Study On The Genetic Mineralogy And Prospecting Of Jilongshan Cu-au Deposit, Southeastern Hubei Province,China

Jilongshan Cu-Au deposit is a important skarn deposit located in the southeastern Hubei metallogenic zone subordinated to the Fe-Cu-Au polymetallic metallogenic belt in Middle-Lower Reaches of The Yangtze River.The particular mineral assemblage formed in the skarn stage contains a lot of genetic information,so it is very necessary to discuss.Jilongshan rock mass, carbonate strata(mainly Daye Formation from Group 4 to6 of Lower Triassic) structures(mainly composed by Zhulintang reverse duplex syncline belonging to nearly EW-trending fold belt, the NW-trending pressure-shear fracture, the NWW-trending tensional or tensional shear faults, and their composite structure parts) and rock mass(Mesozoic intermediate-felsic rocks)together form three major ore-controlling factors of Jilongshan Cu-Au deposit.Different mineral assemblages and mineralization zonation are formed from the inner to the outer contact zone. The metallogenesis of Jilongshan deposit can be divided into five stages:skarn stage, magnetite- hematite stage, quartz-molybdenite stage, gold-copper sulfide stage and late carbonate stage.The total amount of andradite and grossular in garnets of dry skarn stage reaches more than 98%, it can be concluded that the relative change of the content of Fe3+ in andradite and Al3+ in grossular is the main factor to form the zonal structure. The REE distribution patterns of garnet are LREE-rich right-incline(LREE/HREE are9.84~44.59), low Eu positive abnormality(1.12~1.92);The average of schefferite in diopsides is only 0.68%,so the diposides belong to hedenbergite- diopside solid solution, The ingredients of wollastonite are relatively simple; The garnet and diposide composition indicates that this area should form the Au,Cu,Mo skarn deposits,and this is consistent with the major mine production. The amphibole-group minerals in wet skarn stage are mainly actinolite. It have the characteristics of the hornblende from both the mid-acidic magmatic rocks and skarn; Studies on the composition of epidote zone show that it is also formed in the reason of the relative change of the content of Fe3+ and Al3+;The pyroelectricity of pyrite is mainly N-type,has littlediscreteness,shows a positive vertical distribution, P-type occurrence rate increases when close to the surface.δ34S are-2.54~6.1‰;Pb206/Pb204 are 17.358~18.589,Pb207/Pb204 are 15.414~15.745,Pb208/Pb204are37.956~39.094,belong to abnormal lead;δDV-SMOW of rock mass are-80.60~103.50‰,δ18O V-SMOW are 9.60~11.20‰;3He/4He are between10-7 ~ 10-8, 40Ar/36 Ar are 261.2~ 580.2. The study of these stable isotope shows the ore-forming materials derive mainly from the ore-forming rock and little from the strata. The study of hydrogen, oxygen, nitrogen, helium, argon isotopes shows that the ore-forming fluids mainly derive from the magma, but which were significantly affected by crustal fluids and meteoric water in the late mineralization.So this skarn deposit develops gradually from a relatively oxidized and slowly migrated hydrothermal system to a reductive and fast migrated system, then gradually becomes oxidiation and fast migrated hydrothermal fluid, followed by the addition of atmospheric precipitation, finally is repaced gradually by the reductive fluid.Based on the above research, we improved the metallogenic model.