The Characteristics Of Chalcopyrite-Bornite On Zi-Jinshan Cu-Au Deposit

Zijinshan Cu-Au deposit belongs to high sulfidation epithermal deposit which was found firstly in China.It has been confirmed that the vertical thickness of copper ore ex-ceeding 1km but still not bottomed out.So far,the majority of domestic and foreign re-searchers display great enthusiasm for this deposit.However,most scholars have focused on a large number of alteration minerals,pyrite and binary Cu sulfides,rather than chalco-pyrite and bornite.For the purpose of investigating the characteristics of chalcopy-rite-bornite,enrich the mineralogy of the deposit,providing a clue for the genesis of giant thick copper ore,exploring the ending position of the copper ore and discussing if there is new deposit type under the copper ore,some researches have been carried out based on the detailed field geological investigation.After collecting a total of 144 typical samples from different areas of the deposit,namely Southeast,Northwest and Southwest,hand specimen observation,mineragraphy investigation,electron microprobe analysis and X-ray diffrac-tion were carried out.Main results and recognitions are as follows:In this deposit,chalcopyrite and bornite can be found in the three mining areas that the Southwest and Southeast mining area output more,and only a small amount of North-west mining area.The chalcopyrite and bornite mainly occur in fine-grained granite and cryptoexplosive breccia.These minerals behave as crumb collection,filled fine vein mainly,also can be micro disseminated,remnant.Their textures contain exsolution texture,met-asomatic texture chiefly,while secondary exsolution texture,net vein filled texture and ring texture are minor.The solution texture of chalcopyrite-bornite solid solution indicates that the deposit has undergone medium-high temperature evolution.The characteristics of morphology,texture and mineral assemblage could establish the general of the minerals paragenetic sequence as follows:pyrite? tetrahedrite +enargite(luzonite)?galena + sphalerite?bornite + chalcopyrite?digenite?covellite.In addition,bornite and chalcopyrite can be divided into different generations respectively.Composition characteristics show that these two minerals are close to ideal minerals with few elements,such as Pb,Se,Zn,Ag,Bi etc.What is more,the Cu and Fe iso-morphism is only present in the chalcopyrite,which is the major isomorphism type.And their results of X-ray study indicate that their cell parameters are identical to their theoreti-cal characteristics generally.A large number of mineragraphy property show that the bornite is often replaced by digenite,whereas covellite is often substituted for chalcopyrite rather than bornite.Con-sidering the valence of Cu ions,the study found that there are two groups of typomorphic minerals combination.One is chalcopyrite + covellite assemblage indicates a relative to the higher oxygen fugacity and sulfur fugacity environment,and the other is the assemblage of bornite + digenite to the lower oxygen fugacity and sulfur fugacity environment relatively.From the perspective of space,the occurrence of chalcopyrite and bornite is under 700m elevation which belongs to the original mineral.It is shown that from the southwest to the northwest and then to the southeast,the location of these two minerals stepwise changes from shallow to deep.In the Northwest mining area,chalcopyrite-bornite have been taken replacement strongly and present as residual texture.It is inferred that there is prospecting potential of porphyry deposit in the deep of Southeast mining area.