Study On The Exsolution Structure Of Sphalerite And Porphyry Copper Ore

Most of the common metal sulfide minerals in nature are solid solution.When the temperature and（or）pressure drop,these solid solution minerals will be decomposed into two or more mutually intersecting minerals under the solid phase line.This kind of intergrowth structure formed by the decomposition of solid solution is called exsolution structure.In various hydrothermal deposits,the phenomenon of metal sulfide leaching is relatively common.The formation environment and mineralization process of these structures are closely related（such as temperature and pressure conditions,supersaturation,cooling rate,etc.）,and have important typomorphic characteristics and significant genetic indicative significance.However,the exsolution structure is difficult to determine and identify.The coexisting structures of sulfides with and without exsolution origins are relatively similar in morphology,and many so-called"exsolution structures"still have significant controversies about their origins.In this paper,the two most common"exsolution structures"of metal sulfides in hydrothermal deposits are selected:（a）milky drop,lattice chalcopyrite and magnetic pyrite in sphalerite;（b）foliate chalcopyrite in bornite as the research object。Firstly,optical microscopy and scanning electron microscopy were used to observe and study the morphological characteristics of the exsolution structure.Electron probes were used to identify the chemical composition characteristics and changing trends of the main crystal and exsolution in the exsolution structure.Secondly,EBSD is used to analyze the crystallography orientation relationship between the main crystal and the exsolution,analyze the crystallography matching degree of the two minerals in various orientation relationships,and explore the results of internal structure measurement and the crystallography orientation rule in the actual intergrowth structure.Finally,based on the analysis of the origin and indicative significance of the sulfide exsolution structure,on the basis of the geological survey of the deposit and the observation of mineralogy,the crystallography orientation relationship of the sulfide exsolution structure was studied,and its origin was determined by combining the morphology observation,chemical composition analysis,and reference to the phase diagram data.The relationship between the crystallography orientation law contained in the sulfide exsolution structure and the internal structure of the crystal was discussed to clarify its origin.The main conclusions obtained are as follows:The sphalerite of the Xianglushan tungsten deposit in Jiangxi Province contains milk drop and lattice chalcopyrite and magnetite pyrite.The element content of sphalerite is w（S）32.14%～32.76%,w（Zn）52.83%～53.9%,w（Fe）9.67%～11.48%,w（Cu）0.04%～0.58%,respectively,respectively;As the test location gradually approaches chalcopyrite,the Fe content of sphalerite gradually increases,while the Cu content gradually decreases.Similarly,as the test location gradually approaches to magnetite pyrite,the Fe content of sphalerite gradually increases,while the Cu content fluctuates in W shape,and the Zn content gradually decreases.The in chalcopyrite is w（Cu）31.99%～33.47%,w（S）is33.83%～34.19%,w（Fe）is 30.07%～30.61%,and w（Zn）is 1.34%～2.4%;Chalcopyrite particles from the core to the edge,with the test position gradually close to sphalerite,the content of Fe and Cu gradually decreases,while the content of Zn gradually increases.The content of in magnetite pyrite is w（Fe）59.13%～60.61%,w（S）is 37.86%～38.22%,w（Zn）is 1.39%～2.21%,and w（Cu）is 0.07%～0.11%.The content of Fe in magnetite pyrite particles decreases gradually from the core to the edge,and the content of Cu and Zn increases gradually with the test position gradually approaching sphalerite.There is a crystallography orientation relationship between the sphalerite of the Xianglushan tungsten deposit and all the chalcopyrite particles inside it,namely,Sph_（100）//Ccp_{100},Sph_（100）//Ccp_{001},Sph_（110）//Ccp_{110},Sph_{111}//Ccp_{112}.The orientation relationship between sphalerite and magnetic pyrite can be divided into two groups:the orientation relationship between sphalerite and the first group of magnetic pyrite（83.3%）is Sph_（110）//Po_{100},Sph_（111）//Po_{0001};There is no specific crystallography orientation relationship between sphalerite and the second group of magnetite pyrite（16.7%）.The crystallography orientation relationship between sphalerite and chalcopyrite,sphalerite and magnetic pyrite is restricted by the internal structure of the crystal and the matching of the plane network.The sphalerite chalcopyrite metasomatic structure is most likely formed through exsolution,and the sphalerite magnetite pyrite metasomatic structure may be the product of the superposition of exsolution and metasomatism.The bornite in the Dahutang tungsten deposit,Jiangxi Province,contains foliate and lattice chalcopyrite.The energy spectrum test results show that the content of in bornite is w（S）22.37%～24.17%,w（Fe）is 11.07%～13.26%,w（Cu）is 62.73%～66.07%,and w（W）is0.07%～0.72%.From the core to the edge,as the test location gradually approaches chalcopyrite,the Fe content of bornite gradually decreases,while the Cu content gradually increases.The in chalcopyrite is w（Cu）38.45%～43.86%,w（S）is 28.75%～31.27%,w（Fe）is26.83%～29.48%,and w（W）is 0.2%～0.97%.From the core to the edge,the Fe content of chalcopyrite gradually increases and the Cu content gradually decreases as the test location gradually approaches the bornite.The chalcopyrite blades and the main crystals of bornite in the samples of the Dahutang tungsten deposit in Jiangxi Province have specific crystallography orientation relationships,which can be divided into three groups:the first group of chalcopyrite leaves and bornite main crystals have Bn_{100}//Ccp_{001},Bn_{010}//Ccp_（100）,Bn_{001}//Ccp_（100）orientation relationships;The second group of bornite chalcopyrite leaves and the main crystal of bornite have the orientation relationship of Bn_{100}//Ccp_（100）,Bn_{010}//Ccp_（100）,Bn_{001}//Ccp_{001};The third group of chalcopyrite leaves and bornite main crystals have the orientation relationship of Bn_{100}//Ccp_（100）,Bn_{010}//Ccp_（001）,Bn_{001}//Ccp_（100）,Bn_{111}//Ccp_（111）.The occurrence probability of three groups of foliated chalcopyrite exsolution is relatively close,and its distribution in three-dimensional space is controlled by the main crystal of bornite.Combined with mineralogy and SEM observation,it is considered that the foliated chalcopyrite in bornite is the product of directional metasomatism of chalcopyrite to bornite.