The Geological Characteristics And Metallogenic Prognosis Of The Jinchang Au Deposit In Dongning County,Heilongjiang Province

The Jinchang Au deposit is located in the eastern of Xing'an-Mongolian orogenic belt.Metallogenic pianning belongs to Paleo-Asian metallogenic megaprovince,Jinlin-Heilongjiang metallogenic province,taipingling metallogenic belt.The region had experienced complex geodynamic evolution process,such as the development of the Paleozoic Paleo-Asian Ocean,the closure of Mesozoic Mongolia-okhotsk ocean and the subduction of the Paleo-Pacific plate.Therefore there has strong and complex geological structure,continual magmatic activity and favorable metallogenic conditions.The gold mineralization of Jinchang Au deposit is divided into three categories:cryptoexplosive breccia pipe type,like layered micro vein disseminated type and crack control type according to the ore-controlling structure,orebody occurrence and ore characteristics.Cryptoexplosive breccia pipe type ore bodies mainly are controlled by the breccia pipe structure,and present mostly pipe,but breccia type vein on the top of J0 pipe.Ore possesses the typical brecciated structure,and ore minerals are more concentrated in the cement of breccia edge.Like layered micro vein disseminated type concealed ore bodies are controlled by the drilling,and are stratiform or stratoid in the top of the deep granite porphyry on the whole.Metallogenic mode includes fine vein filling and metasomatism.Fine vein and disseminated are the main ore structure.There has obvious phenomenon of wall rock alteration and ore bodies mainly occurred in strong alteration beresitization rock.Crack control type ore bodies are mainly controlled by the ringlike and radial fracture structure.Annular crack control type ore bodies consists of a series of around banjiegou cricoid parallel distribution of ore vein,and radial crack control type ore bodies present large angle intersection with ringlike ore vein.There mainly haveIV thin vein ore bodies,which has clear contact line with surrounding rock and develop abundant metal sulfide-quartz vein with the higher gold grade.In the process of deposit ore-forming,there have the evolution sequence from the cryptoexplosive breccia pipe mineralization to like layered micro vein disseminated mineralization then to crack control mineralization.Fluid inclusion petrography and micro temperature measurement results show that breccia pipe type ore bodies is characterized by the development of melt-fluid inclusions in quartz,and the ore-forming fluid is a kind of complex hot lava;The melt-fluid inclusions not occurred in quartz of like layered micro vein disseminated type ore bodies that emerged a large number of S type inclusions,which shows ore-forming fluid belongs to a sort of high temperature and high salinity of fluid system;The quartz of Crack control type ore bodies mainly developed S and LV type,which reveals the ore-forming fluid has the features of high temperature and low salinity.The symbiotic development of S,SL,VL and less LV type inclusions proves inclusions occurred in a uneven capture system condition,namely strong immiscible effect,which is one of the important ore-forming mechanisms of the enrichment of a large number of the metallogenic material such as metal sulfide and gold.Hydrogen and oxygen isotopic data show that the ore-forming fluid is mainly derived from magmatic water,mixing a small amount of atmospheric water in the late mineralization.Ore sulfur isotope(0.1 ‰ ~ 8.8 ‰)research results display that the metallogenic material mainly dates from deep magma,which is consistent with develop inclusions contain daughter minerals of silicate and sulphide;Lead isotope research results reveal that the surrounding rock and ore body have almost the same source of lead,rooted in the deep magma of crust-mantle mixed source.Chronology research results show Jinchang Au deposit metallogenic epoch of 101~114 Ma.Comprehensive field geological survey and indoor study that Jinchang Au deposit belongs to a typical porphyry metallogenic system,and its ore-forming is closely related to granite porphyry.Detailed studies in ore-forming geological conditions show that NE and NW fault forming ore-forming structure before,is the main ore-controlling structure,with nearly EN fracture together managing breccia pipe that is the main ore-controlling structure for cryptoexplosive breccia pipe type mineralization,associated with the type of ringlike and radial fracture structure being ore-controlling and ore-containing structures for crack-controlling type ore bodies.Indo-chinese epoch diorite and Yanshanian granite and syenogranite is conducive to preliminary enrichment of ore-forming elements;Diorite porphyrite in the enrichment of ore-forming elements have a positive role,and moreoverprovide channels and heat source for the formation of ore body;In addition,the granite porphyry regard as ore-forming parent rock.Through field geological survey and indoor comprehensive study,combined with previous geophysical and geochemical information,the prospecting marks is determined.On geology,the contact zone of different rock mass,granite porphyry vein exposed location,fault development region and different direction fracture intersection zone can be used as a key area of the target zone;On geochemical exploration,on the basis of correlational analysis,cluster analysis and factor analysis results,combined with ore quality control condition,the Au-Ag-Bi-Cu-Pb-Zn as prospecting element combination,selects 8 combination anomaly target areas;On geophysical exploration,based on the different physical parameters of strata,rock mass and mineralized bodies,selects 4 polarization anomaly areas and 7 magnetic anomaly areas.On this basis,combined with geological,geochemical and geophysical information,I,II,III,IV,V,VI prospecting target areas were delineated in Jinchang Au deposit area,which provides the basis for the next step prospecting work in the future.