Law And Significance Of Alteration Mineralization Of The Qulong Superlarge Porphyry Copper Deposit In Tibet

The Qulong porphyry copper(molybdenum)deposit is located in Mozhugongka County,Tibet Autonomous Region,80 km west of Lhasa.The tectonic structure is located in the southern part of the Lhasa-Riduo arc inner confined basin in the volcanomagmatic arc of the eastern margin of Gangdise,it is the largest porphyry copper(molybdenum)deposit discovered to date in the Gangdise metallogenic belt.In this paper,the Qulong deposit is taken as the research object.On the basis of surface exploration,combined with the observation of borehole core and the identification of microscopic minerals under the microscope,we subtly divided the hydrothermal alteration types of the Qulong deposit,described the characteristics of the vein system in detail,and conducted an in-depth study on the relationship between the two and mineralization,analyzed and clarified the law of alteration and mineralization in the Qulong mine area,and predicted the next step prospecting direction.This article gained the following main understanding:By systematically sampling the surface of the Qulong deposit,re-recording boreholes and recording lithology and alteration characteristics in detail,based on previous studies,corrected the lithological boundaries of the mining area and found a small amount of outcrops on the northwest side biotite adamellite.The hydrothermal alteration on the horizontal level is centered on the porphyry from inside to outside: Biotite± Anhydrite belt ? Quartz-Sericite ± Kaolinite ± Anhydrite belt ? SericiteChlorite±Epidote belt?Chlorite-Epidote±Kaolinite±Anhydrite belt?ChloriteEpidote±Calcite belt.Vertically from inside to outside,the Potassium Feldspathization belt?Biotite±Anhydrite belt?Sericite-Chlorite±Epidote belt?Chlorite-Epidote±Kaolinite±Anhydrite belt.The overall alteration superposition is obvious,similar to the " monzonite " model,but not concentrically distributed.According to the detailed observation of a large number of veins in 9 boreholes in the typical cross exploration line section of the Qulong mining area,the veins in the mining area are divided into 4 categories according to mineral assemblage,cut-through relationship and related alteration types(A vein,EB vein,B vein,D vein),31 secondary ore veins.Anhydrite develops from early to late in the veins,and some veins contain magnetite,indicating that the ore-forming fluids of the Qulong deposit have high oxygen fugacity and sulfur-richness.We also found that some high temperature ore veins cut through low temperature ore veins,which also suggests that the ore-forming fluid has the characteristics of repeated circulation and multi-stage surge.According to the spatial distribution and corresponding relationship between alteration-veins-mineralization in the mining area,we believe that the corresponding alteration in the high-grade mineralization area becomes the Potassium Feldsparization belt,Biotite±Anhydrite belt and Quartz-Aericite belt and alteration belt in the areas that are in contact with each other and superimposed,the type of veins produced is mostly B veins,which are cut through from early to late,and the reverse cut through phenomenon is also seen.The fractal dimension of veins width usually less than 1.Therefore,these features can be used as prospecting indicators for the Qulong mining area.