Study On The Indium Occurrence State And Enrichment Regularity In Xianghualing Sn-Pb-Zn Orefield, Southern Hunan

Indium（In）has excellent optical penetration and conductivity,and is widely used in electronic industry,radio,aerospace,medical and other fields.It is an essential raw material to support the high-quality development of high-tech industries.At the same time,In,as a typical dispersed element,is extremely difficult to form an independent deposit,which is usually enriched in Sn-Pb-Zn polymetallic deposits as an associated component.Xianghualing orefield is located in Southern Hunan,which is known as"the hometown of non-ferrous metals".The orefield has abundant resources of Sn,Pb,Zn,W,Nb,Ta and other mineral resources,which may be the potential area of In resources in China.However,the occurrence state,distribution regularities and mineralizing potential of In in Xianghualing orefield are still unknown.In view of this,this paper takes three large and medium-sized tin polymetallic deposits（i.e.,Xinfeng,Tieshaping and Chashan）in Xianghualing area as the research object.On the basis of detailed field geological and mineralogical research,XRF,ICP-MS,EPMA and LA-ICP-MS and other test technologies are applied to systematically carry out whole-rock geochemistry,sphalerite mineral chemistry and in-situ micro-element geochemistry research.The results are as follows:（1）The whole-rock geochemical analysis data show that the enrichment degree of In in the three deposits is significantly different.Among them,Xinfeng is the richest in In,with an average grade of 213.7 ppm;the second is Chashan,with an average grade of 65.3 ppm.However,Tieshaping has the poorest In,with an average grade of 7.1 ppm.In addition,there is a significant positive correlation between In and Zn,indicating that In is mainly enriched in sphalerite.Combined with previous data,it is estimated that the associated In resources in Xianghualing orefield exceeds 15000 t,which has huge economic potential and should be recycled.（2）EPMA and LA-ICP-MS data show that the enrichment degree of In in sphalerite of three deposits is consistent with the above regularity,that is,sphalerite in Xinfeng mining area is the richest in In（usually>400 ppm）,followed by Chashan mining area（150–450ppm）,and sphalerite in Tieshaping deposit is the poorest in In（30–400 ppm）.The variation regularity of Cu in the three deposits is similar to In,and there is a good linear relationship between them.It is speculated that the possible replacement mechanism is In³⁺+Cu⁺（?）2Zn²⁺,and this substitution is particularly significant in Xinfeng mining area.In addition,sphalerite in Xinfeng mining area shows significant"indium window effect".When the cadmium content in sphalerite is 5000–7000 ppm,the indium content increases sharply to more than1000 ppm,but its internal mechanism needs further study.（3）Based on the correlation between the contents of various elements in sphalerite,the LA-ICP-MS time-resolution map of elements and the analysis of area-scan image,it is speculated that Fe,Cd,Mn,In,Ga,etc.are mainly in the form of solid solution in the crystal lattice of sphalerite,while Pb,Ag,Bi,Sb,As,etc.are mainly in the form of microscopic mineral inclusions,and Cu,Sn,Co,etc.are in the form of the above two forms.（4）The element geochemical characteristics of sphalerite of the three ore deposits in the Xianghualing ore field are very similar to those of the typical medium-high temperature magma-hydrothermal deposit sphalerite at home and abroad.According to the actual geological conditions of the mining area,it is proposed that they are genetically similar to the remote skarn deposit.At the same time,the formation temperature of sphalerite obtained by using sphalerite thermometer ranges from 345 to 372℃,and the temperature of Xinfeng mining area is slightly higher.（5）Based on the above analysis results and previous studies,the enrichment degree of In in Xianghualing orefield is mainly controlled by temperature variation.The closer to the rock mass,the higher the temperature is,the more In enrichment,among which the In content in the marmatite is often more above several hundreds of ppm,which is of great economic value.Therefore,more attention should be paid to resource evaluation,beneficiation and metallurgy.