Studies Of The Mineralization System Of The Porphyry-High Sulfidation Epithermal Cu-Au Deposit Of Tiegelongnan In Tibet

The Tiegelongnan deposit is the first case of the super-giant high sulfidation epithermal-porphyry Cu-Au type recently found in the west of the Bangonhu-Nujiang metallogenic belt.The copper resource is>11 million tons and the gold resource is>120 tons.In the research,Electron Probe X-ray Microanalysis?EMPA?,Scanning Electron Microscope-Energy Dispersive Spectrometer?SEM-EDS?,Raman Spectrometer?Raman?,Synchrotron-Based X-ray Fluorescence?SR-XRF?and Micro-thermometry are used to study the primary minerals,trace element minerals and the physical conditions and constituents of the ore-forming fluids,which is helpful to get some essential knowledge of the deposit as described below.Pyrite pyllic alteration zone and advance argillic alteration zone produce the highest quality of metallic ores.The intergrow texture of pyrophyllite and bornite is recognized in the study.At least we can ensure that,there is a certain scale of sub-alteration zone,i.e.,pyrophyllite-bornite±chalcopyrite zone belonging to the early stage of the advanced argillic alteration zone,which produced the important copper bearing mineral,bornite.Besides,three gold bearing minerals are unraveled,i.e.,tennantite,bornite and Bi sulfide.Calaverite with a certain amount of hessite,altaite and melonite,et al are enriched in tennantite yielded in the moderate to shallow depth of the advanced argillic alteration zone;a small quantity of native gold particles are included in bornite;gold and silver bearing Bi sulfide occurs in the silt of the pyrite in the pyrite phyllic alteration zone.Consequently,the f_Te2 and f_S2 conditions of the precipitation of the gold bearing minerals with tennantite mineralization are confined,that is-6.5^-8 and<-11,respectively.A great deal of ore-forming fluids were captured in quartz phenocrysts in the mineralized porphyry.Most of these fluid inclusions were formed after the formation of these porphyry dikes,which are reconginsed as the secondary fluid inclusions and represents ore forming fluids with important ore forming information.Three important characteristics of these fluid inclusion assemblages are uncovered.The first is that these fluid inclusions have cross-cut the quartz phenocryst.The second is that these fluid inclusions share the same peak homogenization temperatures area with those in ore bearing quartz veins.The last is that metallic particles detected in some inclusions of the quartz phenocrysts are the same species as the metallic minerals in the ores.For instance,fluid inclusions in the quartz phenocrysts of the pyrite phyllic alteration zone captured chalcopyrite and hematite particles,while fluid inclusions of the quartz phenocrysts of the advanced argillic alteration zone captured covellite and pyrite particles.Additionally,we constrained the physical conditions of the ore-forming fluids depending on the fluid inclusion assemblage?FIA?study,which is considered a relatively precise approach.In the pyrite-bornite-tennantite-copper sulfide-quartz vein of stage three of the advanced argillic zone,the peak values of homogenization temperatures of the fluid inclusions are from 310 to 320?;the hypersaline inclusions contain 29.6³5.4 wt percent NaCl;the lowest trapping pressures are 74⁸4 bars;and the minimum paleo-depths are from 0.74⁰.84 km,which means the corrosion depths are 0.55 to 0.56 km.In the pyrite-chalcopyrite-bornite-quartz vein of stage two of the pyrite phyllic alteration zone,the peak values of the homogenization temperatures of the fluid inclusions are from 330 to 360?;the hypersaline inclusions contain29.3³5.8 wt percent NaCl;the lowest trapping pressures are 121¹70 bars;the minimum paleo-depths are from at least 1.21 to 1.70 km,which means the corrosion depths are at least 0.18⁰.67 km.Furthermore,the results of the SR-XRF analyses of the fluid inclusion enriched quartz exhibit that Cu,As and Pb are more abundant in the advanced argillic alteration zone,while Rb are relatively enriched in the pyrite phyllic alteration zone,which implies that Cu,As and Pb preferentially entered the vapor phase,while Rb selected to enter the liquid phase when phase separation took place in the deep level of the ore-forming system.This research aims to analyze this newly discovered porphyry related Cu and Au deposit in this area,which discussed issues concerning the discipline of Au distribution,how it transported and precipated and established the link between metallic mineralization and ore forming fluids.This research has a foundation impact in the theory study and is also valid in the exploration.