Metallogenesis And Exploration Model Of The Nating Copper-Gold Deposit At The Duolong Metallogenic Area,Tibet

The Duolong ore cluster（～25Mt Cu and～400t Au）is a giant porphyry-high sulfidation epithermal Cu（Au）system in the Bangong-Nujiang metallogenic belt,Tibet.The large Nating Cu（Au）deposit（>1 Mt Cu with a grade of>0.3%and>100 t Au with a grade of>0.2g/t）is a newly discovered deposit by exploration in recent years.Based on detailed field investigation,core logging,petrographic observation,zircon U-Pb dating,petro-geochemistry,in-situ zircon Hf-O isotope,and H-O-S isotopes of hydrothermal minerals,this thesis identifies key scientific issues such as geological features,alteration and mineralization zones,genetic types of the deposit,petrogenesis,and tectonic setting.Meanwhile,the genesis and exploration model of the Nating deposit was established to further guide mineral exploration.Based on the systematic determination of alteration types and zones,mineralization characteristics,and their spatial distribution,granodiorite porphyry is the ore-forming porphyry.the alteration shows zoned features,with moderate argillic and minor prophylitic zones in shallow part and the transition to potassic zone in deep part.Moreover,gypsum and anhydrite are extensively distributed in this deposit.The Cu（Au）ore body is a hidden tabular shape with east-west spreading and south-dipping.It occurs in granodiorite porphyry and moderate argillic sandstone.The mineralization is mainly composed of veinlet-disseminated chalcopyrite,with local bornite and enargite.Therefore,the deposit is considered to be a porphyry Cu（Au）deposit superimposed by high sulfidation epithermal mineralization.SIMS zircon U-Pb dating show that ore-forming granodiorite porphyry was formed at～118 Ma and belongs to the same magmatic-hydrothermal event as the Duolong ore cluster.This deposit was formed in a continental margin arc during the northward subduction of the Bangong-Nujiang oceanic slab.The Hf-O isotopes(εHf（t）=-2.0-10.3;δ¹⁸O=5.07‰-6.95‰)of the volcanic rocks and mineralized porphyries suggest that the magma may have originated from partial melting of the subduction-metasomatic mantle wedge,which produced basaltic melt and undergone MASH process at the lower crust.The magma also has water-rich characteristics,which is favorable for the formation of porphyry deposit.In addition,H-O isotopic signatures(δ¹⁸O=9.8-11.0‰,δD=-87.9-66.8‰)of quartz and its hosted fluid inclusions from porphyry and veins indicate that ore-forming fluid is essentially consistent with residual magma water,suggesting that the magma underwent large-scale fluid exsolution.The S isotope variation of sulfide is narrow（-8‰～-4‰）and slightly below the magmatic S isotope signature,which may be related to magmatic SO₂ degassing.S-O isotope signature of hydrothermal anhydrite may be caused by the disproportionation reaction of SO₂.Finally,based on the geological features,petrogenesis,ore-forming fluid evolution,genesis model of the Nating deposit was established.Based on the geological features,elemental geochemical anomalies,geophysical and remote sensing spectrum features,and petrogenesis,an exploration model of the Nating deposit was established.The geophysical features include low apparent resistivity rate and medium apparent polarization rate,high magnetic anomalies,and high polarization anomalies.The geochemical feature is the high-temperature elements of Cu,Mo,Bi,Sn,W in the center,gradually transitioning to medium-low temperature Cu,Au,Ag,Pb,and Zn elements in the periphery.The remote sensing spectral features are the intersection of linear and circular structures,accompanied by obvious hydroxyl anomaly and iron staining anomaly.Based on the comprehensive analysis of the metallogenic factors and geophysical information of the Duolong ore cluster,the target area of mineralization is proposed.It is considered that there are still huge extensions of the deep ore bodies in the Nating,Bolong,Duobuza,Tiegelongnan,and Naruo deposits.Especially,the descending wall of the F8 fault in the southwest of the Tiegelongnan deposit has the potential to further expand the scale of the ore body.