Occurrence And Enrichment Mechanism Of Cobalt In Sulfide Of Baicao Mining Area In Panxi

The Baicao mining area in Panxi is located in the northeast of Hongge ore field.The main industrial mineral in the area is V-Ti magnetite.Field exploration shows that there are disseminated,dense massive,patchy and veined sulfide ores in the V-Ti magnetite in this area.The analysis results show that the Co in sulfide ore has reached the industrial grade.In order to study the occurrence and enrichment mechanism of Co in sulfide ore,the mineralogy of Co rich sulfide samples collected in the field was studied to find out the morphological characteristics,structural characteristics and mineral contact relationship of ore minerals;the chemical composition,source of ore-forming material and nature of parent magma characteristics of Co rich sulfide were identified by whole rock geochemical analysis,single mineral primary geochemical analysis and sulfur isotope analysis of pyrrhotite.Combined with the mineralogical and geochemical characteristics of the ore,the occurrence state and enrichment mechanism of Co in Baicao mining area are understood,which can provide some reference for the prospecting and exploration of the key metal cobalt in this area.This study was financially supported by the Foundati on of China(030216190040),a systematic study on cobalt rich sulfide ore in Baicao mining area was carried out.The results are as follows:1.The results of EPMA analysis of sulfide minerals in Baicao mining area show that there are three main forms of occurrence of cobalt in Baicao mining area,which are independent minerals,mainly sulfide and sulfur arsenide such as siegenite and cobaltite;isomorphic substitution form,mainly cobalt occurs in sulfide minerals such as pyrrhotite,pyrite and pentlandite in the form of isomorphic substitution of Fe;exists in the form of mineral particles,and it can be seen that thiocobaltite dissolves in pyrrhotite under the microscope.2.The comparison of Hpo,Mpo and Tr crystal forms of pyrrhotite with the compositions of corresponding mantle xenoliths shows that the ore-forming magma originated from mantle;the S isotope data of pyrrhotite indicate that the ore-forming magma was strongly contaminated by crustal materials and resulted in sulfur supersaturation and segregation.3.The analysis of trace element characteristics of cobalt rich sulfide ore in Baicao mining area shows that the ratios of Ni/Cu,Cu/(Cu+Ni)and Pt/(Pt+Pd)are all within the range of basaltic magma.It is considered that the parental magma of the ore-forming in Baicao mining area is basaltic magma.4.Based on the above-mentioned chemical composition characteristics of sulfide minerals,source of ore-forming materials and properties of parental magma,combined with previous studies on this type of deposit,it is concluded that the enrichment mechanism of Co in Baicao mining area is that the basaltic magma from the mantle undergoes a large degree of crustal contamination under the action of mantle plume,which makes the sulfur in the magma supersaturated and segregation.Because the D_Co^Sul/Sil=230,D_Co^Mag/Sil=3.4,Co tends to enter into sulfide more than silicate magma and V-Ti magnetite magma.With the decrease of temperature,all kinds of cobalt rich sulfide minerals are formed.The average Co/Ni ratio of pyrite in Baicao mining area is 0.76,which is quite different from that in typical Cu-Ni sulfide deposits.Combined with the characteristics of CO and Ni content,the Co rich sulfide minerals in Baicao mining area are magmatic vanadium titanomagnetite type sulfide.