Study On Rock-forming And Ore-forming Of The Lingshan Pluton In The Northern Margin Of Dabie Mountains

The Lingshan granite is located between Henan province of xinyang, lingshan,luoshan and the Hubei province dawu in the northern Dabie orogenic belt. Based ondetailed field study of Lingshan granite and Doupo Mo deposit, Through systematicstudy of petrology, geochemistry and geochronology on the Lingshan granitic plutonand geological characteristics, fluid inclusion, stable isotope and geochronology onDoupo Mo deposit, we have figured out the characteristics and genesis of the Lingshangranitic pluton, revealing type, forming condition and possible source of theore-forming fluid, obtaining accurate rock-forming and ore-forming ages and discussedthe metallogenesis of the Lingshan granitic pluton. The main conclusions have beendrawn as follow:The main body of the Lingshan granitic pluton is composed of intrusions from4stages, which are mainly biotite monzogranite. The main of magma evolution isstructure evolution, then composition evolution. According to the whole-rockgeochemistry, the Lingshan granite is enriched in SiO2and K, ascribed to K-highcalc-alkaline series and the A/CNK values is0.97¹.07（average1.024）, it can beidentified as weak peraluminous-metaluminous granite. The rocks have high andremarkably varying REE, and their distribution patterns show LREE enrichment withgentle right oblique deviation which with the sea-gull type distribution pattern bysignificant negative Eu anomaly. The trace elements compositions are strongly enrichedin LILE and considerably depleted in HFSE, showing that the intrusion has undergonefull evolutionary differentiation. The Lingshan granite share some characteristics ofS-type granite. The magma source is mainly the lower crust with mingling of mantlematerials.The LA-MC-ICP-MS U-Pb dating method of zircon was used to determine the ageof the Lingshan granitic pluton, which yielded4emplacement ages were between108.91±0.64Ma and130.70±0.53Ma. They demonstrate that the Lingshan graniticpluton is the product of the early period of Middle Cretaceous.The hydrothermal alteration types of wall rocks in the Doupo Mo deposit includesilicification, K-felspar alteration, sericitization, and pyritization, etc. and the main ore-forming types are disseminated, veinlet, stockwork and laminated molybdenitemineralizations. The major metallogenic epoch could be devided into4stages:K-felspar-Quartz stage, Quartz-molybdenitestage, Quartz-polymetallic sulfidestage, andQuartz-carbonate stage. The deposit is of typical porphyry Mo deposit type.Aqueous two-phase inclusions is predominant of the main metallogenic epoch influid inclusion. Their homogeneous temperatures of the main metallogenic epochwere concentrated in170.4⁴32.1℃, their salinities were concentrated in0.35¹3.5wt%NaCleq., Their average ore-forming pressures and depths were213.94×10⁵Paand0.79km respectively. Gas composition of fluid inclusions mostly includes H2O、CO₂、N₂and O₂and a small amount of reducing gas like CH₄、C₂H₄、C₂H₆、C₂H₂.Cations of liquid composition are dominant with Ca²⁺、Na⁺、K⁺, followed by Mg²⁺.Anions are mainly consist of SO₄^2-, F^-, Cl^-, with minor Br^-. H-O isotope analysessuggest that the source of ore-forming fluid is probably the combination of magmaticwater and the meteoric water. The S isotope composition shows that it comes from themantle. The Pb isotope composition shows that the metallogenic material was mainlyderived from the crust with mingling of mantle materials.Re-Os isotopic dating of the molybdenites symbiosis with magnetites obtainedmodel ages of （125.4±1.2）Ma, and the LA-MC-ICP-MS U-Pb dating of the deepLingshan grantie is from（122.14±0.38）Ma^124.21±0.28Ma. Doupo Mo deposit wasformed in the early-Cretaceous, which is consistent with the emplacing age of the hostrock Lingshan granitic pluton. These features indicated that they were producted ofthe same structure-magma-fluid activity. The Doupo Mo deposit was formed underan extensional tectonic environment, the corresponding tectonic background can beascribed to Dabie orogenic belt large-scale lithospheric thining, delamination andthermal erosion.