Geological Characteristics And Tailings Element Distribution Rule Of Yangjiazhangzi Molybdenum Deposit,Liaoning Provence

Yangjiazhangzi molybdenum deposit,located 35 km northwest of Huludao City,Liaoning Province,is an important"skarn-porphyry type"ore concentration area in China.The deposits in Lingqian,Songshumou and Lanjiagou are the main deposits of the whole molybdenum deposit concentration.The tailing ponds of Yangjiazhangzi molybdenum deposits cover an area about 2.5 km2,with a current storage capacity about 400,000,000m³.Now,most of the tailing ponds lay idle,which has caused serious pollution to the surrounding environment.In this paper,based on the study of the geological characteristics of the deposit,we present detailed research for the tailings at Yangjiazhangzi molybdenum deposits through grain-size analyzation,polarizing microscope observation,X-ray powder diffraction and major and trace elemental analyzation,combining with the analyzation of the heavy metal elements of the groundwater and soils in and around the tailing ponds,the migration of heavy metal elements in tailings and its effect on the ecological environment are finally discussed.Songshumao mining area is located at the intersection of Yaolugou-Nüerhe fault and Damianshan-Huishan fault.The main strata exposed in this area are Cambrian,Ordovician,Carboniferous-Permian and Quaternary.The structure is dominated by fault structures,followed by the fold structure.The magmatic rocks in this area are mainly granite porphyry and granodiorite,which are obviously controlled by tectonics.The ore body is veined or lentil with stable occurrence,occurring in the outer contact zone between Cambrian-Ordovician limestone and granodiorite,as well as in granitic porphyry,its strike is nearly north-south with a length of about 2000m,which belongs to skarn-porphyry complex molybdenum deposit.The ore types can be divided into granite porphyry type and skarn type.There are a large number of molybdenum and pyrite in ore minerals,followed by chalcopyrite,magnetite,sphalerite,galena.The gangue minerals are mainly composed of calcite,dolomite,garnet,calcium iron garnet and diopside.The ore mainly have leaf,metasomatic,metasomatic star,metasomatic skeletal crystal texture and veinlet,disseminated,dense massive and spotted structure.The wall rock alteration is generally zonal,mainly developing skarnization,silicification,sericitization and carbonation.The microscopic identification of thin section,polished section and XRD analysis of the tailing sands indicate that the main component of tailings is fine-grained sands,with the extremely poorly sorted.The grains around the sand outlet are more coarser,whereas the grain size becomes smaller far away from the outlet.The ore minerals are mainly molybdenite,followed by pyrite,chalcopyrite,galena,sphalerite,hematite,magnetite,etc.Transparent minerals consist of garnet,quartz,plagioclase,orthoclase,perthite,chlorite,augite,tremolite,calcite,actinolite,etc.The analyzation results of the main elements show that the tailings are mainly composed of SiO₂,CaO and Al₂O₃,followed by MgO and Fe₂O₃.The average Mo content in the tailing sands can reach 0.034%,which is higher than the cut-off grade,and these will become the valuable resource for the secondary development and utilization.The trace element test data of tailings sand indicate that Cu,Zn,Co and Cd are enriched near the sand discharge port,Ni is enriched in the middle,Pb and Bi are enriched in the vicinity of the dam.Along the vertical sand discharge direction,Zn,Pb and Cd are enriched on the surface where in the middle of the low-lying area.In the vertical section of A?B?C?D,Hg is concentrated in the shallow stratum;Cd is enriched in the surface of the B section,and in other sections,the enrichment of Cd is migrating downward;the rates of downward migration for Cd,Pb,Zn and As are faster;some elements had a secondary generate enrichment at the depth of 40-80 cm.The heavy metal elements contents in tailings ponds and the surrounding groundwater show that the contents of Mo and Fe are beyond standard at G2 and G8;the contents of Mn,Zn,Mo and Cd are beyond standard at G23;while at G26,the contents of heavy metal elements are not exceeded.As the main metallogenic element,the content of Mo exceeded standard seriously.The G23 is the most polluted body,as besides the affected of the tailing ponds,this point is also on the way of the meeting of the rivers from the north,northeast and northwest,among which the Baisha River in the north flows through Yangjiazhang deposits.From G2-G8-G26,with the gradually away from the tailing ponds,the contents of Fe,Mo,Cd and Hg are decreased.The heavy metal elements contents in tailing ponds and surrounding soil show that the contents of Mo,Pb,Zn and Hg are beyond standard at T1;the contents of Mo?Fe?Pb?Zn and Hg are beyond standard at T2.The content of Mo also exceeded standard seriously.The T4 is the most polluted body,as it was just in the sampling point of the deposit slag in northwestern mining field.From T1,T2,T3,T5,T6,to T7,with gradually away from the tailing ponds,the contents of Mo,Fe,Zn,Pb and Hg are decreased.