Studies On The Geochemical Characteristics Of Ore-bearing Granite Porphyry And Ore Genesis Of The Cunqian Copper Polymetallic Deposit, Jiangxi Province

The Cunqian copper polymetallic deposit, located the east of Qinhangmetallogenic belt, in the junctional zone. Where is the joint of Pingxiang-Lepinggeotectogene in Jiangnan old land and Jiuling-Gaotai mountain mole track, east of theYifeng-Jingdezhen deep fracture. The hosting strata is upper carboniferous huanglongformation-chuanshan formation （C₂h-C₂c）, which is a range of marine carbonate, itslithological association are limestone, dolomite limestone and limestone, withmarmarization and skarnization generally in diggings. Ore-controlling structures ofthe Cunqian deposit are the core and two wings of Cunqian plunging anticline,besides, the angular unconformity crack between upper carboniferous Huanglongformation-chuanshan formation carbonatite and neoproterozoic erathem Shuangqiaomountain group epimetamorphic rock.Ore-bearing rock is a compound intrusive body with hypabyssal-superhypabyssal rock characteristics during the early Yanshan epoch, with lithologicalassociation of biotite granite porphyry, biotite monzonitic granite porphyry, quartzporphyry and cryptoexplosion breccia, which the principal part is biotite graniteporphyry. The whole rocks show uniform major element compositions, with SiO₂average contents of67.76wt.%and （Na₂O+K₂O）=4.09⁹.03wt.%, average contentsof6.55wt.%, w（K₂O）＞w（Na₂O）, A/CNK=0.936².52, average contents of1.39,σ=0.7³.49, average contents of1.76, belong to peraluminous high-K calc-alkalineI-type granite, with geochemical characteristics of Rb, K, Th rich, but Sr, Ba, Nb, Ta,Ti loss. In addition, these rocks with REE patterns right deviation obviously, Eu weakdepletion or without loss. All of above show that the rocks may originate from partial melting of lower crust, without crystal fractionation，lead to lithophile elements enterinto magma preferentially, and HFSE have been preserved in the residual solid phase.There are mainly five ore types in Cunqian copper polymetallic deposit, these aremagnetite ore, magnetite-hematite ore, magnetite-hematite-pyrite-chalcopyrite ore,magnetite-chalcopyrite-sphalerite ore and galena-sphalerite ore. Which with main orestructures of massive structure, lumpy structure, disseminated structure, vein structureand mesh-vein structure, brecciated structure, enterolithic structure, colloformstructure, honeycomb structure et al., with main ore textures of euhedral crystaltexture, dependent-structured crystal texture, poikilitic texture, girdle texture, etchingtexture, network texture, false appearance texture and emulsion texture, lattice texture,gel texture, ball texture, framboidal texture, cataclastic texture and so on. Based onmineralization and the relation of paragenetic association of minerals, themineralixation of the deposit can be divided into three stages, depositional phase,magmatic hydrothermalism phase and surface phase, in addition, magmatichydrothermalism phase can be divide into three stages of mineralization, skarn-oxidestage, quartz-sulfide stage, carbonate-sulfide stage.The Cunqian copper polymetallic deposit formed in early Yanshan Period, itsLA-ICP-MS Zr U-Pb age of biotite granite porphyry is169.3±1.1Ma, just duringtheconversion period of Yanshan inland orogeny, which was at the period of collisioncompressional to post-collisional extension. Result of fluid inclusions research in orebearing quartz vein show that ore-forming temperatures of quartz-sulfide phase arefrom249.6℃to416.5℃, mainly distributed at240℃to340℃, and360℃to380℃,with the average value of321.8℃, belonged to middle-high temperature metallogenicenvironment. The ore-forming pressures are from1.12Mpa to8.99Mpa, mainlydistributed at7MPa to8MPa, belonged to low tension epizone metallogenicenvironment. The salinities of ore-forming fluid are from7.17wt.%to41.05wt.%,with the average value of28.62wt.%, belonged to high salinity fluid, which have thehomologous fluid density of0.70g/cm³to1.11g/cm³, with the average value of1.00g/cm³, have a narrow variation range.δ34S of ores are0.47‰¹.57‰, have a narrow variation range, are identical withsulfur isotopic compositons of ore-bearing rock body, similar with sulfur isotopiccompositons of meteorites, which show that both ores and ore-bearing rock body havethe same sulfur sources that have been from deep. The plumbum isotopes μ value of9.32⁹.32, with Th/U value of4.02⁴.02, has the characteristics of typical lead and itsconstituent characteristics show that ore lead is mainly comes from the earth’s crust, with a small amount of mantle-derived lead contamination.The rock magm has mainlyderived from partial melting of crust with a small amount of mantle-derived magmamixed dye, according to petrology characteristics and geochemical characteristics ofore-bearing rock body.Ore-forming elements contents in the ore-bearing rock bodysuch as Cu, Pb, Zn, Au, Ag et al., are higher than that of regional background values,show that the rock mass is the important condition of ore deposit formation, as animportant source of ore-forming fluid. Metallogenic element background values of thehosting strata are higher than the regional background values, show that uppercarboniferous huanglong formation-chuanshan formation （C₂h-C₂c） is the importantsource bed. In summary, the formation of Cunqian copper polymetallic deposit derivedfrom lower crust intermediate-acid magma formed by partial melting, in the process offormation and the emplacement contaminated by a small amount of mantle-derivedmaterial. the ore-forming fluid separated from the magma, further enrichment byextracted metallogenic material from surrounding rocks. Contact metasomatism orhydrothermal filling occurred between metallogenetic hydrothermal and uppercarboniferous huanglong formation-chuanshan formation carbonate, lead topostmagmatic hydrothermal solution has formed porphyry mineralization in fissuresystem of the rock mass, formed contact metasomatic skarn type ore body in the contactzone between the rock mass and its surrounding rocks or the fissure system ofsurrounding rocks, formed the sediment-reformation epithermal type ore body in thesurrounding rocks. In conclusion, the deposit belongs to copper, lead-zinc metallogenicseries of skarn type, porphyry type, sediment-reformation epithermal type "the trinity",which related to acidic intrusive complexs during the early Yanshan epoch.