Metallogenic Regularity And Prospective Prediction Of Porphyry Molybdenum Deposits In Central Jilin Province,NE China

The central Jilin Province is an important resource base for precious metals and nonferrous metals in China.It's located in the intersection of the southern margin of the eastern Xing'an-Mongolian orogenic belt and the northern margin of North China Craton.In recent years,important ore-prospecting breakthroughs of molybdenite deposit have made in this area.Following the Daheishan large molybdenite deposit,many large to medium scale molybdenite deposits have been discovered,such as Chang'anbu,Fu'anbu and Jidetun,showing great potential for further exploration.All most molybdenum deposits in the central Jilin Province belong to the porphyry single molybdenum deposits,formed in the late Lower Jurassic or early Middle Jurassic.Thanks to large number of ore deposits and huge quantity of resources,domestic and foreign scholars pay attention to ore-forming geological conditions,geological characteristics of deposit,characteristics of ore forming fluids and ore genesis.However,there is fewer studies relative to regional metallogenic regularity,such as metallogenic specialization of magamatic rocks and ore-forming series.The issues of prospecting potential and prospecting target should be defined.On the basis of metallogenic background in central Jilin Province,this paper selects three newly discovered representative porphyry molybdenum deposits?Chang'anbu,Fu'anbu and Jidetun?,Through systematic studies and regional deposit comparisons,ore-forming Geological Conditions mineral alteration features,and the stage of hydrothermal mineralization are identified.Combining previous data with such new data in this study as isotope geochronology,rock geochemistry and H-O-S-Pb isotope,this dissertation summarizes the time of metallogenic intrusions and associated mineralization,material source,spatial distribution law and prospecting criteria.Based on the second development of previous geological,geophysical and gechemical data,multi-element prospecting information has been extracted,and the MRAS evidence weight model has been used to comprehensive information ore prospective mineralization prediction.Some research progresses and conclusions can be listed as followings:1.The porphyry deposits is the major industrial types of molybdenum deposits in central Jilin Province.Except the Chang'anbu deposit,a molybdenum?copper?deposit,the large and medium scaled deposits in this area are all molybdenum deposits,the granitoids associated with NE and NW faults are the main rock-controlling and ore-controlling structures.The ore bodies have complex and diverse shapes,and they are mostly lenticular and irregular.Most of the ore body is produced in the rock body of monzonite granite or granodiorite?porphyry?,while a small part is produced in quartz veins or detonation breccia tubes.The metallic minerals are mainly molybdenite with little pyrite and chalcopyrite.The metallic minerals are are mainly chalcopyrite and molybdenite,associated with a small amount of pyrite and magnetite in Chang'anbao deposit.The alterative zones are obvious,and the alteration type include potassic alteration,silication,chloritization and chloritization.Mineralization can divide to five stage:quartz-pyrite???,quartz-magnetite-pyrite???,quartz-molybdenite???,quartz-polymetallic sulfide stage???and quartz-carbonate stage???.2.The ore-forming materials of the porphyry molybdenum deposits in this area are mainly from granitic magma.The mineralization formed in an active continental margin and related to plate subduction.The ore-forming re-forming porphyries in Chang'anbu,Fu'anbu,Jidetun and other deposits have higher SiO₂?SiO₂=66.67%?75.43%?,higher A1₂O₃ content?12.91%?16.44%?,and lower MgO content?0.09%?1.54%?,Lower Ritman index??=2.09?2.57?,lower Y(3.37×10^-6?20.10×10^-6)and Yb(0.46×10^-6?2.75×10^-6).The trace element composition characteristics are relatively enriched in large ion lithophilic elements?LILE?and light rare earth elements?LREE?,while the content of high field strength elements?HFSE?is relatively low,with a negative Eu.The characteristics are consisted with early Mesozoic granites in Northeast China.The?³⁴S value of sulfides in representative porphyry molybdenum deposits is range 0.3‰to 4.0‰,Pb²⁰⁶/Pb²⁰⁴ value of 18.046?18.775,Pb²⁰⁷/Pb²⁰⁴ value of15.497?15.655,Pb²⁰⁸/Pb²⁰⁴ value of 37.931?38.819;the?D_V-_SMOW in the ore is from-102.2‰to-79.5‰,and the?¹⁸O_V-SMOW value of 8.2‰?11.6‰.3.Large scaled molybdenum deposits in central Jilin Province formed in the late Early Jurassic or early Middle Jurassic and were closely related to the westward subduction of the ancient Pacific plate.The LA-ICP-MS zircon U-Pb age of the ore-bearing rocks in the Chang'anbu deposit is 182.10±1.20Ma,the molybdenite yields weighted average Re-Os of 168.0±1.0Ma;the molybdenite yields Re-Os isotope isochron age of 166.9±6.7Ma of the Fu'anbu deposit,169.1±1.8Ma of Jidetun deposit;and 168.2±3.2Ma of Daheishan deposit.Therefore,large-scale molybdenum mineralization in central Jilin is an important part of the large-scale porphyry diagenesis and mineralization events during Jurassic in northeast China.4.The porphyry molybdenum deposit has signs of prospecting on different scales in central Jilin.The Regional prospecting indicators include Early-Middle Jurassic granite porphyry,granodiorite porphyry,monzonite granite and the hydrothermal breccia,the intersection of faults and secondary faults;On deposit scale,the prospecting criteria include,the widespread Yanshanian granite,NE-and NW structural fissures and breccia tube,and mineralized quartz veins,silicification,potassic alteration,sericitization,and epidotization.5.The geological prospecting model and prediction model of Mo deposits were established in this area.and the Mo exploration potentials was evaluated using the MRAS in central Jilin.13 prediction variables were extracted and constructed as evidence factors and their weights were calculated,and the evaluation of metallogenic favorableness was carried out.Finally,there were 2 A-type prospecting prospects and 3B-type prospecting prospects.The prospecting areas delineating Type A and Type B are basically near the contact zone of the Middle Jurassic monzonite,granite diorite,and alkali feldspar granite,It has higher Mo and Cu,W anomaly near the northwest and northeast faults.Which is similar metallogenic conditions with known deposits.It indicats that the nearby area of the deposits has better metallogenic potential,In the future work,it's the improtanter area for mineral exploration.