Study On The Relationship Between Magmatism Of Qitianling Granitoid Batholith And Tin Mineralization In Southern Hunan

There is a well-known Qianlishan-Qitianling tungsten-tin polymetallic ore district in Hunan Province of our country,which is located in Nanling section,one of the five ridges.The most representative large-scale rock foundation in this area is Qitianling granitoid.The famous Furong super-large tin deposit is located in the southern part of Qitianling composite granites body.Although there are many research results,there are still some disputes.Therefore,based on the regional geological background of Qitianling composite granite body,starting from petrology and petrogeochemistry,and combining with the regional geological research data,this paper discusses the tectonic-magmatic activity process and the tectonic background of southeast Hunan.By comparing various characteristics of granite in different tectonic units and analyzing the evolution characteristics of magma from the early stage to the late stage,I have obtained the following understandings about the magma source and emplacement mechanism of Qitianling granite mass,including the relationship between its magmatism and tin mineralization:1.The main lithology of Qitianling granite mass is adamellite and Orthogranite.Dark minerals include biotite and amphibole,of which biotite accounts for the vast majority.Amphibole is only partially present in the early unit,but not seen in the later period.According to the experimental results,the formation of the rock mass has gone through four important stages,probably dating from 147 to 163 ma.According to this,Qitianling granite mass is divided into two large superunits,Lailing and Furong,and there are some scattered small granite porphyries and fine-grained granite dikes around.Through petrological and petrogeochemical analysis,the contents of amphibole and dark minerals in rocks gradually decrease from early to late,while the increasing trend of magma DI basically reflects its evolution sequence: medium acid granite ?acid granite ? ultraacidic granite,which makes the granite formed rich in a large amount of metallogenetic metal elements such as tungsten,tin,niobium and tantalum.According to the geochemical analysis of major trace elements,and increases slightly according to the time.As for the last three units,Jiangjunzhai,Huangtangling and Huitouwan,they are more inclined to have the characteristics of the late magmatic evolution.2.Based on the results of petrology and geochemistry,Qitianling granite body is characterized by high potassium,calcium,alkaline and metaaluminum,belonging to post-orogenic granite.It is formed under a structural condition in which a transition from a state of extrusion to a state of stretching and stretching starts.Due to several tectonic cycles,the deep fault zone formed in this area provides a channel for magma flow and controls the distribution of tin ore belts.The secondary minor faults and surrounding rock fractures provide a place for the storage and migration of mineral-forming fluids,and control the distribution,shape and occurrence of vein(body).3.The mineralization of Furong tin deposit is closely related to the magmatism of Qitianling granitoid.During the Yanshan period,the acidic evolution trend of magma in Qitianling area made the granite formed in the late stage of the same period enriched with a large amount of important metallogenic elements such as tin and tungsten,especially the magmatic activities of furong superunit and concealed late-stage fine-grained granite are closely related to the genesis of tin deposits in the area and are the main material sources of tin deposits.The natural ore-forming advantage in this area has created a rare Qitianling mine junction,the most representative of which is Furong tin mine.4.The formation of Qitianling granitoid is closely related to the tungsten-tin mineralization in this area.The study of the relationship between the two is not only helpful to establish the genetic model of the deposit,but also helpful to the prediction of other minerals.Due to the multi-stage nature of granite magma activity,mineralization is also multi-stage,and the same ore body is often the result of superposition of multi-stage mineralization.Moreover,the same part of the same ore-body can be a superposition of tin deposits of different stages and types.Different tin ore types can also occur in different parts of the same ore body(or the same ore-hosting space).The detected metal mineralization in Furong Superunit includes tungsten,tin,molybdenum,bismuth,etc.In addition,magnetite,uranium ore and copper ore,etc.,which may accompany tin mineralization,are also worthy of special attention.However,granite porphyry and fine-grained granite dikes formed in the late stage of magmatism have favorable metallogenic conditions because of their high differentiation index and rich Nb,Ta and Sn elements.In addition,the REE content of the Cailing superunit is the highest in the whole rock mass.If the exogenetic conditions are well developed,a REE deposit may also be formed.