the Tayuan-Mohe fault.It belongs to the Great Xing'an Range volcanic zone in the Xingmeng orogenic belt.The study area was influenced by the the Paleo-Asian tectonic system before the Paleozoic and the eastern part was tectonically linked to the Mongol-Okhotsk Ocean closure and the subduction of the Paleo-Pacific Ocean during the Mesozoic.The region,one of the nineteenth major metallogenic belts in the China,belongs to the northern part of the Derbugan metallogenic belt,which has large metallogenic geological conditions and great metallogenic potential.In this paper,based on the study of metallogenic geological conditions and geological characteristics of Bishui lead-zinc deposit,the genetic type of the deposit is determined.According to the analysis and processing of stream sediment survey and geophysical data,the prospecting indicators are extracted and the metallogenic prediction area is delineated,which points out the direction for further exploration and prospecting in this area.The outcropped strata in the study area are mainly volcanic rocks of Cretaceous Guanghua Formation?K₁gn?,Longjiang Formation?K₁l?and Ganhe Formation?K₁g?.Among them,Guanghua Formation is mainly composed of rhyolite,rhyolitic tuff and tuff lava and other intermediate-acid volcanic rocks.It is an important country rock for lead-zinc deposits in the area.The intrusive rocks are mainly middle-fine-grained diorite and granite porphyry of late Yanshanian.Up to now,seven mineralization ore bodies have been found in Bishui lead-zinc mine area,most of which are vein-like and veinlets,most of which occur in NW-trending tectonic fracture zone and at the junction of NW and NE-trending faults.The NW-trending structure is the main ore-controlling structure in the area,and the NNW and NW-trending structures derived from it are the main ore-hosting structures of the deposit.Zircon U-Pb dating of rhyolite from the Guanghua Formation,which is closely related to mineralization,shows that its weighted average age is 141.06±0.69 Ma,interpreted as the formation age is early Cretaceous.Based on the metallogenic epoch of the lead-zinc deposits in the Great Xing'an Range metallogenic belt,we believe that the mineralization epoch of the Bishui lead-zinc deposit is the early Cretaceous.Based on the analysis and processing of geochemical data of 1:10000 soil and stream sediments in the region,190 single element anomalies and 31 multielement combination anomalies were delineated,and geochemical anomalies were mainly distributed in the vicinity of volcanic tectonic fracture zone.Aeromagnetic anomalies in the study area show that the distribution patterns of geological bodies and high magnetic anomalies are roughly the same.Negative anomalies are mainly caused by intermediate-acid volcanic rocks of Guanghua Formation,whereas positive anomalies are caused by volcanic rocks of Ganhe Formation,granite porphyry and diorite of Yanshanian intrusive rocks.The interpretation of high magnetic structure shows that the geological boundary body of the Cretaceous volcanic crater coincides with the outcropping form of intermediate-acid volcanic rocks in the Guanghua Formation,and the NW direction reflected in the form of volcanic ring coincides with the geological boundary of the lead-zinc ore body.This paper summarizes the metallogenic geological conditions and geophysical and geochemical anomaly characteristics of the mining area,and summarizes the following prospecting indicators:1)the discovered ore bodies are closely related to the rhyolitic tuff of the Guanghua Formation,most of which are mineralized,and the intermediate-acid volcanic rocks outcropping on the surface are important stratigraphic indicators of lead-zinc deposits;2)the NW-trending faults developed in the mining area provide important space and passage for magma and hydrothermal fluid,and are the main ore-hosting structures,which are the main indicators of structural prospecting in the mining area;3)silicification,sericitization and pyritization are particularly strong in the adjacent country rocks,which are closely related to mineralization and can be used as important alteration prospecting indicators;4)exploration geochemical characteristics show that Pb-Zn-Ag is associated with large area of element anomaly and high anomaly value,and the concentration center is obviously the main exploration geochemical prospecting indicator;5)the analysis of exploration geophysical characteristics show that the lead-zinc ore bodies are characterized by low resistance and high polarization.The low and gentle positive anomalies associated with low and gentle positive anomalies in high-precision magnetic survey are important prospecting physical indicators for lead-zinc deposits in mining areas.According to the metallogenic geological conditions and prospecting indicators,three metallogenic prognostic areas are delineated in the mining area,including one grade I metallogenic prognostic area and two grade II metallogenic prognostic areas.