Metallogenic Mechanism And Prospecting Orientation Of Daping Gold Deposit In Yuanyang,Yunnan Province

Daping gold deposit,is the one of typical deposits in the Ailaoshan metallogenic belt,the vein type gold polymetallic sulfide deposit commonly develop in close association with the product of collision orogenic environment.To further identify the genesis of type,Combing with the regional geological background and the geological exploration results of the Daping gold deposit in yuanyang county,Yunnan province,the typical deposit characteristics of geologic,mineral assemblages and wall rock alteration,identifying of metallizing phase are analyzed in depth,the ore-forming factors?such as source of ore-forming materials and the ore-controlling structural feature?of the Daping gold deposit are summarized.The reslts show that:?1?The gold deposit was controlled by sinistral strike-slipping shear,The main orebody were formed by filling in the transition part of tense-compression shearing space;?2?The crucial factor for the formation of Daping gold deposit is combined action of multiphase tectonics and metallogenesis,diversity source of metallogenic material,multi-genetic fluid.it is a vein type poly-mental deposit with middle temperature.Fluid inclusions in the various ore veins were studied by using a cooling/heating stage and petrographical analyses,and the results show that the fluid inclusions are dominated by liquid CO₂ inclusions and CO₂-H2 O inclusions with variable ratios of CO₂ /H2 O,and Liquid phase CO₂ containing three-phase inclusions.A lot of gaseous CO₂-rich inclusions are found in the stage scheelite-bearing quartz veins,liquid CO₂ inclusions are dominanted in the major stage auriferous massive polymetallic sulphide ores,The main ore-forming stage?quartz-pyrite stage and polymetallic sulphide stage?gold-rich liquid-rich CO₂ inclusions and three-phase inclusions predominate,with a small amount of rich-gas inclusions and quartz-siderite Belong to the multi-metal sulfide stage,three-phase inclusions accounted for obvious advantages,a small amount of rich gas CO₂ inclusions.Inclusion temperature measurement results show that,the scheelite-bearing quartz stage has homogeneous temperature mainly between 209.4³80.1? with a peak of 309³59?.the quartz-pyrite stage has homogeneous temperature mainly between 163.8³12.3? with a peak of 196²66?.and the quartz-metallic sulfidation stage has homogeneous temperature mainly between 222.3³88.7? with a peak of 270³20?.and the quartz-metallic sulfidation stage has homogeneous temperature mainly between 194³57? with a peak of 274³24?.The temperature of the inclusions in the main ore-forming stage shows that the two-stage temperature changes in the two metallogenic stages,indicating that there may be new fluid additions in the later stage.The ore-forming fluids characteristics of Daping gold deposit are in accordance with the Organic gold deposits that characterized CO₂?fluid composition H₂O-CO₂+ CH₄,N₂,H2S?,low salinity?<5⁸NaCleqv?,medium temperature?250⁴00??,pressure?> 1 4Kb?,which meet ore-forming fluid characteristics.In the course of the rise of the deep source fluid along the leftward strike slip shear,the pressure of the deep-grained fluid decreases with the pressure of the brittle-ductile transition zone,and the fluid differentiation takes place to form the lamprophyric magma and the rich volatiles and the hydrothermal solution,and the strong phase-separation takes place,which is the key to form metallogenic mechanism in this area.In addition,there is a late-stage fluid that mainly lower crust granulite facies dehydrated to form a rich CO₂ fluid system in the early phase,and mainly mantle fluid system in the late phase,both are controlled by a strong crust-mantle mixture.Closely associated with the orebody lamprophyre,the content of SiO₂ is 47.98% 53.21%,K₂O/Na2 O is between 1.31 and 5.31,and the content of phlogopite is relatively high,which is mainly composed of mantle source,suggesting a calc-alkaline series;indicating that the porphyry has mantle-derived characteristics.rocks of the lamprophyre dikes are enriched with large-ion lithosphile elements?Sr,U,Rb,Ba?and LREE and depleted in high-field-strength elements?Ta,Nb,Ti?,assume “TNT” negative anomalies of Ta,Nb and Ti,and have ?Eu values of 0.26⁰.304,with indistinct negative Eu anomalies.It is thus thought that the source rock of the lamprophyre is an early subducting oceanic crust or an enriched mantle which might have been metasoma-tized by the enriched fluids released from the dehydration of the root matterin the orogenic belt.The magma was formed in a post-collision intraplate environment and was mixed with small amounts of crustal matter as it in-truded upward.The lamprophyre in this source area is similar to that of gold mineralization,and it is the product of different stages of deep fluid differentiation.Daping gold deposit has obvious ore-controlling structure,and the ore body is obviously controlled by the Xiao Xinjie fault and the secondary fault.The lamprophyre veins,which are closely related to the orebody,may be the manifestations of the deep mantle-derived fluid in the mineralization.The “Tectonic-fluid?vein rock?-mineralization” has been shown in the direction of the deep and peripheral prospecting.Combing with the ore-controlling factors,it is concluded that the prospecting work should be conducted in the area that the alkali-rich porphyry have strong development and the place fault activities stacking,and the key prospecting portion are lamprophyre and granite porphyry exposed area.In addition,the poly-metallic sulfide enrichment places should also be paid attention.