Fluid Mineralization And Prospect Evaluation Of The Duobaoshan Porphyry Cu(Mo) Deposit, Heilongjiang

The Duobaoshan porphyry Cu(Mo) deposit, located in the eastern part ofXingmeng orogenic belt, is the largest porphyry deposit in theDuobaoshan-Aershan Metallogenic belt on the central and northern Daxinganling.Based on the fine ananlysis of the Duobaoshan porphyry Cu(Mo) deposit andcomparative studies on the typical deposits, this thesis clarified the relationshipbetween alteration and mineralization; clearly put forward thealteration-mineralization stage; explained the reasons for lack of high salinityinclusions within the early stage; constrained fluid properties andphysical-chemical conditions; gave out a new model of fluid evolution; discussedthe ore-forming material source; set up a new metallogenic model after analysedmultistage mineralization; summarized the ore prospecting model; launched theregional prospecting evaluation.Four ore-forming stages are recognized at Duobaoshan deposit:(I) Potassicand silicic stage;(II) Silicification-molybdenum mineralizing stage;(III)Phyllic-copper mineralizing stage; and (IV) carbonate-quartz stage. Fluidinclusions in quartz can be identified as aqueous water, CO2-rich, daughtermineral-bearing and pure CO2.Fluid inclusions of stage (I) are characterized byaqueous, CO2-H2O and pure CO2, with homogenization temperatures of245-400℃, salinities of6-10wt%NaCl eqv., and those of stage II is dominated byaqueous, CO2-H2O, daughter mineral-bearing inclusions, with peakhomogenization temperatures of260-300℃and salinities of1.7~39wt%NaCl eqv.Stage III is also characterized by aqueous and CO2-H2O inclusions, with peakhomogenization temperatures of200-280℃, salinities of0.1-24.8%wt%NaCleqv., whereas stage IV is simply aqueous, with homogenization temperatures of125-170℃, salinities of0.5-12.8wt%NaCl eqv.. Respective trapping pressures forstage I, II, III are110-160MPa,58-80MPa,8-17MPa. The ore-forming fluidgenerally belong to H2O-CO2-NaCl fluid system in the early stage and graduallybecome H2O-NaCl fluid system in the late stage. Mo mineralization is mainlyrelated with CO2-H2O immiscibility, and Cu mineralization is yielded by boilingaction. Compared with typical porphyry deposits, the number of halitecrystal-bearing inclusions are smaller in the Duobaoshan porphyry copper deposit,which is mainly related to the transformation and destruction at Yanshanian. Moreover, the phenomenon that most of the halite crystal-bearing inclusionsappear within stage II instead of stage I suggests possible presence of CO2-H2Oimmiscibility.The34S values of pyrite and chalcopyrite mainly range from-1.6to-4.6permil, suggesting predominantly source of deep magma chamber with lesseramounts of Duobaoshan formation. Hydrogen(D) and oxygen(18O) isotopiccompositions for stage I fluid at the Duobaoshan deposit range from-87.2to-95.5per mil and7.2to8.1per mil, respectively, which are constrained by magmaticfluid. Those for stage III shift evidently toward meteoric water, with the D valuesof-82.2to-104.2per mil and18O values of2.0to3.4per mil, which indicates aevolution process from magmatic hydrothermal fluid to a mixing magmatic andmeteoric fluid. The characteristics of rare earth elements show that Duobaoshangranodiorite and granodiorite porphyry pluton are probably related to the thesubduction and partial melting of ocean crust. Cluster analysis and Factor analysisof trace elements suggest:(1) Mo, Bi, Cu, W have a close correlation, which canbe the indicator elements for mineralization;(2) as the mineralizing center ofporphyry pluton, NW trending schistosity zone where banding phyllic alterationoccur may be influenced by Yanshanian schistosity structure. Geochronologicaldata show that Duobaoshan area are influenced respectively by paleo-asianoceanic subduction at (280Ma±) and by Paleo-Pacific Ocean during the Jurassicperiod (200Ma-160Ma), which lead to at least two mineralizing periods.Druing the work of resource comprehensive evaluation throughout theDuobaoshan area, this thesis applies the improved geological statistics method ofgeological variables to optimize four favorable Cu、Mo mineralizing anomalyareas which occur along NE trending and correspond to regional structures. It isconcluded that NE trending regional structures are the most importantore-controlling Factors. While, NW trending structures also control the location ofthe mineralization. It is thereore the intersection of the two groups of structuresthat are most favorable Cu、Mo mineralizing anomaly areas.