Study On Geological Background And Geochemical Prospecting Prediction Model Of Tellurium Mineralization In Shimian,Sichuan Province

The Dashuigou tellurium deposit,the first independent Te deposit in the world,breaks the traditional understanding that Te cannot be enriched into independent deposits.Actually,Te can not only form associated deposits,but also large or even super large independent Te deposits under certain conditions.The Dashuigou Te deposit has been highly concerned by geologists since its accidental discovery.They studied the regional geology,geology,geochemical characteristics,isotopes and genesis from different angles,and obtained a large number of corresponding results.But whether there are Te deposits similar to the Dashuigou Te deposit in the adjacent area beyond the deposit is worth further discussing by studying the regional geological background of Te mineralization especially the geochemical prospecting prediction model.At present,there is no scientific,reasonable and feasible geochemical prospecting theory and method for similar Te deposits in the vicinity of the Dashuigou Te deposit.On the basis of regional geological background of Te mineralization and geological-geochemical characteristics of the Dashuigou Te deposits,this paper mainly studies the geochemical characteristics of elements in Dashuigou Te mining area and Shimian region,discusses the evolution of Te and its paragenetic elements in strata and intrusive rocks of different ages,divides the geochemical sub areas,and analyzes the relationship between elements and fault.Indicator elements of Te deposit are selected from symbiotic elements of Te in stream sediments,the ratio of it is used as a theoretical method to extract anomalous information of Te,and the geological-geochemical model of the Te deposit is established.Based on the geological background,regional geophysics and geochemical characteristics of Te mineralization,a geochemical prospecting prediction model for Te deposit is established,thus forming a set of geochemical prospecting theory,which provides a new theory and method for prospecting Te deposit similar to the Dashuigou Te deposit.Through the above research,the main achievements are as follows:Firstly,the Shimian region is located in the transition zone between Western Sichuan Plateau and Sichuan Basin.The regional geological background is relatively complex,including multiple intrusions of deep magma and the inheritance of regional deep faults,and the fault structure is widely developed.At the same time,thermal events and metamorphic events have a strong impact on the strata,resulting in its different degrees of metamorphism.In terms of geophysics,it is located in the main ring residual positive gravity anomaly zone,the transitional region of positive and negative anomalies of aeromagnetic survey,and the linear structure and ring structure are developed,which reflect that there has an excellent regional metallogenic geological background.Secondly,the siderophile elements?e.g.Co,Cr,Cu,Ni,and Fe?related to basic and ultrabasic magmatic activities are mainly enriched in Shimian area.The overall content of Te and Bi is not high in stream sediments,Te shows background-strong differentiation and Bi shows low background-extremely strong differentiation.There is a good concentration and matallogenic potential for Te in Permian,Silurian Tonghua formation,Ordovician Dahebian formation,Sinian strata and Permian-Triassic intrusive.The Shimian region is divided into four geochemical sub areas,each of which has different geological and geochemical characteristics.The geochemical sub area of Zoufu-Qilongdong is the most important area for Te prospecting in Shimian,which has potential prospects for Te prospecting.Thirdly,Bi,Te,and Au concentrations in stream sediment samples displayed weak-positive anomalies,while Ag displayed a weak-negative anomaly in the Dashuigou Te deposit.The content of Te and Bi is relatively high in the metamorphic basic volcanic rocks of the first member of Tonghua formation,which may be the source bed of the Te deposit.In fact,the Dashuigou Te deposit does not occur in higher Te-Bi geochemical background region,but in the geochemical area with low background value or background value.The content of Te and Bi tends to be background in large area and to be hyper-enrichment in local,and to be obvious late superimposed enrichment.In other words,the formation of the Te deposit was formed by the enrichment of Te-Bi in the later stage of mineralization.Fourthly,the combination of As,Sb and Hg in stream sediments can designate the spatial location of fault.The combination of Co,Cr,Ni and Fe₂O₃reflects the hydrothermal migration channel of ore-forming fluids provided by the fault,which is a favourable place and location for mineralization.The metallogenic elements of Te,Bi,Au and Ag are obviously controlled by fault.Fifthly,the lead isotopic composition of Te ores and minerals?pyrrhotite and pyrite?is mainly abnormal lead,which has characterized by the mixing source of crust and mantle and is closely related to magmatic activity.The?³⁴S value of sulfur isotopes is basically a small positive value with a small range of variation,which has obvious characteristics of sulfur isotopic composition of magma.The sulfur comes from the deep and is closely related to magmatism.Isotopes show that Te may be homologous with sulfur,carbon and other mineralizers,all of which come from the deep.Sixthly,the main ore-forming elements?Te and Bi?,associated elements?Ag and Au?and meso-hypothermal elements?Cd,Cu,Pb,Sn,W,and Zn?are selected from the stream sediments as indicator elements of Dashuigou-type Te deposit.It tends to form in meso-hypothermal environment.Taking the multiplicative ratio of content?Te×Bi?/?Pb×Zn?as a preliminary judgment of the abnormal strength of elements related to tellurite in supergene medium.The accumulation ratio of content?Te+Bi?/?Au+Ag?,as a direct indicator of Te mineralization,can effectively highlight the substantive ore-induced anomalies of Te and Bi,extract the information of tellurite mineralization anomaly,and provide a new geochemical theoretical method and technical means for the exploration and prediction of Te deposits.Seventhly,base on the geological background,regional geophysical characteristics,geochemical characteristics of elements and geological-geochemical model of the Te deposits,a geochemical prediction model is established for Te deposits.Six locations are identified for prospecting for Te minerals by the model,including the Dashuigou Te deposit area,northeastern Qilongdong,Miaoping,Qilongdong,Jiangguanshan and Northern Jiangguanshan.Already,Te-Bi ore veins have been found in some of these areas.