Geological And Geochemical Features Of The Copper (Molybdenum) Polymetallic Deposit Of Lianhuaxin, Jiangxi Province

Being discovered only in recent years,the Lianhuaxin Copper?Molybdenum?Polymetallic Deposit of Xiushui Prefecture,Jiangxi Province is a medium-sized copper polymetallic deposit belonging to the southwest of the Jiuling sub-belt of the polymetallic metallogenic belt in the middle and lower reaches of Yangtze River.Compared to the adjacent Dahutang Tungsten and Copper polymetallic ore accumulation areas,this deposit has insufficient geological exploration.Strengthening basic geological research in the area can facilitate in achieving breakthroughs in deep prospecting of the ore deposit.Based on field works such as field geological survey,profile measurement,geological mapping and drilling core logging,the present paper mainly studies the Lianhuaxin Copper?Molybdenum?Polymetallic Deposit.Representative rock samples were collected and systematic researches of the geological and geochemical features of the ore deposit were carried out through methods including detailed petrology,petrography,element geochemistry and Sr-Nd-Pb isotope geochemistry,which provide an important basis for exploring concealed ore body.Analysis of main elements in rocks reveals an obvious negative correlation between oxide content of AI₂O_3,CaO,TFe,MgO and TiO₂ and the contents of SiO₂,a nd a positive correlation between K₂O contents with the contents of SiO₂;According to the analysis,there is no obvious linear relationship between the contents of Na₂O and SiO₂,and the contents of MnO and P₂O₅ were quite low,so they have no obvious linear relationship with the contents of SiO_2.The projective points of these five oxides meet at around 70%?Figure 4.2?.The samples of the surrounding rocks are granite and monzonitic granite,which are mainly characterized by peraluminous and high potassic calc-alkaline.In the characteristic analysis of trace elements,there are signs of enrichment of large ion lithophile elements?LILE,such as Cs,Rb,Ba and K?and depletion of high field-strength elements?HFSE,such as Nb,Zr,Hf and Ta?.The range of Th/U ratio varies from 0.4 to 4.2;the Nb/Ta ratio ranges from 5.98 to 9.96?8.55 on average?,and the Zr/Hf ratio is between 23.04 and 33.33?27.88 on average?,which is different from the corresponding value of the primitive mantle?17.8 and 37?and crus?11 and 33?.Therefore,the ore forming minerals in this deposit are probably from the ore-forming hydrothermal solution by later hydrothermal activities and the deposit was resulted from plate convergence margins'subduction and collision tectonic environment.According to the analysis of rare earth elements,the outlier of Ce in the surrounding rock samples is not obvious??Ce ranges from 0.93 to 0.99,and 0.97 on average?;the La/Sm ranging from 2.99 to 5.07?4.32 on average?shows good fractionation degree and high enrichment of LREE in surrounding rock,,which indicates there were magma mixing in the evolution of magma.The outlier of Ce in the ore is also not obvious??Ce ranges from 0.92 to 1.04,and 1.02 on average?;the La/Sm ranging from 1.23 to 2.83?1.99 on average?indicates low fractionation degree of LREE in ore;and Gd/Yb between 1.16 and 2.39?1.7 on average?shows that the HREE is almost not fractionated.The?Ce of quartz vein is between 0.85 and 1.05?0.96 on average?,and the outlier of Ce is not obvious;its La/Sm ranges from 2.47 to6.06?3.91 on average?,which shows weak enrichment of LREE with medium degree of fractionation in the quartz vein;Gd/Yb ranges from 0.34 to 3.44?1.73 on average?,indicating that HREE is almost not fractionated.The formation of quartz veins has multiple stages with the same material source as the ore.The element migration analysis shows that the drag-in and drag-out of K and Na are related to the mineralization of metallic minerals Cu,Mo and Pb,and the potassium kaolinization and medium and low temperature carbonatation,which might be relevant to the enrichment of Cu,Pb and U.In terms of the trace elements characteristics,high field-strength elements such as Zr,Hf and Be are in the trend of increasing,while the large ion lithophile elements like Li and Sc are decreasing.Sr,Nb and Ta decrease in early stage but enrich at the later stage.In terms of rare earth elements characteristics,there is a loss of LREE and enrichment of HREE in the first pair of rocks,but the case is opposite in the latter two pairs of rocks.From altered rock to surrounding rock,the content of ore-forming elements gradually decreases,and the enrichment of ore-forming elements are closely related to hydrothermal alteration.According to the analysis of Sr-Nd-Pb isotopes,there is a significant negative correlation certain correlation between ¹⁴³Nd/¹⁴⁴Nd and ⁸⁷Sr/⁸⁶Sr in the rock:with the increase of ¹⁴³Nd/¹⁴⁴Nd?i.e.?Nd?,⁸⁷Sr/⁸⁶Sr?or?Sr?decreases,and its correlation coefficient is-0.07082,a significant negative correlation within the critical value.The sources of ore-forming materials are complicated:there is lead from the upper crust,and mantle-source lead from the lower crust.In general,it mainly comes from the upper crust,with characteristics of orogenic magmatism of crust mantle mixed source.